Metallurgical characterisation of B2 Ti-based binary alloys with Group VIIIB transition metals

¹ Advanced Materials Division, MINTEK, Private Bag X 3015, Randburg, 2125, South Africa
² School of Physics, University of the Witwatersrand, Private Bag 3, Wits, 2050, South Africa

^* Corresponding author: Bonganing@mintek.co.za & 2623288@students.wits.ac.za

Abstract

B2-CsCl intermetallic compounds exhibit excellent high-temperature stability, corrosion resistance, and mechanical strength. During solidification, these compounds can recrystallise and undergo martensitic phase transformation, a phenomenon widely studied in TiNi and associated with shape memory behaviour. In contrast, the B2 phase of TiRu, with Ru being the least expensive platinum group metal, remains thermodynamically stable down to room temperature, showing no phase change, and is thus not a high-temperature shape memory alloy. This raises a key research question: why does B2 TiRu not exhibit transformation behaviour comparable to TiNi and TiPd, and how does its experimental phase stability differ? This study investigated the metallurgical characterisation of TiRu, TiNi, and TiPd alloys produced via arc melting under argon. X-ray diffraction (XRD) confirmed the stable B2 phase in TiRu, while TiNi and TiPd exhibited multiple secondary phases, indicating B2 instability and potential phase transformations at lower temperatures. Micro-Vickers hardness measurements and optical microscopy revealed relationships between microstructure and mechanical response. Hardness of TiNi and TiPd improved upon annealing due to grain refinement, whereas TiRu softened, likely due to grain coarsening.