The determination of intrinsic deformation parameters inducing grain refinement mechanism of dynamic recrystallization (DRX) contributes to the relative forming process design. For Ni80A superalloy, the processing map...The determination of intrinsic deformation parameters inducing grain refinement mechanism of dynamic recrystallization (DRX) contributes to the relative forming process design. For Ni80A superalloy, the processing maps were constructed by the derivation of the stress-strain data coming from a series of isothermal compression tests at temperatures of 1273^-1473 K and strain rates of 0.01-10 s^-1. According to the processing maps and microstructural validation, the deformation parameter windows with DRX mechanism were separated in an innovative deformation mechanism map. In addition, the deformation activation energy representing deformation energy barrier was introduced to further optimize such windows. Finally, the enhanced processing maps were constructed and the parameter domains corresponding to DRX mechanism and lower deformation barrier were determined as follows: at ε=0.3, domains: 1296-1350 K, 0.056-0.32 s^-1 and 1350-1375 K, 0.035-0.11 s^-1;at ε=0.5, domains: 1290-1348 K, 0.2-0.5 s^-1 and 1305-1370 K, 0.035-0.2 s^-1;at ε=0.7, domains: 1290-1355 K, 0.042-0.26 s^-1;at ε=0.9, domains: 1298-1348 K, 0.037-0.224 s^-1.展开更多
Oxidation characteristics of Alloy 617 and Haynes 230 at 900 oC in simulated helium environment,hot steam environment containing H2 as well as in air and pure helium conditions were investigated.Compared to air condit...Oxidation characteristics of Alloy 617 and Haynes 230 at 900 oC in simulated helium environment,hot steam environment containing H2 as well as in air and pure helium conditions were investigated.Compared to air condition,the oxidation rate of Alloy 617 was not significantly affected in helium and hot steam environments,while Haynes 230 showed lower oxidation rate in helium environment.On the other hand,the oxide morphology and structure of Alloy 617 were strongly affected by the environments,but those of Haynes 230 were less dependent on the environments.For Haynes 230,a Cr2O3 inner layer and a protective MnCr2O4 outer layer were formed in all environments,which contributed to the better oxidation resistance.As the mechanical properties,such as creep and tensile properties,were significantly affected by the oxidation behaviors,surface treatment methods to enhance oxidation resistance of these alloys should be developed.展开更多
The fatigue test between 10^5—10^9 cycles of GH4169 nickel‑based superalloy commonly used in aircraft engines is carried out by ultrasonic fatigue machine at 650℃.The S‑N curve is obtained and the fatigue fracture m...The fatigue test between 10^5—10^9 cycles of GH4169 nickel‑based superalloy commonly used in aircraft engines is carried out by ultrasonic fatigue machine at 650℃.The S‑N curve is obtained and the fatigue fracture morphology is observed.The fatigue S‑N curve presents a“step‑like”shape,with the first inflection point near 1×10^7 cycles and the second inflection point near 1×10^8 cycles.There is no engineering fatigue limit,and it still shows a downward trend after 107 or even 10^9 cycles.The crack initiation location is related to its life.Cracks are generated on the surface below 10^7 cycles,while it is inside above 10^7 cycles.The crack initiation source in the ultra‑high cycle fatigue at 650℃ is mainly the local intergranular fracture and casting defect of the matrix.In the phase of crack propagation,the mixed propagation of intergranular and cleavage is the main form.展开更多
In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic te...In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic testing method(20 KHz) and rotary bending testing method(52.5 Hz),both at room temperatures,to establish stress versus cycles to failure(S-N) relationships.Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency,i.e.,the higher frequency produced an upper shift of the S-N curves.Fractographic analysis suggested that crack initiation and propagation behaviors had large differences:cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface,while in high-frequency tests,cracks mostly originated from a unique source of subsurface inclusions.Subsequently,frequency-involved modeling was proposed,based on the damage accumulation theory,which could well illustrate qualitatively those comparisons due to different loading frequencies.展开更多
