Control of residual stress in metal additive manufacturing by low-temperature solid-state phase transformation: An experimental and numerical study

Abstract

Directed energy deposition (DED) technology commonly known as additive manufacturing (AM), is a rapid prototyping method for fabricating metallic functional components with minimum finishing operations. However, excessive tensile residual stress (RS) is often a potential source of structural failure due to the fact that it can cause surface/subsurface cracking of DED parts. In this work, the RS properties in DED specimens made of the low-temperature transformation (LTT) pre-alloyed powders was investigated. A DED model coupling the finite element (FE) and thermo-mechanical-metallurgical (TMM) analysis was constructed, and was experimentally validated by thermographic system and X-ray diffraction (XRD) stress measurements. An additional set of RS prediction for the DED specimen, using increased inter-track idle time was developed to reveal the effects of thermal history on TMM evolution behavior and RS distribution. The combination of experiment and predictive simulation provided an insight into the non-linear thermo-metallurgical evolution and the formation mechanism of compressive RS during DED of LTT alloy, and showed the great potentiality of LTT powder in minimizing the RS in DED parts by the austenite-to-martensite transformation on cooling.