Titanium Alloys: Processing and Properties

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 March 2020) | Viewed by 85787

Special Issue Editor


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Guest Editor
Institute of Structural Materials, Swansea University, Swansea, SA1 8EN, UK
Interests: fatigue and fracture of structural metals; ceramics and associated composites

Special Issue Information

Dear Colleagues,

Titanium alloys offer distinct advantages over competing metallic systems, particularly where high-performance engineering applications demand a contribution from low density and corrosion resistance. From the mid-twentieth century onwards, a combination of traditional processing techniques and novel, alloy-specific routes was adopted to optimise the microstructural evolution in these alloys in order to control static strength, fatigue behaviour, and creep resistance. Due to the allotropic nature of the alpha/beta constituent phases, the role of microtexture inherently plays a fundamental role in the final mechanical properties. It is hoped that the papers to be commissioned under this current special edition of the Metals journal will address a wide range of issues relating to alloy processing, microstructure, and the control of mechanical properties in this important class of material.

Prof. Martin Bache
Guest Editor

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Keywords

  • Titanium alloys
  • Thermomechanical processing
  • Heat treatment
  • Microstructure
  • Microtexture
  • Fatigue
  • Creep
  • Dwell sensitivity

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Published Papers (16 papers)

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Editorial

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4 pages, 200 KiB  
Editorial
Titanium Alloys: Processing and Properties
by Martin Bache
Metals 2021, 11(9), 1426; https://doi.org/10.3390/met11091426 - 9 Sep 2021
Cited by 3 | Viewed by 2893
Abstract
The invited review paper to accompany this special issue, authored by Williams and Boyer [...] Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)

