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

Deadline for manuscript submissions: closed (30 June 2017) | Viewed by 68029

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Prof. Dr. Mark T. Whittaker

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Materials Science and Engineering, Faculty of Science and Engineering, Swansea University, Swansea, UK
Interests: fatigue; creep; thermo-mechanical fatigue (TMF); superalloys; lifing; nickel alloys; titanium alloys
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Dear Colleagues,

Although titanium was originally discovered in the 18th century, significant developments in the titanium industry only occurred in the middle of the 20th century. These changes resulted from the emergence of the gas turbine engine. Since that time, the aerospace sector has dominated worldwide titanium use; the metal has applications in both engines and airframe structures. Titanium has a highly desirable combination of properties: these include excellent corrosion resistance, a high strength to weight ratio, and good fatigue resistance. Such qualities enable extensive applications; only high extraction and processing costs restrict further implementation.
Although the aerospace industry faces challenges related to increasing operating temperatures and the development of polymer based composites, innovative solutions, including metal matrix composites and titanium aluminides, provide pathways for future development. Furthermore, improvements in extractive metallurgy and processing methods have made titanium-based alloys more accessible to alternative industries. Industries currently utilizing these materials include the sports, biomedical, and marine sectors.
As more traditional applications are supplemented by exciting new opportunities, it is clear that extensive research opportunities are likely to exist in the titanium industry for the foreseeable future.

Dr. Mark T. Whittaker
Guest Editor

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Keywords

extractive metallurgy processing
microstructure evolution
properties
intermetallics
MMCs
aerospace
biomedical

Published Papers (13 papers)

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2 pages, 133 KiB

Open AccessEditorial

Titanium Alloys 2017

by Mark T. Whittaker

Metals 2018, 8(5), 319; https://doi.org/10.3390/met8050319 - 05 May 2018

Cited by 3 | Viewed by 2359

Abstract

n/a Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

Research

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8179 KiB

Open AccessArticle

Study on Hot Deformation Behavior and Microstructure Evolution of Ti55 High-Temperature Titanium Alloy

by Fengyong Wu, Wenchen Xu, Xueze Jin, Xunmao Zhong, Xingjie Wan, Debin Shan and Bin Guo

Metals 2017, 7(8), 319; https://doi.org/10.3390/met7080319 - 20 Aug 2017

Cited by 18 | Viewed by 5083

Abstract

The isothermal compression experiment of as-rolled Ti55 alloy was carried out on a Gleeble-3800 thermal simulation test machine at the deformation temperature range of 700–1050 °C and strain rate range of 0.001–1 s⁻¹. The hot deformation behavior and the microstructure evolution were analyzed during thermal compression. The results show that the apparent activation energy Q in α+β dual-phase region and β single-phase region were calculated to be 453.00 KJ/mol and 279.88 KJ/mol, respectively. The deformation softening mechanism was mainly controlled by dynamic recrystallization of α phase and dynamic recovery of β phase. Discontinuous yielding behavior mainly occurred in β phase region, which weakened gradually with the increase of deformation temperature (>990 °C) and strain rate (0.01–1 s⁻¹) in β phase region. The processing map derived from Murty’s criterion was more accurate in predicting the hot workability than that derived from Prasad’s criterion. The optimized hot working window was 850–975°C/0.001–1 s⁻¹, in which sufficient dynamic recrystallization occurred and α + β-transus microstructure was obtained. When deformed at higher temperature (≥1000 °C), coarsened lath-shape β-transus microstructure was formed, while deformed at lower temperature (≤825 °C) and higher strain rate (≥0.1 s⁻¹), the dynamic recrystallization was not sufficient, thus flow instability appeared because of shear cracking. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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13332 KiB

Open AccessArticle

Self-Propagating High Temperature Synthesis of TiB₂–MgAl₂O₄ Composites

by Nina Radishevskaya, Olga Lepakova, Natalia Karakchieva, Anastasiya Nazarova, Nikolai Afanasiev, Anna Godymchuk and Alexander Gusev

