Materials

11960 KiB

Open AccessArticle

A Model of BGA Thermal Fatigue Life Prediction Considering Load Sequence Effects

by Weiwei Hu, Yaqiu Li, Yufeng Sun and Ali Mosleh

Materials 2016, 9(10), 860; https://doi.org/10.3390/ma9100860 - 24 Oct 2016

Cited by 9 | Viewed by 6192

Accurate testing history data is necessary for all fatigue life prediction approaches, but such data is always deficient especially for the microelectronic devices. Additionally, the sequence of the individual load cycle plays an important role in physical fatigue damage. However, most of the [...] Read more.

Accurate testing history data is necessary for all fatigue life prediction approaches, but such data is always deficient especially for the microelectronic devices. Additionally, the sequence of the individual load cycle plays an important role in physical fatigue damage. However, most of the existing models based on the linear damage accumulation rule ignore the sequence effects. This paper proposes a thermal fatigue life prediction model for ball grid array (BGA) packages to take into consideration the load sequence effects. For the purpose of improving the availability and accessibility of testing data, a new failure criterion is discussed and verified by simulation and experimentation. The consequences for the fatigue underlying sequence load conditions are shown. Full article

(This article belongs to the Special Issue Fracture and Fatigue Mechanics of Materials)

► Show Figures

Figure 1

3895 KiB

Open AccessArticle

An In-Depth Investigation into the Physicochemical, Thermal, Microstructural, and Rheological Properties of Petroleum and Natural Asphalts

by Nader Nciri, Jeonghyun Kim, Namho Kim and Namjun Cho

Materials 2016, 9(10), 859; https://doi.org/10.3390/ma9100859 - 21 Oct 2016

Cited by 30 | Viewed by 6187

Abstract

Over the last decade, unexpected and sudden pavement failures have occurred in several provinces in South Korea. Some of these failures remain unexplained, further illustrating the gaps in our knowledge about binder chemistry. To prevent premature pavement distress and enhance road performance, it [...] Read more.

Over the last decade, unexpected and sudden pavement failures have occurred in several provinces in South Korea. Some of these failures remain unexplained, further illustrating the gaps in our knowledge about binder chemistry. To prevent premature pavement distress and enhance road performance, it is imperative to provide an adequate characterization of asphalt. For this purpose, the current research aims at inspecting the chemistry, microstructure, thermal, and physico-rheological properties of two types of asphalt, namely petroleum asphalt (PA) and natural asphalt (NA). The binders were extensively investigated by using elemental analysis, thin-layer chromatography with flame ionization detection (TLC-FID), matrix-assisted laser desorption ionization time-of-fight mass spectroscopy (MALDI-TOF-MS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), Nuclear magnetic resonance spectroscopy (¹H-NMR), ultraviolet and visible spectroscopy (UV-VIS), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), penetration, softening point, ductility, and viscosity tests. The findings of this research have revealed the distinct variations between the chemical compositions, microstructures, and thermo-rheological properties of the two asphalts and provided valuable knowledge into the characteristics of the binders. Such insight has been effective in predicting the performance or distress of road pavement. This paper will, therefore, be of immediate interest to materials engineers in state highway agencies and asphalt industries. Full article

(This article belongs to the Section Advanced Materials Characterization)

► Show Figures

Figure 1

7768 KiB

Open AccessReview

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

by Nicola H. Perry and Tatsumi Ishihara

Materials 2016, 9(10), 858; https://doi.org/10.3390/ma9100858 - 21 Oct 2016

Cited by 46 | Viewed by 9097

Abstract

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface [...] Read more.

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I²CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS) with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance. Full article

(This article belongs to the Special Issue Recent Advances in Materials for Solid Oxide Cells)

► Show Figures

Figure 1

4239 KiB

Open AccessArticle

Gold Nanoparticle-Based Colorimetric and Electrochemical Methods for Dipeptidyl Peptidase-IV Activity Assay and Inhibitor Screening

by Ning Xia, Xin Wang, Xiaojin Wang and Binbin Zhou

Materials 2016, 9(10), 857; https://doi.org/10.3390/ma9100857 - 21 Oct 2016

Cited by 14 | Viewed by 6061

Abstract

We presented the colorimetric and electrochemical methods for determination of the dipeptidyl peptidase-IV (DPP-IV) activity and screening of its inhibitor using gold nanoparticle (AuNP) as the probe. In the colorimetric assay, the substrate peptide with a sequence of Arg-Pro-Arg induced the aggregation and [...] Read more.

We presented the colorimetric and electrochemical methods for determination of the dipeptidyl peptidase-IV (DPP-IV) activity and screening of its inhibitor using gold nanoparticle (AuNP) as the probe. In the colorimetric assay, the substrate peptide with a sequence of Arg-Pro-Arg induced the aggregation and color change of AuNPs, whereas cleavage of the peptide by DPP-IV prevented the aggregation of AuNPs. Furthermore, the aggregation of AuNPs in the solution was easily initiated on a solid/liquid (electrode/electrolyte) surface, which induced a decrease in the electron-transfer resistance. However, once the peptide was clipped by DPP-IV, the assembly of AuNPs on electrode surface was prevented. Consequently, a higher electron-transfer resistance was observed. The colorimetric and electrochemical assays allowed for the determination of DPP-IV with the detection limits of 70 μU/mL and 0.55 μU/mL, respectively. Meanwhile, the proposed methods were used to determine DPP-IV inhibitor with satisfactory results. Both the colorimetric and electrochemical methods are simple, rapid and sufficiently sensitive for DPP-IV activity assay and inhibitor screening. The results also demonstrated that the AuNP-based colorimetric assay could be converted into an enhanced surface tethered electrochemical assay with improving sensitivity. The simple detection principle may be extended to the design of other peptidases biosensors with easy manipulation procedures. Full article

(This article belongs to the Special Issue Noble Metal Nanoparticles)

► Show Figures

Figure 1

4402 KiB

Open AccessArticle

Tribological Performance of Green Lubricant Enhanced by Sulfidation IF-MoS₂

by Shih-Chen Shi

Materials 2016, 9(10), 856; https://doi.org/10.3390/ma9100856 - 21 Oct 2016

Cited by 36 | Viewed by 6145

Abstract

Biopolymers reinforced with nanoparticle (NP) additives are widely used in tribological applications. In this study, the effect of NP additives on the tribological properties of a green lubricant hydroxypropyl methylcellulose (HPMC) composite was investigated. The IF-MoS₂ NPs were prepared using the newly [...] Read more.