Research

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18 pages, 3913 KiB  
Article
Effect of Oxygen in the Structure, Microstructure and Mechanical Properties of Ti-xNi (x = 5, 10, 15 and 20 wt%) Alloys
by Daniela Cascadan and Carlos Roberto Grandini
Metals 2020, 10(11), 1424; https://doi.org/10.3390/met10111424 - 27 Oct 2020
Cited by 8 | Viewed by 2380
Abstract
Titanium alloys have great potential for use as biomaterials due to good biocompatibility and mechanical properties. The nickel addition to titanium improves the wear, corrosion and mechanical resistance of this element. The objective of this paper was to investigate the effects of oxygen [...] Read more.
Titanium alloys have great potential for use as biomaterials due to good biocompatibility and mechanical properties. The nickel addition to titanium improves the wear, corrosion and mechanical resistance of this element. The objective of this paper was to investigate the effects of oxygen on the structure, microstructure and some selected mechanical properties of this alloy system. The results showed that the samples present the adequate nickel concentration and low concentration of other metals. The alloys exhibit predominantly the α and intermetallic Ti2Ni phases, and the amount of it increases according to the nickel concentration. In the Ti-15Ni and Ti-20Ni alloys, this intermetallic reacted with oxygen forming Ti4Ni2O trioxide. The microstructures varied according to the processing, as well as the microhardness values. Elastic modulus values are slightly above titanium due to the formation of a new intermetallic phase but have not varied significantly with processing and doping with oxygen. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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14 pages, 11359 KiB  
Article
Analysis of Cold Dwell Fatigue Crack Initiation Site in a β-Forged Ti-6242 Disk in Relation with Local Texture
by Lionel Germain, Youssef Samih, Pierre Delaleau, Joseph Gilgert and Nathalie Gey
Metals 2020, 10(7), 951; https://doi.org/10.3390/met10070951 - 15 Jul 2020
Cited by 4 | Viewed by 3154
Abstract
The α and prior β textures and microtextures of a lamellar Ti6242 forged disk were characterized by advanced electron back scattered diffraction (EBSD) and related to crystallographic features of faceted crack initiation sites of dwell fatigue specimens tested along the radial direction (RD). [...] Read more.
The α and prior β textures and microtextures of a lamellar Ti6242 forged disk were characterized by advanced electron back scattered diffraction (EBSD) and related to crystallographic features of faceted crack initiation sites of dwell fatigue specimens tested along the radial direction (RD). Large feather-like structures of α colonies with close orientations were observed at boundaries of elongated prior β grains. Their orientation belongs to the <11-20>α//z fiber, aligning the c-axis in RDs (z: axial direction of the disk). They are inherited from prior β grains belonging to the major <100>β and minor <111>β//z fibers. These feather-like structures are strong regions of the forging that act as a preferential crack initiation site. Adjacent to them, one can observe large colony with evidence of prismatic slip. Thus, the facet formation seems triggered by stress redistribution from “weak” to “strong” regions due to the elastic and plastic anisotropy. Finally, the occurrence of neighboring β grains able to share close oriented feather-like colonies is discussed considering the reconstructed β microtexture and texture. This study may be helpful for further texture control during the forging process. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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12 pages, 2863 KiB  
Article
Microstructural Characterization and Mechanical Properties of Fiber Laser Welded CP-Ti and Ti-6Al-4V Similar and Dissimilar Joints
by Alireza Abdollahi, Ahmed Shaheer Ahnaf Huda and Abu Syed Kabir
Metals 2020, 10(6), 747; https://doi.org/10.3390/met10060747 - 3 Jun 2020
Cited by 8 | Viewed by 3420
Abstract
In this research, the microstructures and mechanical properties of similar and dissimilar autogenous joints of 3 mm thick commercially pure titanium (CP-Ti) and Ti-6Al-4V welded by ytterbium fiber laser (Yb:YAG) were investigated. Two sets of laser power and welding speed were selected in [...] Read more.
In this research, the microstructures and mechanical properties of similar and dissimilar autogenous joints of 3 mm thick commercially pure titanium (CP-Ti) and Ti-6Al-4V welded by ytterbium fiber laser (Yb:YAG) were investigated. Two sets of laser power and welding speed were selected in such a way that the heat input remained constant. Microstructural characterization of the joints was investigated by an optical microscope, and mechanical properties were determined by hardness and tensile tests. The only defects found were porosity and underfill, and no signs of lack of penetration and solidification cracks were observed in any of the joints. Microstructural evaluation of the fusion zone (FZ) showed that in similar Ti-6Al-4V joint, a supersaturated nonequilibrium α′ martensite was formed due to rapid cooling associated with laser welding. In similar CP-Ti, coarse equiaxed grains were observed in the FZ. Unlike the similar joints, a clear interface was observed between the heat-affected zone (HAZ) and the FZ in both the CP-Ti and Ti-6Al-4V sides in dissimilar joints. Among all the joints with different weld parameters, similar Ti-6Al-4V showed the highest strength and the lowest ductility. In similar CP-Ti and dissimilar joints, fractures took place in the CP-Ti base metal, but all the Ti-6Al-4V similar joints failed in the FZ. Significant changes in the strength and hardness with varying laser power and welding speed implied that the mechanical properties of the weld fusion zones were not entirely governed by the heat input but were also affected by individual welding parameters. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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10 pages, 3233 KiB  
