Tribological Properties And Corrosion Resistance To Molten Steel Of (ZrB₂-ZrO₂)/BN Composites

(ZrB2-ZrO2)/BN composites were prepared by reactive hot pressing sintering at 1600℃, under 20MPa for 60 min, using ZrO2, B4C and C as crude materials in this article. Effect of the ratio of ZrB2/ZrO2 on structure and properties of the composites have been systematically studied by the X-ray diffraction (XRD), scanning electron microscopy(SEM), three-point bending test, single-edge-notched beam method, etc . The effects of applied loads, sliding velocities and the ratio of ZrB2/ZrO2 on tribological behaviors of (ZrB2-ZrO2)/BN composites against Ni pin at room temperature, under dry sliding conditions, was revealed. The effects of variety of molten steel and corrosion time on the corrosion resistance to molten steel of the composites has been investigated, then the corrosion mechanism of the composites will be revealed.35vol% (ZrB2-ZrO2)/BN composites, the density of which is more than 92% , were prepared successfully by reactive hot pressing sintering. With the ratio of ZrB2/ZrO2 increasing, the mechanical properties of composites increase firstly and then decrease, reaching a maximum value at ZrB2:ZrO2=3:4 with the vickers' hardness, elastic modulus, flexture strength and fracture toughness of it were 2.32GPa,90GPa,266MPa,3.7 MPa?m1/2,respectively,and the flexture strength under high temperature of the composite decreases first and then increases as the tempareture raises, and reach the maximum at 1100℃, up to 253MPa.When ZrB2:ZrO2=3:4, the friction coefficient of the composites decreases as the load increases, yet the wear rate increases, and there is a threshold contact when the load reaching a contact pressure of 6~7N. On the other hand, as the sliding velocity increases, the friction coefficient will increase first and then decrease, while the wear rate will increase all through. The wear rate goes down and then up as time passes. The friction wear mechanism of the composites is flaking wear, sticking wear and grain abrasion. As the ZrB2 content increases, the corrosion resistance to molten steel of the composites is enhanced. Corroded thickness of the composites with different ratio of ZrB2:ZrO2-0:7,3:4,5:2, are 0.40mm,0.28mm and 0.25mm,respectively. Corroded thickness of the composites increases as the corroded time expands. The effect of A508-3 melten steel on (ZrB2-ZrO2)/BN composites is the worst, then will be 45 steel and 20 steel, it reflects that Mn, etal alloying element affects the corrosion resistance to molten steel of the composites badly. The corrotion mechanism of the composites is chemical erosion.