Biopolymers reinforced with nanoparticle (NP) additives are widely used in tribological applications. In this study, the effect of NP additives on the tribological properties of a green lubricant hydroxypropyl methylcellulose (HPMC) composite was investigated. The IF-MoS₂ NPs were prepared using the newly developed gas phase sulfidation method to form a multilayered, polyhedral structure. The number of layers and crystallinity of IF-MoS₂ increased with sulfidation time and temperature. The dispersity of NPs in the HPMC was investigated using Raman and EDS mapping and showed great uniformity. The use of NPs with HPMC enhanced the tribological performance of the composites as expected. The analysis of the worn surface shows that the friction behavior of the HPMC composite with added NPs is very sensitive to the NP structure. The wear mechanisms vary with NP structure and depend on their lubricating behaviors. Full article

(This article belongs to the Special Issue Selected Papers from IMETI2016)

► Show Figures

Figure 1

2820 KiB

Open AccessFeature PaperArticle

Synthesis of CdSe Quantum Dots Using Fusarium oxysporum

by Takaaki Yamaguchi, Yoshijiro Tsuruda, Tomohiro Furukawa, Lumi Negishi, Yuki Imura, Shohei Sakuda, Etsuro Yoshimura and Michio Suzuki

Materials 2016, 9(10), 855; https://doi.org/10.3390/ma9100855 - 20 Oct 2016

Cited by 34 | Viewed by 6887

Abstract

CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum) were optimized [...] Read more.

CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum) were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were precipitated in the intracellular space, indicating that cadmium and selenium ions were incorporated into the cell and that the quantum dots were synthesized with intracellular metabolites. To reveal differences in F. oxysporum metabolism, cell extracts of F. oxysporum, before and after CdSe synthesis, were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results suggested that the amount of superoxide dismutase (SOD) decreased after CdSe synthesis. Fluorescence microscopy revealed that cytoplasmic superoxide increased significantly after CdSe synthesis. The accumulation of superoxide may increase the expression of various metabolites that play a role in reducing Se⁴⁺ to Se²⁻ and inhibit the aggregation of CdSe to make nanoparticles. Full article

(This article belongs to the Special Issue Biological and Synthetic Organic–Inorganic Composite Materials)

► Show Figures

Graphical abstract

4493 KiB

Open AccessArticle

Synthesis and Characterization of Poly(Ethylene Glycol) Based Thermo-Responsive Hydrogels for Cell Sheet Engineering

by Kuk Hui Son and Jin Woo Lee

Materials 2016, 9(10), 854; https://doi.org/10.3390/ma9100854 - 20 Oct 2016

Cited by 75 | Viewed by 11323

Abstract

The swelling properties and thermal transition of hydrogels can be tailored by changing the hydrophilic-hydrophobic balance of polymer networks. Especially, poly(N-isopropylacrylamide) (PNIPAm) has received attention as thermo-responsive hydrogels for tissue engineering because its hydrophobicity and swelling property are transited around body [...] Read more.

The swelling properties and thermal transition of hydrogels can be tailored by changing the hydrophilic-hydrophobic balance of polymer networks. Especially, poly(N-isopropylacrylamide) (PNIPAm) has received attention as thermo-responsive hydrogels for tissue engineering because its hydrophobicity and swelling property are transited around body temperature (32 °C). In this study, we investigated the potential of poly(ethylene glycol) diacrylate (PEGDA) as a hydrophilic co-monomer and crosslinker of PNIPAm to enhance biological properties of PNIPAm hydrogels. The swelling ratios, lower critical solution temperature (LCST), and internal pore structure of the synthesized p(NIPAm-co-PEGDA) hydrogels could be varied with changes in the molecular weight of PEGDA and the co-monomer ratios (NIPAm to PEGDA). We found that increasing the molecular weight of PEGDA showed an increase of pore sizes and swelling ratios of the hydrogels. In contrast, increasing the weight ratio of PEGDA under the same molecular weight condition increased the crosslinking density and decreased the swelling ratios of the hydrogels. Further, to evaluate the potential of these hydrogels as cell sheets, we seeded bovine chondrocytes on the p(NIPAm-co-PEGDA) hydrogels and observed the proliferation of the seed cells and their detachment as a cell sheet upon a decrease in temperature. Based on our results, we confirmed that p(NIPAm-co-PEGDA) hydrogels could be utilized as cell sheets with enhanced cell proliferation performance. Full article

(This article belongs to the Special Issue Smart Biomaterials and Biointerfaces)

► Show Figures

Figure 1

5497 KiB

Open AccessArticle

Porous Alpha-Tricalcium Phosphate with Immobilized Basic Fibroblast Growth Factor Enhances Bone Regeneration in a Canine Mandibular Bone Defect Model

by Nobuhiro Kobayashi, Yoshiya Hashimoto, Akihisa Otaka, Tetsuji Yamaoka and Shosuke Morita

Materials 2016, 9(10), 853; https://doi.org/10.3390/ma9100853 - 19 Oct 2016

Cited by 14 | Viewed by 5146

Abstract

The effect of porous alpha-tricalcium phosphate (α-TCP) with immobilized basic fibroblast growth factor (bFGF) on bone regeneration was evaluated in a canine mandibular bone defect model. Identical bone defects were made in the canine mandible; six defects in each animal were filled with [...] Read more.

The effect of porous alpha-tricalcium phosphate (α-TCP) with immobilized basic fibroblast growth factor (bFGF) on bone regeneration was evaluated in a canine mandibular bone defect model. Identical bone defects were made in the canine mandible; six defects in each animal were filled with porous α-TCP with bFGF bound via heparin (bFGF group), whereas the other was filled with unmodified porous α-TCP (control group). Micro-computed tomography and histological evaluation were performed two, four and eight weeks after implantation. The bone mineral density of the bFGF group was higher than that of the control group at each time point (p < 0.05), and the bone mineral content of the bFGF group was higher than that of the control group at four and eight weeks (p < 0.05). Histological evaluation two weeks after implantation revealed that the porous α-TCP had degraded and bone had formed on the surface of α-TCP particles in the bFGF group. At eight weeks, continuous cortical bone with a Haversian structure covered the top of bone defects in the bFGF group. These findings demonstrate that porous α-TCP with immobilized bFGF can promote bone regeneration. Full article

(This article belongs to the Section Biomaterials)

► Show Figures

Figure 1

4726 KiB

Open AccessArticle

A Fracture Analysis of Ti-10Mo-8V-1Fe-3.5Al Alloy Screws during Assembly

by Weifang Zhang, Yuanxing Huang, Wei Dai, Xiaoshuai Jin and Chang Yin

Materials 2016, 9(10), 852; https://doi.org/10.3390/ma9100852 - 19 Oct 2016

Cited by 3 | Viewed by 5738

Abstract

Titanium screws have properties that make them ideal for applications that require both a high strength-to-weight ratio and corrosion resistance, such as fastener applications for aviation and aerospace. The fracture behavior of Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy screws during assembly was explored. Besides visual examination, [...] Read more.

