Additively manufactured crack-free nickel-based superalloys with synergistic strength and plasticity via grain refinement and striped oxides inhibition

Abstract

Solidification cracking seriously hinders the laser powder bed fusion (LPBF) prepared Haynes 230 (H230) superalloy from serving in the aerospace field. In this study, the cracking mechanism of H230 alloy was analyzed in detail and a new H230-La alloy adding La2O3 nanoparticles for cracking elimination was successfully prepared. At the high-angle grain boundary (GB), Si, Al and O elements were enriched to form M5-xSi3-zCx+z silicides and brittle Al-oxides. This led to severe strain concentration at the incompletely solidified GB resulting in solidification cracking. After the addition of La2O3 particles, La2O3 particles reacted with Al and O elements to form LaAlO3 particles, avoiding striped Al-rich oxides at GBs. The La atoms decomposed by La2O3 also promoted the nucleation of M23C6 and relieved GB strain caused by silicides. Moreover, grain refinement caused by heterogeneous nucleation also increased the resistance to crack initiation, thus a crack-free alloy was prepared. The prepared H230-La new alloy exhibited well synergy of strength and plasticity, and the deformation mechanism was transformed from dislocation slip plugging to grain rotational deformation. This study proposes a method to eliminate cracking by in situ inhibition of striped brittle oxide formation in superalloys and helps to broaden the wide range of applications of LPBF-prepared superalloys in the aerospace field.