Metals

17 pages, 11648 KiB

Open AccessArticle

Effect of Thermal Ageing at 400 °C on the Microstructure of Ferrite-Austenite Interface of Nickel-Base Alloy Narrow-Gap Dissimilar Metal Weld

by Matias Ahonen, Roman Mouginot, Teemu Sarikka, Sebastian Lindqvist, Zaiqing Que, Ulla Ehrnstén, Iikka Virkkunen and Hannu Hänninen

Metals 2020, 10(3), 421; https://doi.org/10.3390/met10030421 - 24 Mar 2020

Cited by 11 | Viewed by 3165

Abstract

Dissimilar metal welds (DMWs) are a key design feature in nuclear power systems, typically involving ferritic low-alloy steels (LAS), stainless steels (SS), and nickel-base alloys. They are, however, a potential concern regarding the structural integrity of nuclear power systems. In particular, the LAS/nickel-base [...] Read more.

Dissimilar metal welds (DMWs) are a key design feature in nuclear power systems, typically involving ferritic low-alloy steels (LAS), stainless steels (SS), and nickel-base alloys. They are, however, a potential concern regarding the structural integrity of nuclear power systems. In particular, the LAS/nickel-base alloy weld metal interface is known to develop a local strength mismatch upon post-weld heat treatment (PWHT). Very limited data is available on the effect of thermal ageing on the DMW interface. The aim of this study was to investigate the effects of thermal ageing at 400 °C for up to 10,000 h on a narrow-gap DMW mock-up representative of the weld between the reactor pressure vessel nozzle and its safe-end after PWHT, with a special focus on the LAS SA 508/nickel-base Alloy 52 weld metal interface. No significant effect of thermal ageing on the appearing microstructure was observed in either LAS base material, LAS heat-affected zone or Alloy 52 weld metal. However, thermal ageing reduced the local strength mismatch at the LAS/nickel-base weld metal interface formed during PWHT. The reduction of the strength mismatch was detected using nanoindentation measurements and was concluded to be associated with a decrease in the carbon pile-up in the weld metal caused by PWHT. Based on the obtained results, thermal ageing promotes carbon diffusion from the weld metal side of the fusion boundary further away into the weld metal and thus slightly decreases the local strength mismatch. Full article

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11 pages, 4541 KiB

Open AccessArticle

Silicon Nitride Whisker-Reinforced Aluminum Matrix Composites: Twinning and Precipitation Behavior

by Shoujiang Qu, Aihan Feng, Lin Geng, Jun Shen and Daolun Chen

Metals 2020, 10(3), 420; https://doi.org/10.3390/met10030420 - 24 Mar 2020

Cited by 7 | Viewed by 3481

Abstract

Aluminum composites reinforced with ceramic whiskers exhibited a unique combination of high specific strength and superior specific modulus. A 20 vol.% Si₃N_4w/Al-11.5Si-1.0Mg-0.5Cu-0.5Ni (wt.%) composite was fabricated via squeeze casting in the present study. It was observed that the addition [...] Read more.

Aluminum composites reinforced with ceramic whiskers exhibited a unique combination of high specific strength and superior specific modulus. A 20 vol.% Si₃N_4w/Al-11.5Si-1.0Mg-0.5Cu-0.5Ni (wt.%) composite was fabricated via squeeze casting in the present study. It was observed that the addition of silicon nitride (Si₃N₄) whiskers in the Al-Si cast alloy promoted extensive twinning in the eutectic silicon particles due to a coupled role of thermal stresses between the matrix and silicon and residual stresses present in the composite. Double aging peaks were present in the age-hardening curves. The precipitation mechanism involved the formation of Mg₂Si and Al₂CuMg phases. The presence of Si₃N₄ whiskers in the composite retarded the nucleation process of Mg₂Si precipitate while enhancing its growth rate. Full article

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12 pages, 3564 KiB

Open AccessArticle

Effects of Homogenization Conditions on the Microstructure Evolution of Aluminium Alloy EN AW 8006

by Maja Vončina, Kristijan Kresnik, Darja Volšak and Jožef Medved

Metals 2020, 10(3), 419; https://doi.org/10.3390/met10030419 - 24 Mar 2020

Cited by 11 | Viewed by 3991

Abstract

The industrial production of products, such as foil and aluminium alloy strips, begins with the production of semi-finished products in the form of slabs. These are produced by the continuous casting process, which is quick and does not allow the equilibrium conditions of [...] Read more.

The industrial production of products, such as foil and aluminium alloy strips, begins with the production of semi-finished products in the form of slabs. These are produced by the continuous casting process, which is quick and does not allow the equilibrium conditions of solidification. Non-homogeneity—such as micro and macro segregation, non-equilibrium phases and microstructural constituents, as well as stresses arising during non-equilibrium solidification—are eliminated by means of homogenization annealing. In this way, a number of technological difficulties in the further processing of semi-finished products can be avoided. The aim of this research was the optimization of the homogenization annealing of the EN AW 8006 alloy. With the Thermo-Calc software, a thermodynamic simulation of equilibrium and non-equilibrium solidification was performed. Differential scanning calorimetry (DSC) was performed on selected samples in as-cast state and after various regimes of homogenization annealing and was used for the simulation of homogenization annealing. Using an optical microscope (OM), a scanning electron microscope (SEM) and an energy dispersion spectrometer (EDS), the microstructure of the samples was examined. Based on the results, it was concluded that homogenization annealing has already taken place after 8 h at 580 °C to the extent, that the material is then suitable for further processing. Full article

(This article belongs to the Special Issue Structure and Properties of Aluminium Alloys)

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17 pages, 2118 KiB

Open AccessArticle

Spark Plasma Sintering as an Effective Texturing Tool for Reprocessing Recycled HDDR Nd-Fe-B Magnets with Lossless Coercivity

by Awais Ikram, Muhammad Awais, Richard Sheridan, Allan Walton, Spomenka Kobe, Franci Pušavec and Kristina Žužek Rožman

Metals 2020, 10(3), 418; https://doi.org/10.3390/met10030418 - 24 Mar 2020

Cited by 6 | Viewed by 3841

Abstract

The low-pressure hot-deformation methodology was applied to reprocess the nanocrystalline hydrogenation–disproportionation–desorption–recombination (HDDR) Nd-Fe-B powders from end-of-life (EOL) permanent magnets’ waste to determine the mechanism of texture development and the resultant improvement in remanence (and BH_max) in the recycled material. Both the [...] Read more.

