Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.T...Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.The aim of this study is to enhance the understanding of this action by analyzing the mechanism of droplet oscillation.The pendant droplet oscillation phenomenon hinders the stable transfer of droplets to the molten pool and limits the feasibility of manufacturing complex lattice structures by EB–DED.Hence,another aim of this study is to create an oscillation suppression method.An escalating asymmetric amplitude is the main characteristic of droplet oscillation.The primary oscillationinducing force is the recoil force generated from the EB-acted local surface of the droplet.The physical mechanism of this force is the rapid increase and uneven distribution of the local surface temperature caused by the partial action of the EB.The prerequisites for droplet oscillation include vacuum conditions,high power densities,and bypass wire feeding processes.The proposed EB–dynamic surrounding melting(DSM)method can be applied to conveniently and effectively suppress oscillations,enable the accurate transfer of droplets to the molten pool,and achieve stable processes for preparing the strut elements of lattice structures.Lowering the temperature and improving the uniformity of its distribution are the mechanisms of oscillation suppression in EB–DSM.In this study,the physical basis for interpreting the mechanism by which EBs act on droplets and the technical basis for using EB–DED to prepare complex lattice structure parts are provided.展开更多
Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during...Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.展开更多
Continental shale oil is an important strategic supplement to the sustainable development of petroleum industry in China.Based on the thermal maturity of organic matter,most shale oil in China is mediumhigh or medium-...Continental shale oil is an important strategic supplement to the sustainable development of petroleum industry in China.Based on the thermal maturity of organic matter,most shale oil in China is mediumhigh or medium-low mature oil with relatively high density that is usually stored in thin layers and difficult to extract due to strong fluid flow resistance.Most petroliferous basins in China host shale oil but the abundance and distribution are not favorable for operators looking for a commercial exploitation.This study systematically investigates the recent progress of shale oil exploration and development in China.The result shows that the country is facing the following challenges while trying to explore its shale oil resources:complex geological conditions;a lack of established effective development mode;high development cost;and an absence of substantial breakthroughs in key technologies.Given these,the study suggests from research and policy-making perspectives to strengthen the research on basic theories and key technologies,establish demonstration zones for development of different types of shale oil,pursue breakthroughs in a stepwise approach,innovate the management mode to reduce the development cost,set shale oil as an independent mineral type,and give special policy incentives.展开更多
Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its applic...Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its application is restricted currently due to the limitations of traditional processing methods.Recently,our group first successfully prepared this alloy with an unconventional approach named wire-based in-situ additive manufacturing(AM)technology,and great mechanical performance has been obtained.The unbalanced thermal process of AM easily causes inconsistent or undesired microstructures,as well as mechanical properties.Therefore,in this study,we further carried out post-heat treatment research on the as-printed sample so as to optimize its mechanical performance.Results show that theα2-phase will precipitate from the as-deposited samples(B2/β+O)after solution treatment(ST),while all precipitates were dissolved to the B2/β-matrix when the solution temperature was 1100℃.The aging treatment(AT)promoted a great number of O-phases precipitated and led to an increase in its proportion.With the increase in aging temperature,the tensile strength decreased(995 to 821 MPa)gradually coupling the increase of fracture strain(1.65%to 2.12%),while the aging duration time did not show an obvious ef-fect on its performance.In addition,after proper heat treatment,the high temperature(650℃)tensile strength of the samples was as high as 818 and 792 MPa.This research not only promotes the develop-ment of Ti_(2) AlNb-based alloy fabricated through in-situ AM,but also facilitates its further application in the aerospace field.展开更多
Pebble bed reactors use cycling scheme of spherical fuel elements relying on fuel elements cycling system (FECS). The structure and control logic of FECS are very complex. Each control link has strict requirements on ...Pebble bed reactors use cycling scheme of spherical fuel elements relying on fuel elements cycling system (FECS). The structure and control logic of FECS are very complex. Each control link has strict requirements on time and sequence. This increases the difficulties of description and analysis. In this paper, timed places control Petri nets (TPCPN) is applied for the modeling of FECS. On this basis the simulation of two important processes, namely uploading fuel elements into the core for the first time and emptying the core is finished by simulation software Arena. The results show that as TPCPN is able to describe different kinds of logic relationship and has time properties and control properties, it’s very suitable for the modeling and analysis of FECS.展开更多
For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-f...For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.展开更多