Titanium screws have properties that make them ideal for applications that require both a high strength-to-weight ratio and corrosion resistance, such as fastener applications for aviation and aerospace. The fracture behavior of Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy screws during assembly was explored. Besides visual examination, other experimental techniques used for the investigation are as follows: (1) fracture characteristics and damage morphology via scanning electron microscopy (SEM); (2) chemical constituents via energy dispersive spectroscopy (EDS) and hydrogen concentration testing; (3) metallographic observation; (4) stress durability embrittlement testing; and (5) torsion simulation testing. Results show that the fracture mode of the screws is brittle. There is no obvious relation to hydrogen-induced brittle. The main reason for the fracture of titanium alloy screws is internal defects, around which oxygen content is high, increasing brittleness. The internal defects of screws result from grain boundary cracking caused by hot forging. Full article

► Show Figures

Figure 1

4334 KiB

Open AccessArticle

Morphological Influence of Solution-Processed Zinc Oxide Films on Electrical Characteristics of Thin-Film Transistors

by Hyeonju Lee, Xue Zhang, Jaeeun Hwang and Jaehoon Park

Materials 2016, 9(10), 851; https://doi.org/10.3390/ma9100851 - 19 Oct 2016

Cited by 31 | Viewed by 6663

Abstract

We report on the morphological influence of solution-processed zinc oxide (ZnO) semiconductor films on the electrical characteristics of ZnO thin-film transistors (TFTs). Different film morphologies were produced by controlling the spin-coating condition of a precursor solution, and the ZnO films were analyzed using [...] Read more.

We report on the morphological influence of solution-processed zinc oxide (ZnO) semiconductor films on the electrical characteristics of ZnO thin-film transistors (TFTs). Different film morphologies were produced by controlling the spin-coating condition of a precursor solution, and the ZnO films were analyzed using atomic force microscopy, X-ray diffraction, X-ray photoemission spectroscopy, and Hall measurement. It is shown that ZnO TFTs have a superior performance in terms of the threshold voltage and field-effect mobility, when ZnO crystallites are more densely packed in the film. This is attributed to lower electrical resistivity and higher Hall mobility in a densely packed ZnO film. In the results of consecutive TFT operations, a positive shift in the threshold voltage occurred irrespective of the film morphology, but the morphological influence on the variation in the field-effect mobility was evident. The field-effect mobility in TFTs having a densely packed ZnO film increased continuously during consecutive TFT operations, which is in contrast to the mobility decrease observed in the less packed case. An analysis of the field-effect conductivities ascribes these results to the difference in energetic traps, which originate from structural defects in the ZnO films. Consequently, the morphological influence of solution-processed ZnO films on the TFT performance can be understood through the packing property of ZnO crystallites. Full article

(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)

► Show Figures

Figure 1

3034 KiB

Open AccessArticle

Flexural Capability of Patterned Transparent Conductive Substrate by Performing Electrical Measurements and Stress Simulations

by Chang-Chun Lee, Pei-Chen Huang and Ko-Shun Wang

Materials 2016, 9(10), 850; https://doi.org/10.3390/ma9100850 - 19 Oct 2016

Cited by 9 | Viewed by 5746

Abstract

The suitability of stacked thin films for next-generation display technology was analyzed based on their properties and geometrical designs to evaluate the mechanical reliability of transparent conducting thin films utilized in flexural displays. In general, the high bending stress induced by various operation [...] Read more.

The suitability of stacked thin films for next-generation display technology was analyzed based on their properties and geometrical designs to evaluate the mechanical reliability of transparent conducting thin films utilized in flexural displays. In general, the high bending stress induced by various operation conditions is a major concern regarding the mechanical reliability of indium–tin–oxide (ITO) films deposited on polyethylene terephthalate (PET) substrates; mechanical reliability is commonly used to estimate the flexibility of displays. However, the pattern effect is rarely investigated to estimate the mechanical reliability of ITO/PET films. Thus, this study examined the flexible content of patterned ITO/PET films with two different line widths by conducting bending tests and sheet resistance measurements. Moreover, a stress–strain simulation enabled by finite element analysis was performed on the patterned ITO/PET to explore the stress impact of stacked film structures under various levels of flexural load. Results show that the design of the ITO/PET film can be applied in developing mechanically reliable flexible electronics. Full article

(This article belongs to the Special Issue Advances in Bendable and Soft Material Film)

► Show Figures

Figure 1

7297 KiB

Open AccessArticle

Synthesis and Characterization of N-Doped Porous TiO₂ Hollow Spheres and Their Photocatalytic and Optical Properties

by Hongliang Li, Hui Liu, Aiping Fu, Guanglei Wu, Man Xu, Guangsheng Pang, Peizhi Guo, Jingquan Liu and Xiu Song Zhao

Materials 2016, 9(10), 849; https://doi.org/10.3390/ma9100849 - 19 Oct 2016

Cited by 22 | Viewed by 8843

Abstract

Three kinds of N-doped mesoporous TiO₂ hollow spheres with different N-doping contents, surface area, and pore size distributions were prepared based on a sol–gel synthesis and combined with a calcination process. Melamine formaldehyde (MF) microspheres have been used as sacrificial template and [...] Read more.

