Structure Of Titanium Alloys Research Articles

Fabrication and mechanical properties of network structured titanium alloy matrix composites reinforced with Ti2AlC particulates

Network structured Ti-6.5Al–2Zr–1Mo–1V (TA15) matrix composites reinforced with Ti2AlC particles were fabricated by low energy ball milling and subsequent spark plasma sintering (SPS). Microstructures, mechanical properties, and wear resistance properties of the composites were evaluated as a function of Ti2AlC weight fraction. Experimental results showed that the fine Ti2AlC powders were adhered on the surface of the spherical TA15 powders after low-energy milling process and Widmanstatten α+β microstructure with a network architecture was formed after SPS. The Ti2AlC reinforcements were reacted with Ti matrix and formed a Ti3AlC phase at the interface. The hardness, tensile, and compressive strength of the TA15/Ti3AlC composites show significant improvement with less ductility loss. The TA15/1.0 wt% Ti2AlC exhibited tensile yield strength of 929 MPa and ultimate tensile strength of 1013 MPa with ductility of 13.06%. The TA15/Ti3AlC composites had a lower friction coefficient and decreased wear rate with delamination and abrasive wear modes.

Refinement of the grain structure of additive manufactured titanium alloys via epitaxial recrystallization enabled by rapid heat treatment

The coarse prior-β grain structure in titanium alloys produced by additive manufacturing is associated to mechanical anisotropy and limited fatigue life. Here we report a novel methodology to refine such structure by rapid heat treatment of Ti–6Al–4V produced by laser powder-bed fusion. The refinement was analysed using high-temperature EBSD that showed, for the first time, how high angle boundary β grains nucleated and grew with quasi-equiaxed morphology by epitaxial recrystallization. These findings show the potential for such heating regime to be applied to control grain size, morphology and distribution in a wider category of structural alloys produced by additive manufacturing.

Dislocation density informed eigenstrain based reduced order homogenization modeling: verification and application on a titanium alloy structure subjected to cyclic loading

This manuscript presents a dislocation density informed eigenstrain based reduced order homogenization model (DD-EHM), and its application on a titanium alloy structure subjected to cyclic loading. The eigenstrain based reduced order homogenization (EHM) approach has been extended to account for the presence of HCP (primary α phase) and BCC (β phase) grains, within which the deformation process is modeled using a dislocation density based crystal plasticity formulation. DD-EHM has been thoroughly verified to assess the accuracy of the reduced order model in capturing local and global behavior compared with direct crystal plasticity finite element method simulations. A structural scale study of titanium alloy Ti-6242S is performed using DD-EHM to quantify and characterize the spatial distribution and evolution of the dislocation pile-ups subjected to cyclic loading. The evolution of pileups at two spatial scales are tracked using a nonlocal parameter based on dislocation density discrepancy across neighboring grains. The effect of non-uniform texture on the response of the structural component has been investigated.

Deformation and fracture of a titanium alloy during penetration of high-speed impactor to the target

The study of the formation and evolution of structures of titanium alloys during high-speed impact is important for the development of technological processes for their manufacture and for the development of dynamic fracture mechanics as a whole. This work is devoted to a detailed study of the structure of 3M titanium alloy, which is formed during the penetration of a target from this alloy by an irregularly shaped striker at a collision velocity of ~ 2 km/s.

The correlation among chemical composition, structure and mechanical properties in titanium alloys for the elements with increased dynamic ability

This article contains the comparison of physical and mechanical properties of several titanium alloys. The chemical composition influence on mechanical properties is investigated. VT22I and VT35 highly alloyed titanium alloys are the most prominent materials for armor elements production with ultimate tensile strength of 1200-1400 MPa and impact strength of 0,25-0,3 MJ/m2.

The issue of quality assurance of materials in additive manufacturing of metal products

The article addresses the quality issues of additive manufactured products from the perspective of materials science. Additive manufacturing is multilayered step-by-step deposition of a material in micro-volumes following the trajectory controlled by a CNC program. Such heating sources as electric arc, laser, plasma and electron beam can be used to melt the metallic powder. This article investigates the structure and properties of titanium alloy Ti-6Al-4V ELI produced by selective laser melting (SLM). The samples were produced in pure argon environment in a system with a 3D printer EOS M290 (Electro Optical System GmbH, Germany) and then heat-treated in vacuum at 750…800 °C during 3 hours. It was revealed that the main structural defects reducing mechanical properties of material are pores and stress concentrators in the points of contact between titanium alloy particles and the newly built surface of the previous layer. The ways aimed to avoid the structural defects which reduce fracture toughness were suggested.

