Ti-Mo Alloys Research Articles

Investigation of tensile deformation behavior of a TWIP/TRIP metastable β titanium alloy at typical temperature part Ⅰ: Room temperature

The tensile behavior and deformation mechanism of Ti-10Mo alloy at room temperature (298 K) were investigated. The results show that the alloy has an ultimate tensile strength (UTS) of 744 MPa and a high yield strength (YS) of 662 MPa, as well as an excellent elongation (El) after fracture of 38 %, outperforming Ti-15Mo alloy under the same conditions. The superior strength and plasticity of Ti-10Mo alloy at 298 K are attributed to the activation of both {332}〈113> twinning and SIM α“ during deformation. The sequence of different deformation mechanisms is as follows: in the initial stage of deformation, dislocation slip can be extensively activated and continues to occur during subsequent deformation; in the middle stage of deformation, primary and secondary {332}〈113〉 twinning and SIM α” are activated simultaneously, resulting in a continuous increase in work hardening rate; in the later stage of deformation, the alloy can further deform through {1 1 1}α“ twinning. The higher YS may be due to the optimal quantity and size of athermal ω phase in Ti-10Mo alloy, which increases the YS without significantly affecting plasticity. Meanwhile, Quenching vacancies can also increase the YS of the alloy. The three stages of the work hardening rate curve correspond to the activation of the dislocation slip mechanism, the activation of the {332}〈113〉 twinning and SIM α” and the stop of the {332}〈113〉 twinning and SIM α“.

Investigation of tensile deformation behavior of a TWIP/TRIP metastable β titanium alloy at typical temperature part Ⅱ: 20 K

The tensile behavior and deformation mechanism of Ti-10Mo alloy at liquid hydrogen temperature (20 K) were investigated. The results showed that Ti-10Mo alloy has a high UTS of 1553 MPa and a high YS of 1497 MPa at 20 K, as well as an excellent elongation after fracture of 11 %. This is due to the simultaneous activation of {332}<113> twin twins and SIM α“ transformation during deformation, that is, the combination of TWIP and TRIP effects. The activation sequence of different deformation mechanisms is as follows: the primary SIM α” and {332}<113> twins are first activated simultaneously. With the increase of strain, multiple variants of SIM α“ and {332}<113> twins can be activated in a grain. Then the primary SIM α” can be further transformed into {130}<310>α“ twins. With the further increase of strain, some {130}<310>α” twins can continue to be transformed into secondary {332}<113>β twin and some primary {332}<113> twins can also produce secondary α“ to continue the deformation. When necking, a large number of {111}α” twins are activated to further coordinate the plastic deformation. In addition, the multiple necking phenomenon is due to the further activation of {332}<113> twins and SIM α“ during the necking of a certain area due to stress concentration during the stretching process, which causes local strengthening and resulting in the stop of necking. Finally, the serrations on the stress–strain curve may be caused by multiple necking.

Effect of Pre-Rolling Strategy and Aging Precipitation Behaviors on Mechanical Properties and Wear Resistance of Biomedical Ti-15Mo Alloy

Effect of Pre-Rolling Strategy and Aging Precipitation Behaviors on Mechanical Properties and Wear Resistance of Biomedical Ti-15Mo Alloy

Grain size dependence of deformation behavior in Ti–15Mo alloy prepared by powder metallurgy

To the best of our knowledge, this is the first report demonstrating grain refinement to 4 μm via a mass-production method for the Ti–15Mo alloy. Grain sizes ranging from 4 to 38 μm were achieved by controlling thermomechanical processing in powder metallurgy, combined with heat treatment using recycled coarse powders for additive manufacturing. The critical grain size for deformation twinning was investigated, alongside an analysis of the deformation behavior and mechanical properties of the Ti–15Mo alloy with various grain sizes. Upon refining the grain size to 7 μm, deformation twinning is inhibited, shifting the plastic deformation mechanism from mechanical twinning to dislocation slip. The yield strength can be adjusted between 921 and 715MPa, with elongation ranging from 18.4% to 34.4%, by varying the grain size distribution ratio of small to large grains relative to 7 μm from 1.5 to 0.42. This strengthening effect primarily arises from dislocation strengthening, Mo solid solution, texture strengthening, and modifications in the Hall-Petch constant due to changes in deformation behavior during grain refinement.