Article
Effects of Thermomechanical Treatment on Phase Transformation of the Ti50Ni49W1 Shape Memory Alloy
by Tyau-Song Huang, Shih-Fu Ou, Cheng-Hsien Kuo and Cheng-Hsiu Yang
Metals 2020, 10(4), 527; https://doi.org/10.3390/met10040527 - 19 Apr 2020
Cited by 8 | Viewed by 2900
Abstract
The Ti50Ni49W1 alloy has a B2 ↔ 19’ martensitic transformation but slightly lower shape recovery than the Ti50Ni50 alloy. The B19’ martensite structure in the Ti50Ni49W1 has the lattice parameters [...] Read more.
The Ti50Ni49W1 alloy has a B2 ↔ 19’ martensitic transformation but slightly lower shape recovery than the Ti50Ni50 alloy. The B19’ martensite structure in the Ti50Ni49W1 has the lattice parameters a = 0.301 nm; b = 0.423 nm; c = 0.472 nm; and β = 97.5°. The hardness increment and transformation temperature depression of Ti50Ni49W1 are greater than those of Ti50Ni50 under the same degree of cold rolling and the same number of thermal cycles; owing to the Ti50Ni49W1; with higher inherent hardness from solidification strengthening of W atoms. Both thermal cycling and cold rolling on Ti50Ni49W1 also promotes R-phase transformation. The effects of thermal cycling and cold rolling on the martensitic transformation temperature (Ms) of the Ti50Ni49W1 alloy follow a linear trend; and the Ms decreased with the hardness. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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18 pages, 13552 KiB  
Article
Microstructural Control of Fatigue Behaviour in a Novel α + β Titanium Alloy
by Martin Bache, Helen Davies, William Davey, Matthew Thomas and Iain Berment-Parr
Metals 2019, 9(11), 1200; https://doi.org/10.3390/met9111200 - 7 Nov 2019
Cited by 12 | Viewed by 3692
Abstract
The novel titanium alloy TIMETAL® 407 (Ti-407) has been developed as an alternative to Ti-6Al-4V (Ti-6-4), for applications that demand relatively high ductility and energy absorption. Demonstrating a combination of lower strength and greater ductility, the alloy introduces a variety of cost [...] Read more.
The novel titanium alloy TIMETAL® 407 (Ti-407) has been developed as an alternative to Ti-6Al-4V (Ti-6-4), for applications that demand relatively high ductility and energy absorption. Demonstrating a combination of lower strength and greater ductility, the alloy introduces a variety of cost reduction opportunities, including improved machinability. Thermo-mechanical processing and its effects on microstructure and subsequent mechanical performance are characterised, including a detailed assessment of the fatigue and crack propagation properties. Demonstrating relatively strong behaviour under high-cycle fatigue loading, Ti-407 is nevertheless susceptible to time-dependent fatigue effects. Its sensitivity to dwell loading is quantified, and the associated deformation and fracture mechanisms responsible for controlling fatigue life are explored. The intimate relationship between thermo-mechanical processing, micro-texture and fatigue crack initiation through the generation of quasi-cleavage facets is highlighted. Consistent fatigue crack growth kinetics are demonstrated, independent of local microstructure. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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19 pages, 13580 KiB  
Article
Initial β Grain Size Effect on High-Temperature Flow Behavior of Tb8 Titanium Alloys in Single β Phase Field
by Qiuyue Yang, Min Ma, Yuanbiao Tan, Song Xiang, Fei Zhao and Yilong Liang
Metals 2019, 9(8), 891; https://doi.org/10.3390/met9080891 - 15 Aug 2019
Cited by 12 | Viewed by 3968
Abstract
The high-temperature flow behavior of TB8 titanium alloys with two different grain sizes was investigated in this present work. Results show that a significant characteristic of stress drop is visible at the start stage of the hot deformation process when the strain rates [...] Read more.
The high-temperature flow behavior of TB8 titanium alloys with two different grain sizes was investigated in this present work. Results show that a significant characteristic of stress drop is visible at the start stage of the hot deformation process when the strain rates are 100 and 10−1 s−1. With the further increasing of strain, the flow stress initially rises to a maximum value and subsequently attains a plateau for the strain rates of 100 s−1 and a slight decrease for the strain rates of 10−1 s−1. Only dynamic recovery occurs under these deformation conditions. When the strain rates drop to 10−3 s−1, the dynamic recrystallization takes place during hot deformation. The values of deformation activation energy and materials constants at different strains were calculated. The processing maps at different strains were established for the fine- and coarse-grained alloys. The optimal processing parameter for hot processing was attained to be 900 °C/10−3 s−1 for fine-grained alloys and 950 °C/10−3 s−1 for coarse-grained alloys, respectively. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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16 pages, 8675 KiB  
