Ti-Mo Alloys Research Articles

The phase, morphology and surface characterization of Ti–Mo alloy films prepared by magnetron sputtering

Magnetron sputtering is a physical vapor deposition process which allows the formation of metastable materials because of the particle bombardment process.

Microstructural evolution of a ductile metastable β titanium alloy with combined TRIP/TWIP effects

Herein, we investigated the microstructural evolution of a metastable β Ti-12(wt%)Mo alloy under tension, exhibiting combined phase transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects. The deformed samples were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and transmission electron microscopy (TEM) until fracture. Lamella-like {112}〈111〉 nano-twinning was observed at the onset of plastic deformation. Upon straining, {332}〈113〉 twinning and stress induced martensitic (SIM) β->α″ transformation were both identified locally in the deformed β matrix as primary mechanisms. Secondary mechanisms such as 2nd twinning and 2nd SIM, were then observed in the primary β twins. At the end of the uniform plastic deformation, a complex deformation microstructure was observed, showing highly disturbed matrix induced by a high volume fraction of twins and occurrence of multiples secondary mechanisms. Resultant macroscopic mechanical properties of the material display a combination of very high ductility (45%), high strength and superior strain-hardening behavior.

Effect of oxygen content on deformation mode and corrosion behavior in β-type Ti-Mo alloy

This study examined microstructural characteristics and mechanical properties in a β-type Ti-15Mo alloy (mass%) with different oxygen contents, and their corrosion behavior in simulated physiological media. With increasing oxygen content from 0.1–0.5%, lattice parameter of parent β-phase increased from X-ray diffraction profiles, and spots of athermal ω-phase became weak and diffuse through transmission electron microscopy observations. {332}<113> twin density decreased with an increase in oxygen content from 0.1–0.3% based on electron backscattered diffraction analyses, and it became almost zero when further increased oxygen content up to 0.5%. The solute oxygen atoms led to both a transition of {332}<113> twinning to dislocation slip and a suppression of β-phase to ω-phase transformation. Room-temperature tensile testing of this alloy with oxygen content ranging from 0.1–0.5%, revealed that yield strength ranged from 420MPa to 1180MPa and that uniform elongation ranged from 47–0.2%. The oxygen-added alloys kept a low elastic modulus obtained from stress-strain curves, and exhibited good corrosion resistance in Ringer's solution from open-circuit potential and potentiodynamic polarization measurements. A desirable balance between mechanical properties and corrosion resistance is obtainable in this alloy as biomaterials through utilizing oxygen to control the deformation mode.

Crystal structure and bonding characteristics of transformation products of bcc β in Ti-Mo alloys

Abstract Rietveld analysis of X-ray diffraction patterns of α′, α″ and β phases of four alloys of Ti-Mo has been carried out to refine their crystal structures and understand their nature of bonding. The addition of molybdenum to titanium is found to shift the stability of crystal structure from hcp to orthorhombic to bcc, as expected. The unit cell dimensions and the atomic positions of α′, α″ and β phases were evaluated, with excellent reliability indices. The reduction in unit cell dimensions and its volume, bond length and co-ordination number with addition of molybdenum is consistent with the reduced size of solute atom. The orthorhombic α″ phase, a transition phase with a minor distortion of hcp α′, is found to be closer to α′ than β phase, based on the orthorhombicity (b/a) and the volume of equivalent orthorhombic unit cells of the phases and the atomic shuffle y in 4c Wyckoff positions along b axis of α″ phase. The Fourier electron density contour maps suggest that the bonding in all phases is predominantly metallic. However, addition of molybdenum delocalizes the spatial distribution of charge density, suggesting an enhancement of metallic character. Anisotropy in charge density was observed along 〈011〉 and 〈010〉 in (100), 〈101〉 and 〈001〉 in (010) and 〈110〉 and 〈010〉 in (001) plane. This offers direct evidence for the origin of anisotropy in the values of elastic constants, reported in literature.

