X-ray Computed Microtomography Characterization of Ti6Al4V/CoCrMo Biomedical Composite Fabricated by Semi-solid Sintering

The semi-solid sintering of a novel Ti6Al4V/CoCrMo biomedical composite was investigated for the first time by semi-in situ X-ray computed microtomography. Composite was fabricated by dry mixing 15 vol% CoCrMo reinforcing particles with Ti6Al4V particles as matrix. The mixture was poured into a 1 mm diameter quartz capillary. 3D images of the same sample were acquired before and after sintering at different temperatures between 1050 and 1130 °C. Qualitative and quantitative analysis of the 3D images was carried out to observe the evolution of the microstructure. Formation and evolution with temperature of eutectic phase were monitored. It was found that the eutectic reaction started between Ti6Al4V and CoCrMo particles at 1050 °C, first in the contact area and then the liquid of eutectic phase was distributed over the surface of Ti6Al4V particles and filled the interparticle pores. Size and sphericity of Ti6Al4V and CoCrMo particles diminished as the volume fraction of eutectic phase increased. After sintering at 1130 °C most of CoCrMo particles disappeared because they react with Ti6Al4V to form the Ti2Co phase. Porosity is reduced 15% mainly by reducing the smaller pores that can be filled by the eutectic phase. Thus, it was concluded that semi-in situ X-ray computed microtomography is an effective tool to investigate the semi-solid state sintering and to analyze the microstructure evolution and densification mechanisms.