Article
Continuous Electron Beam Post-Treatment of EBF3-Fabricated Ti–6Al–4V Parts
by Alexey Panin, Marina Kazachenok, Olga Perevalova, Sergey Martynov, Alexandra Panina and Elena Sklyarova
Metals 2019, 9(6), 699; https://doi.org/10.3390/met9060699 - 21 Jun 2019
Cited by 31 | Viewed by 5270
Abstract
In the present study, the methods of optical, scanning electron, and transmission electron microscopy as well as X-ray diffraction analysis gained insights into the mechanisms of surface finish and microstructure formation of Ti–6Al–4V parts during an EBF3-process. It was found that [...] Read more.
In the present study, the methods of optical, scanning electron, and transmission electron microscopy as well as X-ray diffraction analysis gained insights into the mechanisms of surface finish and microstructure formation of Ti–6Al–4V parts during an EBF3-process. It was found that the slip band propagation within the outermost surface layer provided dissipation of the stored strain energy associated with martensitic transformations. The latter caused the lath fragmentation as well as precipitation of nanosized β grains and an orthorhombic martensite α″ phase at the secondary α lath boundaries of as-built Ti–6Al–4V parts. The effect of continuous electron beam post-treatment on the surface finish, microstructure, and mechanical properties of EBF3-fabricated Ti–6Al–4V parts was revealed. The brittle outermost surface layer of the EBF3-fabricated samples was melted upon the treatment, resulting in the formation of equiaxial prior β grains of 20 to 30 μm in size with the fragmented acicular α′ phase. Electron-beam irradiation induced transformations within the 70 μm thick molten surface layer and 500 μm thick heat affected zone significantly increased the Vickers microhardness and tensile strength of the EBF3-fabricated Ti–6Al–4V samples. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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19 pages, 6595 KiB  
Article
FAST-forge of Diffusion Bonded Dissimilar Titanium Alloys: A Novel Hybrid Processing Approach for Next Generation Near-Net Shape Components
by Jacob Pope and Martin Jackson
Metals 2019, 9(6), 654; https://doi.org/10.3390/met9060654 - 4 Jun 2019
Cited by 12 | Viewed by 6118
Abstract
Material reductions, weight savings, design optimisation, and a reduction in the environmental impact can be achieved by improving the performance of near-net shape (NNS) titanium alloy components. The method demonstrated in this paper is to use a solid-state approach, which includes diffusion bonding [...] Read more.
Material reductions, weight savings, design optimisation, and a reduction in the environmental impact can be achieved by improving the performance of near-net shape (NNS) titanium alloy components. The method demonstrated in this paper is to use a solid-state approach, which includes diffusion bonding discrete layers of dissimilar titanium alloy powders (CP-Ti, Ti-6Al-4V and Ti-5Al-5Mo-5V-3Cr) using field-assisted sintering technology (FAST), followed by subsequent forging steps. This article demonstrates the hybrid process route, firstly through small-scale uni-axial compression tests and secondly through closed-die forging of dissimilar titanium alloy FAST preforms into an NNS (near-net shape) component. In order to characterise and simulate the underlying forging behaviour of dissimilar alloy combinations, uni-axial compression tests of FAST cylindrical samples provided flow stress behaviour and the effect of differing alloy volume fractions on the resistance to deformation and hot working behaviour. Despite the mismatch in the magnitude of flow stress between alloys, excellent structural bond integrity is maintained throughout. This is also reflected in the comparatively uncontrolled closed-die forging of the NNS demonstrator components. Microstructural analysis across the dissimilar diffusion bond line was undertaken in the components and finite element modelling software reliably predicts the strain distribution and bond line flow behaviour during the multi-step forging process. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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12 pages, 8516 KiB  
Article
The Effect of Initial Annealing Microstructures on the Forming Characteristics of Ti–4Al–2V Titanium Alloy
by Bin Yan, Hongbo Li, Jie Zhang and Ning Kong
Metals 2019, 9(5), 576; https://doi.org/10.3390/met9050576 - 17 May 2019
Cited by 17 | Viewed by 3695
Abstract
In this study, the effect of initial annealing microstructure of Ti–4Al–2V (TA17) alloy on forming characteristic was studied, so as to provide a basis for quality control of plastic forming of titanium alloy parts. The titanium alloy always undergoes annealing treatment before forming, [...] Read more.
