Ti-TiB2 composites consolidated by spark plasma sintering: Reaction mechanism, characteristics of in-situ formed phases and densification behavior

Titanium matrix composites containing 4.8 wt. % TiB2 admixed powder were processed by spark plasma sintering at a temperature range of 750-1350 degrees C for a dwell time of 5 min under an external pressure of 50 MPa in vacuum. The effects of sintering temperature on densification behavior and microstructural evolution were studied, with special attention and emphasis on researching the mechanisms of TiB phase formation. Microstructures of the composites were examined by means of optical microscopy (OM) and scanning electron microscopy (SEM). X-ray diffraction (XRD) patterns and micrographs investigation confirm that sintering temperatures above 900 degrees C are needed for creating the TiB phase through the in situ reaction between Ti and TiB2. The results also show that, along with promoting densification and progress of the Ti/TiB2 reaction, particle fragmentation occurs in contact surfaces between reinforcement and titanium particles during the sintering process. The fracture surfaces of composites exhibit few characteristics of TiB pull-out and particle debonding which indicates that the in-situ formed TiB phases are well bonded to the Ti matrix to transfer load from the matrix to reinforcements. Furthermore, quantitative analysis of the existing phases demonstrates that the reaction between Ti and TiB2 is fairly complete at higher sintering temperature.