Advances in Titanium Alloys: Mechanical Properties, Microstructure and Ultrasonic Impact Treatment

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: 20 March 2024 | Viewed by 5807

Special Issue Editor

Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Sciences, Tomsk 634055, Russia
Interests: additive manufacturing; titanium alloys; microstructure; phase transformation; ultrasonic impact treatment; surface hardening; deformation

Special Issue Information

Dear Colleagues,

Due to the remarkable combination of high strength-to-weight ratio, strong resistance to creep, excellent corrosion resistance, and low heat conductivity, titanium and its alloys have been extensively used in a wide range of applications in aerospace, biomedical, chemical, marine, automotive, and many other industries. However, the poor wear resistance of titanium alloys is still the main shortcoming that restricts their applications, particularly in areas involving friction and wear.

Currently, ultrasonic impact treatment (UIT) and its modifications (ultrasonic impact peening, ultrasonic nanostructural surface modification, etc.) are effective methods for surface hardening that significantly improves functional properties of structural materials, as well as their welded joints. Surface deformation by means of a metallic striker oscillating with ultrasonic frequency is accompanied by refinement of grains and subgrains in polycrystalline materials down to nano- and submicron-size ranges, development of compressive stresses in the surface layer of the specimens, a decrease in surface roughness, etc., that considerably increases the yield point and the tensile strength, the fatigue strength, the wear resistance, the corrosion resistance, and other characteristics of structural materials. Unlike shot peening, sandblasting, SMAT, and other techniques of work hardening of surface layers, the impact force and the strike density in UIT can be precisely controlled that allows more effective treatment of a specimen. Moreover, ultrasonic impact treatment is an inexpensive technique that does not require complex equipment and provides capability to treat hard-to-reach areas and complex parts.

Generally, the nature of morphological changes taking place in the materials during the UIT processing is determined not only by the temperature–rate parameters, but also by their microstructures, phase compositions, the presence of carbide-forming elements, possible polymorphic transformations under severe plastic strains, etc. There is no doubt that explicit identifying the mechanisms of structural and phase transformations during repeated penetrations of a striker into the treated specimen is made possible by computer simulations. In this Special Issue, we welcome articles that focus on the experimental observations, a molecular dynamics simulation and ab initio calculation mechanisms underlying the development of structural and phase transformations in loaded titanium alloys which made it possible to explain the UIT effect on their microstructure, mechanical properties, as well as deformation and fracture behavior under different external actions.

Prof. Dr. Alexey Panin
Guest Editor

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Keywords

  • titanium alloys
  • ultrasonic impact treatment
  • microstructure
  • phase transformation
  • surface hardening
  • deformation
  • mechanical properties

Published Papers (6 papers)

