热处理对增材制造TS5镍基高温合金组织与性能的影响

Effect of heat treatment on microstructure and properties of additive manufacturing TS5 nickel⁃based superalloy

采用选区激光熔化(Selective laser melting,SLM)技术制备TS5镍基高温合金,通过不同保温温度、升温速率和保温时间的热处理工艺,分析了热处理对SLM成形TS5合金的显微组织和力学性能的影响。结果表明,沉积态TS5合金裂纹占比0.07%,平均晶粒截面粒径为66.94μm,具有低的打印成形开裂倾向与稳定的成形组织。沉积态TS5合金以0.1℃/s升温至900℃时,γ′相在升温过程中析出。而较快的升温速率可以抑制TS5合金在升温过程中γ′相的析出,特别是当升温速率大于50℃/s时,γ′相的析出被完全抑制。在850℃下分别保温10、60、240 min时,γ′相体积分数分别为26.2%、37.7%和47.1%,析出量逐渐增加;γ′相尺寸分别为22.2、40.5、58.9 nm。拉伸测试显示,沉积态TS5合金随着热处理温度升高,抗拉强度逐步降低,650℃与750℃的屈服强度分别为873 MPa和768 MPa;850℃和950℃的拉伸过程出现脆断现象。电子背散射衍射(Electron back-scatter diffraction,EBSD)发现裂纹主要出现在大角度晶界处。综上所述,合理的快速升温配合短时保温有利于避免升温过程的相变内应力,有效提升晶界强度,对SLM成形TS5合金避免热处理过程的畸变开裂至关重要。

Nickel⁃based superalloy TS5 was prepared by using selective laser melting(SLM)technology,and the effect of heat treatment with various heating temperatures,rates and holding time on the microstructure and mechanical properties of the alloy was analyzed.The results show that the proportion of cracks in the as⁃deposited TS5 alloy is 0.07%,with the cross⁃sectional average grain diameter of 66.94μm.The TS5 alloy has a low cracking tendency of printing forming and a stable formed microstructure.When the as⁃deposited TS5 alloy is heated up to 900℃with 0.1℃/s,γ′phase precipitates in the heating process,while the faster heating rate can inhibit the precipitation ofγ′phase during the heating process,especially when the heating rate is greater than 50℃/s,the precipitation ofγ′phase is completely inhibited.When holding at 850℃for 10,60 and 240 min respectively,the size ofγ′phase is 22.2,40.5 and 58.9 nm respectively,the volume fraction ofγ′phase is 26.2%,37.7%and 47.1%respectively,meaning that the amount of precipitation gradually increases.The tensile test shows that the tensile strength of the as⁃deposited TS5 alloy gradually decreases with increase of the heat treatment temperature.The yield strength at 650℃and 750℃is 873 MPa and 768 MPa respectively,while the brittle fracture occurs during the tensile process at 850℃and 950℃.The electron back⁃scatter diffraction results show that the cracks mainly occur in the high angle grain boundaries.In summary,a reasonable rapid heating combined with a short isothermal holding time is beneficial for avoiding phase transformation internal stress during the heating process.Moreover,effectively improving grain boundary strength is crucial for the TS5 alloy formed by SLM to resist the deformation and cracking during heat treatment process.