Owing to its outstanding mechanical properties,γ-TiAl is desirable materials for crossgeneration aero-engines.Nearly 70 years of exploration have made it into the initial application.However,the intrinsic brittleness...Owing to its outstanding mechanical properties,γ-TiAl is desirable materials for crossgeneration aero-engines.Nearly 70 years of exploration have made it into the initial application.However,the intrinsic brittleness ofγ-TiAl is still a critical obstacle to its large-scale applications.In this context,researchers have made many attempts to study the machinability ofγ-TiAl.At present,existing relevant reviews have mostly discussed the processing methods ofγ-TiAl.Hence,there is still a lack of a perspective on material properties to analyze the cutting mechanism.Herein,this paper provides the systematic review of such perspectives.Above all,the developmental process,phase transformation,and microstructural evolution ofγ-TiAl are discussed,as well as its deformation mechanism at quasi-static.These topics can provide a materials science foundation for the machining ofγ-TiAl.And then,the review focuses on the cutting mechanism and surface integrity ofγ-TiAl.Moreover,special attention is paid to the microscope deformation mechanism and surface defects evolution ofγ-TiAl during cutting.Finally,the review indicates that the highperformance machining technology ofγ-TiAl faces challenges and proposes potential future research directions.Solving the difficulties during machiningγ-TiAl aero-engine components will accelerate the development of new aero-engines.展开更多
In this work,the thermal conductivity of alkaline earth borate melts was measured using hot-wire method from 1323 to 1623 K,and the thermal diffusivity was extrapolated from the thermal conductivity and heat capacity....In this work,the thermal conductivity of alkaline earth borate melts was measured using hot-wire method from 1323 to 1623 K,and the thermal diffusivity was extrapolated from the thermal conductivity and heat capacity.The compositional dependence of thermophysical properties was interpreted according to the structure in short-range and intermediate-range order.Based on the Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and 11B magic-angle spinning nuclear magnetic resonance(MAS-NMR)spectra,modifier cation with higher field strength prefers the formation of non-bridging oxygens(NBOs)for the charge compensation at high BO_(1.5)/MO ratios.A lower amount of covalent bond and greater isolation of large borate groups lead to a lower thermal conductivity in calcium borate melt compared with strontium and barium borates.But the large size of Ba^(2+)encounters difficulty in fitting around B^[4]-OB^[4]linkages inside the overcrowded large borate groups when BO_(1.5)/BaO=2.5,promoting the formation of NBOs on the edge of borate groups for the charge compensation of modifier cations and leading to the decline in the thermal conductivity.Thermal conductivity plays a major role in regulating the thermal diffusivity at a given temperature since the compositional dependence of volumetric heat capacity is relatively weak compared with that of thermal conductivity.展开更多
In the present work a new thermal conductivity model is developed for two-phase composite materials,which are consisted of a continuous matrix and dispersed 3 D-particles separated from each other by the matrix as a f...In the present work a new thermal conductivity model is developed for two-phase composite materials,which are consisted of a continuous matrix and dispersed 3 D-particles separated from each other by the matrix as a function of grain size and volume ratio of the dispersed particles at different temperatures.The model is applied to reproduce experimental thermal conductivity values of cemented carbide systems WC-Co and WC-Ag.Good agreement was found between measured thermal conductivity data originating from both this work and recent literature and the calculated ones only using semi-empirical parameters for the interfacial thermal resistance(ITR)values at WC/Co,WC/Ag and WC/WC interfaces as a function of temperature.Additionally,the temperature and grain size dependence of the thermal conductivity for WC is established for the first time.The model works well for the case when the matrix(Ag)has a higher thermal conductivity compared to that of the WC particles and also for the case when the matrix(Co)has a lower thermal conductivity compared to that of the WC particles.The new model forms a physically sound basis for further development/materials design of cemented carbides and particlereinforced composite materials.展开更多
基金co-supported by the Science Center for Gas Turbine Project,China(No.P2022-A-IV-001-002)the National Natural Science Foundation of China(Nos.51875473 and 91960203).