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Research

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19 pages, 9311 KiB  
Article
Stiffness of Anatomically Shaped Lattice Scaffolds Made by Direct Metal Laser Sintering of Ti-6Al-4V Powder: A Comparison of Two Different Design Variants
Metals 2024, 14(2), 219; https://doi.org/10.3390/met14020219 - 10 Feb 2024
Viewed by 522
Abstract
The modern approach to the recovery of damaged and missing bone tissue is increasingly focused on the application of implants capable of supporting the growth and recovery of parent tissue, rather than replacing the tissue itself. In this regard, the primary task of [...] Read more.
The modern approach to the recovery of damaged and missing bone tissue is increasingly focused on the application of implants capable of supporting the growth and recovery of parent tissue, rather than replacing the tissue itself. In this regard, the primary task of modern bone implants is to enable the targeted deformation of the implant against the expected load that that piece of bone should bear. The paper presents research related to anatomically shaped lattice scaffolds (ASLSs) made by the direct metal laser sintering (DMLS) of Ti-6Al-4V powder, and refers to the influence of the crossing angle between the outer lattice struts on the rigidity of the scaffold structure. The study includes the measurement of the deformation of two ASLSs designed for the same missing piece of rabbit tibia; these differed in terms of the crossing angle of the struts in the outer lattice and were exposed to quasi-uniaxial compression. The results show that the ASLS with outer struts that intersect at 60° (the angle between the compression direction and the strut axes is 30°) is more flexible compared to the ASLS with outer struts that intersect at 90° (the compression direction and the strut axes are colinear), even though its porosity is lower and volume is bigger. Full article
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22 pages, 9434 KiB  
Article
Adjustable Elasticity of Anatomically Shaped Lattice Bone Scaffold Built by Electron Beam Melting Ti6Al4V Powder
Metals 2023, 13(9), 1522; https://doi.org/10.3390/met13091522 - 27 Aug 2023
Cited by 1 | Viewed by 666
Abstract
This study investigates the elasticity of specific lattice structures made from titanium alloy (Ti6Al4V), namely, anatomically shaped lattice scaffolds (ASLS) aimed for reinforcement of the bone tissue graft that substitute a missing piece of the previously injured bone during its recovery. ASLSs that [...] Read more.
This study investigates the elasticity of specific lattice structures made from titanium alloy (Ti6Al4V), namely, anatomically shaped lattice scaffolds (ASLS) aimed for reinforcement of the bone tissue graft that substitute a missing piece of the previously injured bone during its recovery. ASLSs that were used for testing were fabricated using the Electron Beam Melting (EBM) method. The mechanical properties of the ASLS were examined through uniaxial compression tests. Compression testing revealed the complex non-linear behavior of the scaffold structure’s elasticity, with distinct compression stages and deformation dependencies. The ASLS structures exhibited quasi-elastic deformation followed by the rupture of individual struts. Results demonstrate that the ASLSs can be stiffened by applying appropriate compression load and accordingly achieve the target elasticity of the structure for the specific load range. The modulus of elasticity was determined for different compression stages of ASLS, allowing interpolation of the functional relation between the modulus of elasticity and compressive force that is used for stiffening the ASLS. This study enhances the understanding of the mechanical behavior of the specific lattice structures made of Ti6Al4V and provides insights for the development of mechanically optimized anatomically shaped lattice scaffolds. Full article
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12 pages, 5051 KiB  
Article
Low-Cycle Fatigue Behavior and Fracture Characteristics of Low-Cost Ti-2Fe-0.1B Alloy
Metals 2023, 13(7), 1208; https://doi.org/10.3390/met13071208 - 29 Jun 2023
Viewed by 670
Abstract
In recent decades, the effect of Fe element addition on titanium alloy has been investigated extensively due to the development of low-cost titanium alloys, as well as B microalloying, which could decrease the grain size of titanium alloys during the casting process. As [...] Read more.
In recent decades, the effect of Fe element addition on titanium alloy has been investigated extensively due to the development of low-cost titanium alloys, as well as B microalloying, which could decrease the grain size of titanium alloys during the casting process. As a key structural material, the study of the fatigue behavior of titanium alloys is crucial and always attractive for scientists. Hence, in this paper, the low cycle fatigue (LCF) behavior and fracture characteristics of a low-cost Ti-2Fe-0.1B alloy with a lamellar structure were investigated systematically, five different strain amplitudes (Δεt/2) in the range from 0.6% to 1.4% were selected to control the LCF process. It was found that the Ti-2Fe-0.1B alloy exhibits continuous cyclic softening behavior in the cycle as a whole at Δεt/2 ≤ 1.2%, while at Δεt/2 = 1.4%, it exhibits slight cyclic hardening at the initial stage of the cycle, then shows cyclic softening. Compared with pure titanium and other typical titanium alloys, the Ti-2Fe-0.1B alloy indicated maximum fatigue life under the same strain amplitude, it can be attributed to the fine grain size result from the effect of Fe element and trace B, which could hinder the dislocation movement and crack propagation. Full article
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21 pages, 16417 KiB  
Article
Transformations of the Microstructure and Phase Compositions of Titanium Alloys during Ultrasonic Impact Treatment Part III: Combination with Electrospark Alloying Applied to Additively Manufactured Ti-6Al-4V Titanium Alloy
Metals 2023, 13(5), 932; https://doi.org/10.3390/met13050932 - 10 May 2023
Cited by 1 | Viewed by 1337
Abstract
Scanning electron microscopy, 3D optical surface profilometry, as well as X-ray diffraction and electron backscatter diffraction analysis were implemented for studying the effects of both ultrasonic impact treatment (UIT) and ultrasonic impact electrospark treatment (UIET) procedures on the microstructure, phase composition, as well [...] Read more.
Scanning electron microscopy, 3D optical surface profilometry, as well as X-ray diffraction and electron backscatter diffraction analysis were implemented for studying the effects of both ultrasonic impact treatment (UIT) and ultrasonic impact electrospark treatment (UIET) procedures on the microstructure, phase composition, as well as the mechanical and tribological properties of Ti-6Al-4V samples fabricated by wire-feed electron beam additive manufacturing. It was shown that he UIET procedure with the WC-6%Co striker enabled to deposit the ~10 µm thick coating, which consists of fine grains of both tungsten and titanium-tungsten carbides, as well as titanium oxide. For the UIET process, the effect of shielding gas on the studied parameters was demonstrated. It was found that the UIET procedure in argon resulted in the formation of a dense, continuous and thick (~20 µm) coating. After the UIET procedures in air and argon, the microhardness levels were 26 and 16 GPa, respectively. After tribological tests, wear track surfaces were examined on the as-built sample, as well as the ones subjected to the UIT and UIET procedures. It was shown that the coating formed during UIET in air had twice the wear resistance compared to the coating formed in argon. The evidence showed that the multiple impact of a WC-Co striker with simultaneous electrical discharges was an effective way to improve wear resistance of the Ti-6Al-4V sample. Full article
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33 pages, 93733 KiB  
Article
Corrosion Resistance of the Welded Joints from the Ultrafine-Grained Near-α Titanium Alloys Ti-5Al-2V Obtained by Spark Plasma Sintering
Metals 2023, 13(4), 766; https://doi.org/10.3390/met13040766 - 14 Apr 2023
Viewed by 939
Abstract
A solid-phase diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and electrochemical corrosion was [...] Read more.
A solid-phase diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and electrochemical corrosion was shown to have a preferentially intercrystalline character. In the case of the presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles, and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy are harder and have a higher resistance to hot salt corrosion and electrochemical corrosion. Full article
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Review