The low-pressure hot-deformation methodology was applied to reprocess the nanocrystalline hydrogenation–disproportionation–desorption–recombination (HDDR) Nd-Fe-B powders from end-of-life (EOL) permanent magnets’ waste to determine the mechanism of texture development and the resultant improvement in remanence (and BH_max) in the recycled material. Both the hot-pressed and hot-deformed magnets produced via spark plasma sintering (SPS) were compared in terms of their magnetic properties with respect to forging pressures. Also, a comparison was established with the microstructure to cite the effectiveness of texture development at low deformation rates and pressures which is pivotal for retaining high coercivity. The hot-pressed magnets maintain the high coercivity (better than 100%) of the original recycled powder due to the control of SPS conditions. The hot deformation pressure was varied from 100–150 MPa at 750 °C processing temperature to identify the optimal texture development in the sintered HDDR Nd-Fe-B magnets. The effect of post-hot-deformation thermal treatment was also investigated, which helped in boosting the overall magnetic properties and better than the recycled feedstock. This low-pressure hot deformation process improved the remanence of the hot-pressed magnet by 11% over the starting recycled powder. The M_r/M_S ratio which was 0.5 for the hot-pressed magnets increased to 0.64 for the magnets hot-deformed at 150 MPa. Also, a 55% reduction in height of the sample was achieved with the c-axis texture, indicating approximately 23% higher remanence over the isotropic hot-pressed magnets. After hot deformation, the intrinsic coercivity (H_Ci) of 960 kA/m and the remanence (B_r) value of 1.01 T at 150 MPa is indicative that the controlled SPS reprocessing technique can prevent microstructure related losses in the magnetic properties of the recycled materials. This route also suggests that the scrap Nd-Fe-B magnets can be treated with recoverable magnetic properties subsequently via HDDR technique and controlled hot deformation with a follow-up annealing. Full article

(This article belongs to the Special Issue News Trends in Powder Metallurgy: Microstructures, Properties, Durability)

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7 pages, 891 KiB

Open AccessFeature PaperArticle

Heat Effects Occurring in the Supercooled Liquid State and Upon Crystallization of Metallic Glasses as a Result of Thermally Activated Evolution of Their Defect Systems

by Andrei Makarov, Gennadii Afonin, Yurii Mitrofanov, Nikolai Kobelev and Vitaly Khonik

Metals 2020, 10(3), 417; https://doi.org/10.3390/met10030417 - 24 Mar 2020

Cited by 5 | Viewed by 2496

Abstract

We show that the kinetics of endothermal and exothermal effects occurring in the supercooled liquid state and upon crystallization of metallic glasses can be well reproduced using temperature dependences of their shear moduli. It is argued that the interrelation between the heat effects [...] Read more.

We show that the kinetics of endothermal and exothermal effects occurring in the supercooled liquid state and upon crystallization of metallic glasses can be well reproduced using temperature dependences of their shear moduli. It is argued that the interrelation between the heat effects and shear modulus relaxation reflects thermally activated evolution of interstitial-type defect system inherited from the maternal melt. Full article

(This article belongs to the Special Issue Recent Advancements in Metallic Glasses)

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14 pages, 4691 KiB

Open AccessArticle

Investigation on Strength and Microstructural Evolution of Porous Cu/Cu Brazed Joints Using Cu-Ni-Sn-P Filler

by Mian Muhammad Sami, Tuan Zaharinie, Farazila Yusof and Tadashi Ariga

Metals 2020, 10(3), 416; https://doi.org/10.3390/met10030416 - 24 Mar 2020

Cited by 9 | Viewed by 4355

Abstract

Porous Copper (Cu) was brazed to Cu plates using Cu-9.7Sn-5.7Ni-7P amorphous filler metal. The effects of brazing parameters on the porous Cu and brazed joints were investigated. The furnace brazing temperatures employed were 660 °C and 680 °C, and the holding times were [...] Read more.

Porous Copper (Cu) was brazed to Cu plates using Cu-9.7Sn-5.7Ni-7P amorphous filler metal. The effects of brazing parameters on the porous Cu and brazed joints were investigated. The furnace brazing temperatures employed were 660 °C and 680 °C, and the holding times were 10 and 15 min. After brazing, the microstructure was analyzed using Scanning Electron Microscope (SEM) equipped with Electron Dispersive X-ray Spectroscope (EDS). SEM results showed that the thickness of the brazed seam at the base joint decreased with increasing temperature and time. At low brazing temperature, microvoids and cracks were observed at the joint interface. The microvoids and cracks disappeared in the sample brazed at 680 °C for 15 min, and higher diffusion of the filler was noted in the overall bonded region. The formation of Cu-P, Cu-Ni, and Ni-Sn phases at the joint interface was validated using X-ray diffraction. The phases formed increased the hardness of the brazed joints and porous Copper. It was observed that the rigidity of porous Copper tends to increase due to surface hardening effects. The rigidity of porous Cu after brazing is important in ensuring minimal deformation during cooling device servicing, which is an integral feature of prospect product development. Full article

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29 pages, 13751 KiB

Open AccessFeature PaperReview

Influence of HPT Deformation on the Structure and Properties of Amorphous Alloys

by Dmitry Gunderov and Vasily Astanin

Metals 2020, 10(3), 415; https://doi.org/10.3390/met10030415 - 23 Mar 2020

Cited by 30 | Viewed by 4604

Abstract

Recent studies showed that structural changes in amorphous alloys under high pressure torsion (HPT) are determined by their chemical composition and processing regimes. For example, HPT treatment of some amorphous alloys leads to their nanocrystallization; in other alloys, nanocrystallization was not observed, but [...] Read more.

Recent studies showed that structural changes in amorphous alloys under high pressure torsion (HPT) are determined by their chemical composition and processing regimes. For example, HPT treatment of some amorphous alloys leads to their nanocrystallization; in other alloys, nanocrystallization was not observed, but structural transformations of the amorphous phase were revealed. HPT processing resulted in its modification by introducing interfaces due to the formation of shear bands. In this case, the alloys after HPT processing remained amorphous, but a cluster-type structure was formed. The origin of the observed changes in the structure and properties of amorphous alloys is associated with the chemical separation and evolution of free volume in the amorphous phase due to the formation of a high density of interfaces as a result of HPT processing. Amorphous metal alloys with a nanocluster structure and nanoscale inhomogeneities, representatives of which are nanoglasses, significantly differ in their physical and mechanical properties from conventional amorphous materials. The results presented in this review show that the severe plastic deformation (SPD) processing can be one of the efficient ways for producing a nanocluster structure and improving the properties of amorphous alloys. Full article

(This article belongs to the Special Issue Recent Advancements in Metallic Glasses)

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15 pages, 9455 KiB

Open AccessArticle

Effects of Zn Content on Hot Tearing Susceptibility of Mg–7Gd–5Y–0.5Zr Alloy

by Ziqi Wei, Shimeng Liu, Zheng Liu, Feng Wang, Pingli Mao, Xiaoxia Wang and Xingxing Li

Metals 2020, 10(3), 414; https://doi.org/10.3390/met10030414 - 23 Mar 2020

Cited by 16 | Viewed by 3061

Abstract

Mg–7Gd–5Y–0.5Zr alloy has excellent mechanical properties but poor hot tearing resistance. The latter makes it difficult to cast billets, which limits the size of subsequently processed parts. Therefore, the hot tearing susceptibility of Mg–7Gd–5Y–xZn–0.5Zr (x = 0, 3, 5, 7 [...] Read more.