Design and Performance Evaluation of Porous Titanium Alloy Structures for Bone Implantation

Implant parts prepared by traditional design and manufacturing methods generally have problems of high stiffness and heavy self-weight, which may cause stress shielding effect between the implanted part and the host bone, and eventually cause loosening of the implanted part. Based on the implicit surface function equations, several porous implant models with controlled pore structure were designed. By adjusting the parameters, the apparent elastic modulus of the porous implant model can be regulated. The biomechanical simulation experiment was performed using CAE software to simulate the stress and elastic modulus of the designed models. The experimental results show that the apparent elastic modulus of the porous structure scaffold is close to that of the bone tissue, which can effectively reduce the stress shielding effect. In addition, the osseointegration status between the implant and the host bone was analyzed by implant experiment. The pushout test results show that the designed porous structures have a good osseointegration effect.

Obtaining Spherical Powders of Grade 5 Alloy for Application in Selective Laser Melting Technology

In this paper, the process of obtaining a spherical powder of titanium alloy of the “Grade 5” brand using inductively coupled argon-helium plasma has been studied. The structure of titanium alloy was studied before and after the spheroidization process. The results of particle size and X-ray fluorescent analysis were also obtained. As a result of the analysis of the structure, it was concluded that the crystallite sizes and microstress values change. Keywords: additive technology, plasmachemical synthesis, spheroidization, titanium alloy, grade 5.

Effect of microstructure evolution on mechanical properties of a TiZrAlB alloy rolled by different processes

For the development of structural titanium alloys with excellent mechanical properties, the effect of rolling temperature and cooling rate on phase composition, microstructure evolution, and mechanical properties in a full-α TiZrAlB alloy were investigated. Optical microscopy, scanning electron microscopy, transmission electron microscopy, and statistical analysis, were employed to further understand and control the processing-structure-property relationships. The experimental results of specimens rolled at a temperature range from the α to β phase region demonstrated a significant grain refinement trend as the rolling temperature increased, and the work hardening effect was stronger in specimens rolled at the α+β double phase region than those rolled in the single phase region. The high density of the original β grain boundaries also enhanced the mechanical properties when the specimens were rolled at temperatures around/above the β-transus temperature. The highest strength (σ0.2 = 1121 MPa and σb = 1387 MPa) with a failure elongation of 6.1% was obtained in 840 °C-rolling water-quenched specimens, however, the furnace cooling led to worsened mechanical properties. In sum, the variation in the mechanical properties of the series of rolled alloys was mainly ascribed to the microstructure evolution under the different rolling processes.

A significant increase in the hardness of nanotwinned titanium alloys prepared via the martensitic phase transformation

In this work, a nanotwinned structure of a two-phase titanium (TC21) alloy was prepared via the martensitic phase transformation method. The TC21 alloy forms initially a single phase β when the temperature reaches 1050 °C. Then, it transitions into an orthorhombic martensite (α″) material when quenched in water. After tempering at 500 °C, the martensite transforms into a high-density nanotwinned α phase material. The hardness of the nanotwinned alloy is 25% higher than that of the TC21 raw material.

Low-cost and high-strength powder metallurgy Ti–Al–Mo–Fe alloy and its application

Low-cost and high-performance are main research directions of structural titanium alloys. In this study, a two-phase structural Ti–5Al–3Mo–2Fe alloy was designed and prepared through elemental powder metallurgy (P/M) process, including cold isostatic processing, vacuum sintering, hot rolling and heat treatment. Results indicate that the P/M Ti–5Al–3Mo–2Fe alloy has a multi-phase microstructure with equiaxial primary α phase, needlelike secondary α phase and retained β phase. The room-temperature yield and ultimate strength reach to 1303 MPa and 1422 MPa, respectively, with a balanced elongation of 8.5%. At 400 °C, the alloy still has a high yield strength, ultimate strength and elongation of 850 MPa, 935 MPa and 17%, respectively. The Ti–5Al–3Mo–2Fe alloy was successfully processed into intake valves of automobile engine, which passed the engine test and meet the serving requirement.

