Additive manufacturing of TTFNZ (Ti-4.5Ta-4Fe-7.5Nb-6Zr), a novel metastable β-titanium alloy for advanced engineering applications

Abstract

The alloy Ti‐6Al‐4V (Ti64; wt%) is extensively used for aerospace and medical applications. However, due to potential drawbacks and societal change, intensive research has been conducted to replace this material for medical use, as such various promising alloy systems have been proposed. By implementing additive manufacturing (AM) in the value chain of load-bearing implants, the question of the printability of these promising medical alloy systems arose as none were explicitly developed for AM. In a previous paper, an alloy development methodology for AM (NADFAM [Ackers et al., 2021]) was presented, which allows rapid screening of alloys for laser-based powder bed fusion of metals (PBF-LB/M; ISO/ASTM 52911–1). The method was applied to screen several new titanium alloys and rank the alloys according to target properties for PBF-LB/M of load-bearing implants. Following this screening, a novel metastable β-titanium alloy out of the quinary Ti-Ta-Fe-Nb-Zr system was selected for further investigations, and a refined alloy composition Ti-4.5Ta-4Fe-7.5Nb-6Zr (wt%, denoted as TTFNZ) will be presented and compared to Ti64 in this study. The motivation to investigate a system with a lower allotropic transformation temperature (β/α) than Ti64 derived from the idea that (I) it promises reduced cold cracking tendency in the course of rapid solidification (II) common post-print heat treatments could be performed at lower temperatures or could become redundant using printers with a preheating option and (III) it allows exploring a wide range of microstructures and mechanical properties through thermal processing. The present study reports on: (i) AM feedstock/powder production of TTFNZ, (ii) PBF-LB/M process parameter development, (iii) heat treatment optimisation, related microstructures and their effect on mechanical properties tested via indentation, compression and tensile testing. (iv) Corrosion properties and (v) the PVD coatability of TTFNZ were also studied to discuss its amenability for medical and advanced engineering applications. • First-time atomisation and additive manufacturing of Ti-4.5Ta-4Fe-7.5Nb-6Zr (TTFNZ). • TTFNZ surpasses well-known medical and aerospace alloys in a variety of disciplines. • Investigation of TTFNZ’s microstructure evolution using DSC, EDX/EBSD and XRD. • Compression, tensile and dilatometry results. • Evaluation of TTFNZ’s corrosion properties as well as initial PVD coating trials.