In this study, the effect of initial annealing microstructure of Ti–4Al–2V (TA17) alloy on forming characteristic was studied, so as to provide a basis for quality control of plastic forming of titanium alloy parts. The titanium alloy always undergoes annealing treatment before forming, due to different microstructures present different mechanical properties. The TA17 with different microstructures are obtained by means of various annealing treatment temperatures. The tensile behavior of TA17 is investigated at room temperature and 900 °C under constant strain rate of 0.01 s−1. The experimental results show that the mechanical properties of TA17 are sensitive to the initial microstructure before deformation. The microstructure of TA17 at 850 °C (2 h) is the equiaxed primary α-phase after the annealing process. It exhibits good plasticity at room temperature. This phenomenon is also confirmed from fracture morphology from the scanning electron microscope (SEM) analysis. At 900 °C, which is a high tensile temperature, the alloy with equiaxed primary α-phase performs outstanding plasticity compared with other microstructures. This work establishes a good understanding on the relationship between the mechanical properties and microstructures of TA17 at a wide temperature range. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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14 pages, 18324 KiB  
Article
Identification of Relationships between Heat Treatment and Fatigue Crack Growth of αβ Titanium Alloys
by Vincent Renon, Gilbert Henaff, Céline Larignon, Simon Perusin and Patrick Villechaise
Metals 2019, 9(5), 512; https://doi.org/10.3390/met9050512 - 30 Apr 2019
Cited by 6 | Viewed by 2803
Abstract
This study deals with the influence of microstructure on the fatigue crack growth resistance of αβ titanium alloys: Ti-6Al-4V ELI (Extra Low Interstitial) that may compete with the conventional Ti-6Al-4V alloy in the manufacture of high performance aircraft. Six different microstructures have been [...] Read more.
This study deals with the influence of microstructure on the fatigue crack growth resistance of αβ titanium alloys: Ti-6Al-4V ELI (Extra Low Interstitial) that may compete with the conventional Ti-6Al-4V alloy in the manufacture of high performance aircraft. Six different microstructures have been considered: the as-received bimodal microstructures and five distinct fully lamellar microstructures. The characteristic parameters of these microstructures were determined and crack growth tests were performed with crack closure measurements in order to evaluate the shielding effect induced by closure. A comparison of crack growth rates, fracture surfaces, and crack path was carried out for the different microstructures. The results outline a transition between two propagation regimes from a microstructure-sensitive to microstructure-insensitive propagation. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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15 pages, 7215 KiB  
Article
Hot Deformation Behavior and Microstructure Evolution of a TiBw/Near α-Ti Composite with Fine Matrix Microstructure
by Changjiang Zhang, Yuzhou Lian, Yanfei Chen, Yonggang Sun, Shuzhi Zhang, Hong Feng, Yawei Zhou and Peng Cao
Metals 2019, 9(4), 481; https://doi.org/10.3390/met9040481 - 25 Apr 2019
Cited by 13 | Viewed by 3346
Abstract
The hot deformation behavior and microstructure evolution of a 7.5 vol.% TiBw/near α-Ti composite with fine matrix microstructure were investigated under the deformation conditions in a temperature range of 800–950 °C and strain rate range of 0.001–1 s−1 using plane [...] Read more.
The hot deformation behavior and microstructure evolution of a 7.5 vol.% TiBw/near α-Ti composite with fine matrix microstructure were investigated under the deformation conditions in a temperature range of 800–950 °C and strain rate range of 0.001–1 s−1 using plane strain compression tests. The flow stress curves show different characteristics according to the various deformation conditions. At a higher strain rate (1 s−1), the flow stress of the composite continuously increases until a peak value is reached. The activation energy is 410.40 kJ/mol, much lower than the activation energy of as-sintered or as-forged composites. The decreased activation energy is ascribed to the breaking of the TiBw reinforcement during the multi-directional forging and the resultant fine matrix microstructure. Refined reinforcement and refined matrix microstructure significantly improve the hot deformation ability of the composite. The deformation conditions determine the morphology and fraction of α and β phases. At 800–900 °C and 0.01 s−1 the matrix α grains are much refined due to the continuous dynamic recrystallization (CDRX). The processing map is constructed based on the hot deformation behavior and microstructure evolution. The optimal hot processing window is determined to be 800–950 °C/0.001–0.01 s−1, which lead to CDRX of primary α grains or dynamic recovery (DRV) and dynamic recrystallization (DRX) of β phase. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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14 pages, 1876 KiB  
Article
A Hierarchical Multiscale Modeling Investigation on the Behavior of Microtextured Regions in Ti-6242 α/β Processing
by Ran Ma and Timothy J. Truster
Metals 2019, 9(2), 233; https://doi.org/10.3390/met9020233 - 15 Feb 2019
Cited by 2 | Viewed by 3117
Abstract
Ti-6242 is a near alpha titanium alloy, which has excellent high-temperature creep resistance and is widely used in jet engine compressors. This alloy is susceptible to creep fatigue failure under dwell loading below 473 K. The existence of microtextured regions (MTRs) contributes significantly [...] Read more.
