In-situ synthesis of TiN and its effects on Fe-12Cr-6Al in laser powder bed fusion

Abstract

This study examines the feasibility of in-situ synthesis of various nitride and oxide precipitates and their impact on Fe-12Cr-6Al alloy characteristics using an N2 reactive gas atmosphere and Ti addition during the L-PBF process. This study focused on elucidating the effects of adding Ti on the Fe-12Cr-6Al's melt pool dynamics, microstructure, precipitate characteristics, oxygen/nitrogen content variation, and mechanical properties. Without Ti, the resulting melt pools exhibited a shallow and wide morphology, contrasting with the formation of compact and deeper melt pools in the presence with Ti. Furthermore, Ti-based nitrides yielded a discernible enhancement in grain refinement compared to Al-based nitrides. In-situ Al2O3, AlN, and AlN-O nano precipitates were synthesized within the Fe-12Cr-6Al matrix with the nitrogen process gas. However, adding Ti transformed the nanoparticles, resulting in TiN, TiAl-N, and Al2O3@TiN. The addition of Ti increased the oxygen content from 0.0051 to 0.0315 wt. % and the nitrogen content from 0.02 to 0.08 wt. %. In-situ synthesis of Ti-rich precipitates and the solid solution effect of Ti led to significant mechanical property enhancement, including a yield strength (YS) of ∼109 MPa, ultimate tensile strength (UTS) of ∼200 MPa, a total elongation (TE) of ∼7.4 %, and a Vickers hardness (HV) of ∼47. This study offers compelling and thorough evidence regarding the in-situ synthesis of diverse nitride and oxide nano-precipitates. It explores how the addition of Ti to the FeCrAl alloy alters the types and shapes of nitride and oxide nano-precipitates and assesses the impact of these precipitates on the properties of the Fe-12Cr-6Al alloy.