Effect of hexagonal boron nitride (hBN) addition on microstructure, mechanical, and biocompatible properties of spark plasma sintered titanium (Ti) matrix composites.

Abstract

A novel approach is introduced, utilizing low concentrations of hexagonal boron nitride (hBN) and fabricating titanium matrix composites (TMCs) through ball milling and spark plasma sintering (SPS). The ball-milled Ti-x wt.% hBN (x: 0.1, 0.25, and 0.5) powders sintered at 60 MPa pressure and a 5-min holding time for temperatures ranging from 900 to 1200 °C. The in-situ formation of titanium boride whiskers (TiBw) and Ti(N) solid solution occurred from the Ti and hBN particle reaction during sintering. The XRD pattern of the hBN-added sample shows α-Ti similar to pure Ti without the reaction phase due to a lower hBN fraction in Ti. However, the XRD peak shift toward a lower diffraction angle for the Ti-hBN sample confirms the formation of Ti(N) within the Ti matrix. Microstructure analysis reveals significant grain refinement with increasing hBN fraction; the grain sizes for Ti, Ti-0.1hBN, Ti-0.25hBN, and Ti-0.5hBN are 36, 22, 20, and 18 μm, respectively. The presence of TiBw and Ti(N) leads to a grain refinement effect in higher hardness and enhanced strength in composite samples. The Ti-0.25 wt% hBN sample sintered at 1200 °C exhibited an optimal combination of relative density (99.73 %), hardness (341.8 ± 6 HV), yield strength (1042 ± 21 MPa), compressive strength (1840 ± 23 MPa), and elongation (34.4 ± 1.5 %). The biocompatibility is confirmed through cell adhesion, viability, and cytotoxicity studies, highlighting these composite's excellent biocompatibility and potential for orthopedic implant application.