Preparation of bioactive porous Ti-Sn-Nb alloy for biomedical applications

A porous Ti-16Sn-4Nb alloy with an average pore size of 300 µm and porosity of 60 % was prepared by powder metallurgy, and a bone-like apatite coating was obtained by soaking the samples in a concentrated simulated body fluid (lOx SBF). The changes of the microstructure and composition on the surface with soaking time were investigated by using X-ray diffractometry (XRD), and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), The bone-like apatite granules started to deposit throughout the porous Ti alloy foam aner 1 h soaking, and the number of granules increased with the increase of the soaking time. A uniform bone-like apatite layer covered the entire surface of the sample after soaking in Ihe lOx SBF for 6h. The Ti-16Sn-4Nb foam showed a good bioactivity after a thermochemical process and soaking into a 1Ox SBF.

Mechanical properties of porous Ti-26NB alloy for regenerative medicine

Porous titanium-26at.%niobium (hereafter, Ti-26Nb) alloys with different porosities were prepared by space-holder sintering. The porous structure of the alloys was characterized by scanning electron microscopy (SEM). Mechanical properties of the porous alloys were investigated using compression test. Results indicate that the porous alloys with 60, 70 and 80% porosities exhibit interconnected porous structure with pore sizes of 100-300 µm. The porous structure has the potential to provide new bone tissue ingrowth ability. The mechanical properties of these porous alloys decrease with the increase of porosity. The mechanical properties of the porous Ti-26Nb alloys can be tailored to match those of human bone.

Processing and mechanical properties of porous Ti-Mo alloy for biomedical applications

Titanium and some of its alloys are well accepted as load-bearing implant materials due to their excellent mechanical properties, superior corrosion resistance, and outstanding biocompatibility. However, solid implant materials may suffer from the problems of adverse tissue reaction, biomechanical mismatch and lack of new bone tissue ingrowth ability. In the present study, porous titanium-molybdenum (Ti-Mo) alloy was fabricated by the space-holding sintering method. The pore size, pore shape and porosity can be controlled through choosing appropriate space-holding particle materials. Electron scanning microscopy (SEM) was used for the characterisation of the porous Ti-Mo alloy. The mechanical properties of the porous Ti-Mo alloy samples were investigated by compressive tests. Results indicated that the porous Ti-Mo alloy provides promising potential for new implant materials with new bone tissue ingrowth ability and mechanical properties mimicking those of natural bone.

Effects of process control agent on the microstructure and mechanical properties of Ti-Sn-Nb alloy prepared by mechanical alloying

In the present study, the influence of process control agent (PCA) on the characteristics of powder and bulk sintered Ti-16Sn-4Nb (wt. %) alloy prepared by mechanical alloying has been investigated. The elemental Ti, Sn and Nb powders were mechanically alloyed in a planetary ball mill for a short period of time using two types of PCA, namely stearic acid (SA) and ethylene bis-stearamide (EBS). The powder morphology, microstructural evolution of the bulk sintered alloy, phase formation and hardness of the alloy have been studied as a function of PCA. Results indicated that the addition of PCA leads to a delay in aIloy formation and introduces contaminations (mainly carbon and oxygen) into the material. The microstructural observation of the bulk alloy revealed a homogeneous distribution of fine Nb-rich colonies (ß-phase) within the a-Ti matrix for small amount of PCA. The hardness values of samples exhibited a significant increase with increasing amount of PCA, reaching a value of ~ 600 BV.

Nucleation and growth during reactions in accumulative roll bonding of Ti/Al multilayers

A two-stage process in the formation of TiAl₃ was found in the accumulative roll bonding (ARB) Ti/Al multilayers. The distribution of layer spacing did not become broad enough to lose the main features of the double exothermal behaviour. A modified model based on thin films was set up to describe the kinetic characteristics of the formation of TiAl₃ in ARB samples.

