The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This ...The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.展开更多
An overview of the development and current status of the directional solidification process assisted by liquid metal cooling （LMC） has been presented in this paper. The driving force of the rapid development of the ...An overview of the development and current status of the directional solidification process assisted by liquid metal cooling （LMC） has been presented in this paper. The driving force of the rapid development of the LMC process has been analyzed by considering the demands of （1） newer technologies that can provide higher thermal gradients for alleviated segregation in advanced alloy systems, and （2） better production yield of the large directionally solidified superalloy components. The brief history of the industrialization of the LMC process has been reviewed, followed by the discussion on the LMC parameters including selection of the cooling media, using of the dynamic baffle, and the influence of withdrawal rates and so on. The microstructure and mechanical properties of the traditional superalloys processed by LMC, as well as the new alloys particularly developed for LMC process were then described. Finally, future aspects concerning the LMC process have been summarized.展开更多
Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which...Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which is disadvantageous to extension of creep cracks, Ni-SXs derive the creep strength from intrinsic two-phase microstructure(γ phase and γ’ phase). Main microstructural parameters including volume fraction of γ’ phase and the lattice misfit, and the formation and distribution of precipitated phase are determined by the compositions of alloys. Besides, the creep properties are greatly influenced by these microstructural parameters and precipitated phase. This review has summarized the relationships between different alloying elements and microstructures and indicated their influence on creep properties of Ni-SXs. In addition, with the improvements of experimental methods and characterization technique, some recent discoveries have provided additional evidence to support or challenge the pervious creep theories of superalloys. In view of these new discoveries, this review has provided some perspectives which can be referenced in future compositional design of Ni-SXs.展开更多
Rare metals play an important role in development of superalloys. Over the last two decades, the application of the rare metals in superalloys has achieved progress significantly. They present multi-beneficial effects...Rare metals play an important role in development of superalloys. Over the last two decades, the application of the rare metals in superalloys has achieved progress significantly. They present multi-beneficial effects for strengthening the matrix and the cophase, increasing the lattice misfit, cleaning the grain boundary, improving the carbides and eutectics, refining the grain, stabilizing the oxidation film, etc., so that the elevated temperature rupture life and elevated temperature oxidation resistance are improved significantly, leading to a broad application in the superalloys. In order to meet the higher demand for better superalloys in the future, more intensive research is necessary on the effects of the rare metals on the superalloy, and especially on the combination effect of various rare metals and mutual influence among them. Utilization of the computational materials science and combinatorial high throughput experiment will be of importance in application of rare metals in superalloys.展开更多
基金National Basic Research Program of China (2009CB724403)Program for Changjiang Scholars and Innovative Research Team in University (IRT0837)Program for New Century Excellent Talents in University from Ministry of Education of China (NCET-07-0435)
文摘The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.
文摘An overview of the development and current status of the directional solidification process assisted by liquid metal cooling （LMC） has been presented in this paper. The driving force of the rapid development of the LMC process has been analyzed by considering the demands of （1） newer technologies that can provide higher thermal gradients for alleviated segregation in advanced alloy systems, and （2） better production yield of the large directionally solidified superalloy components. The brief history of the industrialization of the LMC process has been reviewed, followed by the discussion on the LMC parameters including selection of the cooling media, using of the dynamic baffle, and the influence of withdrawal rates and so on. The microstructure and mechanical properties of the traditional superalloys processed by LMC, as well as the new alloys particularly developed for LMC process were then described. Finally, future aspects concerning the LMC process have been summarized.
基金This work was jointly supported by the Fundamental Research Funds for the Central Universities(No.2019QNA4012)the Innovation Fund of the Zhejiang Kechuang New Materials Research Institute(No.ZKN-18-Z01).
文摘Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which is disadvantageous to extension of creep cracks, Ni-SXs derive the creep strength from intrinsic two-phase microstructure(γ phase and γ’ phase). Main microstructural parameters including volume fraction of γ’ phase and the lattice misfit, and the formation and distribution of precipitated phase are determined by the compositions of alloys. Besides, the creep properties are greatly influenced by these microstructural parameters and precipitated phase. This review has summarized the relationships between different alloying elements and microstructures and indicated their influence on creep properties of Ni-SXs. In addition, with the improvements of experimental methods and characterization technique, some recent discoveries have provided additional evidence to support or challenge the pervious creep theories of superalloys. In view of these new discoveries, this review has provided some perspectives which can be referenced in future compositional design of Ni-SXs.
基金The supports from State Basic Research Development Program of China(No.2010BC100404)Shanghai Science and Technology Committee
文摘Rare metals play an important role in development of superalloys. Over the last two decades, the application of the rare metals in superalloys has achieved progress significantly. They present multi-beneficial effects for strengthening the matrix and the cophase, increasing the lattice misfit, cleaning the grain boundary, improving the carbides and eutectics, refining the grain, stabilizing the oxidation film, etc., so that the elevated temperature rupture life and elevated temperature oxidation resistance are improved significantly, leading to a broad application in the superalloys. In order to meet the higher demand for better superalloys in the future, more intensive research is necessary on the effects of the rare metals on the superalloy, and especially on the combination effect of various rare metals and mutual influence among them. Utilization of the computational materials science and combinatorial high throughput experiment will be of importance in application of rare metals in superalloys.