Mg–7Gd–5Y–0.5Zr alloy has excellent mechanical properties but poor hot tearing resistance. The latter makes it difficult to cast billets, which limits the size of subsequently processed parts. Therefore, the hot tearing susceptibility of Mg–7Gd–5Y–xZn–0.5Zr (x = 0, 3, 5, 7 wt%) alloys was studied. It was found that Zn can significantly reduce hot tearing susceptibility of Mg–7Gd–5Y–0.5Zr alloy, which almost linearly decreased with Zn content. When Zn content was 3 wt%, 5 wt% and 7 wt%, hot tearing susceptibility will be reduced by 27%, 83% and 100%, respectively. It was further revealed that the solid solubility of Gd and Y in α-Mg decreased with the increase of Zn content, and the nucleation temperature decreased accordingly, which resulted in the increase of nucleation rate and the refinement of final grains. On the macro level, it showed that the dendrite coherency temperature decreased, the solidification shrinkage stress of α-Mg slowed down, and the residual liquid channel became shorter and hot tearing susceptibility decreased. It was also found that with the increase of Zn content, the content of Zn, Gd and Y enriched on the grain boundary increased, the content of residual liquid phase between dendrites increased after α-Mg crystallization, and the solidified precipitated second phase also changed from Mg₅RE phase to long-period stacking ordered phase + W-phase (a little), long-period stacking ordered phase + W-phase (much) and finally to W-phase only. The feeding effect of sufficient intergranular residual liquid on the shrinkage of α-Mg dendrite and the bridging effect of the precipitated phase at the grain boundary (especially long-period stacking ordered phase which is coherent with the parent phase) also led to the decrease of hot tearing susceptibility. Full article

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15 pages, 9658 KiB

Open AccessArticle

Rational Alloy Design of Niobium-Bearing HSLA Steels

by Rami A. Almatani and Anthony J. DeArdo

Metals 2020, 10(3), 413; https://doi.org/10.3390/met10030413 - 23 Mar 2020

Cited by 3 | Viewed by 3460

Abstract

In the 61 years that niobium has been used in commercial steels, it has proven to be beneficial via several properties, such as strength and toughness. Over this time, numerous studies have been performed and papers published showing that both the strength and [...] Read more.

In the 61 years that niobium has been used in commercial steels, it has proven to be beneficial via several properties, such as strength and toughness. Over this time, numerous studies have been performed and papers published showing that both the strength and toughness can be improved with higher Nb additions. Earlier studies have verified this trend for steels containing up to about 0.04 wt.% Nb. Basic studies have shown that the addition of Nb increases the recrystallization-stop temperature, T_5% or T_nr. These same studies have shown that with up to about 0.05 wt.% of Nb, the T_5% temperature increases in the range of finish rolling, which is the basis of controlled rolling. These studies also have shown that at very high Nb levels, exceeding approximately 0.06 wt.% Nb, the recrystallization-stop temperature or T_5% can increase into the temperature range of rough rolling, and this could result in insufficient grain refinement and recrystallization during rough rolling. However, the question remains as to how much Nb can be added before the detriments outweigh the benefits. While the benefits are easily observed and discussed, the detriments are not. These detriments at high Nb levels include cost, undissolved Nb particles, weldability issues, higher mill loads and roll wear and the lessening of grain refinement that might otherwise occur during plate rough rolling. This loss of grain refinement is important, since coarse grained microstructures often result in failure in the drop weight tear testing of the plate and pipe. The purpose of this paper is to discuss the practical limits of Nb microalloying in controlled rolled low carbon linepipe steels of gauges ranging from 12 to 25 mm in thickness. Full article

(This article belongs to the Special Issue Advances in Low-carbon and Stainless Steels)

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33 pages, 2295 KiB

Open AccessFeature PaperReview

Adsorption Processing for the Removal of Toxic Hg(II) from Liquid Effluents: Advances in the 2019 Year

by Francisco J. Alguacil and Félix A. López

Metals 2020, 10(3), 412; https://doi.org/10.3390/met10030412 - 23 Mar 2020

Cited by 19 | Viewed by 4230

Abstract

Mercury is a toxic metal, thus, it is an element which has more and more restrictions in its uses, but despite the above, the removal of this metal, from whatever the form in which it is encountered (zero valent metal, inorganic, or organic [...] Read more.

Mercury is a toxic metal, thus, it is an element which has more and more restrictions in its uses, but despite the above, the removal of this metal, from whatever the form in which it is encountered (zero valent metal, inorganic, or organic compounds), and from different sources, is of a widespread interest. In the case of Hg(II), or Hg²⁺, the investigations about the treatment of Hg(II)-bearing liquid effluents (real or in most cases synthetic solutions) appear not to end, and from the various separation technologies, adsorption is the most popular among researchers. In this topic, and in the 2019 year, more than 100 publications had been devoted to this field: Hg(II)-removal-adsorption. This work examined all of them. Full article

(This article belongs to the Special Issue Metal Removal and Recycling)

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19 pages, 4351 KiB

Open AccessArticle

Energy Density Effect of Laser Alloyed TiB₂/TiC/Al Composite Coatings on LMZ/HAZ, Mechanical and Corrosion Properties

by Dunja Ravnikar, Uroš Trdan, Aleš Nagode and Roman Šturm

Metals 2020, 10(3), 411; https://doi.org/10.3390/met10030411 - 23 Mar 2020

Cited by 4 | Viewed by 3313

Abstract

In the present work, TiC/TiB₂/Al composite coatings were synthesized onto a precipitation hardened AlSi1MgMn alloy by laser surface alloying (LSA), using 13.3 J/mm² and 20 J/mm² laser energy densities. Microstructure evaluation, microhardness, wear and corrosion performance were investigated and [...] Read more.

In the present work, TiC/TiB₂/Al composite coatings were synthesized onto a precipitation hardened AlSi1MgMn alloy by laser surface alloying (LSA), using 13.3 J/mm² and 20 J/mm² laser energy densities. Microstructure evaluation, microhardness, wear and corrosion performance were investigated and compared with the untreated/substrate Al alloy sample. The results confirmed sound, compact, crackles composite coating of low porosity, with a proper surface/substrate interface. Microstructural analyses revealed the formation of extremely fine nano-precipitates, ranging from of 50–250 nm in the laser melted (LMZ) and large precipitates, accompanied with grain coarsening in the heat-affected zone (HAZ), due to the substrate overheating during the LSA process. Nonetheless, both coatings achieved higher microhardness, with almost 7-times higher wear resistance than the untreated sample as a consequence of high fraction volume of hard, wear resistant TiB₂ and TiC phases inside the composite coatings. Further, cyclic polarization results in 0.5 M NaCl aqueous solution confirmed general improvement of corrosion resistance after LSA processed samples, with reduced corrosion current by more than a factor of 9, enhanced passivation/repassivation ability and complete prohibition of crystallographic pitting, which was detected with the untreated Al alloy. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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15 pages, 5090 KiB

Open AccessArticle

Effect of Heat Treatment Condition on Microstructural and Mechanical Anisotropies of Selective Laser Melted Maraging 18Ni-300 Steel

by Dohyung Kim, Taehwan Kim, Kyeongsik Ha, Jeong-Jung Oak, Jong Bae Jeon, Yongho Park and Wookjin Lee

Metals 2020, 10(3), 410; https://doi.org/10.3390/met10030410 - 23 Mar 2020

Cited by 51 | Viewed by 5253

Abstract

18Ni-300 maraging steel produced by the selective laser melting (SLM) process has a unique microstructure that is different from that of the same alloy processed by conventional methods. In this paper, maraging steels were fabricated by the selective laser melting process and their [...] Read more.