Three kinds of N-doped mesoporous TiO₂ hollow spheres with different N-doping contents, surface area, and pore size distributions were prepared based on a sol–gel synthesis and combined with a calcination process. Melamine formaldehyde (MF) microspheres have been used as sacrificial template and cetyltrimethyl ammonium bromide (CTAB) or polyvinylpyrrolidone (PVP) was selected as pore-directing agent. Core–shell intermediate spheres of titania-coated MF with diameters of 1.2–1.6 μm were fabricated by varying the volume concentration of TiO₂ precursor from 1 to 3 vol %. By calcining the core–shell composite spheres at 500 °C for 3 h in air, an in situ N-doping process occurred upon the decomposition of the MF template and CTAB or PVP pore-directing surfactant. N-doped mesoporous TiO₂ hollow spheres with sizes in the range of 0.4–1.2 μm and shell thickness from 40 to 110 nm were obtained. The composition and N-doping content, thermal stability, morphology, surface area and pore size distribution, wall thickness, photocatalytic activities, and optical properties of the mesoporous TiO₂ hollow spheres derived from different conditions were investigated and compared based on Fourier-transformation infrared (FTIR), SEM, TEM, thermogravimetric analysis (TGA), nitrogen adsorption–desorption, and UV–vis spectrophotoscopy techniques. The influences of particle size, N-doping, porous, and hollow characteristics of the TiO₂ hollow spheres on their photocatalytic activities and optical properties have been studied and discussed based on the composition analysis, structure characterization, and optical property investigation of these hollow spherical TiO₂ matrices. Full article

(This article belongs to the Special Issue Porous Materials for Water Technology)

► Show Figures

Figure 1

3001 KiB

Open AccessArticle

A Novel Nanohybrid Nanofibrous Adsorbent for Water Purification from Dye Pollutants

by Shahin Homaeigohar, Ahnaf Usman Zillohu, Ramzy Abdelaziz, Mehdi Keshavarz Hedayati and Mady Elbahri

Materials 2016, 9(10), 848; https://doi.org/10.3390/ma9100848 - 19 Oct 2016

Cited by 59 | Viewed by 7134

Abstract

In this study, we devised a novel nanofibrous adsorbent made of polyethersulfone (PES) for removal of methylene blue (MB) dye pollutant from water. The polymer shows a low isoelectric point thus at elevated pHs and, being nanofibrous, can offer a huge highly hydroxylated [...] Read more.

In this study, we devised a novel nanofibrous adsorbent made of polyethersulfone (PES) for removal of methylene blue (MB) dye pollutant from water. The polymer shows a low isoelectric point thus at elevated pHs and, being nanofibrous, can offer a huge highly hydroxylated surface area for adsorption of cationic MB molecules. As an extra challenge, to augment the adsorbent’s properties in terms of adsorption capacity in neutral and acidic conditions and thermal stability, vanadium pentoxide (V₂O₅) nanoparticles were added to the nanofibers. Adsorption data were analyzed according to the Freundlich adsorption model. The thermodynamic parameters verified that only at basic pH is the adsorption spontaneous and in general the process is entropy-driven and endothermic. The kinetics of the adsorption process was evaluated by the pseudo-first- and pseudo-second-order models. The latter model exhibited the highest correlation with data. In sum, the adsorbent showed a promising potential for dye removal from industrial dyeing wastewater systems, especially when envisaging their alkaline and hot conditions. Full article

(This article belongs to the Special Issue Green Nanotechnology)

► Show Figures

Graphical abstract

4031 KiB

Open AccessArticle

Effect of Surface Densification on the Microstructure and Mechanical Properties of Powder Metallurgical Gears by Using a Surface Rolling Process

by Jingguang Peng, Yan Zhao, Di Chen, Kiade Li, Wei Lu and Biao Yan

Materials 2016, 9(10), 846; https://doi.org/10.3390/ma9100846 - 19 Oct 2016

Cited by 10 | Viewed by 4446

Abstract

Powder metallurgy (PM) components are widely used in the auto industry due to the advantage of net-shape forming, low cost, and high efficiency. Still, usage of PM components is limited in the auto industry when encountering rigorous situations, like heavy load, due to [...] Read more.

Powder metallurgy (PM) components are widely used in the auto industry due to the advantage of net-shape forming, low cost, and high efficiency. Still, usage of PM components is limited in the auto industry when encountering rigorous situations, like heavy load, due to lower strength, hardness, wear resistance, and other properties compared to wrought components due to the existence of massive pores in the PM components. In this study, through combining the powder metallurgy process and rolling process, the pores in the PM components were decreased and a homogenous densified layer was formed on the surface, which resulted in the enhancement of the strength, hardness, wear resistance, and other properties, which can expand its range of application. In this paper, we study the impact of different rolling feeds on the performance of the components’ surfaces. We found that with the increase of the rolling feed, the depth of the densified layer increased. Full article

(This article belongs to the Special Issue Tribological Behavior of Materials by Surface Engineering)

► Show Figures

Figure 1

10879 KiB

Open AccessArticle

Comparisons of Damage Evolution between 2D C/SiC and SiC/SiC Ceramic-Matrix Composites under Tension-Tension Cyclic Fatigue Loading at Room and Elevated Temperatures

by Longbiao Li

Materials 2016, 9(10), 844; https://doi.org/10.3390/ma9100844 - 19 Oct 2016

Cited by 8 | Viewed by 5229

Abstract

In this paper, comparisons of damage evolution between 2D C/SiC and SiC/SiC ceramic-matrix composites (CMCs) under tension–tension cyclic fatigue loading at room and elevated temperatures have been investigated. Fatigue hysteresis loops models considering multiple matrix cracking modes in 2D CMCs have been developed [...] Read more.

In this paper, comparisons of damage evolution between 2D C/SiC and SiC/SiC ceramic-matrix composites (CMCs) under tension–tension cyclic fatigue loading at room and elevated temperatures have been investigated. Fatigue hysteresis loops models considering multiple matrix cracking modes in 2D CMCs have been developed based on the damage mechanism of fiber sliding relative to the matrix in the interface debonded region. The relationships between the fatigue hysteresis loops, fatigue hysteresis dissipated energy, fatigue peak stress, matrix multiple cracking modes, and interface shear stress have been established. The effects of fiber volume fraction, fatigue peak stress and matrix cracking mode proportion on fatigue hysteresis dissipated energy and interface debonding and sliding have been analyzed. The experimental fatigue hysteresis dissipated energy of 2D C/SiC and SiC/SiC composites at room temperature, 550 °C, 800 °C, and 1100 °C in air, and 1200 °C in vacuum corresponding to different fatigue peak stresses and cycle numbers have been analyzed. The interface shear stress degradation rate has been obtained through comparing the experimental fatigue hysteresis dissipated energy with theoretical values. Fatigue damage evolution in C/SiC and SiC/SiC composites has been compared using damage parameters of fatigue hysteresis dissipated energy and interface shear stress degradation rate. It was found that the interface shear stress degradation rate increases at elevated temperature in air compared with that at room temperature, decreases with increasing loading frequency at room temperature, and increases with increasing fatigue peak stress at room and elevated temperatures. Full article

(This article belongs to the Section Advanced Composites)

► Show Figures

Figure 1

2828 KiB

Open AccessArticle

Optimization of High Temperature and Pressurized Steam Modified Wood Fibers for High-Density Polyethylene Matrix Composites Using the Orthogonal Design Method

by Xun Gao, Qingde Li, Wanli Cheng, Guangping Han and Lihui Xuan

Materials 2016, 9(10), 847; https://doi.org/10.3390/ma9100847 - 18 Oct 2016

Cited by 23 | Viewed by 5930

Abstract

The orthogonal design method was used to determine the optimum conditions for modifying poplar fibers through a high temperature and pressurized steam treatment for the subsequent preparation of wood fiber/high-density polyethylene (HDPE) composites. The extreme difference, variance, and significance analyses were performed to [...] Read more.