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16 pages, 4155 KiB  
Review
Laser Beam Machining of Titanium Alloy—A Review
Metals 2023, 13(9), 1536; https://doi.org/10.3390/met13091536 - 30 Aug 2023
Cited by 1 | Viewed by 1128
Abstract
This study investigates the laser beam machining mechanism, surface formation mechanisms, heat-affected zone, taper formation, and the dimensional deviation of the titanium alloy, based on the information available in literature. The heat induced by the laser beam melts and vaporises titanium alloy, which [...] Read more.
This study investigates the laser beam machining mechanism, surface formation mechanisms, heat-affected zone, taper formation, and the dimensional deviation of the titanium alloy, based on the information available in literature. The heat induced by the laser beam melts and vaporises titanium alloy, which is removed by a high pressure-assisted gas. The machined titanium alloy surface is expected to have craters and resolidified materials which were contributed by the low thermal conductivity of the titanium alloy. Taper and circularity error can be minimised by optimising the laser parameter, but it cannot be avoided in the laser beam machining of titanium alloy. Laser beam machining induces a non-diffusion phase transformation, which slightly changes the surface mechanical properties of the titanium alloys. Laser beam machining is gaining popularity as a way to improve the surface finish quality and properties of titanium components manufactured by additive manufacturing processes. To enhance the machining efficacy of titanium alloys, several hybrid machining processes were proposed. Full article
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