Mapping of microstructure features and micromechanical properties of Ti–xAl–yFe (x=0–6, y=4–10 wt.%) alloys via diffusion couple method

Abstract

In this work, a diffusion couple of Ti–6Al–4Fe/Ti–10Fe (wt. %) was fabricated and heat-treated under BASCA (β-annealing, slow cooling, and aging) processing conditions to facilitate the strengthening and toughening design for low-cost titanium alloys. Assisted by Scanning Electron Microscopy (SEM), Electron Probe Micro analyses (EPMA), and nanoindentation, a picture was constructed to map the composition-dependent microstructure features and micromechanical properties in the composition array of Ti–(0–6)Al–(10–4)Fe (wt. %). The reduction of Al and the enrichment of Fe resulted in the α lamellae in finer appearance and less amount, indicating that the alloys with the same chemical composition as that in the micro-areas would show similar microstructure features. The elastic modulus E obtained from nanoindentation exhibited a decreasing trend with Al impoverishment which was in contrast to a slight increase of nanohardness H. The measured elastic modulus and nanohardness enabled evaluations of wear resistance (H/E), resistance to plastic deformation (H3/E2), elastic recovery rate (Ue/Ut), and plasticity index (Up/Ut) in the micro-areas which served as the property indices analogous to those of the independent alloys with the same chemical compositions. The indices varied monotonously in the composition array. The highest H/E, H3/E2, Ue/Ut and the lowest Up/Ut was discovered at Ti–10Fe terminal, indicating good wear resistance and longer service potentials. Nevertheless, the high modulus E = 145.76 GPa of Ti–4.96Al–4.43Fe is promising in the ballistic application.

Keywords

• Diffusion couple
• Ti-xAl-yFe
• Nanohardness
• Elastic modulus
• Microstructural and micromechanical properties