The orthogonal design method was used to determine the optimum conditions for modifying poplar fibers through a high temperature and pressurized steam treatment for the subsequent preparation of wood fiber/high-density polyethylene (HDPE) composites. The extreme difference, variance, and significance analyses were performed to reveal the effect of the modification parameters on the mechanical properties of the prepared composites, and they yielded consistent results. The main findings indicated that the modification temperature most strongly affected the mechanical properties of the prepared composites, followed by the steam pressure. A temperature of 170 °C, a steam pressure of 0.8 MPa, and a processing time of 20 min were determined as the optimum parameters for fiber modification. Compared to the composites prepared from untreated fibers, the tensile, flexural, and impact strength of the composites prepared from modified fibers increased by 20.17%, 18.5%, and 19.3%, respectively. The effect on the properties of the composites was also investigated by scanning electron microscopy and dynamic mechanical analysis. When the temperature, steam pressure, and processing time reached the highest values, the composites exhibited the best mechanical properties, which were also well in agreement with the results of the extreme difference, variance, and significance analyses. Moreover, the crystallinity and thermal stability of the fibers and the storage modulus of the prepared composites improved; however, the hollocellulose content and the pH of the wood fibers decreased. Full article

► Show Figures

Graphical abstract

6713 KiB

Open AccessArticle

Modification of Lightweight Aggregates’ Microstructure by Used Motor Oil Addition

by Małgorzata Franus, Grzegorz Jozefaciuk, Lidia Bandura, Krzysztof Lamorski, Mieczysław Hajnos and Wojciech Franus

Materials 2016, 9(10), 845; https://doi.org/10.3390/ma9100845 - 18 Oct 2016

Cited by 16 | Viewed by 6139

Abstract

An admixture of lightweight aggregate substrates (beidellitic clay containing 10 wt % of natural clinoptilolite or Na-P1 zeolite) with used motor oil (1 wt %–8 wt %) caused marked changes in the aggregates’ microstructure, measured by a combination of mercury porosimetry (MIP), microtomography [...] Read more.

An admixture of lightweight aggregate substrates (beidellitic clay containing 10 wt % of natural clinoptilolite or Na-P1 zeolite) with used motor oil (1 wt %–8 wt %) caused marked changes in the aggregates’ microstructure, measured by a combination of mercury porosimetry (MIP), microtomography (MT), and scanning electron microscopy. Maximum porosity was produced at low (1%–2%) oil concentrations and it dropped at higher concentrations, opposite to the aggregates’ bulk density. Average pore radii, measured by MIP, decreased with an increasing oil concentration, whereas larger (MT) pore sizes tended to increase. Fractal dimension, derived from MIP data, changed similarly to the MIP pore radius, while that derived from MT remained unaltered. Solid phase density, measured by helium pycnometry, initially dropped slightly and then increased with the amount of oil added, which was most probably connected to changes in the formation of extremely small closed pores that were not available for He atoms. Full article

(This article belongs to the Special Issue Porous Ceramics)

► Show Figures

Graphical abstract

3587 KiB

Open AccessArticle

Interior Fracture Mechanism Analysis and Fatigue Life Prediction of Surface-Hardened Gear Steel under Axial Loading

by Wei Li, Hailong Deng and Pengfei Liu

Materials 2016, 9(10), 843; https://doi.org/10.3390/ma9100843 - 18 Oct 2016

Cited by 20 | Viewed by 5521

Abstract

The interior defect-induced fracture of surface-hardened metallic materials in the long life region has become a key issue on engineering design. In the present study, the axial loading test with fully reversed condition was performed to examine the fatigue property of a surface-carburized [...] Read more.

The interior defect-induced fracture of surface-hardened metallic materials in the long life region has become a key issue on engineering design. In the present study, the axial loading test with fully reversed condition was performed to examine the fatigue property of a surface-carburized low alloy gear steel in the long life region. Results show that this steel represents the duplex S-N (stress-number of cycles) characteristics without conventional fatigue limit related to 10⁷ cycles. Fatigue cracks are all originated from the interior inclusions in the matrix region due to the inhabitation effect of carburized layer. The inclusion induced fracture with fisheye occurs in the short life region below 5 × 10⁵ cycles, whereas the inclusion induced fracture with fine granular area (FGA) and fisheye occurs in the long life region beyond 10⁶ cycles. The stress intensity factor range at the front of FGA can be regarded as the threshold value controlling stable growth of interior long crack. The evaluated maximum inclusion size in the effective damage volume of specimen is about 27.29 μm. Considering the size relationships between fisheye and FGA, and inclusion, the developed life prediction method involving crack growth can be acceptable on the basis of the good agreement between the predicted and experimental results. Full article

(This article belongs to the Special Issue Fracture and Fatigue Mechanics of Materials)

► Show Figures

Figure 1

2892 KiB

Open AccessArticle

Incorporation of Rubber Powder as Filler in a New Dry-Hybrid Technology: Rheological and 3D DEM Mastic Performances Evaluation

by Valeria Vignali, Francesco Mazzotta, Cesare Sangiorgi, Andrea Simone, Claudio Lantieri and Giulio Dondi

Materials 2016, 9(10), 842; https://doi.org/10.3390/ma9100842 - 18 Oct 2016

Cited by 19 | Viewed by 4886

Abstract

In recent years, the use of crumb rubber as modifier or additive within asphalt concretes has allowed obtaining mixtures able to bind high performances to recovery and reuse of discarded tires. To date, the common technologies that permit the reuse of rubber powder [...] Read more.