Sand mold 3D printing technology based on the principle of droplet ejection has undergone rapid development in recent years and has elicited increasing attention from engineers and technicians.However,current sand mol...Sand mold 3D printing technology based on the principle of droplet ejection has undergone rapid development in recent years and has elicited increasing attention from engineers and technicians.However,current sand mold 3D printing technology exhibits several problems,such as single-material printing molds,low manufacturing efficiency,and necessary post-process drying and heating for the manufacture of sand molds.This study proposes a novel high-efficiency print forming method and device for multi-material casting molds.The proposed method is specifically related to the integrated forming of two-way coating and printing and the shortflow manufacture of roller compaction and layered heating.These processes can realize the high-efficiency print forming of high-performance sand molds.Experimental results demonstrate that the efficiency of sand mold fabrication can be increased by 200%using the proposed two-way coating and printing method.The integrated forming method for layered heating and roller compaction presented in this study effectively shortens the manufacturing process for 3D-printed sand molds,increases sand mold strength by 63.8%,and reduces resin usage by approximately 30%.The manufacture of multi-material casting molds is demonstrated on typical wheeled cast-iron parts.This research provides theoretical guidance for the engineering application of sand mold 3D printing.展开更多
Using a password manager is known to be more convenient and secure than not using one, on the assmnption that the password manager itself is safe. However recent studies show that most popular password managers have s...Using a password manager is known to be more convenient and secure than not using one, on the assmnption that the password manager itself is safe. However recent studies show that most popular password managers have security vulnerabilities that may be fooled to leak passwords without users' awareness. In this paper, we propose a new password manager, SplitPass, which vertically separates both the storage and access of passwords into two mutually distrusting parties. During login, all the parties will collaborate to send their password shares to the web server, but none of these parties will ever have the complete password, which significantly raises the bar of a successful attack to compromise all of tile parties. To retain transparency to existing applications and web servers, SplitPass seamlessly splits the secure sockets layer (SSL) and transport layer security (TCP) sessions to process on all parties, and makes the joining of two password shares transparent to the web servers. We have implemented SplitPass using an Android phone and a cloud assistant and evaluated it using 100 apps from top free apps in the Android official market. The evaluation shows that SplitPass securely protects users' passwords, while incurring little performance overhead and power consumption.展开更多
Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different pr...Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different processing histories.Here,the microstructures and wear behavior of different zones(substrate,HAZ,and deposit)are investigated for the IC10 directionally solidified superalloy repaired by the directed energy deposition process.It is found that the microstructure of the deposited layers is strongly textured with a<001>-fiber texture in the building direction,and the texture intensity is continuously increased along the building direction.Two kinds ofγ’phase(primary and secondaryγ’phase)can be found in the heat-affected zone(HAZ),and the average size of primaryγ’phase is smaller than that in the substrate due to liquation.In the deposit layers,the size ofγ’phase is much smaller than those in the substrate and the primaryγ’phase of HAZ;both size and the fraction of theγ’phase decreases with the increase of building height.The wear rate of the substrate is the smallest,indicating the best wear resistance;while the wear rate of HAZ is the largest,indicating the worst wear resistance in the repaired sample.The wear rates in the deposit layers increase from the bottom to the top zones,showing a decreasing wear resistance.Abrasive wear is found to be the dominant wear mechanism of the repaired alloy,and the resistance to which is closely related to the fraction ofγ’phase in the microstructure.The understanding of the influence of microstructure on wear resistance allows for a more informed application of inhomogeneous superalloy components repaired by directed energy deposition in industry.展开更多
Unikernel,specializing a minimalistic libOS with an application,is an attractive design for cloud computing.However,the Achilles’heel of unikernel is the lack of multi-process support,which makes it less flexible and...Unikernel,specializing a minimalistic libOS with an application,is an attractive design for cloud computing.However,the Achilles’heel of unikernel is the lack of multi-process support,which makes it less flexible and applicable.Many applications rely on the process abstraction to isolate different components.For example,Apache with the multi-processing module isolates a request handler in a process to guarantee security.Prior art tackles the problem by simulating multi-process with multiple unikernels,which is incompatible with existing cloud providers and also introduces high overhead.This paper proposes Iso-UniK,a new unikernel design enabling multi-task applications with the support of both functionality and isolation.Iso-UniK leverages a recent hardware feature,named Intel Memory Protection Key(Intel MPK),to provide lightweight and efficient isolation for multi-process in unikernel.Our design has three benefits compared with previous approaches.First,Iso-UniK does not need hypervisor support and is thus compatible with existing cloud computing platforms;second,Iso-UniK promises fast system calls with only 45 cycles;last,a process can be isolated with a flexible configuration.We have implemented a prototype based on OSv,a unikernel system supporting unmodified applications.Iso-UniK can achieve fast fork operation with only 66μs for multi-process applications.Our evaluation shows that the isolation and multi-process support in Iso-UniK will not damage the applications’performance.展开更多
