Study Of The Processing And Properties Of ZrB₂-Cu Composites

During electric discharge machining, the tradition tool materials have severewear. The ZrB2-Cu composite could be a tool material for EDM in the integration ofhigh conductivity, and high hardness and strength which can reduce the tool wear andcost.In this paper, ZrB2-Cu, ZrB2(Ni)-Cu and SiC/ZrB2(Ni)-Cu composites wereprepared by hot pressing sintering, respectively. The phase fraction andmicrostructure of materials were analyzed. And the mechanical properties, electricalperformance, thermal performance, friction and wear properties of the three materialswere characterized and analyzed, respectively. The mainly results were shown asfollowes:(1) ZrB2-Cu material was fabricated by hot-pressing sintering at850oC,900oCand950oC under a20MPa uniaxial load in a vacuum atmosphere for5min. With theincrease of sintering temperature, the relative density of materials increased while thehardness and bending strength increased firstly and then decreased. With the increaseof the content of Cu, the relative density and bending strength increased while thehardness decreased. When the sintering temperature was900oC, the hardness ofZrB2-60vol.%Cu reached a maximum of3.7GPa; while the bending strength ofZrB2-70vol.%Cu reached the maximum of258MPa.(2) ZrB2(Ni)-Cu composites were prepared by hot-pressing sintering method at850oC,900oC and950oC respectively under a20MPa uniaxial load for5min.When the sintering temperature was900oC, the ZrB2(Ni)-50vol.%Cu had themaximum hardness value of4.4GPa, while the ZrB2(Ni)-70vol.%Cu had themaximum bending strength value of375MPa, respectively. The thermal conductivityof materials increased with the increase of sintering temperature and the content ofCu, and reached a maximum value of191.71W/(m·K) at950oC and60vol.%Cu.The electrical resistivity of ZrB2(Ni)-Cu material decreased with the increase ofsintering temperature and the content of Cu, and reached a minimum value of3.1μ·cm at900oC and70vol.%Cu. (3) SiC/ZrB2(Ni)-Cu composites were prepared by adding SiC sinteringadditives to ZrB2(Ni)-Cu matrix, using hot-pressing sintering method at900oC undera20MPa uniaxial load for5min. The thermal conductivity of materials was increasedsignificantly with the introduction of SiC, and reached a maximum value of221.71W/(m·K) at10vol.%SiC and particle size of2μm. The electrical resistivity ofmaterial increased with the increase of the content of SiC, and reached a minimumvalue of11μ·cm at5vol.%SiC and particle size of10μm.(4) The wear resistance of ZrB2-Cu composites were better than other coppermatrix composites in the literature. ZrB2(Ni)-60Cu samples’ wear resistance hadimproved significantly after electroless nickel plating. The main wear mechanism ofZrB2-Cu composites was adhesive wear. A amount of spalling was observed on theworn surfaces. The interface bonding between ZrB2and Cu was poor, ZrB2-60Cusample was easily broken in the interface. ZrB2had good interface bonding with Cuafter electroless nickel, the wear resistance of ZrB2(Ni)-60Cu increased significantly.