Densification characteristics, microstructure and wear behaviour of spark plasma sintering processed titanium-niobium pentoxide (Ti-Nb₂O₅) based composites

The present study investigated the densification behavior, microstructure and wear properties of Ti-Nb₂O₅ based composites processed by spark plasma sintering (SPS). The SPS process was performed using sintering temperature of 1000 °C, holding time 10 min, heating rate 100 °C/min and applied pressure 50 MPa, as sintering process parameters. Optical and Scanning electron microscopy, X-Ray diffractometry, Relative density and hardness measurement, coefficient of friction and wear rate evaluation were used to characterize the composites produced. The CpTi and Ti-Nb₂O₅ composites attained full densification (relative densities ranged from 99.57 to 99.94%), and the total sintering times and densification stages were independent of the Nb₂O₅ reinforcement. However,the sinterability of the composites improved with increase in Nb₂O₅ content. The punch displacement curve of the Nb₂O₅ reinforced CpTi composite grades were higher compared to the CpTi. Also, the hardness values increased progressively with increase in Nb₂O₅ content. The microstructures that the addition of Nb₂O₅ resulted in structural transformation from lamellar (α) in the Cp Ti to bimodal (α + β) structures in the Ti-Nb₂O₅ composites accompanied with decrease in average grain size with increase in Nb₂O₅ content. The steady-state friction coefficients for all the composite samples ranged from 0.3 to 0.6. However, there was largely progressive increase in friction coefficient with Nb₂O₅ content. Generally, the wear resistance increased with increase in Nb₂O₅ content with the wear mechanism of the composites from wear track assessment, established to be mixed mode of adhesive and abrasive wear.