In recent years, the use of crumb rubber as modifier or additive within asphalt concretes has allowed obtaining mixtures able to bind high performances to recovery and reuse of discarded tires. To date, the common technologies that permit the reuse of rubber powder are the wet and dry ones. In this paper, a dry-hybrid technology for the production of Stone Mastic Asphalt mixtures is proposed. It allows the use of the rubber powder as filler, replacing part of the limestone one. Fillers are added and mixed with a high workability bitumen, modified with SBS (styrene-butadiene-styrene) polymer and paraffinic wax. The role of rubber powder and limestone filler within the bituminous mastic has been investigated through two different approaches. The first one is a rheological approach, which comprises a macro-scale laboratory analysis and a micro-scale DEM simulation. The second, instead, is a performance approach at high temperatures, which includes Multiple Stress Creep Recovery tests. The obtained results show that the rubber works as filler and it improves rheological characteristics of the polymer modified bitumen. In particular, it increases stiffness and elasticity at high temperatures and it reduces complex modulus at low temperatures. Full article

► Show Figures

Graphical abstract

1752 KiB

Open AccessArticle

Cubic C₃N: A New Superhard Phase of Carbon-Rich Nitride

by Qun Wei, Quan Zhang, Haiyan Yan and Meiguang Zhang

Materials 2016, 9(10), 840; https://doi.org/10.3390/ma9100840 - 17 Oct 2016

Cited by 18 | Viewed by 5742

Abstract

Using the particle swarm optimization technique, we proposed a cubic superhard phase of C₃N (c-C₃N) with an estimated Vicker’s hardness of 65 GPa, which is more energetically favorable than the recently proposed o-C₃N. The [...] Read more.

Using the particle swarm optimization technique, we proposed a cubic superhard phase of C₃N (c-C₃N) with an estimated Vicker’s hardness of 65 GPa, which is more energetically favorable than the recently proposed o-C₃N. The c-C₃N is the most stable phase in a pressure range of 6.5–15.4 GPa. Above 15.4 GPa, the most energetic favorable high pressure phase R3m-C₃N is uncovered. Phonon dispersion and elastic constant calculations confirm the dynamical and mechanical stability of c-C₃N and R3m-C₃N at ambient pressure. The electronic structure calculations indicate that both c-C₃N and R3m-C₃N are indirect semiconductor. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

► Show Figures

Graphical abstract

5833 KiB

Open AccessArticle

Polymer-Cement Composites Containing Waste Perlite Powder

by Paweł Łukowski

Materials 2016, 9(10), 839; https://doi.org/10.3390/ma9100839 - 17 Oct 2016

Cited by 24 | Viewed by 6728

Abstract

Polymer-cement composites (PCCs) are materials in which the polymer and mineral binder create an interpenetrating network and co-operate, significantly improving the performance of the material. On the other hand, the need for the utilization of waste materials is a demand of sustainable construction. [...] Read more.

Polymer-cement composites (PCCs) are materials in which the polymer and mineral binder create an interpenetrating network and co-operate, significantly improving the performance of the material. On the other hand, the need for the utilization of waste materials is a demand of sustainable construction. Various mineral powders, such as fly ash or blast-furnace slag, are successfully used for the production of cement and concrete. This paper deals with the use of perlite powder, which is a burdensome waste from the process of thermal expansion of the raw perlite, as a component of PCCs. The results of the testing of the mechanical properties of the composite and some microscopic observations are presented, indicating that there is a possibility to rationally and efficiently utilize waste perlite powder as a component of the PCC. This would lead to creating a new type of building material that successfully meets the requirements of sustainable construction. Full article

► Show Figures

Figure 1

10530 KiB

Open AccessArticle

Metal-Promoted Assembly of Two Collagen Mimetic Peptides into a Biofunctional “Spiraled Horn” Scaffold

by Kevin Strauss and Jean Chmielewski

Materials 2016, 9(10), 838; https://doi.org/10.3390/ma9100838 - 17 Oct 2016

Cited by 7 | Viewed by 4504

Abstract

Biofunctional scaffolds for the delivery of living cells are of the utmost importance for regenerative medicine. Herein, a novel, robust “spiraled horn” scaffold was elucidated through the Co²⁺-promoted hierarchical assembly of two collagen mimetic peptides, NCoH and HisCol. Each “horn” [...] Read more.

Biofunctional scaffolds for the delivery of living cells are of the utmost importance for regenerative medicine. Herein, a novel, robust “spiraled horn” scaffold was elucidated through the Co²⁺-promoted hierarchical assembly of two collagen mimetic peptides, NCoH and HisCol. Each “horn” displayed a periodic banding pattern with band lengths corresponding to the length of the collagen peptide triple helix. Strand exchange between the two peptide trimers resulted in failure to form this intricate morphology, lending support to a precise metal-ligand-based mechanism of assembly. Little change occurred to the observed morphology when the Co²⁺ concentration was varied from 0.5 to 4.0 mM, and the scaffold was found to be fully formed within two minutes of exposure to the metal ion. The horned network also displayed biological functionality by binding to a His-tagged fluorophore and associating with cells. Full article

(This article belongs to the Special Issue Biological and Synthetic Organic–Inorganic Composite Materials)

► Show Figures

Graphical abstract

3318 KiB

Open AccessArticle

Surface Structures Formed by a Copper(II) Complex of Alkyl-Derivatized Indigo

by Akinori Honda, Keisuke Noda, Yoshinori Tamaki and Kazuo Miyamura

Materials 2016, 9(10), 837; https://doi.org/10.3390/ma9100837 - 15 Oct 2016

Cited by 8 | Viewed by 5077

Abstract

Assembled structures of dyes have great influence on their coloring function. For example, metal ions added in the dyeing process are known to prevent fading of color. Thus, we have investigated the influence of an addition of copper(II) ion on the surface structure [...] Read more.

Assembled structures of dyes have great influence on their coloring function. For example, metal ions added in the dyeing process are known to prevent fading of color. Thus, we have investigated the influence of an addition of copper(II) ion on the surface structure of alkyl-derivatized indigo. Scanning tunneling microscope (STM) analysis revealed that the copper(II) complexes of indigo formed orderly lamellar structures on a HOPG substrate. These lamellar structures of the complexes are found to be more stable than those of alkyl-derivatized indigos alone. Furthermore, 2D chirality was observed. Full article

(This article belongs to the Special Issue Functional Organic Dyes and Pigments)

► Show Figures

Graphical abstract

4834 KiB

Open AccessArticle

Physical Properties of PDMS (Polydimethylsiloxane) Microfluidic Devices on Fluid Behaviors: Various Diameters and Shapes of Periodically-Embedded Microstructures

by Changhyun Roh, Jaewoong Lee and ChanKyu Kang

Materials 2016, 9(10), 836; https://doi.org/10.3390/ma9100836 - 15 Oct 2016

Cited by 13 | Viewed by 5514

Abstract

Deformable polydimethylsiloxane (PDMS) microfluidic devices embedded with three differently-shaped obstacles (hexagon, square, and triangle) were used to examine the significant challenge to classical fluid dynamics. The significant factors in determining a quasi-steady state value of flow velocity (v)_QS and pressure [...] Read more.