Fatigue behavior of As-built selective laser melted titanium scaffolds with sheet-based gyroid microarchitecture for bone tissue engineering

Selective laser melting (SLM) has enabled the production of porous titanium structures with biological and mechanical properties that mimic bone for orthopedic applications. These porous structures have a reduced effective stiffness which leads to improved mechanotransduction between the implant and bone. Triply periodic minimal surfaces (TMPS), specifically the sheet-based gyroid structures, have improved compressive fatigue resistance due lack of stress concentrations. Sheet-based gyroid microarchitectures also have high surface area, permeability, and zero mean curvature. This study examines the effects of the gyroid microarchitectural design in parallel with SLM parameters on structure and function of as-built titanium alloy (Ti6Al4V ELI) scaffolds. Scaffold design was varied by varying unit cell size and wall thickness to produce scaffolds with porosity within the range of trabecular bone (50–90%). Manufacturer’s default and refined laser parameters were used to examine the effect of input energy density on mechanical properties. Scaffolds exhibited a stretching-dominated deformation behavior under both compressive and tensile loading, and porosity dependent stiffness and strength. Internal void defects were observed within the walls of the gyroids structure, serving as sites for crack initiation leading to failure. Refinement of laser parameters resulted in increased compressive and tensile fatigue behavior, particularly for thicker walled gyroid microarchitectures, while thinner walls showed no significant change. The observed properties of as-built gyroid sheet microarchitectures indicates that these structures have potential for use in bone engineering applications. Furthermore, these results highlight the importance of parallel design and processing optimization for complex sheet-based porous structures produced via SLM. Statement of SignificanceSelective laser melting (SLM) is an additive manufacturing technology which produces complex porous scaffolds for orthopedic applications. Titanium alloy scaffolds with novel sheet-based gyroid microarchitectures were produced via SLM and evaluated for mechanical performance including fatigue behavior. Gyroid structures are function based topologies have been hypothesized to be promising for tissue engineering scaffolds due to the high surface area to volume ratio, zero mean curvature, and high permeability. This paper presents the effects of scaffold design and processing parameters in parallel, a novel study in the field on bone tissue scaffolds produced via additive manufacturing. Additionally, the comparison of compressive and tensile behavior of scaffolds presented is important in characterizing behavior and failure mechanisms of porous metals which undergo complex loading in orthopedic applications.

Effects of magnetic field on microstructures and mechanical properties of titanium alloys in ultra-precision diamond turning

In this study, a magnetic field was superimposed in single point diamond turning (SPDT) of titanium alloys, aimed at enhancing the mechanical and microstructural properties of machined titanium alloy surface. The experimental results showed that the grain size decreased under an influence of magnetic field, showing grain refinements and reductions of grain pile up near grain boundaries on the machined surface, which grain pile up in machining of titanium alloys denotes as coarse colonies of alpha laths near grain boundary on the machined surface. Also, microhardness and ductility of the machined surfaces were enhanced simultaneously by using a magnetic field in SPDT. The study proposes a novel machining technology to enhance mechanical properties and the grain structure of machined titanium alloys in SPDT.

The energy absorption and bearing capacity of light-weight bio-inspired structures produced by selective laser melting

Sandwich structures are widely used in aviation and aerospace fields because they can absorb vast energy due to their excellent continuous compression behaviors. And in this work, the light-weight bio-inspired sandwich structure of titanium alloy was designed based on cybister elytra and produced by selective laser melting (SLM). The results show that bio-inspired structures can realize the light-weight effectively by increasing the core height. The specific and ultimate flatwise compressive strengths first increase and then decrease when core height increases. The load-displacement curves of bio-inspired structures during flatwise compression consists of elastic deformation, buffer and compaction zone. Comparatively, the edgewise compression lacks buffer zone. And the bio-inspired structure has an excellent flatwise comprehensive performance when its core height is 6 mm, whose peak flatwise compressive strength and specific volume energy absorption are 84.30 MPa, 101.30 MJ/m3, respectively. The specific ultimate strength of bio-inspired structures is optimized at the core height of 4 mm on the edgewise compression tests. And the fracture of the side arc damaged area shows an obviously ductile fracture and the panel and core of the middle area are brittle fracture in the flatwise compressive tests. Finally, The ANSYS simulation results are consistent with experimental results during the whole compressions, which will provide an accurate guidance in next researches

