A Melt Pool Temperature Model in Laser Powder Bed Fabricated CM247LC Ni Superalloy to Rationalize Crack Formation and Microstructural Inhomogeneities

Di Wang,Guowei Deng,Sheng Li,Moataz M Attallah,Yang Liu

doi:10.1007/s11661-021-06457-5

Abstract

This study of the laser powder bed fusion (LPBF) of γ′-strengthened Ni superalloy CM247LC focuses on the development of a melt pool temperature model to predict crack density within the alloy. This study also analyzes spatter and elemental evaporation, which might cause defects and inhomogeneities, at different melt pool temperatures. The melt pool temperature model provides more accurate predictions than the widely used energy density model. Spatter particles were collected and characterized to study their sizes and chemical compositions, compared with the virgin powder, recycled powder, and as-built samples, to probe the impact of their entrapment into the melt pool. This study also investigated Al evaporation, revealing that its extent does not correlate with the laser energy density and is believed to be rather limited by comparing the chemistry of the virgin powder and the build. Last, the impact of LPBF process parameters on the formation of these inhomogeneities, and accordingly crack formation, was studied using finite element analysis by estimating the maximum melt pool temperature and correlating it with the formation of the microstructural inhomogeneities. The morphology of the various cracking modes was associated with the process parameters.

Highlights

AND LITERATURE REVIEWNICKEL superalloys have been widely used for critical components in extreme conditions due to their excellent high-temperature strength, fatigue life, good creep performance, and oxidation resistance,[1] with c¢-strengthened cast alloys being used within high-temperature aeroengine sections due to their superior performances.[2]
Due to the reheating and remelting associated with laser powder bed fusion (LPBF), ductility dip cracking (DDC)[9] could occur, associated with the poor ductility of Ni superalloys at intermediate temperature ranges, resulting in crack formations under the action of the residual stresses
This study focuses on the influence of spatter and elemental evaporation on microstructural inhomogeneity in LPBF-processed Ni superalloy CM247LC and the subsequent microsegregation and cracking

Summary

Introduction

AND LITERATURE REVIEWNICKEL superalloys have been widely used for critical components in extreme conditions due to their excellent high-temperature strength, fatigue life, good creep performance, and oxidation resistance,[1] with c¢-strengthened cast alloys being used within high-temperature aeroengine sections due to their superior performances.[2]. CM247LC, a chemically modified version of MAR-M247, has reduced C content, lower impurities, and improved grain boundary strength in comparison Localized contractions of the solid cause cavities to form within the liquid film, generating ‘‘hot tear’’ cracks These defects can propagate under thermal residual stress.[7] Besides the solidification cracking, there is associated grain boundary cracking with the formation of a liquid film along a grain boundary, opening a crack under the influence of the thermal residual stresses during cooling.[8] Due to the reheating and remelting associated with LPBF, ductility dip cracking (DDC)[9] could occur, associated with the poor ductility of Ni superalloys at intermediate temperature ranges, resulting in crack formations under the action of the residual stresses. Carter et al.[11] used process parameter optimization to reduce

Methods

Results

Conclusion