Titanium alloys exhibit an excellent combination of properties, including high specific strength and excellent bio-compatibility. Recently, parts made from titanium alloys such as Ti-6Al-4V have been manufactured by metal injection moulding (MIM) and exhibited excellent tensile properties (UTS > 800 MPa and 15%). However to date, few information concerning the fatigue properties of such material has been presented in the literature. Thus, in the present study, the influence on the high cycle four point bending fatigue behaviour of Ti-6Al-4V alloy processed by standard and MIM techniques was examined. The first results indicated that the fatigue strength of components fabricated by MIM technique is significant lower than parts made by standard process. This behaviour is discussed in terms of mechanical properties, microstructure, composition, surface quality and crack initiation mechanisms.

Fatigue and tensile mechanical properties of Ti-6Al-4V alloy processed by metal injection moulding (MIM) technology were evaluated in this investigation. Two critical parameters, binder content of the feedstock and maximum sintering temperature, were studied. Samples sintered at 1350 °C exhibited higher tensile strength than those sintered at 1250 °C. Higher content of binder promoted an increase of the surface quality of MIM components. Consequently, the fatigue endurance limit increased from ~350 MPa (components with lower binder content) to ~400 MPa (samples with a higher binder content). Furthermore, reduction of ductility was observed for changing from closed to open porosity; however, the fatigue resistance did not follow the same trend. This is probably due to the fact that better surface quality and smaller grain size compensated the negative influence of porosity on the fatigue behaviour.

This study presents the results of systematic variation of essential processing parameters with regard to thermal debinding and sintering of components fabricated by MIM using Ti-6Al-4V powder. The investigation aims at the understanding of the particular influence these parameters have on the mechanical properties of the sintered parts. This study shows that the debinding parameters appear to be rather uncritical, whereas sintering and cooling rates as well as maximum temperature are important in terms of their effect on tensile strength. Contrary to the strength, the ductility remains nearly unaffected. Based on these results, samples displaying a yield strength of 757 MPa, UTS of 861 MPa and a plastic elongation of more than 14% were produced. These values meet the requirements of the ASTM B 348-02 for titanium alloy grade 23. * 3. Manuscript Click here to view linked References

The effect of boron additions on the sintering behavior, microstructural development, and mechanical properties of a Ti‐6Al‐4V alloy fabricated by metal injection moulding (MIM) was studied. The addition of boron promotes a significant refinement of the microstructure by changing the microstructure from the typical lamellar to a more equiaxed morphology. The presence of both features: α colonies and α grains were confirmed by electron backscatter diffraction (EBSD) experiments. Furthermore, the pinning effect of TiB particles on grain boundary motion enhances the densification process due to the fact that the separation of pores and grain boundaries is suppressed. As a result of the refinement of the microstructure achieved by adding 0.5 wt% boron to the Ti‐6Al‐4V alloy, excellent tensile (σ0.2 = 787 MPa, UTS = 902 MPa and ε = 12%) and fatigue (endurance limit = 640 MPa) properties were obtained.

Permanent implants have to fulfill a great variety of requirements related to both material and geometry. In addition, manufacturing costs play a role, which is getting steadily more and more important. Metal Injection Molding (MIM) of titanium alloy powders may contribute to the development of implants with higher functionality without increasing the price. High degree of freedom with regard to geometry, high material efficiency, and the possibility to create even porous structures are main benefits from applying this technique. Today, even long‐term implants made from Ti–6Al–4V by MIM are commercially available. However, in order to improve fatigue behavior it is beneficial to perform a minor variation of Ti–6Al–4V by adding a low amount of boron. In this paper the mechanical, biological, and corrosion properties of specimens manufactured from Ti–6Al–4V–0.5B alloy by MIM are presented. In order to exclude unknown reactions in the body environment due to the boron content, corrosion, and biological tests are performed. Tensile and fatigue tests characterize the mechanical properties. Potentiodynamic polarization and electrochemical impedance spectroscopy are done in comparison to wrought and to MIM processed Ti–6Al–4V material. For cell experiments cancellous bone cells are cultured to perform adhesion, proliferation, and viability experiments. The results presented here show that the alloy Ti–6Al–4V–0.5B satisfies all basic needs of a material for highly loaded permanent implants manufactured by MIM.