TG700A镍基合金在持久过程中的晶界析出相转变及断裂行为
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摘要
在770℃、不同应力(160,200,260MPa)下对TG700A镍基合金进行持久试验,研究了该合金的显微组织及持久断裂行为。结果表明:试验合金的原始显微组织为等轴奥氏体,晶粒内部析出有均匀分布的细小球状γ′相,晶界处存在颗粒状的富铬M_(23)C_6碳化物;持久断裂后组织中未发现新析出相,晶界附近出现严重粗化的γ′相,晶界上存在γ′相贫化区;试验合金的持久断裂模式以沿晶断裂为主,晶界处的局部塑性变形导致了局部应力集中,促进了蠕变空洞或裂纹的形成,裂纹沿γ相和γ′相界面或γ′相贫化区扩展。
The stress rupture tests at 770℃ under different stresses(160,200,260 MPa)were conducted on TG700A nickel-based alloy.The microstructure and stress rupture behavior of the alloy were studied.The results show that the original microstructure of the tested alloy was composed of equiaxed austenite;fine spherical γ′ phase precipitated in the grains uniformly,and granular Cr-rich M_(23)C_6 carbides existed at the grain boundaries.After stress rupture,no new precipitates were found in the microstrucutre,and coarsened γ′ phase near grain boundaries and γ′ phase depletion zone at grain boundaries appeared.The stress rupture mode of the tested alloy was mainly intergranular fracture.The localized plastic deformation at grain boundaries led to localized stress concentration,promoting the formation of creep voids or cracks.The crack propagated along the interface between γ and γ′ phases or the γ′ phase depletion zone.
The stress rupture tests at 770℃ under different stresses(160,200,260 MPa)were conducted on TG700A nickel-based alloy.The microstructure and stress rupture behavior of the alloy were studied.The results show that the original microstructure of the tested alloy was composed of equiaxed austenite;fine spherical γ′ phase precipitated in the grains uniformly,and granular Cr-rich M_(23)C_6 carbides existed at the grain boundaries.After stress rupture,no new precipitates were found in the microstrucutre,and coarsened γ′ phase near grain boundaries and γ′ phase depletion zone at grain boundaries appeared.The stress rupture mode of the tested alloy was mainly intergranular fracture.The localized plastic deformation at grain boundaries led to localized stress concentration,promoting the formation of creep voids or cracks.The crack propagated along the interface between γ and γ′ phases or the γ′ phase depletion zone.
引文
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[3]毛健雄.700℃超超临界机组高温材料研发的最新进展[J].电力建设,2013,34(8):69-76.
[4]张燕平,蔡小燕,黄树红.700℃超超临界燃煤发电机组材料研发现状[J].中国电力,2012,45(2):16-21.
[5]陈石富,秦鹤勇,张文云,等.700℃超超临界锅炉用镍基合金管材的研究进展[J].机械工程材料,2012,36(11):1-4.
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[7]YAN C,LIU Z,GODFREY A,et al.Microstructure evolution and mechanical properties of Inconel 740H during aging at 750℃[J].Materials Science and Engineering:A,2014,589:153-164.
[8]郭岩,周荣灿,张红军,等.镍基合金740H的组织结构与析出相分析[J].中国电机工程学报,2015,35(17):4439-4444.
[9]REED R.The superalloys:Fundamentals and applications[M].New York:Cambridge University Press,2006:53-54.
[10]LI H,YE F,ZHAO J,et al.Grain boundary migrationinduced directional coarsening of the γ′ phase in advanced ultra-supercritical superalloy[J].Materials Science and Engineering:A,2018,714:172-178.
[11]BECHETTI D H,DUPONT J N,WATANABE M,et al.Characterization of discontinuous coarsening reaction products in INCONEL?alloy 740H?fusion welds[J].Metallurgical and Materials Transactions A,2017,48(4):1727-1743.
[12]谢锡善,赵双群,董建新,等.超超临界电站用Inconel 740镍基合金的组织稳定性及其改型研究[J].动力工程学报,2011,31(8):638-643.
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[14]KROL T,BAITHER D,NEMBACH E.Softening of the superalloy NIMONIC PE16by precipitate free zones along grain boundaries[J].Materials Science and Engineering:A,2004,387(1):214-217.
[15]SCHWARTZ A J,KUMAR M,ADAMS B L,et al.Electron backscatter diffraction in materials science[M].New York:Springer US,2009:251-262.