Effect of hexagonal boron nitride (hBN) addition on microstructure, mechanical, and biocompatible properties of spark plasma sintered titanium (Ti) matrix composites
Satyavan Digole, Smriti Bohara, Chandrasekhar R. Kothapalli, Bharat Bajaj, Tushar Borkar
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.