A molten Mg corrosion method for preparing porous Ti foam as self-supported Li–O2 battery cathodes

All-metal self-supported cathodes, especially porous noble metals, are attractive alternatives for settling the issue of carbon- and binder-decomposition in Li–O2 batteries. However, the high cost of noble metals hinders their practical application. In the present study, nanoporous Ti foam is prepared using a molten Mg corrosion method for the first time. Electron microscope images demonstrate that, nanoporous Ti foam is obtained by treating Ti-Mo alloy plates in molten Mg at 650°C for 3hours. Then, the foam is coated with a layer of Au nanoparticles by cool-sputtering and used as self-supported Li–O2 battery cathodes. The nanoporous foam can decrease the consumption of gold markedly compared with traditional porous Au foam. Benefiting from the high stability, conductivity, and porosity of Ti foam, the Li–O2 batteries exhibit good durability (cycling 118 rounds at 1C rate within a 1000mAhg−1 capacity limitation).

Change in the deformation mode resulting from beta-omega compositional partitioning in a Ti[sbnd]Mo alloy: Room versus elevated temperature

The effect of beta-omega compositional partitioning, introduced via isothermal annealing, on the deformation behavior of a TiMo alloy was investigated via tensile testing at room and elevated temperatures. While beta with compositionally congruent athermal omega precipitates primarily exhibits twinning, after beta-omega compositional partitioning the same alloy deforms via slip. This change in deformation mode can be rationalized based on the solute content within the beta matrix, with reference to the Bo-Md plot. Tensile testing at elevated temperatures revealed that both conditions deformed via slip while exhibiting serrated flow.

Enhancement of Mechanical Biocompatibility of Titanium Alloys by Deformation-Induced Transformation

Metastable β-type titanium alloys are highly suitable for use as structural biomaterials applied to hard tissue, i.e., as cortical bone (hereafter, bone) replacing implants. However, their mechanical biocompatibitities, such as the Young’s modulus, strength and ductility balance, fatigue strength, resistance against fatigue crack propagation and fracture toughness, require improvenent for increased compatibility with bone. Through deformation, the metastable β-phase in a metastable β-type titanium alloy is transformed into various phases, such as α’ martensite, α” martensite, and ω-phases with exact phase depending by metastable β-phase stability. In addition, twinning is also induced by deformation. Deformation twinning effectively enhances the work hardening in the metastable β-type titanium alloy, leading to increased strength and ductility. This improvement is accompanied by with other deformation-induced transformations including the appearance of deformation-induced martensite and ω-phase transformation. The enhancement of the mechanical biocompatibility of various materials using the abovementioned deformation-induced transformation is described in this paper, for both newly developed metastable β-type Ti-Mo and Ti-Cr alloys for biomedical applications.

Characterization of Phase Transitions Occurring in Solution Treated Ti-15Mo during Heating by Thermal Expansion and Electrical Resistance Measurements

Metastable β titanium alloy Ti-15Mo was investigated in this study. In-situ electrical resistance and thermal expansion measurements conducted on solution treated material revealed influence of ongoing phase transitions on measured properties. The monotonicity of the dependence of electrical resistance on temperature changes at 225, 365 and 560 °C The thermal expansion deviates from linearity between 305 and 580 °C.

Microhardness and microstructure evolution of ultra-fine grained Ti-15Mo and TIMETAL LCB alloys prepared by high pressure torsion

Two metastable β-Ti alloys, Ti-15Mo and Ti-6.8Mo-4.5Fe-1.5Al (TIMETAL LCB) were solution treated and subjected to severe plastic deformation by high pressure torsion. The evolution of microhardness, microstructure and elastic constants with increasing strain imposed by high pressure torsion was investigated.Fragmentation of the microstructure with increasing strain was observed by scanning electron microscopy. Significant twinning in system {1 1 2} <111> after high pressure torsion was observed in both studied alloys by electron backscatter diffraction. Multiple twinning contributes significantly to the fragmentation of grains and consequently to the overall refinement of the microstructure.Microhardness significantly increases with increasing strain and was fitted using the Hollomon and Voce laws. Hollomon's hardenability exponent is much higher for both studied β-Ti alloys than for the commonly used Ti-6Al-4V alloy. It reflects high capability of strengthening β-Ti alloys by intensive plastic deformation.The measurement of elastic constants using resonant ultrasound spectroscopy showed that the deformation by high pressure torsion increases the Young's modulus as compared to solution treated material. On the other hand, further straining causes subsequent decrease of the Young's modulus.

Effect of Sn and Zr addition on the martensitic transformation behavior of Ti-Mo shape memory alloys

The effect of Sn and Zr addition on the martensitic transformation temperature and lattice deformation strain of Ti-3 mol % Mo alloys was systematically investigated by differential scanning calorimetry and X-ray diffractometry. The addition of Sn and Zr to the Ti-3 mol % Mo alloy stabilized the parent β phase and decreased the temperature of the reverse martensitic transformation by 149 K/mol % Sn and 38 K/mol % Zr, respectively. Changes in the lattice deformation strains due to the Sn and Zr addition were evaluated from the lattice parameters of the β and α″ phases. Compared with β stabilizing elements, such as Nb, Mo, and Ta, Sn and Zr decrease the martensitic transformation temperatures without decreasing the lattice deformation strains.

Hydriding of TiMo alloys at high hydrogen pressures

We studied the interaction of Ti0.40Mo0.60 and Ti0.34Mo0.66 alloys with hydrogen and obtained hydrogen desorption isotherms at pressures of up to 250 MPa. At high hydrogen pressures, we observed the formation of Ti0.40Mo0.60Н1.1 and Ti0.34Mo0.66Н0.8 hydride phases. According to X-ray diffraction data, the hydrides consisted of phases with a body-centered cubic and face-centered cubic (CaF2 structure) lattices. The structure of the deuteride based on the Ti0.40Mo0.60 alloy was studied by neutron diffraction. We identified the sites occupied by deuterium atoms and determined their occupancies.

Nanotubes Growth on Ti-15Mo Alloys by Anodization at Low Voltage

Surface modification by nanotubes growth is an efficient technique to improve the interaction between implant and biological environment. Several studies indicate who low voltages anodizations are able to generate nanotubes with smaller diameters, positive characteristic for the post-implantation cell growth. The aim of this study was to characterize the morphology of the nanotubes formed on Ti-15Mo surfaces applying 5 or 10 V as anodizing voltage. For both conditions were used glycerol based electrolyte with ammonium fluoride and the anodization time was 24 hours. The samples were cleaned in an ultrasonic bath and annealed at 450 ° for 1 hour after anodization. In order to characterize the surfaces were performed scanning electron microscopy images, contact angle measurements and X-ray diffraction analysis. The results confirmed the formation of nanotubes evenly distributed on the surfaces and a direct relation between anodizing voltage and nanotubes diameters.

Alpha plus beta annealed and aged Ti-15 Mo alloy for high strength implant applications.

Management of femur fractures requires titanium alloy implants that provide a good combination of static strength and ductility plus sufficient high cycle fatigue strength to resist repetitive loading. A research program was initiated to determine whether aging treatments could increase the strength of alpha + beta Ti-15Mo while maintaining acceptable tensile ductility. A pilot heat treating study indicated the best combination of strength and ductility was obtained using an α + β annealing temperature of 705°C ± 10°C followed by an aging treatment of 482°C ± 10°C. EBSD data for four suppliers revealed that the alpha phase ratios ranged from 16.3% to 18.6% and the beta phase ratios ranged from 81.4% to 83.7%. Mean beta grain size diameters ranged between 1.42 and 1.78 µm. Tensile testing qualification data from four suppliers was statistically analyzed and reviewed. Minimum reproducible tensile values were established and incorporated into ASTM F2066-13 implant material standard. Cantilever fatigue testing was performed with proximal femoral nail implants that were fabricated into fully finished implant constructs. Fatigue results for 125°, 130°, and 135° implant constructs met the acceptance criteria regarding the fatigue runout load limits and failure modes that were identified. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2010-2018, 2017.

