@phdthesis{Zhao2014, author = {Zhao, Dapeng}, title = {Metal Injection Moulding of Titanium-Niobium alloys for biomedical applications}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-30515}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {The main subject of this work was the investigation of sintering behavior, microstructure, mechanical properties and biocompatibility of metal injection moulded (MIM) Ti-Nb alloys for biomedical applications. Commercially pure titanium (CP-Ti) samples were also fabricated by MIM as a reference. The sintering behavior of MIM Ti-Nb alloys was studied at first, in order to roughly determine the sintering parameters in the following investigations. Dilatometry was applied to investigate the linear shrinkage of MIM Ti-Nb samples from room temperature to 1500 °C at a heating rate of 3 °C/min under argon atmosphere. Various sintering parameters and Nb contents were used to investigate their influences on microstructure and mechanical properties of MIM Ti-Nb alloys by means of density measurements, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical testing. Transmission electron microscopy (TEM) and high energy X-ray diffraction (HEXRD) measurement were applied to investigate the nature and precipitation of the unexpected titanium carbide precipitates in MIM Ti-Nb alloys. Initial cell adhesion and cell proliferation assays of human umbilical cord perivascular cells (HUCPV) on MIM Ti-Nb alloys were performed for biocompatibility characterization. The results of this work show that MIM Ti-Nb and MIM CP-Ti samples have been successfully fabricated and the as-sintered samples show good shape retention without distortion compared to the green sample. The sintering process of MIM Ti-Nb alloys consists of three main steps - Ti-diffusion step, Ti-Nb-diffusion step and Matrix-diffusion step. With increasing sintering temperatures and time, MIM Ti-Nb alloys exhibit lower porosity and higher Young's modulus. A higher Nb content in MIM Ti-Nb alloys leads to an increase of carbide area fraction and porosity. The three factors - Nb content, carbide area fraction and porosity - determine the mechanical properties of MIM Ti-Nb alloys. An increase of Nb content and amount of carbides as well as a lowered porosity lead to a higher tensile strength. A decrease of Young's modulus can be expected with higher Nb content and porosity. A high amount of titanium carbides can result in very poor ductility, but annealing and quenching process can significantly improve the elongation by dissolving the carbides. MIM Ti-Nb alloys exhibit good biocompatibility, indicating their potential for implant applications.}, subject = {Metallpulver; Spritzgießen; Sintern; Titanlegierung; Nioblegierung; Ti-Nb Legierungen; Metallspritzgießen; Sintern; Titan-Karbid; Mechanische Eigenschaft; Ti-Nb alloys; Metal injection moulding; Sintering; Titanium carbide; Mechanical behaviour}, language = {en} } @phdthesis{Soyama2014, author = {Soyama, Juliano}, title = {Development of creep resistant titanium aluminide alloys for the Metal Injection Moulding process}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-31610}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Titanium aluminides show great technological potential due to their light weight and excellent creep resistance. Their utilisation thus offers a potential to decrease fuel consumption and simultaneously improve the performance of components subjected to stress at high temperatures. However, shaping of titanium aluminides is still a very challenging and costly task considering their brittleness and the sensitivity on chemical composition. Therefore powder metallurgy near-net shape manufacturing techniques are very attractive to decrease material waste and reduce overall processing costs. This research work was focused on the preparation, characterisation and optimisation of creep resistant titanium aluminides for the Metal Injection Moulding (MIM) process. Considering the little information available regarding processing of titanium aluminides by MIM, this work had firstly the goal of assessing the creep behaviour of a reference titanium aluminide alloy. Secondly, alloy variations with compositions based on the reference material were designed with the objective of improving the creep resistance, especially concerning primary creep. The basic strengthening mechanisms applied involved the addition of slow diffusing elements and elements that cause precipitation of hard particles. The specimens were prepared by using pre-alloyed powder and mixtures of a master alloy (pre-alloyed) and elemental powders. Consequently, a great deal of effort was spent in the characterisation of the sintering behaviour in order to achieve reliable test pieces. Even though both methods can deliver sound specimens, the pre-alloyed powder approach led to the best results in terms of residual porosity and microstructural homogeneity. The mechanical testing results indicate that processing of titanium aluminides by MIM is feasible and acceptable creep properties can be achieved with the proper sintering parameters. Even though the ductility at room temperature was considerably limited due to the residual porosity and high amounts of impurities intrinsic to the MIM process, alloys developed within this study showed improved primary creep resistance in the high stress - high temperature regime. In particular alloy variations containing additions of Mo, Si and Gd led to a considerable improvement of the primary creep resistance in comparison to the reference material at 800°C - 350 MPa loading.}, subject = {Titanium Aluminides; Creep; Metal Injection Moulding; Metallpulverspritzguss; Kriechen; Titanaluminide; Titanaluminide; Kriechen; Metallpulver; Spritzgießen}, language = {en} }