Microstructure Evolution, mechanical Properties, and biological Response of Ti-Nb-Zr-Ta (TNZT)/hBN metal matrix composites processed via spark plasma sintering (SPS)

• TNZT-hBN composites fabricated via ball milling and SPS. • hBN addition facilitates in-situ α (Ti, N) and TaB 2 precipitates in the β-matrix. • TNZT-0.5hBN exhibits an optimal combination of mechanical characteristics. • Biocompatibility study shows excellent biocompatibility of TNZT-hBN samples. Beta Ti (β-Ti) alloys, characterised by a lower modulus, serve as a promising candidate for load-bearing implant material, but inferior mechanical and wear characteristics limit their applicability. This study incorporated 0.25, 0.5, and 1 wt% hBN into Ti-35Nb-7Zr-5Ta (TNZT) alloy via ball milling followed by spark plasma sintering to enhance its mechanical strength. Microstructural investigations reveal the formation of in-situ α (Ti, N) and T a B 2 precipitates within the β-matrix facilitated by hBN addition. The SEM and EBSD analysis show significant grain refinement with increasing hBN fraction. The TNZT-0.5hBN sample exhibits an optimum combination of hardness (286.4 HV), yield strength (1080 MPa), ultimate strength (1290 MPa), and ductility (38.7 %), attributed to uniform dispersion of in situ precipitates within the matrix. Furthermore, the elastic modulus from UT testing for optimum composition is 84.6 GPa, which is still lower than that of the commonly used Ti-6Al-4 V alloy for implant applications. The quantitative evaluation of strengthening mechanisms indicates that the improved yield strength observed in TNZT-hBN composites results from dislocation strengthening, precipitation strengthening, and grain refinement strengthening. Excellent biocompatibility of TNZT-hBN with cell survival (>95 %), cell proliferation (>95 %), and cell adhesion similar to TNZT, highlighting potential candidates for load-bearing orthopaedic implant applications.