Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It ...Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It plays a pivotal role in fabricating intricate,high-quality components.After its inception in the early 1900s,various CGC processes have emerged,such as low-pressure,counter-pressure,vac-uum suction,and adjusted pressure casting,which are explored in this discourse with an eye toward further advancements.Despite CGC’s superiority over traditional gravity casting and other manufacturing methodologies,specific issues and constraints persist within CGC.This paper endeavors to provide a com-prehensive overview of the historical progression of CGC,its recent developments,and the associated re-search aspects,encompassing topics like filling processes,solidification,microstructural transformations,and the resultant mechanical properties of the fabricated products.Additionally,this paper offers insights into the future challenges and opportunities of CGC.展开更多
A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or exc...A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or excessive infiltrating can hardly be found in the foam samples prepared by counter-gravity infiltration casting. The foam materials exhibit excellent mechanical properties. The void content strongly affects the mechanical properties of aluminum foams. The yield stress and plateau stress significantly increase with the decrease of void content. Raising pre-heating temperature and increasing packing pressure are effective to lower the void content in aluminum foams.展开更多
To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different pro...To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.展开更多
The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the al...The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. 13 grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties＇ comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing （HIP）. The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.展开更多
Shallow crustal faults are passive features mobilized by the dissipation of the potential energy and the shear stress accumulated in the brittle volume surrounding them.However,the stored energy in the volume differs ...Shallow crustal faults are passive features mobilized by the dissipation of the potential energy and the shear stress accumulated in the brittle volume surrounding them.However,the stored energy in the volume differs from the tectonic setting,i.e.,it is mainly gravitational in extensional tectonic settings,whereas it is elastic in strike-slip and contractional tectonic environments.In extensional settings,below about 1 km,the horizontal tensile stress is overwhelmed by the confining pressure of the lithostatic load,and it becomes positive,i.e.compressive.Therefore,there is no horizontal tension in extensional tectonic settings and the pro-gravity motion of the crustal volume is provided by the lithostatic load,which is the vertical maximum principal stress.The elastic energy is rather accumulated by the maximum horizontal principal stresses,i.e.,iso-gravity in transcurrent settings and counter-gravity in contractional tectonic settings.The different relation with the gravitational force in the different tectonic settings generates several relevant differences in the three main tectonic environments.The extensional tectonic settings,both in continental and oceanic rift zones generate normal fault-related earthquakes,i.e.,pro-gravity movements,or graviquakes.They differ from the other tectonic setting because are marked by(i)lower energy and lower differential stress to activate faults with respect to strike-slip and contractional tectonics;(ii)lower maximum earthquake magnitude;(iii)a larger number of low magnitude earthquakes in extensional settings because the crust moves downward as soon as it can move,whereas contractional settings require larger accumulation of energy to move counter-gravity;(iv)consequently,the b-value of the Gutenberg-Richter is higher than 1 and the aftershocks are more numerous and last longer in extensional settings;(v)the downward motion of the hangingwall determines more diffuse cataclastic deformation with respect to the other tectonic settings because the lithostatic load works everywhere,whereas in the other tectonic settings is concentrated where the elastic energy accumulates;(vi)in extensional settings the volume dimension is determined by thickness of the brittle layer,and its length is in average three times the seismogenic thickness;in strike-slip and contractional settings dominates the elastic energy(elastoquakes),and the mobilized volume may be ten to thirty times longer in a single seismic sequence,being its size proportional both to the brittle thickness and the relative speed of plates.These differences characterize the seismic cycle of graviquakes with respect to the elastoquakes.The bigger the volume,the wider the seismogenic fault in all tectonic settings.The interplay between the horizontal tectonic forces and the lithostatic load,which is ubiquitous,varies in the three main tectonic settings,generating different seismotectonic styles and an increase of magnitude as the effect of the vertical gravitational force becomes a minority relative to the elastic storage and coseismic rebound.展开更多
Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental resu...Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size;along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process.展开更多
基金supported by the National Sci-ence and Technology Major Project of China(No.J2019-VI-0004-0117)the National Natural Science Foundation of China(Nos.52071205 and 51821001)+3 种基金the Aeronautical Science Fund of China(No.2023Z053057003)the Science and Technology Commission of Shanghai Municipality,China(No.23ZR1428800)the Shanghai Industrial Collaborative Innovation Project(No.XTCX-KJ-2022-41)The authors are thankful to Prof.Diran Apelian(University of Cal-ifornia,Irvine),Prof.Enrique Lavernia(Texas A&M University),and Prof.Alan A.Luo(Ohio State University)for their constructive and helpful comments during manuscript preparation.