Ti-6242 is a near alpha titanium alloy, which has excellent high-temperature creep resistance and is widely used in jet engine compressors. This alloy is susceptible to creep fatigue failure under dwell loading below 473 K. The existence of microtextured regions (MTRs) contributes significantly to this fast crack propagation. Mechanical processing in the alpha + beta region has been employed to eliminate MTRs, but the efficiency depends significantly on the applied strain path. Previous investigations based on crystal plasticity finite element (CPFE) simulations have demonstrated the relationship between breakdown efficiency and loading direction. Therein, MTRs with regular geometry and pure initial orientation were used to isolate the effect of loading direction from initial microstructure. In this paper, the behavior of MTRs with realistic initial microstructure was investigated using a hierarchical multiscale modeling framework, and the microscale results were analyzed in detail to understand the behavior of MTRs under different loading conditions. It was shown that a hierarchical multiscale model with realistic initial microstructure at the microscale can reflect the influences from different strain paths, initial orientation distributions, and positions of the region simultaneously. The combined effect of initial orientation distribution and loading direction on the MTR breakdown efficiency is discussed in detail. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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13 pages, 10637 KiB  
Article
Effect of Temperature and Dwell Time on Fatigue Crack Growth Behavior of CP-Ti
by Chuan-Yi Su, Chang-Yu Zhou, Lei Lu, Jian Li, Peng-Yan Sun and Xiao-Hua He
Metals 2018, 8(12), 1031; https://doi.org/10.3390/met8121031 - 6 Dec 2018
Cited by 9 | Viewed by 3771
Abstract
In this paper, the effects of temperature and dwell time on the Fatigue Crack Growth (FCG) behavior of commercial pure titanium were studied under high and low load ratios. Besides, combined with the fracture surface morphology, the specific characteristics of FCG were analyzed [...] Read more.
In this paper, the effects of temperature and dwell time on the Fatigue Crack Growth (FCG) behavior of commercial pure titanium were studied under high and low load ratios. Besides, combined with the fracture surface morphology, the specific characteristics of FCG were analyzed under pure fatigue and dwell fatigue conditions. The experiment results show that the FCG rate of commercial pure titanium (CP-Ti) increases with the temperature under low load ratio, and the dwell time increases the FCG rate. Also, the enhancement of the dwell time increases as the temperature rises. The dwell effect tends to be saturated when the temperature rises to 200 °C. Under high load ratio, the FCG rate of CP-Ti also exhibits a temperature-sensitive enhancement. The enhancement effect of the dwell time on the FCG rate under high load ratio is more significant. However, the effect of the hold time on the FCG rate does not increase at 300 °C. The da/dN–ΔK/E FCG curves for CP-Ti have a tendency to approach each other under different load ratios, which indicates that the E-modulus is an important factor for the difference. The effect of dwell time on the FCG behavior of CP-Ti is dominated by the creep deformation mechanism under different load ratios from room temperature to 300 °C. At the same time, the oxidation effect gradually becomes significant as the load ratio increases to 300 °C. The fracture surface morphology shows that the secondary cracks and the roughness increase with temperature or dwell time under low load ratio condition, while, under high load ratio, the effect of creep deformation on the FCG behavior is more obviously enhanced, and plastic deformation is gradually significant with increase of the dimples. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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8 pages, 2372 KiB  
Article
TiFe Precipitation Behavior and its Effect on Strengthening in Solution Heat-Treated Ti-5Al-3.5Fe During Isothermal Aging
by Hye-Jeong Choe, Jong Woo Won, Yong-Taek Hyun, Ka Ram Lim and Seog-Young Yoon
Metals 2018, 8(11), 875; https://doi.org/10.3390/met8110875 - 26 Oct 2018
Cited by 6 | Viewed by 2778
Abstract
We investigated the TiFe precipitation behavior of solution heat-treated Ti-5Al-3.5Fe during isothermal aging, quantified the effect of precipitation on strengthening by evaluating the hardness, and compared it to the effect of Ti3Al precipitation in Ti-6Al-4V. TiFe precipitates formed both at grain [...] Read more.
We investigated the TiFe precipitation behavior of solution heat-treated Ti-5Al-3.5Fe during isothermal aging, quantified the effect of precipitation on strengthening by evaluating the hardness, and compared it to the effect of Ti3Al precipitation in Ti-6Al-4V. TiFe precipitates formed both at grain boundaries (GBs) and within the grain matrices. Phase transformation from the β to α phase also occurred during isothermal aging; this transformation generated lamellar interphase boundaries between the transformed α phase and remaining β phase in prior β grains. These interphase boundaries enabled the formation of in-grain TiFe precipitates by acting as a nucleation site. GB precipitation did not require prior βα phase transformation to generate nucleation sites (i.e., interphase boundaries), so TiFe precipitation could occur immediately upon isothermal aging. Thus, GB precipitation proceeded more quickly than in-grain precipitation; as a result, precipitates were larger and more spherical at the GBs than in grains. The strengthening behavior exhibited by TiFe precipitation differed obviously from that caused by Ti3Al precipitation in Ti-6Al-4V because of its differing precipitation kinetics and related microstructural evolution. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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Review