文摘Owing to its outstanding mechanical properties,γ-TiAl is desirable materials for crossgeneration aero-engines.Nearly 70 years of exploration have made it into the initial application.However,the intrinsic brittleness ofγ-TiAl is still a critical obstacle to its large-scale applications.In this context,researchers have made many attempts to study the machinability ofγ-TiAl.At present,existing relevant reviews have mostly discussed the processing methods ofγ-TiAl.Hence,there is still a lack of a perspective on material properties to analyze the cutting mechanism.Herein,this paper provides the systematic review of such perspectives.Above all,the developmental process,phase transformation,and microstructural evolution ofγ-TiAl are discussed,as well as its deformation mechanism at quasi-static.These topics can provide a materials science foundation for the machining ofγ-TiAl.And then,the review focuses on the cutting mechanism and surface integrity ofγ-TiAl.Moreover,special attention is paid to the microscope deformation mechanism and surface defects evolution ofγ-TiAl during cutting.Finally,the review indicates that the highperformance machining technology ofγ-TiAl faces challenges and proposes potential future research directions.Solving the difficulties during machiningγ-TiAl aero-engine components will accelerate the development of new aero-engines.
基金financially supported by the Ministry of Science and ICT(MSIT)through the National Research Foundation of Korea(NRF)(Grant No.2018R1A2B2006609)。
文摘In this work,the thermal conductivity of alkaline earth borate melts was measured using hot-wire method from 1323 to 1623 K,and the thermal diffusivity was extrapolated from the thermal conductivity and heat capacity.The compositional dependence of thermophysical properties was interpreted according to the structure in short-range and intermediate-range order.Based on the Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and 11B magic-angle spinning nuclear magnetic resonance(MAS-NMR)spectra,modifier cation with higher field strength prefers the formation of non-bridging oxygens(NBOs)for the charge compensation at high BO_(1.5)/MO ratios.A lower amount of covalent bond and greater isolation of large borate groups lead to a lower thermal conductivity in calcium borate melt compared with strontium and barium borates.But the large size of Ba^(2+)encounters difficulty in fitting around B^[4]-OB^[4]linkages inside the overcrowded large borate groups when BO_(1.5)/BaO=2.5,promoting the formation of NBOs on the edge of borate groups for the charge compensation of modifier cations and leading to the decline in the thermal conductivity.Thermal conductivity plays a major role in regulating the thermal diffusivity at a given temperature since the compositional dependence of volumetric heat capacity is relatively weak compared with that of thermal conductivity.
基金financially supported by the National Natural Science Foundation of China(No.52031017)the National Key R&D Program of China(No.2019YFC1904901)+1 种基金the Special Funds for the Construction of Hunan Innovation Province(No.2019GK2052)supported by nano-Ginop Project GINOP-2.3.2-15-2016-00027 in the framework of the Szechenyi 2020 program supported by the European Union。
文摘In the present work a new thermal conductivity model is developed for two-phase composite materials,which are consisted of a continuous matrix and dispersed 3 D-particles separated from each other by the matrix as a function of grain size and volume ratio of the dispersed particles at different temperatures.The model is applied to reproduce experimental thermal conductivity values of cemented carbide systems WC-Co and WC-Ag.Good agreement was found between measured thermal conductivity data originating from both this work and recent literature and the calculated ones only using semi-empirical parameters for the interfacial thermal resistance(ITR)values at WC/Co,WC/Ag and WC/WC interfaces as a function of temperature.Additionally,the temperature and grain size dependence of the thermal conductivity for WC is established for the first time.The model works well for the case when the matrix(Ag)has a higher thermal conductivity compared to that of the WC particles and also for the case when the matrix(Co)has a lower thermal conductivity compared to that of the WC particles.The new model forms a physically sound basis for further development/materials design of cemented carbides and particlereinforced composite materials.