The kinetics of two-stage formation of TiAl3 in multilayered Ti/Al foils prepared by accumulative roll bonding

The solid-state reactions of Ti/Al multilayered samples produced by Accumulative Roll Bonding (ARB) have been investigated using differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. The kinetics of the formation of the intermetallic compound TiAl3 was highlighted. Experimental evidence and analysis of the data shows that, there was a two-stage process in the formation of TiAl₃ in the ARB Ti/Al reactive multilayered samples. Calorimetric and microstructural analyses also suggest that the interdiffusion of Al and Ti which led to solid solutions preceded the formation of intermetallic compounds. Despite the apparent chaos in the thickness of the ARB multilayered samples, the distribution of layer spacing did not become broad enough to lose the main features of the double exothermal behaviour. Isothermal DSC shows a larger Avarami constant in ARB Ti/Al multilayered structures than was found in Ti/Al thin films. A modified model based on thin films was set up to describe the kinetic characteristics of the formation of the intermetallic compound TiAl₃ in ARB samples.

In vitro cytotoxicity of binary TI alloys for bone implants

Interest in using titanium (Ti) alloys as load-bearing implant materials has increased due to their high strength to weight ratio, lower elastic modulus, and superior biocompatibility and enhanced corrosion resistance compared to conventional metals such as stainless steel and Co-Cr alloys. In the present study, the in vitro cytotoxicity of five binary titanium alloys, Ti15Ta, Ti15Nb, Ti15Zr, Ti15Sn and Ti15Mo, was assessed using human osteosarcoma cell line, SaOS-2 cells. The Cell proliferation and viability were determined, and cell adhesion and morphology on the surfaces of the binary Ti alloys after cell culture were observed by SEM. Results indicated that the Ti binary alloys of Ti15Ta, Ti15Nb and Ti15Zr exhibited the same level of excellent biocompatibility; Ti15Sn alloy exhibited a moderate biocompatibility while Ti15Mo alloy exhibited a moderate cytotoxicity. The SaOS-2 osteoblast-like cells had flattened and spread across the surfaces of the Ti15Ta, Ti15Nb, Ti15Zr and Ti15Sn groups; however, the cell shapes on the Ti15Mo alloy was shrinking and unhealthy. These results indicated that the Mo contents should be limited to a certain level in the design and development of new Ti alloys for implant material applications.

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.

Fabrication of nanoscale Ti honeycombs by focused ion beam

Ti honeycombs with the side of 800 and 400 nm were fabricated by focused ion beam (FIB), though the surfaces of the bottom and wall of the Ti honeycombs were rough, as compared with the surfaces of the bottom and wall of the Si honeycomb. It is demonstrated that the nanoscale Ti components can be fabricated in a short time by FIB.

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.

Use of residual hydrogen to produce CP-Ti powder compacts for low temperature rolling

The present work investigates the optimal level of residual hydrogen in partially de-hydrogenated powder to produce CP-Ti plate compacts using ECAP with back pressure which are subsequently rolled at low temperature. A comparative study of the compaction of two TiH₂ powders and a CP-Ti powder, with particle sizes 150 um, 50um and 45 um respectively, has been carried out. The hydride powders have also been compacted in a partially de-hydrogenated state. The optimal level of residual hydrogen with respect to the density of the resulting compact and the associated mechanical properties has been defined. ECAP at 300°C produced compacts from these partially de-hydrogenated powders of 99.5% theoretical density, while CP-Ti was compacted to almost full theoretical density under the same ECAP conditions. Therefore, the compaction of powder by ECAP does not benefit from temporary hydrogen alloying.

These compacts then were rolled at temperatures ranging from room temperature to 500°C with an 80% reduction in a single pass. Heat treatment after the rolling can modify the microstructure to improve the resulting mechanical properties and in this regard the temporary alloying with hydrogen has been observed to offer some significant benefits. It is shown the ECAP followed by low temperature rolling is a promising route to the batch production of fully dense CP-Ti wrought product from powder feedstock that avoids the need to subject the material to temperatures greater than 500°C. This low temperature route is expected to be efficient from an energy point of view and it also avoids the danger of interstitial contamination that accompanies most high temperature powder processing.

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 %.

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.