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22 pages, 5591 KiB  
Review
Opportunities and Issues in the Application of Titanium Alloys for Aerospace Components
by James C. Williams and Rodney R. Boyer
Metals 2020, 10(6), 705; https://doi.org/10.3390/met10060705 - 27 May 2020
Cited by 293 | Viewed by 29415
Abstract
The metal titanium (Ti) and its alloys have many attributes which are attractive as structural materials, but they also have one major disadvantage, high initial cost. Nevertheless, Ti and Ti alloys are used extensively in airframes, gas turbine engines (GTE), and rocket engines [...] Read more.
The metal titanium (Ti) and its alloys have many attributes which are attractive as structural materials, but they also have one major disadvantage, high initial cost. Nevertheless, Ti and Ti alloys are used extensively in airframes, gas turbine engines (GTE), and rocket engines (RE). The high cost is a deterrent, particularly in airframe applications, in that the other alloys it competes with are, for the most part, significantly lower cost. This is less of a concern for GTE and RE where the cost of titanium is closer to and sometimes even lower than some of the materials it competes with for these applications. In spacecraft the weight savings are so important that cost is a lesser concern. Ti and its alloys consist of five families of alloys; α-Ti, near α-alloys, α + β alloys, β-alloys, and Ti-based intermetallic compounds. The intermetallic compounds of primary interest today are those based on the compound TiAl which, at this time, are only used for engine applications because of their higher temperature capability. These TiAl-based compounds are used in a relatively low, but growing, amounts. The first production application was for low pressure turbine blades in the GE engine (GEnx) used on the Boeing 787, followed by the GE LEAP engine used on A-320neo and B-737MAX. These air foils are investment cast and machined. The next application is for the GE90X which will power the Boeing B-777X. These air foils will be made by additive manufacturing (AM). Unalloyed titanium and titanium alloys are typically melted by vacuum arc melting and re-melted either once (2X VAR) or twice (3X VAR); however a new and very different melting method (cold hearth melting) has recently become favored, mainly for high performance applications such as rotors in aircraft engines. This process resulted in higher quality ingots with a significant reduction in melt-related defects. Once melted and cast into ingots, the alloys can be processed using all the standard thermomechanical working and casting processes used for making components of other types of structural alloys. Because of their limited ductility, the TiAl-based intermetallic compounds are quite difficult to process using ordinary wrought methods. Consequently, the low-pressure turbine blades currently in service are investment cast and machined to net shape. The AM air foils will require minimal machining, which is an advantage. This paper describes some relatively recent developments as well as some issues and opportunities associated with the production and use of Ti and its alloys in aerospace components. Included are new Ti alloys, new applications of Ti alloys, and the current status of several manufacturing processes including a discussion of the promise and current reality of additive manufacturing as a potentially revolutionary method of producing Ti alloy components. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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