Inconel 740H合金原位高温拉伸微裂纹萌生扩展研究
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摘要
利用自主研发的SEM原位高温拉伸台,研究了750℃高温条件下镍基高温合金Inconel 740H单轴拉伸变形过程中微观组织演变规律及微裂纹萌生与扩展机制。结果表明,在室温和高温条件下,Inconel 740H合金变形过程中晶界是主要的裂纹萌生源,但是在室温时微裂纹也会在晶内萌生。通过对原位变形机制的分析表明,750℃高温不仅降低了滑移系的开启能量,使更多的滑移系容易开动,而且弱化了晶界强度,使晶界具有弯曲和滑移的变形特性,从而增强了合金的塑性协调变形能力,但是却降低了合金的屈服强度和抗拉强度,高温同时也使合金晶界的相对强度弱化,导致微裂纹更易从晶界处萌生并扩展。
As a result of increasing energy demands and accelerated environmental problems, there is an urgent need to improve the thermal efficiency of ultra supercritical(USC) power plants. To achieve this goal, advanced ultra-supercritical(A-USC) technologies with the main steam temperature of 700~750 ℃ and pressure of 35 MPa have been developed quickly in recent years. One of the most promising candidate Ni-based superalloys for the main steam pipe of 700 ℃ ultra-supercritical coal-fired power plants is Inconel 740 H, which is a modified version of Inconel 740 developed by Special Metals Corp(SMC). Compared with IN740, the Ti/Al ratio in IN740 H is lowered in order to stabilise the microstructure at long ageing times. In addition, the Nb content is lowered to improve the weldability. In this work, the microstructure evolutions, the nucleation and propagation mechanisms of microcracks in the nickel base superalloy Inconel 740 H at 750 ℃ high temperature were studied by the self-developed in situ high temperature tensile stage inside a SEM. The results showed that under the uniaxial tensile stress at 22 ℃ room temperature and 750 ℃ high temperature conditions, the grain boundaries of Inconel 740 H alloy are always the most primary crack sources. The strength of grain boundaries is higher than that of grains under the room temperature, and the microcracks will be nucleated at the grains as well, but the relative strength of grain boundaries will be weaken under the high temperature, which makes the microcracks tend to nucleate at grain boundaries. The experimental results also showed that the influence of high temperature on the mechanical properties is very significant, the high temperature reducing the activate energy of slip and weakening the strength of the grain boundaries, so that more slip systems activated and the grain boundaries occurring bending and sliding deformation, so further enhance the ability of plastic deformation of alloy. However, the reduction of relative strength of alloy grain boundaries leads to microcracks nucleation and propagation more easily from grain boundaries and lower the yield strength and tensile strength of alloy.
As a result of increasing energy demands and accelerated environmental problems, there is an urgent need to improve the thermal efficiency of ultra supercritical(USC) power plants. To achieve this goal, advanced ultra-supercritical(A-USC) technologies with the main steam temperature of 700~750 ℃ and pressure of 35 MPa have been developed quickly in recent years. One of the most promising candidate Ni-based superalloys for the main steam pipe of 700 ℃ ultra-supercritical coal-fired power plants is Inconel 740 H, which is a modified version of Inconel 740 developed by Special Metals Corp(SMC). Compared with IN740, the Ti/Al ratio in IN740 H is lowered in order to stabilise the microstructure at long ageing times. In addition, the Nb content is lowered to improve the weldability. In this work, the microstructure evolutions, the nucleation and propagation mechanisms of microcracks in the nickel base superalloy Inconel 740 H at 750 ℃ high temperature were studied by the self-developed in situ high temperature tensile stage inside a SEM. The results showed that under the uniaxial tensile stress at 22 ℃ room temperature and 750 ℃ high temperature conditions, the grain boundaries of Inconel 740 H alloy are always the most primary crack sources. The strength of grain boundaries is higher than that of grains under the room temperature, and the microcracks will be nucleated at the grains as well, but the relative strength of grain boundaries will be weaken under the high temperature, which makes the microcracks tend to nucleate at grain boundaries. The experimental results also showed that the influence of high temperature on the mechanical properties is very significant, the high temperature reducing the activate energy of slip and weakening the strength of the grain boundaries, so that more slip systems activated and the grain boundaries occurring bending and sliding deformation, so further enhance the ability of plastic deformation of alloy. However, the reduction of relative strength of alloy grain boundaries leads to microcracks nucleation and propagation more easily from grain boundaries and lower the yield strength and tensile strength of alloy.