18Ni-300 maraging steel produced by the selective laser melting (SLM) process has a unique microstructure that is different from that of the same alloy processed by conventional methods. In this paper, maraging steels were fabricated by the selective laser melting process and their microstructures and mechanical properties were investigated in terms of post heat treatment conditions. Moreover, the effect of different heat treatments on the mechanical anisotropy was studied in detail. The micro Vickers hardness in the as-built state was around 340 Hv and could be increased to approximately 600 Hv by aging heat treatments. It was found that the solution heat treatment was not necessary to obtain a fully hardened state. From tensile tests of the maraging steels heat treated with different conditions, it was found that the highest strength was achieved by aging and solution treatment (ST) temperatures lower than the commonly used temperatures. In the direction parallel to the laser scanning, the highest ultimate tensile strength was obtained when 450 °C aging was done without solution heat treatment. In the other two directions tested, i.e., directions normal to the building and 45 degrees to the laser scanning direction, the highest tensile strength was obtained when aging was done at 450 °C after 750 °C solution treatment. Full article

(This article belongs to the Special Issue Clad Metals: Fabrication, Properties and Applications)

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12 pages, 6032 KiB

Open AccessArticle

Effect of CO₂/H₂S and Applied Stress on Corrosion Behavior of 15Cr Tubing in Oil Field Environment

by Xuehui Zhao, Wei Huang, Guoping Li, Yaorong Feng and Jianxun Zhang

Metals 2020, 10(3), 409; https://doi.org/10.3390/met10030409 - 23 Mar 2020

Cited by 13 | Viewed by 4063

Abstract

The corrosion behavior of a 15Cr-6Ni-2Mo martensitic stainless steel (15Cr stainless steel) in a CO₂/H₂S environment was investigated by conducting high-temperature/high-pressure immersion tests combined with scanning electron microscopy and metallographic microscopy. The presence of H₂S decreased the [...] Read more.

The corrosion behavior of a 15Cr-6Ni-2Mo martensitic stainless steel (15Cr stainless steel) in a CO₂/H₂S environment was investigated by conducting high-temperature/high-pressure immersion tests combined with scanning electron microscopy and metallographic microscopy. The presence of H₂S decreased the corrosion resistance of the 15Cr tubing steel. The critical H₂S partial pressure (P_H2S) for stress corrosion cracking in the 15Cr tubing steel in the simulated oil field environment with a CO₂ partial pressure of 4 MPa and an applied stress of 80% σ_s was identified. The 15Cr tubing steel mainly suffered uniform corrosion with no pitting and cracking when the P_H2S was below 0.5 MPa. When the P_H2S increased to 1 MPa and the test temperature was 150 °C, the pitting and cracking sensitivity increased. The stress corrosion cracking at a higher P_H2S is attributed to the sulfide-induced brittle fracture. Full article

(This article belongs to the Special Issue Localized Corrosion of Metals and Alloys)

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12 pages, 5460 KiB

Open AccessArticle

In Situ Development and High Temperature Features of CoCrFeNi-M₆C_p High Entropy-Alloy Based Hardmetal

by Huizhong Li, He Lin, Xiaopeng Liang, Weiwei He, Bin Liu, Yong Liu and Li Wang

Metals 2020, 10(3), 408; https://doi.org/10.3390/met10030408 - 23 Mar 2020

Cited by 5 | Viewed by 3172

Abstract

In this work, an in-situ CoCrFeNi-M₆C_p high entropy-alloy (HEA) based hardmetal with a composition of Co₂₅Cr₂₁Fe₁₈Ni₂₃Mo₇Nb₃WC₂ was fabricated by the powder metallurgy (PM) method. Microstructures and mechanical [...] Read more.

In this work, an in-situ CoCrFeNi-M₆C_p high entropy-alloy (HEA) based hardmetal with a composition of Co₂₅Cr₂₁Fe₁₈Ni₂₃Mo₇Nb₃WC₂ was fabricated by the powder metallurgy (PM) method. Microstructures and mechanical properties of this HEA were characterized and analyzed. The results exhibit that this HEA possesses a two-phase microstructure consisting of the face-centered cubic (FCC) matrix phase and the carbide M₆C phase. This HEA has an average grain size of 2.2 μm, and the mean size and volume fraction of carbide particles are 1.2 μm and 20%. The tensile tests show that the alloy has a yield strength of 573 MPa, ultimate tensile strength of 895 MPa and elongation of 5.5% at room temperature. The contributions from different strengthening mechanisms in this HEA were calculated. The grain boundary strengthening is the dominant strengthening mechanism, and the carbide particles are significant for the further enhancement of yield strength by the dislocation strengthening and Orowan strengthening. In addition, with increasing temperatures from 600 °C to 900 °C, the HEA shows a reduced yield strength (YS) from 473 MPa to 142 MPa, a decreased ultimate tensile strength (UTS) from 741 MPa to 165 MPa and an enhanced elongation from 10.5% to 31%. Full article

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10 pages, 3722 KiB

Open AccessArticle

Comparative Study of Laser-Arc Hybrid Welding for AA6082-T6 Aluminum Alloy with Two Different Arc Modes

by Xiaohui Han, Zhibin Yang, Yin Ma, Chunyuan Shi and Zhibin Xin

Metals 2020, 10(3), 407; https://doi.org/10.3390/met10030407 - 22 Mar 2020

Cited by 15 | Viewed by 2821

Abstract

The effects of arc modes on laser-arc hybrid welding for AA6082-T6 aluminum alloy were comparatively studied. Two arc modes were employed: pulsed metal inert gas arc and cold metal transfer arc. The results indicated that joints without porosity, undercutting, or other defects were [...] Read more.