Metals 2017, 7(8), 295; https://doi.org/10.3390/met7080295 - 03 Aug 2017

Cited by 11 | Viewed by 4096

Abstract

Metal borides are widely used as heat-insulating materials, however, the range of their application in high-temperature conditions with oxidative medium is significantly restricted. To improve the thermal stability of structural materials based on titanium boride, and to prevent the growth of TiB₂ crystals, additives based on alumina-magnesia spinel with chemical resistant and refractory properties have been used. The aim of this work is to study the structure of TiB₂ with alumina-magnesia spinel additives obtained by self-propagating high-temperature synthesis (SHS). TiB₂ structure with uniform fine-grained distribution was obtained in an MgAl₂O₄ matrix. The material composition was confirmed by X-ray diffraction analysis (DRON-3M, filtered Со kα-emission), FTIR spectroscopy (Thermo Electron Nicolet 5700, within the range of 1300–400 cm⁻¹), and scanning electron microscopy (Philips SEM 515). The obtained material represents a composite, where the particles of TiB₂ with a size of 5 µm are uniformly distributed in the alloy of alumina-magnesia spinel. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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12159 KiB

Open AccessArticle

Sintering Behavior and Microstructure of TiC-Me Composite Powder Prepared by SHS

by Elena N. Korosteleva, Victoria V. Korzhova and Maksim G. Krinitcyn

Metals 2017, 7(8), 290; https://doi.org/10.3390/met7080290 - 31 Jul 2017

Cited by 21 | Viewed by 6290

Abstract

Titanium, its alloys, and refractory compounds are often used in the compositions of surfacing materials. In particular, under the conditions of electron-beam surfacing the use of synthesized composite powder based on titanium carbide with a metal binder (TiC-Me) has a positive effect. These powders have been prepared via the self-propagating high-temperature synthesis (SHS) present in a thermally-inert metal binder. The initial carbide particle distribution changes slightly in the surfacing layer in the high-energy rapid process of electron-beam surfacing. However, these methods also have their limitations. The development of technologies and equipment using low-energy sources is assumed. In this case, the question of the structure formation of composite materials based on titanium carbide remains open, if a low-energy and prolonged impact in additive manufacturing will be used. This work reports the investigation of the sintered powders that were previously synthesized by the layerwise combustion mode of a mixture of titanium, carbon black, and metal binders of various types. The problems of structure formation during vacuum sintering of multi-component powder materials obtained as a result of SHS are considered. The microstructure and dependences of the sintered composites densification on the sintering temperature and the composition of the SH-synthesized powder used are presented. It has been shown that under the conditions of the nonstoichiometric synthesized titanium carbide during subsequently vacuum sintering an additional alloy formation occurs that can lead to a consolidation (shrinkage) or volumetric growth of sintered TiC-Me composite depending on the type of metal matrix used. Full article

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11650 KiB

Open AccessArticle

Effects of Trace Si Addition on the Microstructures and Tensile Properties of Ti-3Al-8V-6Cr-4Mo-4Zr Alloy

by Hongbo Ba, Limin Dong, Zhiqiang Zhang and Xiaofei Lei

Metals 2017, 7(8), 286; https://doi.org/10.3390/met7080286 - 27 Jul 2017

Cited by 11 | Viewed by 4648

Abstract

The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-4Zr titanium alloys with various Si contents were investigated. The results revealed that the addition of trace Si and the presence of Zr induced the formation of (TiZr)₆Si₃ silicides, in the size range from 100 nm to 300 nm. The fine silicide precipitates refined β grains. The tensile strength increased about 40 MPa due to precipitation strengthening and grain refinement, and the ductility of the two alloys was similar. The tensile fracture mode of the alloys was dimple ductile fracture. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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14451 KiB

Open AccessArticle

Microstructural Evolution during Pressureless Sintering of Blended Elemental Ti-Al-V-Fe Titanium Alloys from Fine Hydrogenated-Dehydrogenated Titanium Powder

by Changzhou Yu, Peng Cao and Mark Ian Jones

Metals 2017, 7(8), 285; https://doi.org/10.3390/met7080285 - 26 Jul 2017

Cited by 10 | Viewed by 5812

Abstract

A comprehensive study was conducted on microstructural evolution of sintered Ti-Al-V-Fe titanium alloys utilizing very fine hydrogenation-dehydrogenation (HDH) titanium powder with a median particle size of 8.84 μm. Both micropores (5–15 μm) and macropores (50–200 μm) were identified in sintered titanium alloys. Spherical micropores were observed in Ti-6Al-4V sintered with fine Ti at the lowest temperature of 1150 °C. The addition of iron can help reduce microporosity and improve microstructural and compositional homogenization. A theoretical calculation of evaporation based on the Miedema model and Langmuir equation indicates that the evaporation of aluminum could be responsible for the formation of the macropores. Although reasonable densification was achieved at low sintering temperatures (93–96% relative density) the samples had poor mechanical properties due mainly to the presence of the macroporosity and the high inherent oxygen content in the as-received fine powders. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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6469 KiB