文摘Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It plays a pivotal role in fabricating intricate,high-quality components.After its inception in the early 1900s,various CGC processes have emerged,such as low-pressure,counter-pressure,vac-uum suction,and adjusted pressure casting,which are explored in this discourse with an eye toward further advancements.Despite CGC’s superiority over traditional gravity casting and other manufacturing methodologies,specific issues and constraints persist within CGC.This paper endeavors to provide a com-prehensive overview of the historical progression of CGC,its recent developments,and the associated re-search aspects,encompassing topics like filling processes,solidification,microstructural transformations,and the resultant mechanical properties of the fabricated products.Additionally,this paper offers insights into the future challenges and opportunities of CGC.
基金Project (51074185) supported by the National Natural Science Foundation of ChinaProjects (CX2009B037, CX2010B120) supported by Doctor Innovative Program of Hunan Province, China
文摘A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or excessive infiltrating can hardly be found in the foam samples prepared by counter-gravity infiltration casting. The foam materials exhibit excellent mechanical properties. The void content strongly affects the mechanical properties of aluminum foams. The yield stress and plateau stress significantly increase with the decrease of void content. Raising pre-heating temperature and increasing packing pressure are effective to lower the void content in aluminum foams.
基金financially supported by the National Natural Science Foundation of China(No.51375391)the Xi’an Municipal Science and Technology Bureau in China(No.CX12180(5))
文摘To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.3102014JCQ01026)the Program of Introducing Talents of Discipline to Universities(Grant No.B08040)
文摘The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. 13 grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties＇ comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing （HIP）. The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.
文摘Shallow crustal faults are passive features mobilized by the dissipation of the potential energy and the shear stress accumulated in the brittle volume surrounding them.However,the stored energy in the volume differs from the tectonic setting,i.e.,it is mainly gravitational in extensional tectonic settings,whereas it is elastic in strike-slip and contractional tectonic environments.In extensional settings,below about 1 km,the horizontal tensile stress is overwhelmed by the confining pressure of the lithostatic load,and it becomes positive,i.e.compressive.Therefore,there is no horizontal tension in extensional tectonic settings and the pro-gravity motion of the crustal volume is provided by the lithostatic load,which is the vertical maximum principal stress.The elastic energy is rather accumulated by the maximum horizontal principal stresses,i.e.,iso-gravity in transcurrent settings and counter-gravity in contractional tectonic settings.The different relation with the gravitational force in the different tectonic settings generates several relevant differences in the three main tectonic environments.The extensional tectonic settings,both in continental and oceanic rift zones generate normal fault-related earthquakes,i.e.,pro-gravity movements,or graviquakes.They differ from the other tectonic setting because are marked by(i)lower energy and lower differential stress to activate faults with respect to strike-slip and contractional tectonics;(ii)lower maximum earthquake magnitude;(iii)a larger number of low magnitude earthquakes in extensional settings because the crust moves downward as soon as it can move,whereas contractional settings require larger accumulation of energy to move counter-gravity;(iv)consequently,the b-value of the Gutenberg-Richter is higher than 1 and the aftershocks are more numerous and last longer in extensional settings;(v)the downward motion of the hangingwall determines more diffuse cataclastic deformation with respect to the other tectonic settings because the lithostatic load works everywhere,whereas in the other tectonic settings is concentrated where the elastic energy accumulates;(vi)in extensional settings the volume dimension is determined by thickness of the brittle layer,and its length is in average three times the seismogenic thickness;in strike-slip and contractional settings dominates the elastic energy(elastoquakes),and the mobilized volume may be ten to thirty times longer in a single seismic sequence,being its size proportional both to the brittle thickness and the relative speed of plates.These differences characterize the seismic cycle of graviquakes with respect to the elastoquakes.The bigger the volume,the wider the seismogenic fault in all tectonic settings.The interplay between the horizontal tectonic forces and the lithostatic load,which is ubiquitous,varies in the three main tectonic settings,generating different seismotectonic styles and an increase of magnitude as the effect of the vertical gravitational force becomes a minority relative to the elastic storage and coseismic rebound.
基金Project(51304254) supported by the National Natural Science Foundation of ChinaProject(2013GK4064) supported by the Strategic Emerging Industry Program of the Ministry of Science and Technology of Hunan Province,China
文摘Contrastive research was carried out to study the thermal properties of open-celled aluminum foams prepared by counter-gravity infiltration casting system and the traditional process respectively.The experimental results show that the thermal conductivity coefficients of aluminum foams prepared by two different infiltration methods have similar increasing trend with the increase of particle size;along with the reducing porosity,the thermal conductivity coefficients will be enhanced oppositely.However,with the same particle size,the open-celled aluminum foam prepared by the former method has a higher thermal conductivity coefficient obviously.It is largely because that the sample prepared by counter-gravity infiltration casting has a lower void content and better dense crystallization of metal-matrix after the constant pressure process.