Deformable polydimethylsiloxane (PDMS) microfluidic devices embedded with three differently-shaped obstacles (hexagon, square, and triangle) were used to examine the significant challenge to classical fluid dynamics. The significant factors in determining a quasi-steady state value of flow velocity (v)_QS and pressure drop per unit length (∆P/∆x)_QS were dependent on the characteristic of embedded microstructures as well as the applied flow rates. The deviation from the theoretical considerations due to PDMS bulging investigated by the friction constant and the normalized friction factor revealed that the largest PDMS bulging observed in hexagonal obstacles had the smallest (∆P/∆x)_QS ratios, whereas triangle obstacles exhibited the smallest PDMS bulging, but recorded the largest (∆P/∆x)_QS ratios. However, the influence of (v)_QS ratio on microstructures was not very significant in this study. The results were close to the predicted values even though some discrepancy may be due to the relatively mean bulging and experimental uncertainty. The influence of deformable PDMS microfluidic channels with various shapes of embedded microstructures was compared with the rigid microchannels. The significant deviation from the classical relation (i.e., f~1/Re) was also observed in hexagonal obstacles and strongly dependent on the channel geometry, the degree of PDMS deformation, and the shapes of the embedded microstructures. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

► Show Figures

Figure 1

7923 KiB

Open AccessArticle

Pentaethylenehexamine-Loaded Hierarchically Porous Silica for CO₂ Adsorption

by Changchun Ji, Xin Huang, Lei Li, Fukui Xiao, Ning Zhao and Wei Wei

Materials 2016, 9(10), 835; https://doi.org/10.3390/ma9100835 - 15 Oct 2016

Cited by 27 | Viewed by 6716

Abstract

Recently, amine-functionalized materials as a prospective chemical sorbent for post combustion CO₂ capture have gained great interest. However, the amine grafting for the traditional MCM-41, SBA-15, pore-expanded MCM-41 or SBA-15 supports can cause the pore volume and specific surface area of sorbents [...] Read more.

Recently, amine-functionalized materials as a prospective chemical sorbent for post combustion CO₂ capture have gained great interest. However, the amine grafting for the traditional MCM-41, SBA-15, pore-expanded MCM-41 or SBA-15 supports can cause the pore volume and specific surface area of sorbents to decrease, significantly affecting the CO₂ adsorption-desorption dynamics. To overcome this issue, hierarchical porous silica with interparticle macropores and long-range ordering mesopores was prepared and impregnated with pentaethylenehexamine. The pore structure and amino functional group content of the modified silicas were analyzed by scanning electron microscope, transmission electron microscope, N₂ adsorption, X-ray powder diffraction, and Fourier transform infrared spectra. Moreover, the effects of the pore structure as well as the amount of PEHA loading of the samples on the CO₂ adsorption capacity were investigated in a fixed-bed adsorption system. The CO₂ adsorption capacity reached 4.5 mmol CO₂/(g of adsorbent) for HPS−PEHA-70 at 75 °C. Further, the adsorption capacity for HPS-PEHA-70 was steady after a total of 15 adsorption-desorption cycles. Full article

► Show Figures

Figure 1

5732 KiB

Open AccessArticle

Microstructural Evolution, Thermodynamics, and Kinetics of Mo-Tm₂O₃ Powder Mixtures during Ball Milling

by Yong Luo, Guang Ran, Nanjun Chen, Qiang Shen and Yaoli Zhang

Materials 2016, 9(10), 834; https://doi.org/10.3390/ma9100834 - 15 Oct 2016

Cited by 15 | Viewed by 4914

Abstract

The microstructural evolution, thermodynamics, and kinetics of Mo (21 wt %) Tm₂O₃ powder mixtures during ball milling were investigated using X-ray diffraction and transmission electron microscopy. Ball milling induced Tm₂O₃ to be decomposed and then dissolved into [...] Read more.

The microstructural evolution, thermodynamics, and kinetics of Mo (21 wt %) Tm₂O₃ powder mixtures during ball milling were investigated using X-ray diffraction and transmission electron microscopy. Ball milling induced Tm₂O₃ to be decomposed and then dissolved into Mo crystal. After 96 h of ball milling, Tm₂O₃ was dissolved completely and the supersaturated nanocrystalline solid solution of Mo (Tm, O) was obtained. The Mo lattice parameter increased with increasing ball-milling time, opposite for the Mo grain size. The size and lattice parameter of Mo grains was about 8 nm and 0.31564 nm after 96 h of ball milling, respectively. Ball milling induced the elements of Mo, Tm, and O to be distributed uniformly in the ball-milled particles. Based on the semi-experimental theory of Miedema, a thermodynamic model was developed to calculate the driving force of phase evolution. There was no chemical driving force to form a crystal solid solution of Tm atoms in Mo crystal or an amorphous phase because the Gibbs free energy for both processes was higher than zero. For Mo (21 wt %) Tm₂O₃, it was mechanical work, not the negative heat of mixing, which provided the driving force to form a supersaturated nanocrystalline Mo (Tm, O) solid solution. Full article

► Show Figures

Figure 1

2613 KiB

Open AccessArticle

Peanut Shell-Derived Carbon Solid Acid with Large Surface Area and Its Application for the Catalytic Hydrolysis of Cyclohexyl Acetate

by Wei Xue, Lijun Sun, Fang Yang, Zhimiao Wang and Fang Li

Materials 2016, 9(10), 833; https://doi.org/10.3390/ma9100833 - 15 Oct 2016

Cited by 16 | Viewed by 5530

Abstract

A carbon solid acid with large surface area (CSALA) was prepared by partial carbonization of H₃PO₄ pre-treated peanut shells followed by sulfonation with concentrated H₂SO₄. The structure and acidity of CSALA were characterized by N₂ [...] Read more.