Heterogeneous dynamic restoration of Ti–15Mo alloy during hot compression

Near-β titanium alloys have shown low Young's modulus and good strength, making them excellent implant candidates. However, their processing using thermomechanical routes in single phase β region results in heterogeneous microstructures due to high content alloying elements and consequent slow diffusion-controlled processes such as dynamic recovery. This study investigates the deformation behaviour of a Ti–15Mo alloy through hot compression experiments using a Gleeble ® 3800 device in the single β domain at strain rates from 0.01 s−1 to 10 s−1, reaching final strains of 0.50 and 0.85 followed by immediate water quench. The findings show that the material presents a low strain rate sensitivity. The flow curves show significant strain hardening before reaching a steady-state regime, particularly at high strain rates. The strain hardening exponent calculations support the effect of molybdenum on retarding softening mechanisms such as dynamic recovery. Electron backscatter diffraction (EBSD) measurements of deformed samples revealed that dynamic recovery is the primary restoration mechanism, with continuous and geometric dynamic recrystallisation evidence. Due to the slow restoration process, we observe the subgrain formation for different deformation parameters. Therefore, we introduced an EBSD-based method to quantify dynamic recovery and subgrain size. We concluded that for a given deformation, the areas of dynamically recovered and recrystallised regions decrease with increasing strain rate and decreasing temperature, exhibiting negligible variation at higher strain rates.

Microstructure development and strengthening behaviour in hot-extruded Ti-Mo alloys with exceptional strength-ductility balance

A series of strong and ductile Ti-Mo alloys containing 2.5, 5, 7.5 and 10 wt% Mo was experimentally investigated by a two-stage blended-elemental powder metallurgy process. This process consisted of a spark plasma sintering stage for powder-consolidation and in-situ-homogenisation, and a hot extrusion stage for densification and microstructure enhancement. Microstructures in the extruded alloys changed from α dominant to β dominant with molybdenum addition. Simultaneously, a grain refinement effect was observed due to suppressed α precipitation and increase β retention. A significant strengthening effect was observed with molybdenum addition. In comparison with similarly processed commercially pure titanium, Ti-10Mo exhibited a yield strength improvement of 290 % to 1382.8 MPa, and an ultimate tensile strength improvement of 239 % to 1496.5 MPa. Meanwhile, Ti-5Mo exhibited a yield strength improvement of 211 % (1007.9 MPa) without any substantial reduction in ductility, resulting in an exceptional tensile toughness of 361.3 MJ.m−3. A quantitative analysis of strengthening mechanisms reveals considerable strengthening effects from solid solution strengthening, dislocation strengthening, and grain refinement effects. These factors arise from the novel multi-modal microstructures formed by thermomechanical processing at super-transus temperatures. The newly achieved balance of strength and ductility appears to be unrivalled amongst all previously reported binary Ti-Mo alloys.

Role of Mo and Zr Additions in Enhancing the Behavior of New Ti–Mo Alloys for Implant Materials

