Graphene has excellent theoretical properties and a wide range of applications in metal-based composites. However, because of defects on the graphene surface, the actual performance of the material is far below theore...Graphene has excellent theoretical properties and a wide range of applications in metal-based composites. However, because of defects on the graphene surface, the actual performance of the material is far below theoretical expectations. In addition, graphene containing defects could easily react with a matrix alloy, such as Al, to generate brittle and hydrolyzed phases that could further reduce the performance of the resulting composite. Therefore, defect repair is an important area of graphene research. The repair methods reported in the present paper include chemical vapor deposition, doping, liquid-phase repair, external energy graphitization, and alloying. Detailed analyses and comparisons of these methods are carried out, and the characterization methods of graphene are introduced. The mechanism, research value, and future outlook of graphene repair are also discussed at length. Graphene defect repair mainly relies on the spontaneous movement of C atoms or heteroatoms to the pore defects under the condition of applied energy. The repair degree and mechanism of graphene repair are also different according to different preparations. The current research on graphene defect repair is still in its infancy, and it is believed that the problem of defect evolution will be explained in more depth in the future.展开更多
The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for ...The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for up to 200 cycles was explored.Specifically,the thermal conductivity(λ)of the composites was measured and scanning electron microscopy of specific areas in the same samples was carried out to achieve quasi-in situ observations.The interface between the(100)plane of diamond and the Al matrix was well bonded with a zigzag morphology and abundant needle-like Al4C3 phases.By contrast,the interface between the(111)plane of diamond and the Al matrix showed weak bonding and debonded during thermal cycling.The debonding length increased rapidly over the first 100 thermal cycles and then increased slowly in the following 100 cycles.Theλof the diamond/Al composites decreased abruptly over the initial 20 cycles,increased afterward,and then decreased monotonously once more with increasing number of thermal cycles.Decreases in theλof the Al matrix and the corresponding stress concentration at the diamond/Al interface caused by thermal mismatch,rather than interfacial debonding,may be the main factors influencing the decrease inλof the diamond/Al composites,especially in the initial stages of thermal cycling.展开更多
Solidification or crystallization of phase change emulsion in the form of fine emulsion drops in a direct contact coolant at temperatures below their freezing point was studied. This work is mainly focused on the size...Solidification or crystallization of phase change emulsion in the form of fine emulsion drops in a direct contact coolant at temperatures below their freezing point was studied. This work is mainly focused on the size and shape of the generated particles from phase change emulsified fats. Size of the particles is the major or key factor being considered during their formation, however, other factors that govern the particle size and shape were also observed. The operating parameters of the process were optimized in order to obtain particles of smaller size ranges in the window of current operating conditions. The crystallization of complex emulsion matrices is very difficult to control in the bulk at desired requirement. Hence, the emulsion drop to particle formation has advantage in comparison with the bulk solidification or crystallization. The main objective of this work is to achieve spherical emulsion particles in a direct contact cooling system. Parameters like: stability, characterization, viscosity, and the effect of different energy inputs were examined. Moreover, the effects of the capillary size, interfacial tension, temperature of the emulsion on the particle size were also monitored.展开更多
Graphene/aluminum(Gr/Al)composites have attracted the attention of researchers all over the world due to their excellent properties.However,graphene agglomerates easily because of the van der Waals force between graph...Graphene/aluminum(Gr/Al)composites have attracted the attention of researchers all over the world due to their excellent properties.However,graphene agglomerates easily because of the van der Waals force between graphite sheets,thereby affecting the performance of the composites.Decreasing the agglomeration of graphene and dispersing it uniformly in the Al matrix is a key challenge.In the preparation process,predispersion treatment and deformation treatment can play important roles in graphene dispersion.Researchers have conducted a series of research and literature reviews of the graphene predispersion and consolidation of composites.However,they paid less attention to post-deformation processing.This review summarizes different deformation treatments involved in the preparation process of Gr/Al composites and the evolution of the microstructure during the process.Research on deformation parameters is expected to further improve the properties of Gr/Al composites and would provide a deep understanding of the strengthening effect of graphene.展开更多
