Indentation creep behavior of pulsed Tungsten inert gas welded Ti-5Al-2.5Sn alloy joints by nanoindentation and atomic force microscopy

Indentation creep was used to analyze the heterogeneity of the mechanical properties in base metal, heat affected zone and fusion zone of titanium alloy weldments obtained using TIG welding process which is generally employed in aerospace industries. For all the weld zones, creep deformation was analyzed using nanoindenter, AFM and microhardness testing. Nanoindentation creep depth was plotted with respect to time using data from the hold stage and CSRs were calculated using empirical relations. The analysis of creep stress exponents (CSE) was indicative of an active creep mechanism for all the weld zones however, a notable variation between the stress exponents and creep mechanism was observed among base metal, heat affected zone and fusion zone. Moreover, Vickers microindentation was used to measure creep of Ti-5Al-2.5Sn alloy weldment using Sargent-Ashby model. However, it did not give the realistic values creep behavior when compared to literature and nanoindentation measurements. It was observed that the phase change, grain size and the loading strain rate (LSR) significantly affected the creep behavior of the Ti-5Al-2.5Sn weldment.