AbstractThe utilization of Ti–Mo alloys in biomedical applications has gained attention for use in biomedical applications owing to their non-toxicity, reasonable cost, and favorable properties. In the present study, Ti–12Mo–6Zr and Ti–15Mo–6Zr alloys were prepared using elemental blend and mechanical alloying techniques. The effect of alloying elements Mo and Zr of Ti–Mo alloy, as well as the effect of fabrication techniques of Ti–Mo–Zr trinary alloys, were investigated. Thermodynamic calculations supported by CALPHAD analysis revealed that the addition of Zr increases lattice distortion, which contributes to enhancing the strength. Conversely, adding Mo decreases the enthalpy, facilitating improved mixing and solid solution formation. The as-sintered samples were characterized by X-ray diffraction, optical microscope, and scanning electron microscopy, and their microhardness, compressive, and corrosion behavior were investigated. Among all the investigated alloys, Ti–15Mo–6Zr alloy prepared by the mechanical alloying technique, milled for six hours at 300 rpm, compacted at 600 MPa, and sintered at 1250 ℃, shows good comprehensive mechanical properties with a preferable compressive strength (− 1710 MPa) and hardness (396 HV5), as well as the lowest wear rate (0.69%) and corrosion rate (0.557 × 10–3 mm/year). This can be related to the solid solution strengthening and relative density, together with dispersion and precipitation strengthening of the α phase. Remarkably, the combination of high mechanical and corrosion properties can be achieved by tailoring the content of the α phase, controlling the density, and providing new fabricating techniques for β Ti alloys. Graphical Abstract

Enhancing Passivation Behaviors and Wear Resistance of Biomedical Ti-15Mo Alloy via {332} Twinning Pre-Tension and Aging

The purpose of this investigation was to determine the extent to which a combination of pre-deformation and aging procedures could enhance the corrosion and wear resistance of the Ti-15Mo alloy for biomedical materials. The initial grains were refined with {332} twins and other defects after the pre-deformation, increasing the amount of precipitation nucleation and forming finer α phases during aging. The finer precipitates with numerous boundaries are beneficial in forming a thicker passivation film in phosphate-buffered saline (PBS) solution, and the corrosion resistance of the 20% pre-deform plus aged alloy is improved by 4.23 times. The result indicates that the corrosion passivation behavior and film structure of the biomedical Ti-15Mo alloy are significantly influenced by its microstructure. The worn track and debris of the alloy after pre-tension and aging gradually decreases with the increase in pre-deformation rates, caused by the increase in the hardness and wear resistance. The mechanism of corrosion and wear resistance in PBS solution were revealed, which showed the pre-tension and aging processes that were performed on the Ti-15Mo alloy. This study proposes that pre-tension with {332} twins contributed to precipitation refinement, which would enhance the passivation behaviors and wear resistance of the biomedical β titanium alloy.

Effect of Zr addition on the corrosion resistance of Ti-Mo alloy in the H2O2-containing inflammatory environment

Reactive oxygen species (ROS), produced by immune cells during inflammatory reaction, are known to promote corrosion of standard biomedical materials such as CP-Ti and Ti-6Al-4V. Electrochemical corrosion in the ROS environment can be further accelerated in the vicinity of fretting regions, where titanium can be polarized towards negative potentials. This study considers both of these aspects and presents corrosion analysis under complex inflammatory conditions for Ti-Mo and Ti-Mo-Zr alloys, which offer exceptional strain-hardening behavior and ductility. Combining electrochemical impedance spectroscopy (EIS) and atomic emission spectroelectrochemistry (AESEC) allowed us to understand the origin of ROS-induced corrosion. At free corrosion conditions, Zr was found to suppress oxide layer growth without any significant effect on the dissolution process. On the other hand, Zr suppressed dissolution rate under cathodic potentials. Although applying cathodic potential resulted in a rapid increase of dissolution rate, cross-section transmission electron microscopy (TEM) analysis did not reveal significant influence of the short cathodic polarization on the oxide film growth during further prolonged exposure at free corrosion conditions.

Enhancing the mechanical properties and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer {332} twins via cyclic deformation

Mechanical properties, passivation behaviors and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer twins were investigated. Cyclic deformation was conducted to activating more {332} twin variants via periodic changes of tension and compression. Microstructural refinement via numerous twins with the stable boundaries is different from other mechanisms, resulting in a higher hardness and maintaining the low elastic modulus after deformation and annealing. The results of electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy tests, revealed that twin boundaries are beneficial to enhancing passivation behaviors via forming a thicker oxide film in PBS solution. The alloy with ultra-finer {332} twins exhibit a better corrosion resistance due to a lower passivation current. The expected biomedical performance was obtained in the alloy after ±3 % amplitude cyclic deformation and 730 °C/7 min annealing, in contrast to the initial alloy with coarse grains, increasing 8.8 % of the hardness, decreasing 46 % of the corrosion current and maintaining the low elastic modulus.

