Martensite Decomposition and Ultrafine Grain Formation during Small Punch Creep Testing of Additively Manufactured Ti64

The creep behaviour of as-built additive-manufactured Ti-6Al-4V alloy was studied through small punch creep test (SPCT) experiments at 450 and 500 degrees C. The couple stress/minimum strain rate deduced from these tests made it possible to draw a Norton plot showing good agreement with tensile test creep results. The microstructure characterisation within the SPCT specimen evidenced the effect of local strain on microstructure evolution. After interrupted creep at 450 degrees C, in most deformed areas, the as-built martensite structure was fully decomposed to the alpha + beta equilibrium phases, giving rise to a submicron equiaxed grain structure.