Unikernel,specializing a minimalistic libOS with an application,is an attractive design for cloud computing.However,the Achilles’heel of unikernel is the lack of multi-process support,which makes it less flexible and...Unikernel,specializing a minimalistic libOS with an application,is an attractive design for cloud computing.However,the Achilles’heel of unikernel is the lack of multi-process support,which makes it less flexible and applicable.Many applications rely on the process abstraction to isolate different components.For example,Apache with the multi-processing module isolates a request handler in a process to guarantee security.Prior art tackles the problem by simulating multi-process with multiple unikernels,which is incompatible with existing cloud providers and also introduces high overhead.This paper proposes Iso-UniK,a new unikernel design enabling multi-task applications with the support of both functionality and isolation.Iso-UniK leverages a recent hardware feature,named Intel Memory Protection Key(Intel MPK),to provide lightweight and efficient isolation for multi-process in unikernel.Our design has three benefits compared with previous approaches.First,Iso-UniK does not need hypervisor support and is thus compatible with existing cloud computing platforms;second,Iso-UniK promises fast system calls with only 45 cycles;last,a process can be isolated with a flexible configuration.We have implemented a prototype based on OSv,a unikernel system supporting unmodified applications.Iso-UniK can achieve fast fork operation with only 66μs for multi-process applications.Our evaluation shows that the isolation and multi-process support in Iso-UniK will not damage the applications’performance.展开更多
基金the financial support for this work from the National Natural Science Foundation of China(No.52205334)the Natural Science Foundation of Hunan Province,China(No.2022JJ40495)+2 种基金the Changsha Key Research and Development Project,China(No.kh2201275)the Changsha Municipal Natural Science Foundation,China(No.kq2202196)the Tribology Science Fund of State Key Laboratory of Tribology in Advanced Equipment,China(No.SKLTKF21B08)。
基金supported by the National Natural Science Foundation of China(52375349)the Beijing Municipal Natural Science Foundation(3222008).
文摘Electron beam–directed energy deposition(EB–DED)has emerged as a promising wire-based metal additive manufacturing technique.However,the effects of EBs on pendant droplets at wire tips have not yet been determined.The aim of this study is to enhance the understanding of this action by analyzing the mechanism of droplet oscillation.The pendant droplet oscillation phenomenon hinders the stable transfer of droplets to the molten pool and limits the feasibility of manufacturing complex lattice structures by EB–DED.Hence,another aim of this study is to create an oscillation suppression method.An escalating asymmetric amplitude is the main characteristic of droplet oscillation.The primary oscillationinducing force is the recoil force generated from the EB-acted local surface of the droplet.The physical mechanism of this force is the rapid increase and uneven distribution of the local surface temperature caused by the partial action of the EB.The prerequisites for droplet oscillation include vacuum conditions,high power densities,and bypass wire feeding processes.The proposed EB–dynamic surrounding melting(DSM)method can be applied to conveniently and effectively suppress oscillations,enable the accurate transfer of droplets to the molten pool,and achieve stable processes for preparing the strut elements of lattice structures.Lowering the temperature and improving the uniformity of its distribution are the mechanisms of oscillation suppression in EB–DSM.In this study,the physical basis for interpreting the mechanism by which EBs act on droplets and the technical basis for using EB–DED to prepare complex lattice structure parts are provided.
基金financially supported by the National Excellent Young Scientists Fund(NO.51525503)
文摘Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.
文摘Continental shale oil is an important strategic supplement to the sustainable development of petroleum industry in China.Based on the thermal maturity of organic matter,most shale oil in China is mediumhigh or medium-low mature oil with relatively high density that is usually stored in thin layers and difficult to extract due to strong fluid flow resistance.Most petroliferous basins in China host shale oil but the abundance and distribution are not favorable for operators looking for a commercial exploitation.This study systematically investigates the recent progress of shale oil exploration and development in China.The result shows that the country is facing the following challenges while trying to explore its shale oil resources:complex geological conditions;a lack of established effective development mode;high development cost;and an absence of substantial breakthroughs in key technologies.Given these,the study suggests from research and policy-making perspectives to strengthen the research on basic theories and key technologies,establish demonstration zones for development of different types of shale oil,pursue breakthroughs in a stepwise approach,innovate the management mode to reduce the development cost,set shale oil as an independent mineral type,and give special policy incentives.
