Stress relaxation of inconel 718 superalloy manufactured by selective laser melting (SLM)

Abstract

Stress relaxation behaviour of Inconel 718 superalloy manufactured by selective laser melting (SLM) at the temperatures rang of 650–750 °C and 2 % strain were experimentally investigated and compared with IN718 forged material. During SLM manufacturing process the material is exposed to the cyclic thermal histories and fast local solidification process. Therefore, internal stresses are generated in the component during the SLM process and they may impact the material performance and cause early failure. Stress relaxation in the components such as fasteners may alter the integrity of the whole structure. It was found that the relaxation behavior of the SLM IN718 specimens are differs from forged manufactured specimens. The comparison results show that the decrease of relaxation limit for SLM specimens is more than 90 % when the temperature rises from 650 °C to 750 °C which is much higher than that of forged specimens. The stress relaxation stability of forged specimens is higher than that of SLM specimens at all tested temperatures. The homogenization and solution heat treatment process was performed on SLMed IN718 specimen shows a higher stress relaxation rate compared with as-received SLMed specimens. The stress exponent, n, for power law creep relation was determined for SLMed and forged IN718 at 700 °C and it was found that dislocation motion predominantly controls the stress relaxation mechanism in the IN718 alloy at this temperature. The investigations reveal that the analytical results closely matched the results obtained from experiments.