The effects of arc modes on laser-arc hybrid welding for AA6082-T6 aluminum alloy were comparatively studied. Two arc modes were employed: pulsed metal inert gas arc and cold metal transfer arc. The results indicated that joints without porosity, undercutting, or other defects were obtained with both laser-pulsed metal inert gas hybrid welding (LPMHW) and laser-cold metal transfer hybrid welding (LCHW). Spatter was reduced, and even disappeared, during the LCHW process. The sizes of equiaxed dendrites and the width of the partially melted zone in the LPMHW joint were larger than those in the LCHW joint. The microhardness in each zone of the LPMHW joint was lower than that of the LCHW joint. The softening region in the heat-affected zone of the LPMHW joint was wider than that of the LCHW joint. The tensile strength of the LCHW joint was higher than that of the LPMHW joint. For the two joints, the fractures all occurred in the softening region in the heat-affected zone, and the fracture morphologies showed ductile fracture features. The dimples in the fractograph of the LCHW joint were deeper than those of the LPMHW joint. Full article

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14 pages, 7376 KiB

Open AccessArticle

Effect of TiO₂-Nanoparticles on Ni Electrodeposition on Copper Wire

by Samiha Saad, Zakaria Boumerzoug, Anne Laure Helbert, François Brisset and Thierry Baudin

Metals 2020, 10(3), 406; https://doi.org/10.3390/met10030406 - 22 Mar 2020

Cited by 5 | Viewed by 3621

Abstract

The objective of this work is to study, on a copper wire, the effect of TiO₂-nanoparticles on electrodeposited nickel. Both the microstructure and surface morphology (texture) of the coating were investigated. This deposit is obtained from baths of sulfated electroplating Watts. [...] Read more.

The objective of this work is to study, on a copper wire, the effect of TiO₂-nanoparticles on electrodeposited nickel. Both the microstructure and surface morphology (texture) of the coating were investigated. This deposit is obtained from baths of sulfated electroplating Watts. The Ni-TO₂ composite coating is deposited at a temperature of 45 °C. The composite deposit is prepared by adding nanoparticles of TiO₂ to the electrolyte. The characterization has been carried out by X-ray diffraction, scanning electron microscopy, microhardness measurements, and electron backscatter diffraction (EBSD). Vickers microhardness was used to characterize the mechanical properties of the electrodeposited nickel. The results showed the effects of the TiO₂ on the composition, the surface morphology, and the hardness of the deposited layer. However, there was not an effect of TiO₂ nanoparticles on texture. Full article

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12 pages, 6687 KiB

Open AccessFeature PaperArticle

Study of Wire Deformation Characterization and Size Effects during the Micro-Flat-Rolling Process

by Haibo Xie, Ken-ichi Manabe and Zhengyi Jiang

Metals 2020, 10(3), 405; https://doi.org/10.3390/met10030405 - 22 Mar 2020

Cited by 4 | Viewed by 3429

Abstract

A comprehensive research on the flat rolling deformation characterization of microwire has been conducted systematically through finite element simulation and testified by the results from the experimental analysis. The obtained results are compared in terms of lateral spread, geometrical characteristic, contact area width [...] Read more.

A comprehensive research on the flat rolling deformation characterization of microwire has been conducted systematically through finite element simulation and testified by the results from the experimental analysis. The obtained results are compared in terms of lateral spread, geometrical characteristic, contact area width and surface roughness considering the effects of pass reduction and initial wire diameter. The size effect has been identified and surface layer modeling has been set up based on surface grain share and grain size distribution. The numerical method combined with varied flow stress has been verified by experimental value with a maximum difference of 3.7% for the 1.5 mm wire. With the increase of the height reduction, the curvature radius is decreased while the lateral spread and contact area width are increased. Surface roughness evolution in the range of 0.52–0.85 µm for the rolled wire has also been investigated. Full article

(This article belongs to the Special Issue Metal Micro-forming)

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17 pages, 9643 KiB

Open AccessArticle

Effects of ATIG Welding on Weld Shape, Mechanical Properties, and Corrosion Resistance of 430 Ferritic Stainless Steel Alloy

by Kamel Touileb, Abousoufiane Ouis, Rachid Djoudjou, Abdeljlil Chihaoui Hedhibi, Hussein Alrobei, Ibrahim Albaijan, Bandar Alzahrani, El-Sayed M. Sherif and Hany S. Abdo

Metals 2020, 10(3), 404; https://doi.org/10.3390/met10030404 - 22 Mar 2020

Cited by 19 | Viewed by 4554

Abstract

Flux activated tungsten inert gas (ATIG) welding is a variant of tungsten inert gas (TIG) welding process with high production efficiency, high quality, low energy consumption, and low cost. The study of activating flux mechanism by increasing weld penetration has direct significance in [...] Read more.

Flux activated tungsten inert gas (ATIG) welding is a variant of tungsten inert gas (TIG) welding process with high production efficiency, high quality, low energy consumption, and low cost. The study of activating flux mechanism by increasing weld penetration has direct significance in developing flux and welding process. This study has been conducted on 430 ferritic stainless steel alloy. Design of experiment is used to get the best formulation of flux. Based on Minitab17 software, nineteen compositions of flux were prepared using the mixing method. Fluxes are combinations of three oxides (MoO₃-TiO₂-SiO₂). Using the optimizer module available in Minitab 17 software, the best formulation was obtained to achieve the best weld depth. Hence, the obtained depth is twice greater than that achieved by conventional TIG welding. Moreover, mechanical properties and corrosion resistance have been investigated for TIG and ATIG welds respectively in tensile, impact, and hardness tests, and in potentiodynamic polarization measurement test. Full article

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11 pages, 3145 KiB

Open AccessArticle

Role of Ag⁺ in the Bioleaching of Arsenopyrite by Acidithiobacillus ferrooxidans

by Yan Zhang, Qian Li and Xiaoliang Liu

Metals 2020, 10(3), 403; https://doi.org/10.3390/met10030403 - 22 Mar 2020

Cited by 8 | Viewed by 2887

Abstract

Arsenopyrite (FeAsS) is often associated with gold, but pre-treatment is necessary prior to gold leaching, mainly due to the gold encapsulation in the matrix of FeAsS. Bio-oxidation is attractive and promising, largely due to its simplicity, low cost and environmental friendliness. A critical [...] Read more.

Arsenopyrite (FeAsS) is often associated with gold, but pre-treatment is necessary prior to gold leaching, mainly due to the gold encapsulation in the matrix of FeAsS. Bio-oxidation is attractive and promising, largely due to its simplicity, low cost and environmental friendliness. A critical problem that still impedes the large-scale applications of this green technology is its slow leaching kinetics. Some metal ions such as Ag⁺ have previously been found to expedite the bioleaching process. In this paper, the role of Ag⁺ in the arsenopyrite bioleaching by Acidithiobacillus ferrooxidans was investigated in detail by bioleaching experiments and a series of analyses including thermodynamics, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Experimental results suggested that addition of 5 mg/L Ag⁺ to the leaching system could significantly improve the final As leaching efficiency from 30.4% to 47.8% and shorten the bioleaching period from 19 days to 15 days. Thermodynamic analysis indicates that Ag⁺ destabilises As₂S₂, As₂S₃ and S⁰ via forming Ag₂S, which is confirmed by the XRD analysis on the phase transformation during bioleaching. SEM and XPS analyses further showed that Ag⁺ removed the passivating film consisting mainly of As₂S₂, As₂S₃ and S⁰ because Ag₂S formed on the arsenopyrite surface from the start bioleaching of 36 h. In the presence of Fe³⁺, Ag₂S could easily be dissolved to Ag⁺ again, likely leading to the establishment of the Ag⁺/Ag₂S cycle. The bacteria utilised the two synergistic cycles of Fe³⁺/Fe²⁺ and Ag⁺/Ag₂S to catalyse the bioleaching of arsenopyrite. Full article