Microstructure and mechanical behavior of high volume content SiCp/7xxxAl composites have not been explored yet. Therefore, in the present work, 45 vol.% SiCp/7075Al composite has been prepared by pres- sure infiltrat...Microstructure and mechanical behavior of high volume content SiCp/7xxxAl composites have not been explored yet. Therefore, in the present work, 45 vol.% SiCp/7075Al composite has been prepared by pres- sure infiltration method. High density dislocations were found around SiC/Al interface in SiCp/7075Al composite after water-quenching and aging treatment. Fine dispersed nano-η' phases were observed after the aging treatment. Adverse to other SiCp/Al composites prepared by the pressure infiltration method, an interface layer was observed between SiC particles and AI matrix. Furthermore, high-resolution trans- mission electron microscopy (HRTEM) observation indicated that this interface layer was coherent/semi- coherent with that of the SiC particles. 45 vol.% SiCp/7075Al composite demonstrated high tensile strength (630 MPa) and micro-ductility. Compared to aged SiCp/2024Al composite, the aged SiCp/7075Al com- posite showed an increase of about 200% in the tensile strain and 90% in the tensile strength, respectively. It is speculated that nano-η' phases in the Al matrix significantly contributed to the strengthening effect while the interface layer between SiC and AI matrix might be beneficial to the strength and plasticity of SiCp/7075Al composite.展开更多
In the present work, the wire electrical discharge machining(WEDM) process of the 65 vol% SiCp/2024 Al composite prepared by pressure infiltration methods has been investigated. The microstructure of the machined co...In the present work, the wire electrical discharge machining(WEDM) process of the 65 vol% SiCp/2024 Al composite prepared by pressure infiltration methods has been investigated. The microstructure of the machined composite was characterized by scanning electron microscope, the average surface roughness(Ra), X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy(TEM) techniques. Three zones from the surface to the interior(melting zone, heat affected zone and un-affected zone) were found in the machined composites, while the face of SiC particles on the surface toward the outside was ‘‘cut'' to be flat. Increase in Al and Si but decrease in C and O were observed in the core areas of the removed particles. Si phase, which was generated due to the decomposition of SiC, was detected after the WEDM process. The irregular and spherical particles were further observed by TEM. Based on the microstructure observation, it is suggested that the machining mechanism of 65 vol% SiCp/2024 Al composite was the combination of the melting of Al matrix and the decomposition of SiC particles.展开更多
基金Project(20080430895)supported by China Postdoctoral Science FoundationProject(2008RFQXG045)supported by Special Fund of Technological Innovation of Harbin,ChinaProject(HITQNJS.2009.021)supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology,China
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51871073,51871072,51771063,61604086,and U1637201)China Postdoctoral Science Foundation(Nos.2016M590280 and 2017T100240)+1 种基金Heilongjiang Postdoctoral Foundation(No.LBH-Z16075)the Fundamental Research Funds for the Central Universities(Nos.HIT.NSRIF.20161 and HIT.MKSTISP.201615).
文摘Graphene has excellent theoretical properties and a wide range of applications in metal-based composites. However, because of defects on the graphene surface, the actual performance of the material is far below theoretical expectations. In addition, graphene containing defects could easily react with a matrix alloy, such as Al, to generate brittle and hydrolyzed phases that could further reduce the performance of the resulting composite. Therefore, defect repair is an important area of graphene research. The repair methods reported in the present paper include chemical vapor deposition, doping, liquid-phase repair, external energy graphitization, and alloying. Detailed analyses and comparisons of these methods are carried out, and the characterization methods of graphene are introduced. The mechanism, research value, and future outlook of graphene repair are also discussed at length. Graphene defect repair mainly relies on the spontaneous movement of C atoms or heteroatoms to the pore defects under the condition of applied energy. The repair degree and mechanism of graphene repair are also different according to different preparations. The current research on graphene defect repair is still in its infancy, and it is believed that the problem of defect evolution will be explained in more depth in the future.
基金financially supported by the National Natural Science Foundation of China(Nos.1871072,51871073,52171136,51771063,61604086,and U1637201)the China Postdoctoral Science Foundation(Nos.2016M590280 and 2017T100240)+1 种基金the Heilongjiang Postdoctoral Foundation(Nos.LBH-Z16075 and LBH-TZ2014)the Fundamental Research Funds for the Central Universities,China(Nos.HIT.NSRIF.20161 and HIT.MKSTISP.201615).
文摘The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for up to 200 cycles was explored.Specifically,the thermal conductivity(λ)of the composites was measured and scanning electron microscopy of specific areas in the same samples was carried out to achieve quasi-in situ observations.The interface between the(100)plane of diamond and the Al matrix was well bonded with a zigzag morphology and abundant needle-like Al4C3 phases.By contrast,the interface between the(111)plane of diamond and the Al matrix showed weak bonding and debonded during thermal cycling.The debonding length increased rapidly over the first 100 thermal cycles and then increased slowly in the following 100 cycles.Theλof the diamond/Al composites decreased abruptly over the initial 20 cycles,increased afterward,and then decreased monotonously once more with increasing number of thermal cycles.Decreases in theλof the Al matrix and the corresponding stress concentration at the diamond/Al interface caused by thermal mismatch,rather than interfacial debonding,may be the main factors influencing the decrease inλof the diamond/Al composites,especially in the initial stages of thermal cycling.