Development of new β Ti-10-Mo-Mn alloys for biomedical applications

Metallic biomaterials play a crucial role in various biomedical applications, particularly in developing implants and prostheses. Hence, this study aimed to produce and analyze the structure, microstructure, hardness, and preliminary cytotoxicity of Ti-10Mo-xMn system alloys (with x ranging from 0 to 8 wt%) intended for biomedical applications as biomaterials. The alloys underwent thorough characterization, including chemical composition analysis through EDS measurements, mapping, and density assessments. Structural and microstructural analyses were conducted using x-ray diffraction (XRD), Rietveld refinement, optical (OM), and scanning electron microscopy (SEM), while Vickers microhardness testing provided insights into mechanical properties. Rapid cytotoxicity tests via MTT were also performed to assess biocompatibility. Results indicated that the produced alloys exhibited good quality and homogeneity regarding chemical composition. Adding Mn to the Ti-10Mo alloy facilitated the formation of the β phase, transforming it from a biphasic (α" + β) to a single-phase alloy.Moreover, Mn-induced reductions in lattice parameters and average crystallite size of the β phase were observed due to the smaller atomic radius of substituting Mn than Ti. Despite a decrease in hardness attributed to β phase formation, all alloys demonstrated non-cytotoxic behavior in cell adhesion and viability assays, with values exceeding 70 %. Overall, these findings highlight the potential of Ti-10Mo-xMn alloys as viable biomaterials, warranting further exploration and development in biomedical engineering.

Laser-Directed Energy Deposition of Ti-Mo Biomaterials: Influencing Mechanisms of Molybdenum on Microstructure and Performance

Ti-Mo alloys with variable molybdenum (Mo) contents were fabricated by the laser-directed energy deposition process. The in-depth influencing mechanisms of the Mo element on microstructure and performance were quantitatively analyzed by experiment and first-principal calculation. Increasing Mo content decreased the formation and cohesive energies and stabilized the 𝛽 phase. The grain refining efficiency was increased, and the relative grain size was decreased by increasing the Mo content. The MS temperature decreased, and the acicular martensite formed with increasing Mo content. Both the solid-solution hardening and fine grain strengthening effects had positive influences, while the 𝛽 phase softening effect had a negative influence on the hardness and wear performance with increasing Mo content.

Surface characterization and antibacterial efficiency of TiO2 nanotubes on Ti15Mo alloy

The aim of this work is to investigate wettability and antibacterial properties of the well-ordered titanium dioxide (TiO2) nanotube (TNTs) surfaces on new-generation titanium–15 molybdenum (Ti15Mo) alloys for dental and orthopedic implant applications. Thus, the well-ordered TNTs and flat oxide surfaces were fabricated at various potentials such as 20, 40 and 60 V on Ti15Mo alloy by anodic oxidation (AO) technique. Uniform elemental distributions were obtained across all surfaces. In particular, the nanotube surfaces produced at 60 V showed hydrophilic behavior, whereas the flat and nanotube surfaces produced at 20 and 40 V were hydrophobic, respectively. The in vitro antibacterial activity of all surfaces against Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) bacteria was investigated in detail. Compared with bare Ti15Mo alloys, the flat and TNTs surfaces showed antibacterial activity. Furthermore, the antibacterial efficiency of TNTs produced on titanium–15 molybdenum alloy improved with increasing AO potential values.