Properties Anisotropy of Additive Manufactured High-Porous Titanium Alloy with Non-Equiaxial Cellular Structure

Numeric simulation of compression test was carried out for a high-porous structure of a titanium alloy produced by additive manufacturing method with non-equiaxial performance of pore cells. The stress-strain state of a cellular titanium alloy with diamond-shaped unit cells was determined by the finite element method (FEM) in ABAQUS software for the plane formulation of the problem. The distribution of stresses, as well as the modulus of elasticity of the cellular material, was proved to depend on the loading direction.

The Influence of Structure and Phase Composition of Titanium Alloy on Superplastic Deformation

The paper presents research into the behavior of high-temperature plastic deformation of titanium alloy Ti–4.74 wt.% Al–5.57 wt.% Mo–5.04 wt.% V alloy (VT22) depending on its structure and phase composition. It is shown that the formation of fine-grain structure in this alloy is not a sufficient condition for realizing superplastic deformation. It is found that the formation of the ultra-fine grain structure in VT22 alloy leads to the temperature decrease down to 823 K at the beginning of plastic deformation. This allows achieving the percent elongation of the alloy specimens over 1300% within the temperature range of 973–1073 K and at a 6.9·10–3 s–1 initial tensile rate. The grain boundary sliding is considered to be the main deformation mechanism.

Prediction of structure and mechanical properties of titanium alloy Ti-6Al-4V during layer formation of 3D products by additive technology of electron beam cladding

The problem of providing the necessary operational properties of titanium alloy structural elements produced by additive technologies using filler materials, in particular xBeam 3D Metal Printer electron beam welding technology, is considered. An analytical review of the existing data on the dependence of mechanical properties, grain size and microstructure of the titanium alloy Ti-6Al-4V on the cooling rate of the material has been carried out. On the base of mathematical modeling, temperature fields in the process of multilayer formation of a 3D fillet sample from Ti-6Al-4V alloy, residual stress and distortions are determined. Then macro and microstructure, as well as mechanical properties of the sample material are predicted. Comparison with the results of the experimental study of the macrostructure showed satisfactory accuracy of the modeling. The developed approach can be used to predict the macrostructure and mechanical properties of titanium alloy products obtained by additive layer-forming technologies. But there is a need to obtain experimental data for high cooling rates of material in the range of 100-700 degrees/c.

Low temperature ion nitriding titanium alloy TI-6AL-4V in the coarse grained and ultrafine-grained states

The paper presents the study of the influence of ion nitriding modes on the structure and mechanical properties of titanium alloy TI-6AL-4V in ultrafine-grained (UFG) state obtained via equal channel angular extrusion (ECAE). Optical images of a microstructure using scanning electron microscopy (SEM) were obtained. Microhardness testing by the depth of the modified layer was conducted.

Ultrasonic Burnishing of Titanium Alloys

This paper presents research results concerning the influence of ultrasonic burnishing on the structure and mechanical properties of ultra-fine grain titanium alloys: commercial pure titanium BT1-0 and an over stoichiometric alloy with the shape memory Ti49.3Ni50.7. It was shown by the methods of optical microscopy and transmission electronic microscopy that in the surface layer of 20 μm thickness, the ultrasonic burnishing in coarse-grained titanium forms a nanostructure with a grain size of 100 nm, and it additionally decreases the size of crystals from 100 to 30 nm in the nanostructural titanium nickelide. The ultrasonic treatment of alloys greatly increases the strength and micro- and nanohardness of the surface layer, decreases the roughness, forms the gradient nanostructure, improves the lifetime, and expands the functionalities of the items.

Main factors affecting the structure and properties of titanium and cobalt alloys manufactured by the 3D printing

This paper is short review the main factors affecting the structure and properties of the metals manufactured by additive technology (selective laser melting). A comparative analysis of the structure and properties of Ti6Al4V or CoCrMo alloys obtained by selective laser melting is presented. We describe the capabilities of laser melting method for producing materials with high density and high mechanical properties. The optimized process parameters for 3D printed medicine materials Ti6Al4V and CoCrMo with high density of are discussed.