Influence of post-heat treatments on microstructural and mechanical properties of LPBF-processed Ti6Al4V alloy

Abstract

The present study investigates the different post-heat treatments (PHTs) (850 °C, 950 °C, and 1050 °C) to tailor the microstructure and mechanical properties of laser powder bed fusion (LPBF)-processed Ti6Al4V alloy. The microstructural features, chemical composition and micro-hardness of as-printed and heat-treated Ti6Al4V samples in longitudinal and transverse directions were characterised using optical microscopy, SEM, EDS, X-ray diffraction (XRD) and Vickers’ micro-hardness tester. Detailed XRD analysis was performed to quantify the phase volume fractions in the heat-treated samples. The microstructure of the heat-treated Ti6Al4V samples differed from the as-printed samples in grain structure and morphology. The width of α lath increased nearly twice with PHT temperature (from 850 to 1050 °C) in LPBF-processed samples. During PHT under furnace cooling, the growth of α lath width marginally increases due to a slower cooling rate than air cooling. XRD investigation revealed that the presence of β phase content in the PHTs at 950 °C and 1050 °C was consistent. Further, PHT at a higher temperature (i.e. 1050 °C) favours a higher amount of β phase content than the other PHT temperatures. The presence of (002)-closed pack planes was significantly lower for LPBF-processed Ti6Al4V samples, heat-treated under 1050 °C. The heat-treated LPBF-processed Ti6Al4V sample at 1050 °C exhibited a higher hardness (~ 27%) than the as-printed Ti6Al4V sample due to the higher β content among all the samples. The studied PHTs schemes were beneficial in generating the homogeneous and desirable microstructures for distinctive LPBF parts made of Ti6Al4V alloy befitting practical industrial applications. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.