基金financially supported by the National Natural Sci-ence Foundation of China(No.51875309)the Beijing Municipal Natural Science Foundation(CN)(No.3222008).
文摘Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its application is restricted currently due to the limitations of traditional processing methods.Recently,our group first successfully prepared this alloy with an unconventional approach named wire-based in-situ additive manufacturing(AM)technology,and great mechanical performance has been obtained.The unbalanced thermal process of AM easily causes inconsistent or undesired microstructures,as well as mechanical properties.Therefore,in this study,we further carried out post-heat treatment research on the as-printed sample so as to optimize its mechanical performance.Results show that theα2-phase will precipitate from the as-deposited samples(B2/β+O)after solution treatment(ST),while all precipitates were dissolved to the B2/β-matrix when the solution temperature was 1100℃.The aging treatment(AT)promoted a great number of O-phases precipitated and led to an increase in its proportion.With the increase in aging temperature,the tensile strength decreased(995 to 821 MPa)gradually coupling the increase of fracture strain(1.65%to 2.12%),while the aging duration time did not show an obvious ef-fect on its performance.In addition,after proper heat treatment,the high temperature(650℃)tensile strength of the samples was as high as 818 and 792 MPa.This research not only promotes the develop-ment of Ti_(2) AlNb-based alloy fabricated through in-situ AM,but also facilitates its further application in the aerospace field.
文摘Pebble bed reactors use cycling scheme of spherical fuel elements relying on fuel elements cycling system (FECS). The structure and control logic of FECS are very complex. Each control link has strict requirements on time and sequence. This increases the difficulties of description and analysis. In this paper, timed places control Petri nets (TPCPN) is applied for the modeling of FECS. On this basis the simulation of two important processes, namely uploading fuel elements into the core for the first time and emptying the core is finished by simulation software Arena. The results show that as TPCPN is able to describe different kinds of logic relationship and has time properties and control properties, it’s very suitable for the modeling and analysis of FECS.
基金This work was financially supported by the Tribology Science Fund of the State Key Laboratory of Tribology(No.SKLT2022C20)the National Natural Science Foundation of China(Nos.51875309 and 51905310)the Natural Science Foundation of Shandong Province(No.ZR2020YQ39).
文摘For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.
基金This research was supported by the National Excellent Young Scientists Fund(Grant No.51525503).
文摘Sand mold 3D printing technology based on the principle of droplet ejection has undergone rapid development in recent years and has elicited increasing attention from engineers and technicians.However,current sand mold 3D printing technology exhibits several problems,such as single-material printing molds,low manufacturing efficiency,and necessary post-process drying and heating for the manufacture of sand molds.This study proposes a novel high-efficiency print forming method and device for multi-material casting molds.The proposed method is specifically related to the integrated forming of two-way coating and printing and the shortflow manufacture of roller compaction and layered heating.These processes can realize the high-efficiency print forming of high-performance sand molds.Experimental results demonstrate that the efficiency of sand mold fabrication can be increased by 200%using the proposed two-way coating and printing method.The integrated forming method for layered heating and roller compaction presented in this study effectively shortens the manufacturing process for 3D-printed sand molds,increases sand mold strength by 63.8%,and reduces resin usage by approximately 30%.The manufacture of multi-material casting molds is demonstrated on typical wheeled cast-iron parts.This research provides theoretical guidance for the engineering application of sand mold 3D printing.
基金This work was supported by the National Key Research and Development Program of China under Grant No. 2016YFB1000104, the National Natural Science Foundation of China under Grant Nos. 61572314 and 61525204, and the Young Scientists Fund of the National Natural Science Foundation of China under Grant No. 61303011.
文摘Using a password manager is known to be more convenient and secure than not using one, on the assmnption that the password manager itself is safe. However recent studies show that most popular password managers have security vulnerabilities that may be fooled to leak passwords without users' awareness. In this paper, we propose a new password manager, SplitPass, which vertically separates both the storage and access of passwords into two mutually distrusting parties. During login, all the parties will collaborate to send their password shares to the web server, but none of these parties will ever have the complete password, which significantly raises the bar of a successful attack to compromise all of tile parties. To retain transparency to existing applications and web servers, SplitPass seamlessly splits the secure sockets layer (SSL) and transport layer security (TCP) sessions to process on all parties, and makes the joining of two password shares transparent to the web servers. We have implemented SplitPass using an Android phone and a cloud assistant and evaluated it using 100 apps from top free apps in the Android official market. The evaluation shows that SplitPass securely protects users' passwords, while incurring little performance overhead and power consumption.
