Microstructure and mechanical properties of crack-free Inconel 738 fabricated by laser powder bed fusion

Microstructure and mechanical properties of crack-free Inconel 738 fabricated by laser powder bed fusion

This study reports the successful crack-free fabrication of the non-weldable high gamma' Ni-superalloy IN 738 by laser powder bed fusion. The as-fabricated texture was composed of columnar grains with preferred orientation along < 100 > direction. Scanning electron microscopy and X-ray diffraction analysis revealed the presence of M(Ti, Ta, W, Mo, Nb)C and M(Cr, Mo, W)(23)C-6 carbides along the grain boundaries. A heat treatment used for IN 738 castings yielded a bimodal distribution of gamma' precipitates with a primary gamma' volume of 25% and size of similar to 226 nm and secondary gamma' with a volume of 43% and a size of similar to 88 nm. The carbides observed in the as-built condition were maintained. The heat treatment increased the hardness from 408 HV to 487 HV. The specimen exhibited an excellent room temperature yield strength, ultimate tensile strength, and elongation of 1010 MPa, 1444 MPa, and 13%, respectively. The coupons showed yield strength of 560 MPa and 388 MPa, the ultimate tensile strength of 765 MPa and 538 MPa, and an elongation of 17% and 14% at 850 degrees C and 927 degrees C, respectively. Finally, fracture analysis was used to better understand fracture behavior.

本研究报道了通过激光粉末床熔融技术成功制造无裂纹的不可焊接高γ′镍基高温合金IN 738。所制造的织构由沿<100>方向择优取向的柱状晶粒组成。扫描电子显微镜和X射线衍射分析表明，沿晶界存在M(Ti, Ta, W, Mo, Nb)C和M(Cr, Mo, W)₂₃C₆碳化物。用于IN 738铸件的热处理产生了γ′析出相的双峰分布，一次γ′体积分数为25%，尺寸约为226 nm，二次γ′体积分数为43%，尺寸约为88 nm。在制造态下观察到的碳化物得以保留。热处理使硬度从408 HV提高到487 HV。试样在室温下表现出优异的屈服强度、极限抗拉强度和伸长率，分别为1010 MPa、1444 MPa和13%。试样在850℃和927℃时分别表现出560 MPa和388 MPa的屈服强度、765 MPa和538 MPa的极限抗拉强度以及17%和14%的伸长率。最后，通过断裂分析更好地理解断裂行为。