Evaluations of Mechanical Properties and Functionalities of the Al- and Zr-Tailored Ti–5.5Mo Shape Memory Alloys for Biomedical Applications

AbstractDue to the critical world population aging issue, biomaterials are important topics in the biomedical community. Among the biomedical materials, shape memory alloys (SMAs) are considered to be promising materials owing to their functionalities, such as shape memory effect (SME) and superelasticity (SE). Ti–Mo–Al-based alloys, which are biocompatible materials, are basic materials in the Ti-based SMAs due to the evaluation of the phase stability through the calculations of Mo and Al equivalents. This study, in addition, introduced Zr into the Ti–Mo–Al-based alloys for its highly biocompatibility and being a fine modifier to tune the phase stability. The mechanical (i.e., strength and elongation) and functional (i.e., SME and SE) properties have been investigated in this study to reveal the practicability of the biomedical applications for human usage. It was found that addition of Zr to the Ti–Mo alloy shows slight influence on the mechanical properties of the binary Ti–Mo alloy. With the addition of Al, that is, ternary Ti–Mo–Al alloys, two-stage yielding was found in the tensile examinations. Among all the alloys, the Ti–5.5Mo–4Al, the Ti–5.5Mo–4Al–6Zr, and the Ti–5.5Mo–8Al–6Zr (mol pct) alloys performed excellent shape recovery of about 100 pct in the bending and heating tests. Especially, the Ti–5.5Mo–4Al–6Zr and the Ti–5.5Mo–8Al–6Zr alloys further show high strength. Results in this study could be a guideline for the design of the fundamental Ti–Mo–Al-based SMAs.

The influence of solution treatment on the phase evolution and tensile properties of binary Ti-Mo alloys

The influence of solution treatment on the phase evolution and tensile properties of Ti-Mo alloys was investigated to assess their potential use in biomedical applications. Phase formation and microstructural evolution were studied using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The mechanical properties were characterized by means of tensile tests and bending strength. XRD analysis showed that solution treatment increased the volume fraction of ß phase and supressed the α" phase. The microstructures of the as-cast alloys consisted of ß equiaxed grains with sub-grain structures of different sizes, while the solution treated alloys comprised ß equiaxed grains only except for Ti-10.02Mo, which comprised needle-like a" structures. EBSD showed an increase in the volume fraction of the ω and α" phases in all the alloys after solution treatment. The elastic modulus and UTS of all the alloy significantly decreased after solution treatment, except for Ti-15.05Mo, whereas the elongation significantly increased. The fracture surfaces of all the alloys after solution treatment indicated more ductile behaviour than brittle.

Role of {332} twinning on adiabatic shear behavior during dynamic loading in β-type Ti–15Mo alloy

The microstructural evolution and formation mechanism of the adiabatic shear band (ASB) in {332}<113> twinning-induced plasticity (TWIP) Ti–15Mo alloy were investigated by applying stopper rings in a split Hopkinson pressure bar apparatus. Accompanied by activation of numerous {332}<113> twins, ASB consisting of elongated fine-grains initiated in the dynamically compressed sample with 0.28 true strain. Multiple twins adjacent to the ASB region were severely distorted and refined along the shear direction. Further deformation led to refinement of elongated twins into elongated subgrains, then some of them were subdivided into equiaxed fine-grains. The morphology of the fine-grains within the ASB underwent a complete transition from elongated to equiaxed as the strain increased to 0.33. The equiaxed fine-grains exhibited a random distribution of orientation, which was regarded as the result of dynamic recrystallization. The formation of equiaxed fine-grains was found to obey rotational dynamic recrystallization mechanism through the thermodynamic and kinetic calculations.

Electrochemical modification of the Ti[sbnd]15Mo alloy surface in solutions containing Ag2O, Ag3PO4 and Ca3(PO4)2 particles

Implants with bioactive coatings are becoming increasingly popular in bioengineering. The incorporation of silver nanoparticles into the oxide layer supports the antibacterial effect. This article describes the surface modification of Ti15Mo alloy subjected to the plasma electrochemical oxidation (PEO) process in baths containing Ag compounds: Ag2O, Ag3PO4, and Ag3PO4+ Ca(PO4)2 to incorporate antibacterial silver particles into the oxide layer on the surface of the tested alloy. Scanning electron microscopy revealed changes in the surface porosity of the obtained oxide layers. Energy dispersive analysis, Raman spectroscopy, and X-ray electron spectroscopy determined the chemical composition and distribution of elements on the sample's surface. The tests showed the presence of embedded silver particles and uniform distribution on the surface. The bioactivity of the obtained layer was tested by adhesion tests of bacteria and fungi: Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), and Candida albicans (ATCC 2091).