A carbon solid acid with large surface area (CSALA) was prepared by partial carbonization of H₃PO₄ pre-treated peanut shells followed by sulfonation with concentrated H₂SO₄. The structure and acidity of CSALA were characterized by N₂ adsorption–desorption, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), ¹³C cross polarization (CP)/magic angle spinning (MAS) nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), titration, and elemental analysis. The results demonstrated that the CSALA was an amorphous carbon material with a surface area of 387.4 m²/g. SO₃H groups formed on the surface with a density of 0.46 mmol/g, with 1.11 mmol/g of COOH and 0.39 mmol/g of phenolic OH. Densities of the latter two groups were notably greater than those observed on a carbon solid acid (CSA) with a surface area of 10.1 m²/g. The CSALA catalyst showed better performance than the CSA for the hydrolysis of cyclohexyl acetate to cyclohexanol. Under optimal reaction conditions, cyclohexyl acetate conversion was 86.6% with 97.3% selectivity for cyclohexanol, while the results were 25.0% and 99.4%, respectively, catalyzed by CSA. The high activity of the CSALA could be attributed to its high density of COOH and large surface area. Moreover, the CSALA showed good reusability. Its catalytic activity decreased slightly during the first two cycles due to the leaching of polycyclic aromatic hydrocarbon-containing SO₃H groups, and then remained constant during following uses. Full article

(This article belongs to the Special Issue Green Chemistry - both precursors and processes - to Hierarchical Materials)

► Show Figures

Figure 1

3728 KiB

Open AccessLetter

Evolution Law of Helium Bubbles in Hastelloy N Alloy on Post-Irradiation Annealing Conditions

by Jie Gao, Liangman Bao, Hefei Huang, Yan Li, Jianrong Zeng, Zhe Liu, Renduo Liu and Liqun Shi

Materials 2016, 9(10), 832; https://doi.org/10.3390/ma9100832 - 14 Oct 2016

Cited by 26 | Viewed by 4472

Abstract

This work reports on the evolution law of helium bubbles in Hastelloy N alloy on post-irradiation annealing conditions. After helium ion irradiation at room temperature and subsequent annealing at 600 °C (1 h), the transmission electron microscopy (TEM) micrograph indicates the presence of [...] Read more.

This work reports on the evolution law of helium bubbles in Hastelloy N alloy on post-irradiation annealing conditions. After helium ion irradiation at room temperature and subsequent annealing at 600 °C (1 h), the transmission electron microscopy (TEM) micrograph indicates the presence of helium bubbles with size of 2 nm in the depth range of 0–300 nm. As for the sample further annealed at 850 °C (5 h), on one hand, a “Denuded Zone” (0–38 nm) with rare helium bubbles forms due to the decreased helium concentration. On the other hand, the “Ripening Zone” (38–108 nm) and “Coalescence Zone” (108–350 nm) with huge differences in size and separation of helium bubbles, caused by different coarsening rates, are observed. The mechanisms of “Ostwald ripening” and “migration and coalescence”, experimentally proved in this work, may explain these observations. Full article

(This article belongs to the Special Issue Modelling and Characterization of Defects in Metals)

► Show Figures

Figure 1

12929 KiB

Open AccessArticle

A Constitutive Relationship between Fatigue Limit and Microstructure in Nanostructured Bainitic Steels

by Inga Mueller, Rosalia Rementeria, Francisca G. Caballero, Matthias Kuntz, Thomas Sourmail and Eberhard Kerscher

Materials 2016, 9(10), 831; https://doi.org/10.3390/ma9100831 - 14 Oct 2016

Cited by 29 | Viewed by 5880

Abstract

The recently developed nanobainitic steels show high strength as well as high ductility. Although this combination seems to be promising for fatigue design, fatigue properties of nanostructured bainitic steels are often surprisingly low. To improve the fatigue behavior, an understanding of the correlation [...] Read more.

The recently developed nanobainitic steels show high strength as well as high ductility. Although this combination seems to be promising for fatigue design, fatigue properties of nanostructured bainitic steels are often surprisingly low. To improve the fatigue behavior, an understanding of the correlation between the nanobainitic microstructure and the fatigue limit is fundamental. Therefore, our hypothesis to predict the fatigue limit was that the main function of the microstructure is not necessarily totally avoiding the initiation of a fatigue crack, but the microstructure has to increase the ability to decelerate or to stop a growing fatigue crack. Thus, the key to understanding the fatigue behavior of nanostructured bainite is to understand the role of the microstructural features that could act as barriers for growing fatigue cracks. To prove this hypothesis, we carried out fatigue tests, crack growth experiments, and correlated these results to the size of microstructural features gained from microstructural analysis by light optical microscope and EBSD-measurements. Finally, we were able to identify microstructural features that influence the fatigue crack growth and the fatigue limit of nanostructured bainitic steels. Full article

(This article belongs to the Special Issue Fracture and Fatigue Mechanics of Materials)

► Show Figures

Figure 1

3995 KiB

Open AccessArticle

A New Compact Double-Negative Miniaturized Metamaterial for Wideband Operation

by Md. Mehedi Hasan, Mohammad Rashed Iqbal Faruque, Sikder Sunbeam Islam and Mohammad Tariqul Islam

Materials 2016, 9(10), 830; https://doi.org/10.3390/ma9100830 - 13 Oct 2016

Cited by 86 | Viewed by 7632

Abstract

The aim of this paper is to introduce a compact double-negative (DNG) metamaterial that exhibits a negative refractive index (NRI) bandwidth of more than 3.6 GHz considering the frequency from 2 to 14 GHz. In this framework, two arms of the designed unit [...] Read more.

The aim of this paper is to introduce a compact double-negative (DNG) metamaterial that exhibits a negative refractive index (NRI) bandwidth of more than 3.6 GHz considering the frequency from 2 to 14 GHz. In this framework, two arms of the designed unit cell are split in a way that forms a Modified-Z-shape structure of the FR-4 substrate material. The finite integration technique (FIT)-based Computer Simulation Technology (CST) Microwave Studio is applied for computation, and the experimental setup for measuring the performance is performed inside two waveguide ports. Therefore, the measured data complies well with the simulated data of the unit cell at 0-degree and 90-degree rotation angles. The designed unit cell shows a negative refractive index from 3.482 to 7.096 GHz (bandwidth of 3.61 GHz), 7.876 to 10.047 GHz (bandwidth of 2.171 GHz), and 11.594 to 14 GHz (bandwidth of 2.406 GHz) in the microwave spectra. The design also exhibits almost the same wide negative refractive index bandwidth in the major region of the C-band and X-band if it is rotated 90 degrees. However, the novelty of the proposed structure lies in its effective medium ratio of more than 4, wide bandwidth, and compact size. Full article

► Show Figures

Figure 1

Journal Menu

Journal Browser

Materials, Volume 9, Issue 10 (October 2016) – 66 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI