The martensitic transformation texture in Ti-6Al-4V

The transformation texture associated with martensite formation in the titanium alloy Ti- 6Al-4V has been investigated. Samples were heated into the fully b phase and quenched to form a microstructure of very fine a' martensite with no evidence of diffusional transformation at the prior b grain boundaries. EBSD texture measurements on the martensite showed that within each prior b grain, although typically all 12 variants of a’ were formed, the fractions of variants was far from uniform. The a’ texture was markedly different from values calculated using equal variant probability, also indicating that significant variant selection was occurring during martensitic transformation. This effect was modelled on the basis of elastic interaction between martensite events.

Porous Ti-Nb-Zr alloy through powder metallurgy for biomedical applications

This work investigated the structure and properties relationship, surface modification, biocompatibility and bioactivity of a porous Ti-Nb-Zr alloy. The porous alloy exhibited inter-connected porous structure, good biocompatibility and high mechanical strength with an elastic modulus close to that of bone. Porous Ti-Nb-Zr alloys are thus promising biomaterials for hard tissue replacement.

Ceramic-polymer interface in composite electrolytes of lithium aluminium titanium phosphate and polyetherurethane polymer electrolyte

Composite electrolytes of the lithium-ion-conducting ceramic Li_1.3Al_0.3Ti_1.7(PO₄)₃ and polyetherurethane/lithium triflate polymer electrolyte have been prepared. Microscopy has shown that adhesion between the ceramic and polymer phases is poor, with gaps up to 1 μm at the interface. When dry, the composites are no more conductive than the pure polymer electrolyte. Exposing the samples to the vapour of solvents such as DMF, acetonitrile or water produces a significant increase in conductivity, over and beyond simple plasticization of the polymer. Pretreating the ceramic with a compatibilizing agent improves adhesion at the interface with the polymer, but decreases overall conductivity in the case investigated.

Design of a new biocompatible ti-based shape memory alloy and its superelastic deformation behaviour

Titanium-nickel (Ti-Ni) shape memory alloys have been widely used for biomedical applications in recent years. However, it is reported that Ni is allergic and possibly carcinogenic for the human body. Therefore, it is desirable to develop new Ni-free Ti-based shape memory alloys for biomedical applications. In the present study, a new Ti-18Nb-5Mo-5Sn (wt.%) alloy, containing only biocompatible alloying elements, was designed with the aid of molecular orbital method and produced by vacuum arc melting. Both β and α″ martensitic phases were found to coexist in the alloy after ice-water quenching, indicating the martensitic transformation. The phase transformation temperatures of the Ti-18Nb-5Mo-5Sn alloy were M_s = 7.3 °C, M_f = −31.0 °C, A_s = 9.9 °C, and A_f = 54.8 °C. Superelasticity was observed in the alloy at a temperature higher than the A_f temperature. A totally recovered strain of 3.5 % was achieved for the newly designed Ti-based shape memory alloy with a pre-strain of 4 %.

Simultaneously enhanced strength and ductility of titanium via multimodal grain structure

Commercial Ti with a multimodal grain structure was successfully produced using cryorolling, followed by low-temperature annealing. This multimodal grain structure Ti exhibited a combination of high yield strength (926 MPa), a uniform elongation of 11% and a failure elongation of 23%. The strength enhancement was mainly derived from the ultrafine equiaxed grains, while the improved ductility originated from the large fraction of high-angle grain boundaries and the multimodal grain structure.

Study on the role of stearic acid and ethylene-bis-stearamide on the mechanical alloying of a biomedical titanium based alloy

The present study examines the influence of different contents and types of process control agent (PCA), i.e., stearic acid (SA) and ethylene-bis-stearamide (EBS), on the microstructural evolution and characteristics of Ti-16Sn-4Nb (wt pct) alloy powders and bulk samples. The characterization of the powders and bulk samples was carried out by using chemical analysis, optical microscopy, scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), and X-ray diffractometry. Results indicated that the powder recovered from the ball milling containers increased with increasing amounts of SA and EBS. Furthermore, adding more SA or EBS to the powder mixture resulted in a considerably smaller particle size, with a flaky-shaped morphology for the given ball milling time. Also, a slightly higher effectiveness was found for EBS when compared to SA. Meanwhile, the addition of both SA and EBS led to a delay in the alloy formation during mechanical alloying (MA) and caused contamination of the material with mainly carbon (C) and oxygen (O). An optimum amount of 1 wt pct PCA led to a good balance between cold welding and fracturing, and thus favored the formation of the titanium alloy. The microstructural observation of the bulk alloy showed a homogeneous distribution of fine Nb-rich ß-phase colonies within the α-Ti matrix with the addition of PCA less than 1 wt pct.

Titanium-based shape memory alloys and scaffolds for biomedical applications

Porous Ti-50.5Ni shape memory alloys with different porosities were produced using a space-holder sintering method. A new Ni-free Ti-based shape memory alloy, Ti-18Nb-5Mo-5Sn, was developed for potential biomedical applications, and a novel one-step hydrothermal process was applied to produce hydroxyapatite coatings on the surface of Ti alloy.

Thermodynamics approach to the hydrogen diffusion and phase transformation in titanium particles

The hydrogen diffusion and phase transformation in a titanium particle were studied based on thermodynamic calculation. The mechanisms of hydrogen diffusion in different phases (alpha-Ti, beta-Ti and TiHx) were analyzed. A mobility database was developed for titanium– hydrogen system based on the experimental works on hydrogen diffusion coefficient reported in literature and the fundamental of diffusion. To implement the calculation, a commercial software package for the simulation of diffusion-controlled phase transformation was used. The hydrogen diffusion process, hydrogen distribution, phase transformation and phase growth rate during hydrogenization of a titanium particle at temperatures of 560 K, 800K and 1000K were discussed. The thermodynamics and kinetics analysis provided quantitative insight into the diffusion process and improved the understanding of diffusion mechanism and phase transformation.

Compressive deformation and damage of Mg-based metallic glass interpenetrating phase composite containing 30-70 vol% titanium

Mg-based metallic glass interpenetrating phase composites (IPCs) containing 30-70 vol% titanium was fabricated in this study. The effects of reinforced phase volume fraction and interspace on the mechanical properties were investigated systematically. With increasing the volume fraction of titanium, the fracture strength and strain increased up to 1860 MPa and 44%, respectively. The results showed that the critical volume fraction (around 40%) of Ti metal should be required for significantly improving plasticity of IPC. Decreasing the interspace of the titanium phase could lead to enhancement of yield and fracture strength. The deformation behavior and strengthening mechanisms were discussed in detail.

Surface evolution of a gradient structured Ti in hydrogen peroxide solution

In this work, the interaction between hydrogen peroxide (H₂O₂) and a gradient structured Ti was investigated extensively. The gradient structured Ti (SMAT Ti) was produced by surface mechanical attrition treatment (SMAT), and then it was immersed in H₂O₂ solution for different time until 48 h at room temperature (25 °C). The structure and surface morphology evolution were examined by Raman spectra and scanning electron microscopy (SEM). The formation mechanism of nanoporous titania was discussed based on above results.

Characteristics of electron beam welded Ti & Ti alloys

Similar and dissimilar butt joint welds comprising combinations of commercially pure grade 4 titanium (CP-Ti), Ti-6Al-4V (Ti-64) and Ti-5Al-5V-5Mo-3Cr (Ti-5553) were created using the electron beam process. The resultant welds were studied by means of metallography, optical microscopy, mechanical testing and scanning electron microscopy. Mechanical testing was performed on welded samples to study the joint integrity and fracture characteristics. A scanning electron microscope investigation was performed on the fracture surface to reveal their fracture modes. While all weldments were crack free and most weldments exhibited mechanical properties comparable to the base metal, negligible ductility was exhibited during tensile testing joints of Ti- 5553 welded to either Ti-64 or Ti-5553.

Thermodynamic and kinetic modelling hydrogenation of titanium particles and sheets

Use of hydrogen as a temporary alloying element in Ti alloys is an attractive approach to improve the mechanical properties of the materials, enhance processability and thereby reduce manufacturing costs. In this paper, the hydrogen diffusion process and the phase transformation both between Ti particles and in Ti sheets were simulated to analyze the mechanism of hydrogen diffusion in different phases (α-Ti, β-Ti and TiHx). With the simulation based on the kinetics and thermodynamics, quantitative behaviors of the hydrogen diffusion and the phase transformation were analyzed. The simulation results provide an insight into the diffusion process and improve the fundamental understanding of the mechanism of diffusion and phase transformation.

Wear behaviour of pure Ti with a nanocrystalline surface layer

A nanocrystalline (NC) layer with the thickness of 30 µm was produced on pure titanium surface by surface mechanical attrition treatment (SMAT). Microstructure observation indicated that the grain size increases with depth from the treated surface. The friction coefficient decreases and the wear resistance increases with the SMAT sample as compared to its coarse-grained counterpart. The improvement of the wear properties could be attributed to the higher hardness of SMAT sample.