Study Of ZrB₂ Reinfoced Copper Matrix Composites

Copper matrix composites have attracted increasing attention for applications in petrochemical and aerospace as well as in electronic industry because they exhibit good combination of high mechanical strength and high electrical/thermal conductivity.In this paper,ZrB₂ ceramic particles with high strength,high modulus,high electrical conductivity and good thermal stability were selected as reinforcement to enhance Cu matrix and ZrB₂/Cu composites were successfully prepared by hot-pressed powder metallurgy.The effects of sintering temperature,ZrB₂ particle content as well as dispersant content on the phase compositions,microstructure,mechanical properties and electrical conductivity of the ZrB₂/Cu composites were studied.In addition,ZrB₂/Cu composite with good interface bonding were manufactured by in-situ self-generated method.The effects of the holding time on the formation of in-situ ZrB₂and the effects of sintering temperature on its density,mechanical properties,electrical properties and microstructure were also focused on.The research results for ZrB₂/Cu composites fabricated using a hot-pressed sintering method under different sintering temperatures of 760℃,800℃,840℃,880℃,920℃indicates that the relative density and electrical conductivity of the composites are improved with the increase of sintering temperature.The microhardness of the composites increases firstly and then decreases.A maximum microhardness of 92.2 HV_0.2.2 is achieved at 840℃.The grain growth of Cu matrix with the increase of sintering temperature has been confirmed by XRD and SEM.In addition,ZrB₂/Cu composites with micro-size ZrB₂ from 0-9wt%were also fabricated at 840℃by a hot pressing sintering.The microstructure,mechanical properties and electrical properties were investigated.The results indicate that the addition of ZrB₂ particles effectively inhibits Cu grain growth during the sintering process.Most of the ZrB₂ particles distribute evenly over Cu matrix when ZrB₂ content is less than 7wt%.However,when the content of ZrB₂particles is up to 7wt%,the agglomeration of ZrB₂ particles becomes severe.The relative density and electrical conductivity of the produced composites decrease with increasing Zr B₂ particle content.However,the microhardness increases as ZrB₂ content is up to 7wt%and further increase of ZrB₂ content results in a decrease of microhardness.TEM observation confirms that the hexagonal shaped Zr B₂ crystals with several micrometers in size are embedded in Cu matrix.The interfacial zone consists of both amorphous transition layer and sharp interfaces.The research results indicates that when the content of the reinforcement is higher,the particles will agglomerate on the matrix,which are harmful to the mechanical properties and electrical conductivity of the composite materials.For this reason,the polyethylene glycol（PEG）and sodium polyphosphate（STPP）dispersants are selected and the effects of their contents on the disperse of ZrB₂ particles in the Cu matrix are investigated.Furthermore,the influence of PEG and STPP on the related density,microhardness and electrical conductivity of ZrB₂/Cu composites were discussed.The results show that an appropriate amount of dispersant can improve the dispersion of ZrB₂ particles and the optimized content of PEG is 0.4wt%,whereas the STPP is 0.1wt%.With the increase of PEG or STPP contents,the relative density,microhardness and electrical conductivity of ZrB₂/Cu composites increase firstly and then decrease.When the contend of PEG was 0.4wt%,the relative density,microhardness and electrical conductivity of the composite are increased by 1.37%,9.16%and 18.09%respectively,compared to that without dispersant.When the content of STPP is 0.1wt%,the relative density increases by 1.89%,the microhardness increases by 24.79%and the conductivity increases by25.08%.In this study,ZrB₂/Cu composites were also successfully prepared by an in-situ hot-pressed sintering route using B powders,Cu-Zr alloy powders and Cu powders.The effects of holding time and sintering temperature on the properties and microstructure of the composites are studied.The results show that prolonging the holding time benefits to the formation of in-situ ZrB₂.The size of the in-situ formed ZrB₂ particles ranges from 3 to 15μm and most of them can be evenly dispersed in the matrix.The density and electrical conductivity of the composites increase with increasing the sintering temperature while the microhardness decreases firstly and then increases.