Buffered Oxide Etch: A Safer, More Effective Etchant for Additively Manufactured Ti-Alloys

Kroll’s reagent is effective for the metallographic etching of traditional Ti-alloys but struggles with the intricate, refined microstructures of newer Ti-alloy compositions like Ti-Cu and Ti-Mo alloys, which are created through additive manufacturing. The presence of fine intermetallic compounds in these alloys results in limited contrast between grains and phases when using Kroll’s reagent, highlighting the need for an alternative etchant. This study systematically investigates the use of buffered oxide etch, a common etchant for micro-electronics, on a range of additively manufactured Ti-alloys. The results show that buffered oxide etch provides superior etching outcomes compared to Kroll’s reagent and ammonium bifluoride, with a clear colour contrast between grains and fine phases. Furthermore, ammonium bifluoride with an F− ion concentration similar to 40% buffered oxide etch (5.60 mmol/ml) is found to reveal microstructural details effectively. These findings suggest that the buffered oxide etch is a reliable tint etchant for additively manufactured Ti-alloys, and could potentially be used to etch other additively manufactured alloy systems for metallographic studies. Both these etchants supply F− ions without the low pH, significantly improving safety by removing the need for HF in the etching process.

Formation of nanocrystalline and nanolaminate structures in a twinning induced plasticity Ti-12Mo alloy: The role played by {332} 〈113〉 twinning

Grain refinement is an effective strategy to strengthen metastable β titanium alloys. {332}<113> twinning, a typical deformation mode, its role on grain refinement still remains unelucidated. Here, we produced a gradient nanostructured layer with a depth of 800 μm in a metastable twinning induced plasticity β-Ti-12Mo (wt.%) alloy by means of surface mechanical rolling treatment. We found that {332}<113> deformation twinning, mainly dominated the deformation at moderate strain and strain rates, refining coarse grains into submicro-structures. With increasing strain and strain rates, dislocation slip instead of {332}<113> twinning prevailed. These dislocations were first arranged into extended boundaries and then into laminated structures to coordinate deformation. Eventually, shear banding and fragmentation of laminates result in the formation of nanocrystalline with size of 34 ± 8 nm. The nanostructured Ti-12Mo alloy exhibited the high hardness of 4.9 GPa at subsurface. The surface hardness decreased to 4.4 GPa which was mainly caused by the inhibition of stress-induced martensitic transformation α″ and the occurrence of its reversal transformation due to adiabatic heating induced by the high strain rate. This work expands our knowledge on strengthening β titanium alloys by {332}<113> twinning induced grain refinement at different deformation conditions.

Effect of milling time on structural, mechanical and tribological properties of nanostructured HIPed near type Ti-15Mo alloys

The study aimed to analyze how milling time (2 h-24 h) affects structural, mechanical, and tribological properties of Ti-15Mo alloys, these last has evaluated by using XRD, SEM, and a ball-on-disk tribometer. The wear tests were carried out under applied, loads of 2, 8 and 16 N respectively. Results revealed that crystallite size decreased to, 25.5 nm, while lattice parameter increased to 5.34 Å, and porosity reduced to 0.07%, Conversely, mean pore size decreased to 31 nm after 24 h. Moreover, relative density, and Young's modulus increased with prolonged milling. Coefficient of friction, wear, volume, and rate increased with applied load (2–16 N) but decreased with milling time, especially in binary titanium alloys under 16 N load. Optimal conditions were identified, at 24 h milling and 16 N load