引文
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[11]Tan Y,Liao J,Li J Y,et al.Microstructure evolution and microhardness of Inconel 740 Alloy in different heat-treatment conditions prepared by electron beam melting[J].J.Mater.Eng.,2015,43(4):19(谭毅,廖娇,李佳艳等.电子束熔炼Inconel 740合金不同热处理状态下的组织演变与显微硬度[J].材料工程,2015,43(4):19)
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[13]Zhang H J,Zhou R C,Hou S F,et al.Study on microstructure stability of Inconel 740 for advanced ultra supercritical unit[J].Proc.CSEE,2011,31(8):108(张红军,周荣灿,侯淑芳等.先进超超临界机组用Inconel 740合金的组织稳定性研究[J].中国电机工程学报,2011,31(8):108)
[14]Shingledecker J P,Evans N D,Pharr G M.Influences of composition and grain size on creep-rupture behavior of Inconel?alloy740[J].Mater.Sci.Eng.,2013,A578:277
[15]Kontis P,Alabort E,Barba D,et al.On the role of boron on improving ductility in a new polycrystalline superalloy[J].Acta Mater.,2017,124:489
[16]Di Martino S F,Faulkner R G,Hogg S C.Characterisation of microstructure and creep predictions of alloy IN740 for ultrasupercritical power plants[J].Mater.Sci.Technol.,2015,31:48
[17]Jiang H,Dong J X,Zhang M C,et al.Oxidation behavior and mechanism of Inconel 740H alloy for advanced ultra-supercritical power plants between 1050 and 1170℃[J].Oxid.Met.,2015,84:61
[18]Lu J T,Yang Z,Xu S Q,et al.High temperature oxidation behavior of Inconel alloy 740H in pure steam[J].Mater.Mech.Eng.,2015,39(10):37(鲁金涛,杨珍,徐松乾等.Inconel 740H合金在纯水蒸气环境中的高温氧化行为[J].机械工程材料,2015,39(10):37)
[19]Lu X D,Du J H,Deng Q.In situ observation of high temperature tensile deformation and low cycle fatigue response in a nickelbase superalloy[J].Mater.Sci.Eng.,2013,A588:411
[20]Torres E A,Ramírez A J.In situ scanning electron microscopy[J].Sci.Technol.Weld.Join.,2011,16:68
[21]Chakkedath A,Boehlert C J.In situ scanning electron microscopy observations of contraction twinning and double twinning in extruded Mg-1Mn(wt.%)[J].JOM,2015,67:1748
[22]Mishra R,Kubic R.In situ EBSD of microstructure evolution during deformation[J].Microsc.Microanal.,2008,14(suppl.2):552
[23]Tarzimoghadam Z,Ponge D,Kl?wer J,et al.Hydrogen-assisted failure in Ni-based superalloy 718 studied under in situ hydrogen charging:The role of localized deformation in crack propagation[J].Acta Mater.,2017,128:365
[24]Lischewski I,Kirch D M,Ziemons A,et al.Investigation of the ag-a phase transformation in steel:High-temperature in situ EBSD measurements[J].Texture Stress Microstruct.,2008,2008:294508
[25]Summers W D,Alabort E,Kontis P,et al.In-situ high-temperature tensile testing of a polycrystalline nickel-based superalloy[J].Mater.High Temp.,2016,33:338
[2]Patel S J,de Barbadillo J J,Baker B A,et al.Nickel base superalloys for next generation coal fired AUSC power plants[J].Proced.Eng.,2013,55:246
[3]Shingledecker J P,Pharr G M.The role of eta phase formation on the creep strength and ductility of INCONEL alloy 740 at 1023 K(750℃)[J].Metall.Mater.Trans.,2012,43A:1902
[4]Dang Y Y,Zhao X B,Yuan Y,et al.Predicting long-term creeprupture property of Inconel 740 and 740H[J].Mater.High Temp.,2016,33:1
[5]Chong Y,Liu Z D,Godfrey A,et al.Detrimental effect of cellular precipitation on the creep strength of Inconel 740H[J].Phil.Mag.Lett.,2013,93:688
[6]Guo Y,Li T J,Wang C X,et al.Microstructure and phase precipitate behavior of Inconel 740H during aging[J].Trans.Nonferrous Met.Soc.China,2016,26:1598
[7]Cowen C J,Danielson P E,Jablonski P D.The microstructural evolution of Inconel alloy 740 during solution treatment,aging,and exposure at 760℃[J].J.Mater.Eng.Perform.,2011,20:1078