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16 pages, 4230 KiB

Open AccessFeature PaperArticle

Formation and Thermal Stability of ω-Ti(Fe) in α-Phase-Based Ti(Fe) Alloys

by Mario J. Kriegel, Martin Rudolph, Askar Kilmametov, Boris B. Straumal, Julia Ivanisenko, Olga Fabrichnaya, Horst Hahn and David Rafaja

Metals 2020, 10(3), 402; https://doi.org/10.3390/met10030402 - 21 Mar 2020

Cited by 14 | Viewed by 4369

Abstract

In this work, the formation and thermal stability of the ω-Ti(Fe) phase that were produced by the high-pressure torsion (HPT) were studied in two-phase α-Ti + TiFe alloys containing 2 wt.%, 4 wt.% and 10 wt.% iron. The two-phase microstructure was achieved by [...] Read more.

In this work, the formation and thermal stability of the ω-Ti(Fe) phase that were produced by the high-pressure torsion (HPT) were studied in two-phase α-Ti + TiFe alloys containing 2 wt.%, 4 wt.% and 10 wt.% iron. The two-phase microstructure was achieved by annealing the alloys at 470 °C for 4000 h and then quenching them in water. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilized to characterize the samples. The thermal stability of the ω-Ti(Fe) phase was investigated using differential scanning calorimetry (DSC) and in situ high-temperature XRD. In the HPT process, the high-pressure ω-Ti(Fe) phase mainly formed from α-Ti. It started to decompose by a cascade of exothermic reactions already at temperatures of 130 °C. The decomposition was finished above ~320 °C. Upon further heating, the phase transformation proceeded via the formation of a supersaturated α-Ti(Fe) phase. Finally, the equilibrium phase assemblage was established at high temperatures. The eutectoid temperature and the phase transition temperatures measured in deformed and heat-treated samples are compared for the samples with different iron concentrations and for samples with different phase compositions prior to the HPT process. Thermodynamic calculations were carried out to predict stable and metastable phase assemblages after heat-treatments at low (α-Ti + TiFe) and high temperatures (α-Ti + β-(Ti,Fe), β-(Ti,Fe)). Full article

(This article belongs to the Special Issue Severe Plastic Deformation and Thermomechanical Processing: Nanostructuring and Properties)

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15 pages, 3248 KiB

Open AccessArticle

Silicon Steel Strip Profile Control Technology for Six-High Cold Rolling Mill with Small Work Roll Radius

by Hainan He, Jian Shao, Xiaochen Wang, Quan Yang and Xiawei Feng

Metals 2020, 10(3), 401; https://doi.org/10.3390/met10030401 - 21 Mar 2020

Cited by 3 | Viewed by 4948

Abstract

Due to the requirement of magnetic properties of silicon steel sheets, producing high-precision size strips is the main aim of the cold rolling industry. The tapered work roll shifting technique of the six-high cold rolling mill is effective in reducing the difference in [...] Read more.

Due to the requirement of magnetic properties of silicon steel sheets, producing high-precision size strips is the main aim of the cold rolling industry. The tapered work roll shifting technique of the six-high cold rolling mill is effective in reducing the difference in transverse thickness of the strip edge, but the effective area is limited, especially for a high crown strip after the hot rolling process. The six-high mill with a small work roll size can produce a strip with higher strength and lower thickness under a smaller rolling load. At the same time, the profile of the strip can be substantially improved. By advancing a well-established analytical method, a series of simulation analyses are conducted to reveal the effectiveness of a small work roll radius for the strip profile in the six-high cold rolling process. Through the analysis of flattening deformation and deflection deformation on the load, the change rule of the strip profile produced by the work roll with a small roll diameter can be obtained. Combined with theoretical analysis and industrial experiments, it can be found that the improvement effect of the small work roll radius on the profile of the silicon strip is as significant. Full article

(This article belongs to the Special Issue Advanced Magnetic Materials)

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13 pages, 3578 KiB

Open AccessArticle

Investigation by Digital Image Correlation of Mixed Mode I and II Fracture Behavior of Metallic IASCB Specimens with Additive Manufactured Crack-Like Notch

by Ivo Campione, Tommaso Maria Brugo, Giangiacomo Minak, Jelena Janković Tomić, Nebojša Bogojević and Snežana Ćirić Kostić

Metals 2020, 10(3), 400; https://doi.org/10.3390/met10030400 - 20 Mar 2020

Cited by 10 | Viewed by 3803

Abstract

This work investigates the fracture behavior of maraging steel specimens manufactured by the selective laser sintering (SLS) technology, in which a crack-like notch (sharp notch) was directly produced during the additive manufacturing (AM) process. For the evaluation of the fracture toughness, the inclined [...] Read more.

This work investigates the fracture behavior of maraging steel specimens manufactured by the selective laser sintering (SLS) technology, in which a crack-like notch (sharp notch) was directly produced during the additive manufacturing (AM) process. For the evaluation of the fracture toughness, the inclined asymmetrical semi-circular specimen subjected to three points loading (IASCB) was used, allowing to cover a wide variety of Mode I and II combinations. The effectiveness of manufacturing crack-like notches via the SLS technique in metals was evaluated by comparing the obtained experimental results with the ones obtained with pre-cracks induced by fatigue loading. The investigation was carried out by using the digital image correlation (DIC) technique, that allowed the evaluation of the full displacement fields around the crack tip. The displacement field was then used to compute the stress intensity factors (SIFs) for various combinations of Mode I and II, via a fitting technique which relies on the Williams’ model for the displacement. The SIFs obtained in this way were compared to the results obtained with the conventional critical load method. The results showed that the discrepancy between the two methods reduces by ranging from Mode I to Mode II loading condition. Finally, the experimental SIFs obtained by the two methods were described by the mixed mode local stress criterium. Full article

(This article belongs to the Special Issue Selected Papers from the 8th International Conference on Mechanics and Materials in Design (M2D 2019))

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14 pages, 2655 KiB

Open AccessArticle

The Relationship between Nil-Strength Temperature, Zero Strength Temperature and Solidus Temperature of Carbon Steels

by Petr Kawulok, Ivo Schindler, Bedřich Smetana, Ján Moravec, Andrea Mertová, Ľubomíra Drozdová, Rostislav Kawulok, Petr Opěla and Stanislav Rusz

Metals 2020, 10(3), 399; https://doi.org/10.3390/met10030399 - 20 Mar 2020

Cited by 9 | Viewed by 3898

Abstract

The nil-strength temperature, zero strength temperature and solidus temperature are significant parameters with respect to the processes of melting, casting and welding steels. With the use of physical tests performed on the universal plastometer Gleeble 3800 and calculations in the IDS software, the [...] Read more.