基金Project(cstc2018jcyj AX0459)supported by Chongqing Basic Research and Frontier Exploration,ChinaProject(P2017-020)supported by Open Fund Project of State Key Laboratory of Materials Processing and Die&Mould Technology,ChinaProject(SKLMTZZKT-2017M15)supported by Research Project of State Key Laboratory of Mechanical Transmission,China
文摘The determination of intrinsic deformation parameters inducing grain refinement mechanism of dynamic recrystallization (DRX) contributes to the relative forming process design. For Ni80A superalloy, the processing maps were constructed by the derivation of the stress-strain data coming from a series of isothermal compression tests at temperatures of 1273^-1473 K and strain rates of 0.01-10 s^-1. According to the processing maps and microstructural validation, the deformation parameter windows with DRX mechanism were separated in an innovative deformation mechanism map. In addition, the deformation activation energy representing deformation energy barrier was introduced to further optimize such windows. Finally, the enhanced processing maps were constructed and the parameter domains corresponding to DRX mechanism and lower deformation barrier were determined as follows: at ε=0.3, domains: 1296-1350 K, 0.056-0.32 s^-1 and 1350-1375 K, 0.035-0.11 s^-1;at ε=0.5, domains: 1290-1348 K, 0.2-0.5 s^-1 and 1305-1370 K, 0.035-0.2 s^-1;at ε=0.7, domains: 1290-1355 K, 0.042-0.26 s^-1;at ε=0.9, domains: 1298-1348 K, 0.037-0.224 s^-1.
基金supported by the MEST/NRF (Nuclear R&D Program,2005-2004718 and 2009 0083392) of Korea
文摘Oxidation characteristics of Alloy 617 and Haynes 230 at 900 oC in simulated helium environment,hot steam environment containing H2 as well as in air and pure helium conditions were investigated.Compared to air condition,the oxidation rate of Alloy 617 was not significantly affected in helium and hot steam environments,while Haynes 230 showed lower oxidation rate in helium environment.On the other hand,the oxide morphology and structure of Alloy 617 were strongly affected by the environments,but those of Haynes 230 were less dependent on the environments.For Haynes 230,a Cr2O3 inner layer and a protective MnCr2O4 outer layer were formed in all environments,which contributed to the better oxidation resistance.As the mechanical properties,such as creep and tensile properties,were significantly affected by the oxidation behaviors,surface treatment methods to enhance oxidation resistance of these alloys should be developed.
基金supported by the Tianjin Technical Expert Project (No.19JCTPJC43800)the Tianjin Science and Technology Planning Project (No. 19YFFCYS00090)+1 种基金the Key Project of Science and Technology Cultivation of Tianjin Sino-German University of Applied Technology(No. zdkt2017-006)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘The fatigue test between 10^5—10^9 cycles of GH4169 nickel‑based superalloy commonly used in aircraft engines is carried out by ultrasonic fatigue machine at 650℃.The S‑N curve is obtained and the fatigue fracture morphology is observed.The fatigue S‑N curve presents a“step‑like”shape,with the first inflection point near 1×10^7 cycles and the second inflection point near 1×10^8 cycles.There is no engineering fatigue limit,and it still shows a downward trend after 107 or even 10^9 cycles.The crack initiation location is related to its life.Cracks are generated on the surface below 10^7 cycles,while it is inside above 10^7 cycles.The crack initiation source in the ultra‑high cycle fatigue at 650℃ is mainly the local intergranular fracture and casting defect of the matrix.In the phase of crack propagation,the mixed propagation of intergranular and cleavage is the main form.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10872105 and 51071094)
文摘In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic testing method(20 KHz) and rotary bending testing method(52.5 Hz),both at room temperatures,to establish stress versus cycles to failure(S-N) relationships.Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency,i.e.,the higher frequency produced an upper shift of the S-N curves.Fractographic analysis suggested that crack initiation and propagation behaviors had large differences:cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface,while in high-frequency tests,cracks mostly originated from a unique source of subsurface inclusions.Subsequently,frequency-involved modeling was proposed,based on the damage accumulation theory,which could well illustrate qualitatively those comparisons due to different loading frequencies.