Titanium Ti6Al4V alloy reinforced by the addition of nano yttria stabilized zirconia fabricated by selective additive manufacturing: microstructure and mechanical investigations

Additive manufactured Ti6Al4V reinforced with nano yttria-zirconia (nYSZ) parts were fabricated using selective laser melting technology (SLM). The as-received Ti6Al4V powder and two powder mixtures of Ti6Al4V mixed with several nYSZ contents (1wt% and 2.5wt%) were prepared and then SLM processed. Parts were further subjected to a stress relief heat treatment. Besides, hot isostatic pressure (HIP) was used in order to eliminate residual porosities. The pycnometer-based technique was used to measure the mass density. XRD and EBSD analysis were performed to investigate the influence of nYSZ additions on the microstructure and subsequent mechanical properties via microhardness and compression tests. It was found that addition of nYSZ increases the density of the reinforced parts and produces a fine α martensite phase. Besides, the grain size was refined compared to that of heat treated Ti6Al4V. As a consequence, a significant increase in both the hardness and the compressive strength for the reinforced Ti6Al4V were obtained while the elongation to failure was kept. These improved mechanical properties are discussed in relation to the effect of nYSZ addition, which includes latice distortions and strengthening from grain size refinement and/or α formation.