Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane nor...Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane normal to the building direction.This work studied effects of post heating strategy on the microstructure and especially the grain size to improve the high temperature creep resistance.The asbuilt microstructure exhibited a fine grain size and large quantities of MC carbides that could effectively hinder grain growth.It was found that unconventional two-step heat treatments could lead to substantial grain growth,and the effect is particularly prominent at a specific temperature.The ease of grain growth was explained after classifying the microstructural evolution(boundary carbide transformation)during each heating step and related to the reduced grain boundary pinning force from MC carbides.Creep tests validated the effect of the new heat treatment scheme on the SLM-processed IN738LC at 850℃.An extended creep fracture life(1.5 to 4 times improvement)and lower secondary creep rates were achieved with samples subjected to the newly optimized two-step heat treatment.The complete creep curves are also firstly presented for SLM-IN738LC,confirming the effectiveness of grain growth and highlighting the importance of dedicated heat treatment for SLM superalloys.展开更多
基金financially supported by"Industrial Transformation Research Hub for Transforming Australia’s Manufacturing Industry through High Value Additive Manufacturing"of the Australian Research Council(grant No.IH130100008)the use of instruments and scientific and technical assistance at the Monash Centre for Electron Microscopy,a Node of Microscopy Australiathe financial support from the Monash Graduate Research Scholarship(MGS)and International Monash Postgraduate Research Scholarship(IMPRS)from the Monash University。
文摘Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane normal to the building direction.This work studied effects of post heating strategy on the microstructure and especially the grain size to improve the high temperature creep resistance.The asbuilt microstructure exhibited a fine grain size and large quantities of MC carbides that could effectively hinder grain growth.It was found that unconventional two-step heat treatments could lead to substantial grain growth,and the effect is particularly prominent at a specific temperature.The ease of grain growth was explained after classifying the microstructural evolution(boundary carbide transformation)during each heating step and related to the reduced grain boundary pinning force from MC carbides.Creep tests validated the effect of the new heat treatment scheme on the SLM-processed IN738LC at 850℃.An extended creep fracture life(1.5 to 4 times improvement)and lower secondary creep rates were achieved with samples subjected to the newly optimized two-step heat treatment.The complete creep curves are also firstly presented for SLM-IN738LC,confirming the effectiveness of grain growth and highlighting the importance of dedicated heat treatment for SLM superalloys.