基金the Department of Chemical Engineering,COMSATS Institute of Information Technology,Lahore,Pakistan,for relieving them from their duties,and Higher Education Commission,Pakistan(A/07/96851)for providing the financial assistance to carry out Ph D study in cooperation with the German Academic Exchange Service(DAAD)
文摘Solidification or crystallization of phase change emulsion in the form of fine emulsion drops in a direct contact coolant at temperatures below their freezing point was studied. This work is mainly focused on the size and shape of the generated particles from phase change emulsified fats. Size of the particles is the major or key factor being considered during their formation, however, other factors that govern the particle size and shape were also observed. The operating parameters of the process were optimized in order to obtain particles of smaller size ranges in the window of current operating conditions. The crystallization of complex emulsion matrices is very difficult to control in the bulk at desired requirement. Hence, the emulsion drop to particle formation has advantage in comparison with the bulk solidification or crystallization. The main objective of this work is to achieve spherical emulsion particles in a direct contact cooling system. Parameters like: stability, characterization, viscosity, and the effect of different energy inputs were examined. Moreover, the effects of the capillary size, interfacial tension, temperature of the emulsion on the particle size were also monitored.
基金financially supported by the National Natural Science Foundation of China(Nos.51871073,51871072,51771063,61604086,and U1637201)the China Postdoctoral Science Foundation(Nos.2016M590280 and 2017T100240)+1 种基金the Heilongjiang Postdoctoral Foundation(No.LBH-Z16075)the Fundamental Research Funds for the Central Universities(Nos.HIT.NSRIF.20161 and HIT.MKSTISP.201615)。
文摘Graphene/aluminum(Gr/Al)composites have attracted the attention of researchers all over the world due to their excellent properties.However,graphene agglomerates easily because of the van der Waals force between graphite sheets,thereby affecting the performance of the composites.Decreasing the agglomeration of graphene and dispersing it uniformly in the Al matrix is a key challenge.In the preparation process,predispersion treatment and deformation treatment can play important roles in graphene dispersion.Researchers have conducted a series of research and literature reviews of the graphene predispersion and consolidation of composites.However,they paid less attention to post-deformation processing.This review summarizes different deformation treatments involved in the preparation process of Gr/Al composites and the evolution of the microstructure during the process.Research on deformation parameters is expected to further improve the properties of Gr/Al composites and would provide a deep understanding of the strengthening effect of graphene.
基金the financial support of the project from "Key Laboratory Fund (5780011513) of Harbin Institute of Technology""University Basic Fund (5710011113) of Harbin Institute of Technology""the Fundamental Research Funds for the Central Universities" (Grant No. HIT. NSRIF. 20161)
文摘Microstructure and mechanical behavior of high volume content SiCp/7xxxAl composites have not been explored yet. Therefore, in the present work, 45 vol.% SiCp/7075Al composite has been prepared by pres- sure infiltration method. High density dislocations were found around SiC/Al interface in SiCp/7075Al composite after water-quenching and aging treatment. Fine dispersed nano-η' phases were observed after the aging treatment. Adverse to other SiCp/Al composites prepared by the pressure infiltration method, an interface layer was observed between SiC particles and AI matrix. Furthermore, high-resolution trans- mission electron microscopy (HRTEM) observation indicated that this interface layer was coherent/semi- coherent with that of the SiC particles. 45 vol.% SiCp/7075Al composite demonstrated high tensile strength (630 MPa) and micro-ductility. Compared to aged SiCp/2024Al composite, the aged SiCp/7075Al com- posite showed an increase of about 200% in the tensile strain and 90% in the tensile strength, respectively. It is speculated that nano-η' phases in the Al matrix significantly contributed to the strengthening effect while the interface layer between SiC and AI matrix might be beneficial to the strength and plasticity of SiCp/7075Al composite.
基金supported by the National Natural Science Foundation of China(No.51501047)China Postdoctoral Science Foundation(No.2016M590280)the Fundamental Research Funds for the Central Universities(Nos.HIT.NSRIF.20161,HIT.MKSTISP.201615)
文摘In the present work, the wire electrical discharge machining(WEDM) process of the 65 vol% SiCp/2024 Al composite prepared by pressure infiltration methods has been investigated. The microstructure of the machined composite was characterized by scanning electron microscope, the average surface roughness(Ra), X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy(TEM) techniques. Three zones from the surface to the interior(melting zone, heat affected zone and un-affected zone) were found in the machined composites, while the face of SiC particles on the surface toward the outside was ‘‘cut'' to be flat. Increase in Al and Si but decrease in C and O were observed in the core areas of the removed particles. Si phase, which was generated due to the decomposition of SiC, was detected after the WEDM process. The irregular and spherical particles were further observed by TEM. Based on the microstructure observation, it is suggested that the machining mechanism of 65 vol% SiCp/2024 Al composite was the combination of the melting of Al matrix and the decomposition of SiC particles.