Experimental and Calphad Methods for Evaluating Residual Stresses and Solid-State Shrinkage after Solidification

Abstract

Laser powder bed fusion is an additive manufacturing method that is based on melting and solidification of powder material. Due to the local heating above the melting point, thermal stresses are usually formed in the final part. Mitigation of residual stresses is usually assessed by laser scan strategies and not by alloy tailoring. In this paper a segregation-based residual stress formation mechanism is proposed and assessed computationally. Additionally, an experimental setup for rapid screening of residual stress formation in various alloys is proposed. The results should ease material development of metal alloys tailored for additive manufacturing by allowing the comparison of residual stress formation tendency (e.g., solid state shrinkage) between alloys. The proposed computational method is comparative in nature and forecasting absolute residual stress values would require known temperature dependent elastoplastic properties for the alloys as well as exact thermal history. The proposed experimental method is quantitative but its reliability depends on material properties such as yield strength.

Nitrogen alloyed austenitic Ni-free stainless steel for additive manufacturing

“…However, formation of gas phase during Scheil simulation is not allowed in the used version of TC. Therefore, gas phase formation during metastable solidification was studied using a local equilibrium approach, first demonstrated by Antikainen et al for thermal expansion of solidified alloys, 14 by plotting phase-fraction versus temperature graphs for the entire gradient of solidified compositions. The same study was done for the nominal Forta H500 composition and for the atomized Forta H500 compositions with reduced nitrogen content.…”

Effect of Laser Power on the Recrystallization Temperature of an Additively Manufactured IN718

“…The recrystallization observed in the additively manufactured materials can be attributed to various driving forces [28,30,31]. These forces encompass tensile deformation caused by solidification shrinkage around the melt pool, as well as accumulated tensile and compressive deformations arising from repetitive heating and cooling cycles.…”