The effect of Mo addition on microstructural characteristics of a nickel-base single crystal superalloy containing 4 wt% Re was investigated. The γ/γ’ partitioning ratios determined by energy dispersive spectromete...The effect of Mo addition on microstructural characteristics of a nickel-base single crystal superalloy containing 4 wt% Re was investigated. The γ/γ’ partitioning ratios determined by energy dispersive spectrometer attached to a transmission electron microscope showed that the addition of Mo enhanced the partitioning of Re,W and Cr in the g matrix while decreased the concentration of Ta in the matrix. Synchrotron radiation diffraction was adopted to measure the γ/γ’ lattice misfit at room temperature. The results indicated that Mo addition changed the γ/γ’ lattice misfit towards larger negative as well as increased the tetragonal distortion of the γ lattice. Additionally,Mo addition led to microstructural instability and altered the precipitation behavior of topologically close-packed phases during 1100 C exposure. Instead of precipitating directly from the matrix,the μ phase was observed to be converted from the α phase which precipitated preferentially as a metastable intermediate in the alloy with high Mo content.展开更多
Evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417 G and DD33, has been investigated. The morphology of MC carbides evolves from...Evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417 G and DD33, has been investigated. The morphology of MC carbides evolves from faceted to script-like with increasing cooling rate. Varying the carbon content from 40X10-6 to 320X10-6, the morphology of carbides changes from blocky, rod-like into script-like. Scanning electron microscopy observation of deep-etched samples indicates that these carbides evolve from octahedral to dendritic and then into welldeveloped dendrites accordingly in a three-dimensional manner. The morphology evolution is discussed from the viewpoint of the preferential growth orientation of fcc crystals and the carbide growth rate during directional solidification.展开更多
The low-cycle fatigue （LCF） properties of DD10 （single-crystal） and DZ53 （columnar-grained） superalloys solidified by liquid-metal cooling （LMC） and high-rate solidification （HRS） processes have been systema...The low-cycle fatigue （LCF） properties of DD10 （single-crystal） and DZ53 （columnar-grained） superalloys solidified by liquid-metal cooling （LMC） and high-rate solidification （HRS） processes have been systematically investi- gated. It was found that the LCF life of DZ53 solidified by LMC was obviously better than that solidified by HRS. In contrast, for DD10, LMC showed no remarkable influences on LCF properties at high temperature and only improved LCF properties at intermediate temperature. Microstructure examination showed that the cracks generally initiated at microp- ores in the subsurface at intermediate temperature. However, the cracks occurred on the surface due to oxidation, or persistent slip bands near script-MC at high temperature. Therefore, the benefits of LMC technique can be attributed to both of the reduced casting defects which significantly affect the LCF properties at intermediate temperature and the improved microstructural homogeneity which was strongly correlated to the LCF properties of alloys at high temperature.展开更多
The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated sample...The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated samples. During long term thermal exposure at 700 C, fine M12 C carbides precipitated preferentially at grain boundaries. These carbides coexisted with the pre-exiting M6 C. The stress rupture life of700 C/1000 h exposed sample under creep testing at 650 C/324 MPa is 93 h. It is much longer than that of the solid solution samples. No noticeable changes could be detected in both the microstructure and stress rupture lives when the samples were exposed for time longer than 1000 h M12 C carbides were found to be beneficial to the creep properties. The cracks initiated at the interface of M6 C carbides and matrix, which led to a lower creep rupture life.展开更多
Hot isostatic pressing （HIP） with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy （Mgl） turbocharger blade to explore the healing process of casting pores...Hot isostatic pressing （HIP） with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy （Mgl） turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron naicroscopy （SEM） observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally locate at the solidification front of γ/γ＇ eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4 h, most of the pores were closed. Based on phase characteristics, these pores were healed by the formation of γ matrix with finer and irregular-shaped γ＇ precipitates. Healing interface can be easily distinguished by SEM. Line scan by using energy dispersive X-ray spectroscopy （EDS） reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ＇-forming elements Al and Ti near the healing interface contributes to the precipitation of γ＇ in the healed region in the succeeding cooling process after HIP.展开更多
基金the Shanghai Synchrotron Radiation Facility (SSRF)the financial support of the project from the National Basic Research Program of China (No.2010CB631201)the National High Technology Research and Development Program of China (No.2012AA03A511 and No.2012AA03A513)
文摘The effect of Mo addition on microstructural characteristics of a nickel-base single crystal superalloy containing 4 wt% Re was investigated. The γ/γ’ partitioning ratios determined by energy dispersive spectrometer attached to a transmission electron microscope showed that the addition of Mo enhanced the partitioning of Re,W and Cr in the g matrix while decreased the concentration of Ta in the matrix. Synchrotron radiation diffraction was adopted to measure the γ/γ’ lattice misfit at room temperature. The results indicated that Mo addition changed the γ/γ’ lattice misfit towards larger negative as well as increased the tetragonal distortion of the γ lattice. Additionally,Mo addition led to microstructural instability and altered the precipitation behavior of topologically close-packed phases during 1100 C exposure. Instead of precipitating directly from the matrix,the μ phase was observed to be converted from the α phase which precipitated preferentially as a metastable intermediate in the alloy with high Mo content.