基金financial support to this work from the Tribology Science Fund of the State Key Laboratory of Tribology(SKLT2020C09)National Natural Science Foundation of China(No.51675303)National Key Research and Development Program of China(2017YFB1103300)。
文摘Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different processing histories.Here,the microstructures and wear behavior of different zones(substrate,HAZ,and deposit)are investigated for the IC10 directionally solidified superalloy repaired by the directed energy deposition process.It is found that the microstructure of the deposited layers is strongly textured with a<001>-fiber texture in the building direction,and the texture intensity is continuously increased along the building direction.Two kinds ofγ’phase(primary and secondaryγ’phase)can be found in the heat-affected zone(HAZ),and the average size of primaryγ’phase is smaller than that in the substrate due to liquation.In the deposit layers,the size ofγ’phase is much smaller than those in the substrate and the primaryγ’phase of HAZ;both size and the fraction of theγ’phase decreases with the increase of building height.The wear rate of the substrate is the smallest,indicating the best wear resistance;while the wear rate of HAZ is the largest,indicating the worst wear resistance in the repaired sample.The wear rates in the deposit layers increase from the bottom to the top zones,showing a decreasing wear resistance.Abrasive wear is found to be the dominant wear mechanism of the repaired alloy,and the resistance to which is closely related to the fraction ofγ’phase in the microstructure.The understanding of the influence of microstructure on wear resistance allows for a more informed application of inhomogeneous superalloy components repaired by directed energy deposition in industry.
基金Sponsored by Program of Shanghai Academic/Technology Research Leader(No.19XD1401700).
文摘Unikernel,specializing a minimalistic libOS with an application,is an attractive design for cloud computing.However,the Achilles’heel of unikernel is the lack of multi-process support,which makes it less flexible and applicable.Many applications rely on the process abstraction to isolate different components.For example,Apache with the multi-processing module isolates a request handler in a process to guarantee security.Prior art tackles the problem by simulating multi-process with multiple unikernels,which is incompatible with existing cloud providers and also introduces high overhead.This paper proposes Iso-UniK,a new unikernel design enabling multi-task applications with the support of both functionality and isolation.Iso-UniK leverages a recent hardware feature,named Intel Memory Protection Key(Intel MPK),to provide lightweight and efficient isolation for multi-process in unikernel.Our design has three benefits compared with previous approaches.First,Iso-UniK does not need hypervisor support and is thus compatible with existing cloud computing platforms;second,Iso-UniK promises fast system calls with only 45 cycles;last,a process can be isolated with a flexible configuration.We have implemented a prototype based on OSv,a unikernel system supporting unmodified applications.Iso-UniK can achieve fast fork operation with only 66μs for multi-process applications.Our evaluation shows that the isolation and multi-process support in Iso-UniK will not damage the applications’performance.
基金Sponsored by Program of Shanghai Academic/Technology Research Leader(No.19XD1401700).
文摘Unikernel,specializing a minimalistic libOS with an application,is an attractive design for cloud computing.However,the Achilles’heel of unikernel is the lack of multi-process support,which makes it less flexible and applicable.Many applications rely on the process abstraction to isolate different components.For example,Apache with the multi-processing module isolates a request handler in a process to guarantee security.Prior art tackles the problem by simulating multi-process with multiple unikernels,which is incompatible with existing cloud providers and also introduces high overhead.This paper proposes Iso-UniK,a new unikernel design enabling multi-task applications with the support of both functionality and isolation.Iso-UniK leverages a recent hardware feature,named Intel Memory Protection Key(Intel MPK),to provide lightweight and efficient isolation for multi-process in unikernel.Our design has three benefits compared with previous approaches.First,Iso-UniK does not need hypervisor support and is thus compatible with existing cloud computing platforms;second,Iso-UniK promises fast system calls with only 45 cycles;last,a process can be isolated with a flexible configuration.We have implemented a prototype based on OSv,a unikernel system supporting unmodified applications.Iso-UniK can achieve fast fork operation with only 66μs for multi-process applications.Our evaluation shows that the isolation and multi-process support in Iso-UniK will not damage the applications’performance.