Open AccessArticle

Effect of Hybrid Reinforcements on the Microstructure and Mechanical Properties of Ti-5Al-5Mo-5V-Fe-Cr Titanium Alloy

by Shuyu Sun and Weijie Lu

Metals 2017, 7(7), 250; https://doi.org/10.3390/met7070250 - 05 Jul 2017

Cited by 4 | Viewed by 3752

Abstract

In order to investigate the different effects of trace TiB and TiC on the microstructure and the mechanical properties of Ti-5Al-5Mo-5V-1Fe-1Cr Ti alloy, two different modified Ti-5Al-5Mo-5V-1Fe-1Cr Ti alloys are fabricated via a consumable vacuum arc-remelting furnace in this work. Though the volume fractions of the reinforcements are the same in the two alloys, the molar ratio of short fibers to particles is different. The materials are subjected to thermomechanical processing and heat treatment. The effects of TiB short fibers and TiC particles on the spheroidization of α phase or the refinement of β phase have no obvious difference during heat treatment. Subsequently, the room temperature tensile test is carried out. The area covered by the σ-ε curve of the tensile test is used to compare toughness. It is revealed that the refinement of the β phase and the load bearing of TiB play key roles in promoting the toughness of the alloys. TiB tends to parallel the external load during tensile tests. The distribution of TiB also changes during isothermal compression test. Owing to the competition of dynamic softening with dynamic hardening, the length direction of TiB tends to parallel to the direction of maximum shear stress during the compression, which makes TiB play the role of load bearing better. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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6209 KiB

Open AccessArticle

High Temperature Oxidation and Wear Behaviors of Ti–V–Cr Fireproof Titanium Alloy

by Guangbao Mi, Kai Yao, Pengfei Bai, Congqian Cheng and Xiaohua Min

Metals 2017, 7(6), 226; https://doi.org/10.3390/met7060226 - 19 Jun 2017

Cited by 11 | Viewed by 4811

Abstract

The high temperature oxidation and wear behaviors of Ti–35V–15Cr–0.3Si–0.1C fireproof titanium alloy were examined at 873 and 1073 K. The oxidation weight gain after oxidation at 1073 K for 100 h was significantly larger than that at 873 K. Based on the analyses of the oxidation reaction index and oxide layer, the oxidation process at 1073 K was mainly controlled by oxidation reaction at the interface between the substrate and oxide layer. Dry sliding wear tests were performed on a pin-on-disk tester in air conditions. The friction coefficient was smaller at 1073 K than that at 873 K, while the volume wear rate at 1073 K was larger due to formation of amount of oxides on the worn surface. When the wearing temperature increased from 873 to 1073 K, the wear mechanism underwent a transition from a combination of abrasive wear and oxidative wear to only oxidative wear. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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12421 KiB

Open AccessArticle

The Microstructure Evolution, Mechanical Properties and Densification Mechanism of TiAl-Based Alloys Prepared by Spark Plasma Sintering

by Dongjun Wang, Hao Yuan and Jianming Qiang

Metals 2017, 7(6), 201; https://doi.org/10.3390/met7060201 - 02 Jun 2017

Cited by 23 | Viewed by 5015

Abstract

The microstructure evolution and mechanical properties of a Ti-Al-Cr-Nb alloy prepared by spark plasma sintering (SPS) at different temperatures and stresses were investigated in detail. Sintering temperature plays a key role in the densification process and phase transformation, which determines the microstructure. The mechanical properties of the sintered alloys depend on the microstructure caused by the sintering. Furthermore, the densification process and mechanism of TiAl-based metallic powders during SPS were studied based on experimental results and theoretical analysis, the results of which will help fabricate these kinds of intermetallic alloys using a powder metallurgy technique and accelerate their industrial applications. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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5327 KiB

Open AccessArticle

The Effect of Initial Structure on Phase Transformation in Continuous Heating of a TA15 Titanium Alloy

by Xiaoguang Fan, Qi Li, Anming Zhao, Yuguo Shi and Wenjia Mei

Metals 2017, 7(6), 200; https://doi.org/10.3390/met7060200 - 01 Jun 2017

Cited by 21 | Viewed by 6031

Abstract

The effect of initial structure on phase evolution in continuous heating of a near-α TA15 titanium alloy (Ti-6Al-2Zr-1Mo-1V) was experimentally investigated. To this end; three microstructures were obtained by multiple heat treatment: I-bimodal structure with 50% equaixed α, II-bimodal structure with 15% equiaxed α, III-trimodal structure with 18% equiaxed α and 25% lamellar α. Differential scanning calorimetry (DSC), dilatometry and quantitative metallography were carried out on specimens with the three initial structures at heating rates from 5 to 40 °C/min. The transformation kinetics was modeled with the Johnson–Mehl–Avrami (JMA) approach under non-isothermal condition. It was found that there exists a four-stage transformation for microstructures I and III. The secondary and third stages overlap for microstructure II. The four stages of phase transformation overlap with increasing heating rate. In the presence of α laths, the phase transformation kinetics is affected by the composition difference between lamellar α and primary equiaxed α. Phase transformation is controlled by the growth of existing large β phase. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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9361 KiB