The nil-strength temperature, zero strength temperature and solidus temperature are significant parameters with respect to the processes of melting, casting and welding steels. With the use of physical tests performed on the universal plastometer Gleeble 3800 and calculations in the IDS software, the nil-strength temperatures, zero strength temperatures and solidus temperatures of nine non-alloy carbon steels have been determined. Apart from that, solidus temperatures were also calculated by the use of four equations expressing a mathematical relation of this temperature to the chemical composition of the investigated steels. The nil-strength and zero strength temperatures and the solidus temperatures decreased with increasing carbon content in the investigated steels. Much higher content of sulfur in free-cutting steel resulted in a decrease of all the temperatures investigated. The zero strength temperatures determined by calculation in the IDS software during solidification were approximately 43–85 °C higher than the nil-strength temperatures determined experimentally during heating of the investigated steels. The linear dependence of experimentally measured nil-strength temperature on the calculated zero strength temperature for the investigated steels was determined. Based on regression analyses, there were determined mathematical relations which described with high accuracy a linear dependence of the nil-strength and zero strength temperatures on the solidus temperature of the investigated steels. Full article

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14 pages, 9315 KiB

Open AccessArticle

Preparation of Ultrafine-Grained Continuous Chips by Cryogenic Large Strain Machining

by Haitao Chen, Baoyu Zhang, Jiayang Zhang and Wenjun Deng

Metals 2020, 10(3), 398; https://doi.org/10.3390/met10030398 - 20 Mar 2020

Cited by 3 | Viewed by 2515

Abstract

Conventional orthogonal machining is an effective severe plastic deformation (SPD) method to fabricate ultrafine-grained (UFG) materials. However, UFG materials produced by room temperature-free machining (RT-FM) are prone to dynamic recovery, which decreases the mechanical properties of UFG materials. In this study, the cryogenic [...] Read more.

Conventional orthogonal machining is an effective severe plastic deformation (SPD) method to fabricate ultrafine-grained (UFG) materials. However, UFG materials produced by room temperature-free machining (RT-FM) are prone to dynamic recovery, which decreases the mechanical properties of UFG materials. In this study, the cryogenic orthogonal machining technique was implemented to fabricate chips that have an abundant UFG microstructure. Solution-treated Al-7075 bulk has been processed in cryogenic temperature (CT) and room temperature (RT) with various machining parameters, respectively. The microstructure, chip morphology and mechanical properties of CT and RT samples have been investigated. CT samples can reach a microhardness of 167.46 Hv, and the hardness of CT samples is higher than that of the corresponding RT samples among all parameters, with an average difference of 5.62 Hv. Piecemeal chip obtained under RT has cracks on its free surface, and elevated temperature aggravates crack growth, whereas all CT samples possess smoother surfaces and continuous shape. CT suppresses dynamic recovery effectively to form a heavier deformation microstructure, and with a higher dislocation density in CT samples, they further improve the chips’ hardness. Also, CT inhibits the formation of solute cluster and precipitation to enhance the formability of material, so that continuous chips are formed. Full article

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10 pages, 2781 KiB

Open AccessArticle

Thermal and Mass Spectroscopic Analysis of BF and BOF Sludges: Study of Their Behavior under Air and Inert Atmosphere

by Mamdouh Omran, Timo Fabritius, Yaowei Yu and Guo Chen

Metals 2020, 10(3), 397; https://doi.org/10.3390/met10030397 - 19 Mar 2020

Cited by 3 | Viewed by 3391

Abstract

Differential thermal analysis (DTA), thermogravimetry (TG), and mass spectrometry (MS) were used to study the thermal behavior of the blast furnace (BF) and basic oxygen furnace (BOF) sludges generated from the iron-making industry. The results indicated that under air atmosphere the two types [...] Read more.

Differential thermal analysis (DTA), thermogravimetry (TG), and mass spectrometry (MS) were used to study the thermal behavior of the blast furnace (BF) and basic oxygen furnace (BOF) sludges generated from the iron-making industry. The results indicated that under air atmosphere the two types of sludge are different in their thermal behavior. In BF sludge, the exothermic carbon gasification (CO/CO₂) reaction dominated the process, while in BOF sludge, the significant reaction occurred at 755 °C and was associated with a slight mass gain owing to the partial oxidation of Fe₃O₄ to Fe₂O₃. Under inert atmosphere, the thermal behavior of both BF and BOF sludges were dominated by a reduction reaction. In BF sludge, the endothermic reactions ranged from 785 to 1115 °C due to the reduction of iron oxides as follows: Fe₂O₃ → Fe₃O₄ → FeO → Fe. A total mass loss of about 27.78% was observed in the TG curve. While in BOF sludge, the endothermic peaks corresponded to magnetite reduction to iron (Fe). The overall mass loss of the BOF was approximately 16.92%. The mass spectrum of gases evolution for both BF and BOF sludges revealed that CO/CO₂ gases were released from the sludges. Full article

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19 pages, 17675 KiB

Open AccessArticle

Monotonic Response of Exposed Base Plates of Columns: Numerical Study and a New Design Method

by Héctor Díaz, Eduardo Nuñez and Claudio Oyarzo-Vera

Metals 2020, 10(3), 396; https://doi.org/10.3390/met10030396 - 19 Mar 2020

Cited by 5 | Viewed by 10373

Abstract

This paper describes a numerical study of the behavior of exposed base plates of columns under the action of axial and bending loads. The aim of this research is to evaluate numerically the failure mechanisms on stiffened and non-stiffened base plates and propose [...] Read more.

This paper describes a numerical study of the behavior of exposed base plates of columns under the action of axial and bending loads. The aim of this research is to evaluate numerically the failure mechanisms on stiffened and non-stiffened base plates and propose a new design method. The effects of base plate thickness, location of anchor rods, location of stiffeners and tensile strength of anchor rods were considered in the analysis. Sixteen finite elements simulations were performed considering different combinations of the above mentioned parameters. The results show a fragile response in the base plates when high resistance anchor rods are used. The anchor rods worked as fuse elements in base plates with a large thickness or many stiffeners. Additionally, the models with anchor bars located outside of the column flanges showed lower flexural strength and rotational stiffness compared to the models with anchor rods located between column flanges. The simulations showed that the base plate strength was determined by the simultaneous failure mechanisms of two or more components, different to what is stated in current design guides. Finally, the new method is suitable to design base plates with stiffened and not stiffened configurations, which unlike traditional design methods, show a good adjustment with numerical models. Full article

(This article belongs to the Special Issue Advances in Structural Steel Research)

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12 pages, 6641 KiB

Open AccessArticle

Application of the Progressive Forming Method in Simulation and Experimental Study of Rectangular Fins in a Heat Exchanger

by Chul Kyu Jin

Metals 2020, 10(3), 395; https://doi.org/10.3390/met10030395 - 19 Mar 2020

Cited by 2 | Viewed by 3503

Abstract

A progressive forming method is applied where stamping is continuously executed to produce the rectangular fins of the plate fin heat exchanger. This process produced the fins one-by-one instead of by bundles. In order to produce a fin having a depth of more [...] Read more.