First principles studies on structural, elastic and electronic properties of new Ti[sbnd]Mo[sbnd]Nb[sbnd]Zr alloys for biomedical applications

Stress shielding phenomenon has become a major drawback to the use of metallic biomaterials for orthopaedic implants applications. In this study, a TiMo(Nb, Zr and Nb+Zr) alloy system was investigated to design and develop novel low elastic Young's modulus Ti based alloy for implant application. The development and application of predictive modelling and simulation are transforming the materials engineering discovery process. To this end, ab initio calculation was used to evaluate the effects of composition on structural, elastic and electronic properties of the materials. The data obtained from both theory and experiment were analysed and compared with each other. Notable findings include low elastic Young's modulus values of 70.2GPa, 80.6GPa, 76.5GPa, 59.1GPa and 32.3GPa for the Ti6Mo6Zr, Ti6Mo6Nb, Ti6Mo6Nb2Zr, Ti6Mo5Nb3Zr and Ti6Mo4Nb4Zr alloys, respectively ascribed to the unique elastic softening of their C′ and C44 shear moduli. The consistency in both results is discussed in terms of the sensitivity of the physical and electronic properties to the alloying additions. Thus, the result indicates the approach can enhance the reduction of elastic Young's modulus of metallic biomaterials for replacing some commonly used high modulus materials and prevent stress shielding in orthopaedic implants.

Hybrid oxide-polymer layer formed on Ti-15Mo alloy surface enhancing antibacterial and osseointegration functions

Abstract Poly( d , l -lactide- co -glycolide) 50/50 layer was formed on the previously anodized Ti-15Mo alloy surface and evaluated in terms of morphology (SEM), electrochemical analysis and biocompatibility (cell adhesion and biofilm formation tests). The polymer uniformly covered the porous oxide layer and filled the pores. The molar ratio of the comonomers in the copolymer was chosen to obtain the material, with degradation time of 4 weeks. The degradation process of polymer-oxide coatings was evaluated using 1 H and 13 C NMR. The oxide and polymer-oxide layers were cytocompatible, and osteoblast-like MG-63 cells were well adhered to the modified surfaces. The hybrid gentamicin-PLGA loaded coatings formed on the titanium alloy surface exhibited antimicrobial activity against Staphylococcus aureus . The coatings improved the corrosion resistance of the substrate in Ringer solution. Formation of the hybrid polymer-oxide layer on the Ti-15Mo alloy surface is a promising approach to obtain ‘smart materials’.

Martensitic microstructures and mechanical properties of as-quenched metastable β-type Ti–Mo alloys

Microstructures and tensile properties were investigated in metastable β-type Ti–10Mo, Ti–15Mo, and Ti–20Mo alloys after solution treatment. In addition to β phase, different martensitic structures with various sizes and morphologies were found in these alloys. In the Ti–10Mo alloy, acicular α″ plates were uniformly distributed in the β matrix. Transmission electron microscopy (TEM) revealed {111} α″-type twins had formed in α″ plates, and the orientation relationship between the β and α″ is close to (110) β//(001) α″, ( $$ 1\bar{1}2 $$ ) β//(110) α″, and [ $$ \bar{1}11 $$ ] β//[ $$ \bar{1}10 $$ ] α″. In the Ti–15Mo alloy, nanoparticles of athermal ω phase containing {112} β-type twins were observed in the β matrix. Smaller ω particles were found in the Ti–20Mo alloy than in the Ti–15Mo alloy. When tensile tested, the Ti–10Mo and Ti–15Mo alloys exhibited large plastic strains of 24 and 29 %, respectively, with ultimate tensile stresses of 756 and 739 MPa. The Ti–20Mo alloy displayed a higher ultimate tensile stress of 792 MPa but much smaller plastic strain (2 %). Although β phase dominates in all the metastable β-type Ti–Mo alloys, the nanostructured martensites also play an important role in the mechanical properties of the alloys.

