Special Issue "Titanium Alloys: Processing and Properties"

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

Deadline for manuscript submissions: closed (31 May 2019)

Special Issue Editor

Guest Editor
Prof. Martin Bache

Institute of Structural Materials, Swansea University, Swansea, UK
Website | E-Mail
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

Manuscript Submission Information

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Keywords

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

Published Papers (8 papers)

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Research

Open AccessFeature PaperArticle
Continuous Electron Beam Post-Treatment of EBF3-Fabricated Ti–6Al–4V Parts
Metals 2019, 9(6), 699; https://doi.org/10.3390/met9060699
Received: 23 May 2019 / Revised: 15 June 2019 / Accepted: 19 June 2019 / Published: 21 June 2019
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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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Open AccessArticle
FAST-forge of Diffusion Bonded Dissimilar Titanium Alloys: A Novel Hybrid Processing Approach for Next Generation Near-Net Shape Components
Metals 2019, 9(6), 654; https://doi.org/10.3390/met9060654
Received: 19 May 2019 / Revised: 1 June 2019 / Accepted: 3 June 2019 / Published: 4 June 2019
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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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Open AccessArticle
The Effect of Initial Annealing Microstructures on the Forming Characteristics of Ti–4Al–2V Titanium Alloy
Metals 2019, 9(5), 576; https://doi.org/10.3390/met9050576
Received: 6 May 2019 / Revised: 15 May 2019 / Accepted: 16 May 2019 / Published: 17 May 2019
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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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Open AccessArticle
Identification of Relationships between Heat Treatment and Fatigue Crack Growth of αβ Titanium Alloys
Metals 2019, 9(5), 512; https://doi.org/10.3390/met9050512
Received: 8 March 2019 / Revised: 10 April 2019 / Accepted: 18 April 2019 / Published: 30 April 2019
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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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Open AccessArticle
Hot Deformation Behavior and Microstructure Evolution of a TiBw/Near α-Ti Composite with Fine Matrix Microstructure
Metals 2019, 9(4), 481; https://doi.org/10.3390/met9040481
Received: 25 March 2019 / Revised: 23 April 2019 / Accepted: 24 April 2019 / Published: 25 April 2019
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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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Open AccessArticle
A Hierarchical Multiscale Modeling Investigation on the Behavior of Microtextured Regions in Ti-6242 α/β Processing
Metals 2019, 9(2), 233; https://doi.org/10.3390/met9020233
Received: 15 December 2018 / Revised: 30 January 2019 / Accepted: 6 February 2019 / Published: 15 February 2019
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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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Open AccessArticle
Effect of Temperature and Dwell Time on Fatigue Crack Growth Behavior of CP-Ti
Metals 2018, 8(12), 1031; https://doi.org/10.3390/met8121031
Received: 8 November 2018 / Revised: 28 November 2018 / Accepted: 30 November 2018 / Published: 6 December 2018
Cited by 1 | PDF Full-text (10637 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle
TiFe Precipitation Behavior and its Effect on Strengthening in Solution Heat-Treated Ti-5Al-3.5Fe During Isothermal Aging
Metals 2018, 8(11), 875; https://doi.org/10.3390/met8110875
Received: 16 October 2018 / Revised: 23 October 2018 / Accepted: 24 October 2018 / Published: 26 October 2018
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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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