[8]Dang Y Y,Zhao X B,Yin H F,et al.Microstructure stability of Inconel 740H alloy after long term exposure at 750℃[J].J.Mater.Eng.,2016,44(9):58(党莹樱,赵新宝,尹宏飞等.Inconel 740H合金750℃长期时效后的组织稳定性[J].材料工程,2016,44(9):58)
[9]Fu R,Lin F S,Zhao S Q,et al.Influence of strengthening elements on precipitation of thermodynamic equilibrium phases in Inconel alloy 740H[J].J.Chin.Soc.Power Eng.,2013,33:405(符锐,林富生,赵双群等.Inconel 740H主要强化元素对热力学平衡相析出行为的影响[J].动力工程学报,2013,33:405)
[10]Guo Y,Li T J,Wang C X,et al.Microstructure and phase precipitate behavior of Inconel 740H during aging[J].Trans.Nonferrous.Met.Soc.China,2016,26:1598
[11]Tan Y,Liao J,Li J Y,et al.Microstructure evolution and microhardness of Inconel 740 Alloy in different heat-treatment conditions prepared by electron beam melting[J].J.Mater.Eng.,2015,43(4):19(谭毅,廖娇,李佳艳等.电子束熔炼Inconel 740合金不同热处理状态下的组织演变与显微硬度[J].材料工程,2015,43(4):19)
[12]Xie X S,Zhao S Q,Dong J X,et al.Structural stability and improvement of Inconel alloy 740 for ultra supercritical power plants[J].J.Chin.Soc.Power Eng.,2011,31:638(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,2011,31:638)
[13]Zhang H J,Zhou R C,Hou S F,et al.Study on microstructure stability of Inconel 740 for advanced ultra supercritical unit[J].Proc.CSEE,2011,31(8):108(张红军,周荣灿,侯淑芳等.先进超超临界机组用Inconel 740合金的组织稳定性研究[J].中国电机工程学报,2011,31(8):108)
[14]Shingledecker J P,Evans N D,Pharr G M.Influences of composition and grain size on creep-rupture behavior of Inconel?alloy740[J].Mater.Sci.Eng.,2013,A578:277
[15]Kontis P,Alabort E,Barba D,et al.On the role of boron on improving ductility in a new polycrystalline superalloy[J].Acta Mater.,2017,124:489
[16]Di Martino S F,Faulkner R G,Hogg S C.Characterisation of microstructure and creep predictions of alloy IN740 for ultrasupercritical power plants[J].Mater.Sci.Technol.,2015,31:48
[17]Jiang H,Dong J X,Zhang M C,et al.Oxidation behavior and mechanism of Inconel 740H alloy for advanced ultra-supercritical power plants between 1050 and 1170℃[J].Oxid.Met.,2015,84:61
[18]Lu J T,Yang Z,Xu S Q,et al.High temperature oxidation behavior of Inconel alloy 740H in pure steam[J].Mater.Mech.Eng.,2015,39(10):37(鲁金涛,杨珍,徐松乾等.Inconel 740H合金在纯水蒸气环境中的高温氧化行为[J].机械工程材料,2015,39(10):37)
[19]Lu X D,Du J H,Deng Q.In situ observation of high temperature tensile deformation and low cycle fatigue response in a nickelbase superalloy[J].Mater.Sci.Eng.,2013,A588:411
[20]Torres E A,Ramírez A J.In situ scanning electron microscopy[J].Sci.Technol.Weld.Join.,2011,16:68
[21]Chakkedath A,Boehlert C J.In situ scanning electron microscopy observations of contraction twinning and double twinning in extruded Mg-1Mn(wt.%)[J].JOM,2015,67:1748
[22]Mishra R,Kubic R.In situ EBSD of microstructure evolution during deformation[J].Microsc.Microanal.,2008,14(suppl.2):552
[23]Tarzimoghadam Z,Ponge D,Kl?wer J,et al.Hydrogen-assisted failure in Ni-based superalloy 718 studied under in situ hydrogen charging:The role of localized deformation in crack propagation[J].Acta Mater.,2017,128:365
[24]Lischewski I,Kirch D M,Ziemons A,et al.Investigation of the ag-a phase transformation in steel:High-temperature in situ EBSD measurements[J].Texture Stress Microstruct.,2008,2008:294508
[25]Summers W D,Alabort E,Kontis P,et al.In-situ high-temperature tensile testing of a polycrystalline nickel-based superalloy[J].Mater.High Temp.,2016,33:338
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