基金supported by the National Basic Research Program of China (Grant No. 2010CB631201)the National Natural Science Foundation of China (Grant No. 51201164)
文摘Evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417 G and DD33, has been investigated. The morphology of MC carbides evolves from faceted to script-like with increasing cooling rate. Varying the carbon content from 40X10-6 to 320X10-6, the morphology of carbides changes from blocky, rod-like into script-like. Scanning electron microscopy observation of deep-etched samples indicates that these carbides evolve from octahedral to dendritic and then into welldeveloped dendrites accordingly in a three-dimensional manner. The morphology evolution is discussed from the viewpoint of the preferential growth orientation of fcc crystals and the carbide growth rate during directional solidification.
基金financially supported by the National Natural Science Foundation of China under Grant Nos.51631008,51101160 and 2010CB631201
文摘The low-cycle fatigue （LCF） properties of DD10 （single-crystal） and DZ53 （columnar-grained） superalloys solidified by liquid-metal cooling （LMC） and high-rate solidification （HRS） processes have been systematically investi- gated. It was found that the LCF life of DZ53 solidified by LMC was obviously better than that solidified by HRS. In contrast, for DD10, LMC showed no remarkable influences on LCF properties at high temperature and only improved LCF properties at intermediate temperature. Microstructure examination showed that the cracks generally initiated at microp- ores in the subsurface at intermediate temperature. However, the cracks occurred on the surface due to oxidation, or persistent slip bands near script-MC at high temperature. Therefore, the benefits of LMC technique can be attributed to both of the reduced casting defects which significantly affect the LCF properties at intermediate temperature and the improved microstructural homogeneity which was strongly correlated to the LCF properties of alloys at high temperature.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA020404040)the National High Technology Research and Development Program of China (Grant No. 2012AA03A511)
文摘The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated samples. During long term thermal exposure at 700 C, fine M12 C carbides precipitated preferentially at grain boundaries. These carbides coexisted with the pre-exiting M6 C. The stress rupture life of700 C/1000 h exposed sample under creep testing at 650 C/324 MPa is 93 h. It is much longer than that of the solid solution samples. No noticeable changes could be detected in both the microstructure and stress rupture lives when the samples were exposed for time longer than 1000 h M12 C carbides were found to be beneficial to the creep properties. The cracks initiated at the interface of M6 C carbides and matrix, which led to a lower creep rupture life.
基金financial support from the Ministry of Science and Technology of the People’s Republic of China(No.2012CB932201)the National Natural Science Foundation of China(No.51231006)+1 种基金the International Cooperation Program funded by National Natural Science Foundation of China(No.51261130091)the Key Research Program of Chinese Academy of Sciences(No.KGZD-EW-T06)
文摘Hot isostatic pressing （HIP） with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy （Mgl） turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron naicroscopy （SEM） observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally locate at the solidification front of γ/γ＇ eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4 h, most of the pores were closed. Based on phase characteristics, these pores were healed by the formation of γ matrix with finer and irregular-shaped γ＇ precipitates. Healing interface can be easily distinguished by SEM. Line scan by using energy dispersive X-ray spectroscopy （EDS） reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ＇-forming elements Al and Ti near the healing interface contributes to the precipitation of γ＇ in the healed region in the succeeding cooling process after HIP.