Open AccessArticle

The Effects of Prestrain and Subsequent Annealing on Tensile Properties of CP-Ti

by Le Chang, Chang-Yu Zhou and Xiao-Hua He

Metals 2017, 7(3), 99; https://doi.org/10.3390/met7030099 - 17 Mar 2017

Cited by 17 | Viewed by 6111

Abstract

The aim of the present work is to investigate the effects of prestrain and subsequent annealing on tensile properties of commercial pure titanium (CP-Ti). According to tensile test results, yield strength and ultimate tensile strength increase with the increase of prestrain. Elongation and uniform strain decrease linearly with prestrain. In the case of prestrain that is higher than 3.5%, the macro-yield of specimens changes from gradual yielding to discontinuous yielding. It is supposed that considerable numbers of dislocations introduced into the material lead to the appearance of yield plateau. The quantitative analysis of the contribution of dislocation hardening to the strain hardening shows that dislocation-associated mechanisms play an important role in strain hardening. Moreover, a modified Fields-Backofen model is proposed to predict the flow stress of prestrained CP-Ti at different strain rates. Both strain rate sensitivity and strain hardening exponent decrease with prestrain. Fracture surfaces of the specimens show that fracture mechanism of all tested specimens is dimple fracture. The more ductile deformation in prestrained CP-Ti after annealing indicates that its ductility is improved by annealing. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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5299 KiB

Open AccessFeature PaperArticle

Titanium Powder Sintering in a Graphite Furnace and Mechanical Properties of Sintered Parts

by Changzhou Yu, Peng Cao and Mark Ian Jones

Metals 2017, 7(2), 67; https://doi.org/10.3390/met7020067 - 22 Feb 2017

Cited by 18 | Viewed by 8578

Abstract

Recent accreditation of titanium powder products for commercial aircraft applications marks a milestone in titanium powder metallurgy. Currently, powder metallurgical titanium production primarily relies on vacuum sintering. This work reported on the feasibility of powder sintering in a non-vacuum furnace and the tensile properties of the as-sintered Ti. Specifically, we investigated atmospheric sintering of commercially pure (C.P.) titanium in a graphite furnace backfilled with argon and studied the effects of common contaminants (C, O, N) on sintering densification of titanium. It is found that on the surface of the as-sintered titanium, a severely contaminated porous scale was formed and identified as titanium oxycarbonitride. Despite the porous surface, the sintered density in the sample interiors increased with increasing sintering temperature and holding time. Tensile specimens cut from different positions within a large sintered cylinder reveal different tensile properties, strongly dependent on the impurity level mainly carbon and oxygen. Depending on where the specimen is taken from the sintered compact, ultimate tensile strength varied from 300 to 580 MPa. An average tensile elongation of 5% to 7% was observed. Largely depending on the interstitial contents, the fracture modes from typical brittle intergranular fracture to typical ductile fracture. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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4770 KiB

Open AccessArticle

Fretting Behavior of SPR Joining Dissimilar Sheets of Titanium and Copper Alloys

by Xiaocong He, Cong Deng and Xianlian Zhang

Metals 2016, 6(12), 312; https://doi.org/10.3390/met6120312 - 09 Dec 2016

Cited by 17 | Viewed by 4457

Abstract

The fretting performance of self-piercing riveting joining dissimilar sheets in TA1 titanium alloy and H62 copper alloy was studied in this paper. Load-controlled cyclic fatigue tests were carried out using a sine waveform and in tension-tension mode. Scanning electron microscopy and energy-dispersive X-ray techniques were employed to analyze the fretting failure mechanisms of the joints. The experimental results showed that there was extremely severe fretting at the contact interfaces of rivet and sheet materials for the joints at relatively high loads levels. Moreover, the severe fretting in the region on the locked sheet in contact with the rivet was the major cause of the broken locked sheet for the joints at low load level. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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