A progressive forming method is applied where stamping is continuously executed to produce the rectangular fins of the plate fin heat exchanger. This process produced the fins one-by-one instead of by bundles. In order to produce a fin having a depth of more than 6.0 mm, the forming load and effective stress according to the size of the edge radii of punch and die are predicted by forming simulation. Furthermore, the process of forming the second, as well as the third, fins is predicted. As the edge radii of the die and those of the punch became smaller, the effective stresses generated during deformation became smaller. The forming load during deformation also became smaller. The sizes of the edge radii of die and punch were set to 0.5 mm and 0.2 mm, respectively. When the second fin was formed, overforming occurred at the ribs. The punch was therefore modified so that the rib could be compressed at the same time the fin was formed. With the designed process, the inner fins close to the target size could be manufactured. The resulting fins had right-angled ribs, although the fin width was a slightly opened isosceles trapezoid due to the spring-back. Full article

(This article belongs to the Special Issue Application of FEM-Simulation in Metal Forming)

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21 pages, 8392 KiB

Open AccessArticle

Effects of Processing Parameters on the Corrosion Performance of Plasma Electrolytic Oxidation Grown Oxide on Commercially Pure Aluminum

by Getinet Asrat Mengesha, Jinn P. Chu, Bih-Show Lou and Jyh-Wei Lee

Metals 2020, 10(3), 394; https://doi.org/10.3390/met10030394 - 19 Mar 2020

Cited by 18 | Viewed by 3794

Abstract

The plasma electrolyte oxidation (PEO) process has been considered an environmentally friendly surface engineering method for improving the corrosion resistance of light weight metals. In this work, the corrosion resistance of commercially pure Al and PEO treated Al substrates were studied. The PEO [...] Read more.

The plasma electrolyte oxidation (PEO) process has been considered an environmentally friendly surface engineering method for improving the corrosion resistance of light weight metals. In this work, the corrosion resistance of commercially pure Al and PEO treated Al substrates were studied. The PEO layers were grown on commercially pure aluminum substrates using two different alkaline electrolytes with different addition concentrations of Si₃N₄ nanoparticles (0, 0.5 and 1.5 gL⁻¹) and different duty cycles (25%, 50%, and 80%) at a fixed frequency. The corrosion properties of PEO coatings were investigated by the potentiodynamic polarization and electrochemical impedance spectroscopy test in 3.5 wt.% NaCl solutions. It showed that the weight gains, layer thickness and surface roughness of the PEO grown oxide layer increased with increasing concentrations of Si₃N₄ nanoparticles. The layer thickness, surface roughness, pore size, and porosity of the PEO oxide layer decreased with decreasing duty cycle. The layer thickness and weight gain of PEO coating followed a linear relationship. The PEO layer grown using the Na₂B₄O₇∙10H₂O contained electrolyte showed an excellent corrosion resistance and low surface roughness than other PEO coatings with Si₃N₄ nanoparticle additives. It is noticed that the corrosion performance of PEO coatings were not improved by the addition of Si₃N₄ nanoparticle in the electrolytic solutions, possibly due to its detrimental effect to the formation of a dense microstructure. Full article

(This article belongs to the Special Issue Plasma Treatment on Alloys' Surface)

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15 pages, 3573 KiB

Open AccessArticle

Investigation into the Effect of Increasing Target Temperature and the Size of Cavity Confinements on Laser-Induced Plasmas

by Hongbing Yao, Emmanuel Asamoah, Pengyu Wei, Jiawei Cong, Lin Zhang, James Kwasi Quaisie, Anita Asamoah, Kwaku Ayepah and Weihua Zhu

Metals 2020, 10(3), 393; https://doi.org/10.3390/met10030393 - 19 Mar 2020

Cited by 7 | Viewed by 2606

Abstract

In this work, the effect of the sample temperature on the magnesium (Mg) and titanium (Ti) plasmas generated by a Q-switched Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser operating at its fundamental wavelength of 1064 nm has been investigated. We observed that increasing the [...] Read more.

In this work, the effect of the sample temperature on the magnesium (Mg) and titanium (Ti) plasmas generated by a Q-switched Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser operating at its fundamental wavelength of 1064 nm has been investigated. We observed that increasing the sample temperature significantly enhanced the emission intensities of the plasmas. Comparing the emission peak intensities of the case of 100 °C to the case of 300 °C, we recorded a substantial enhancement of the peak intensities of the latter compared to the former. From these results it can be observed that increasing the sample temperature has a significant effect on the emission intensities of the plasmas. We also studied the plasma dynamics and found that increasing the sample temperature also decreases the air density around the Mg sample surface. The reduction in the air density resulted in a decrease in the radiation process and lowers collision probability. Furthermore, as the plasma expands, the plasma pressure also decreases. In addition, we also employed circular and square cavities to confine the titanium plasma, and investigated the effect of the sizes of the circular and square cavities on the titanium plasma. We observed a general improvement in the emission intensities with both the circular and square cavities and attributed this improvement to the plasma compression effect of the shock waves produced by the plasma within the cavities. Full article

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19 pages, 7494 KiB

Open AccessFeature PaperArticle

The Influence of Vanadium Additions on Isothermally Formed Bainite Microstructures in Medium Carbon Steels Containing Retained Austenite

by Irina Pushkareva, Babak Shalchi-Amirkhiz, Sébastien Yves Pierre Allain, Guillaume Geandier, Fateh Fazeli, Matthew Sztanko and Colin Scott

Metals 2020, 10(3), 392; https://doi.org/10.3390/met10030392 - 19 Mar 2020

Cited by 15 | Viewed by 3847

Abstract

The influence of V additions on isothermally formed bainite in medium carbon steels containing retained austenite has been investigated using in-situ high energy X-ray diffraction (HEXRD) and ex-situ electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDX) techniques in the transmission [...] Read more.

The influence of V additions on isothermally formed bainite in medium carbon steels containing retained austenite has been investigated using in-situ high energy X-ray diffraction (HEXRD) and ex-situ electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDX) techniques in the transmission electron microscope (TEM). No significant impact of V in solid solution on the bainite transformation rate, final phase fractions or on the width of bainite laths was seen for transformations in the range 375–430 °C. No strong influence on the dislocation density could be detected, although quantitative analysis was impeded by ferrite tetragonality. A reduction in the carbon content of retained austenite C_γ that is not believed to be due to competition with VC or cementite precipitation was observed. No influence of V on the carbon supersaturation in bainitic ferrite C_b could be directly measured, although carbon mass balance calculations suggest C_b slightly increases. A beneficial refinement of blocky MA and a corresponding size effect induced enhancement in austenite stability were found at the lowest transformation temperature. Overall, V additions result in a slight increase in strength levels. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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