Multilayer coatings formed on titanium alloy surfaces by plasma electrolytic oxidation-electrophoretic deposition methods

Tricalcium phosphate was deposited on the surface of anodized titanium alloys (Ti-6Al-7Nb, Ti-13Nb-13Zr and Ti-15Mo) using the electrophoretic technique (EPD). The multilayer coatings were formed by a three-step experiment. The influences of voltage (step I), time (step II) and concentration of TCP in the suspensions (step III) on the ceramic particle deposition was investigated. The appropriate conditions were determined for each titanium alloy surface modification. The total thickness of the anodized titanium alloys increased, the surface roughness decreased and the wettability increased after TCP particle deposition. A TL-XRD investigation showed that the multilayer coatings were mainly amorphous. All the coatings adhered well to the substrate. The surface modifications increased the corrosion resistance in Ringer’s solution, particularly for the Ti-15Mo alloy. In addition, the multilayer coatings formed on this titanium alloy exhibited the best cytocompatibility with MG-63 osteoblast-like cells.

Internal Friction and Microstructure of Ti and Ti-Mo Alloys Containing Oxygen

Ti-Mo alloys are promising materials for use as biomaterials, because these alloys have excellent corrosion resistance and a good combination of mechanical properties such as fatigue, low elastic modulus, hardness, and wear resistance. The objective of this paper was to study the effect of heavy interstitial atoms on anelastic properties of Ti-Mo alloys using mechanical spectroscopy. The internal friction and Young’s modulus were measured as a function of temperature using dynamic mechanical analyser. The internal friction spectra were brought about by relaxation processes attributed to shortrange stress induced reorientation of interstitial and substitutional complexes in solid solution. It is suggested that the nature of the relaxing entities can be worked out in further research on Ti-Mo single crystals.

A nano-scale instability in the β phase of dilute Ti–Mo alloys

A nano-scale instability in the β phase resulting in the formation of the disordered orthorhombic O′ phase has been discovered in a fairly dilute binary Ti–Mo alloy, using selected area electron diffraction and high resolution scanning transmission electron microscopy. The O′ phase is formed in the alloy when the Mo content exceeds a critical value. The instability occurs in β-solutionized samples that have been quenched to room temperature and is found to co-exist with athermal ω phase. Interestingly, this nano-scale instability, involving the 110<11¯0> soft-phonon shuffle, occurs in the β phase without deliberate additions of either interstitial or substitutional solutes.

On the electropolishing and anodic oxidation of Ti-15Mo alloy

This paper presents research on modifying the surface of Ti-15Mo alloy using electropolishing and anodic passivation. The electropolishing process was carried out in solutions containing sulfuric acid, ethylene glycol, ammonium fluoride and oxalic acid. Whereas a voltage range from 20 to 100V and a 1M orthophosphoric acid solution were used during the anodic passivation. The influence of above mentioned processes parameters on the quality of the obtained oxide layer on Ti-15Mo alloy was investigated. The analysis of Ti-15Mo surface after modification was performed using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), ellipsometry, and mechanical tests. Moreover, the corrosion resistance was investigated using a potentiostatic method in Ringer’s solution. It was found that electropolishing leads to an increase in the surface homogeneity and to the form of an oxide layer, which consisted of TiO2 and MoO3. Whereas the oxide layers obtained during anodic passivation were characterized by different properties depending on the applied voltage. The anodic passivation at various voltages (20–100V) increased the surface wettability (94.5°–87.6°) in comparison to the electropolished sample (97.5°). Moreover, the obtained oxide layer after anodization exhibited a high hardness. The electrolytic polishing and anodic passivation of Ti-15Mo also improved corrosion resistance of the alloy in contact with Ringer's solution. The sample anodized at 80V presented the highest corrosion resistance by the smallest corrosion current density (1.4 nAcm−2) and the highest polarization resistance (37.4MΩcm2).