With the rapid development of the third-generation semiconductors SiC and GaN,traditional packaging materials,such as Si-based lead-free solder,cannot satisfy the requirements of high-power density and high-temperature loading in power electronic devices any more.Nowadays,the joints packaged by Cu nanoparticle sintering technique can not only be bonded at low-temperature and then serve at high-temperature,but also exhibit excellent thermal conductivity,electrical conductivity and relatively lower cost comparing with Ag nanoparticles.Thus,more and more attention has been attracted in the field of Cu nanoparticle sintering technique for power electronic packaging,which makes Cu nanoparticles become one of the most potential high-temperature-resistant packaging and interconnection materials.In this work,the current research progress of Cu nanoparticle sintering technique was summarized,including the fabrication of Cu nanoparticle pastes,the factors affecting the performance of sintered joints and the reliability of joints.Meanwhile,the oxidation behavior as well as the anti-oxidation methods of Cu nanoparticle were introduced.Besides,the high-temperature working reliability and failure mechanism of Cu nanoparticle sintered joints were discussed.This review aims to promote the application of low-cost Cu nanoparticle sintering technique for high-performance and high-reliability power electronic packaging.

Heterojunction solar cells have the advantage of high cell efficiency and show great potential in the field of solar photovoltaics.Low-temperature metallization is an important process in the manufacturing of heterojunction solar cells,which is used to form metal grids on the cell surface.Currently,low-temperature-cured silver paste combined with screen printing is widely used.However,the high consumption of expensive low-temperature silver paste is one of the reasons for the high cost of the cells.The photovoltaic industry is working hard to improve and optimize metallization process to reduce silver consumption.This paper reviewed the research progress on metallization technologies for heterojunction solar cells,and summarized in detail the effect of the components of low-temperature silver paste as well as the curing process on the overall performance.In addition,the main metallization approaches used to increase cell effectiveness were introduced and compared,including silver paste reduction strategies such as multi-busbar and pattern transfer printing technologies,and non-silver metallization strategies such as silver-coated copper and copper plating technologies.Finally,the challenges of different metallization processes for heterojunction solar cells were analyzed and their future development directions were also prospected.

Due to its low coefficient of thermal expansion,high temperature strength,high elastic modulus and other characteristics,molybdenum metal is widely used in aerospace,military,petrochemical and nuclear industries and other cutting-edge industries,which is an indispensable material to promote the development of high-tech fields.Molybdenum powder is the basic material of molybdenum products,and its physicochemical properties are closely related to the properties of molybdenum products.Compared with ordinary molybdenum powder,ultrafine molybdenum powder has larger specific surface area,higher activity and lower sintering temperature.At present,the main methods for preparing ultrafine molybdenum powder are thermal reduction method and thermal decomposition method.Thermal reduction method can prevent grain growth by adjusting the reduction process.The development of thermal decomposition method mainly involves the upgrading of equipment and the optimization of process.In this paper,focusing on the preparation process,reaction mechanism and product state of ultrafine molybdenum powder,the development process and technical characteristics of the typical process were analyzed,the research status and progress of the preparation technology of ultrafine molybdenum powder were summarized,and the issues in the current technology and the future research direction were put forward,in order to provide ideas for the development and industrial application of the preparation technology of ultrafine molybdenum powder.

Selective laser melting(SLM)is an advanced digitalized technology that has been extensively applied in the fabrication of superalloys.This paper reviewed the microstructure of superalloys prepared by SLM,summarized the type and features of pores,and categorized the development of models interpreting the formation of cracks.The application of computational science in the research of preparation of superalloys was also reviewed.Finally,the prospect of SLM in superalloys was discussed.

Al-30Zn-3Cu-2.5Si high Zn Al-based alloy was taken as the research object,the effects of Er and Zr on the microstructure and mechanical properties of as-cast and heat-treated alloys were investigated,and the action mechanism was analyzed and discussed.The results show that the grain size of the alloy can be obviously refined by adding 0.10wt%Er and 0.10wt%Zr,the average grain size is reduced from 74.28μm to 60.01μm,and the grains ofα-Al are changed into fine equiaxed grains.The addition of rare earth elements Er and Zr can form fine particles of Al3(Er,Zr)in the alloy and pin dislocations to improve the mechanical properties of the alloy.After adding Er and Zr,the tensile strength of as-cast alloy increases from 323.01 MPa to 358.29 MPa,which increases by 10.93%;the yield strength increases from 309.33 MPa to 315.00 MPa,which increases by 1.83%;the elongation barely changes.The tensile strength and yield strength of the alloy strengthened by solution-aging heat treatment are 449.48 and 408.51 MPa,which are 25.45%and 29.68%higher than those of the as-cast alloy,respectively.The coarse second phase exists at the grain boundary,which results in the poor elongation of the alloy.

On the premise of performance satisfaction,to acquire the boundary of the heat treatment parameters is significant for property optimization of FGH96 turbine disks,especially the boundary of the minimum cooling of FGH96 alloy with certain grain size on the premise of performance satisfaction.The tensile behavior at 25,650 and 750℃of FGH96 specimens with different grain sizes was investigated during the cooling process from solution temperature at different cooling rates,and the microstructures were observed.The results show that the results obtained by the multi-mechanistic strengthening model including the effect of chemical composition,grain size,size and volume fraction ofγ′agree well with the experimental measurements.Through the strengthening model,the relationship between minimum cooling rate and grain size was studied:the grain size should be smaller than 14μm if the cooling rate is 55℃/min,the grain size should be smaller than 16.8μm if the cooling rates is 72℃/min,and the grain size should be smaller than 20μm if the cooling rates is 81℃/min.The relationship between minimum cooling rate and grain size can be used as a criterion for the guidance of parameter design of heat treatment process through simulation.