Study On Preparation And Properties Of WC-Co-Ni-cBN Composites

Cemented carbide has been widely used in modern tool materials and wear-resisting materials due to excellent properties of high strength,high hardness,high modulus of elasticity and low thermal expansion.Cubic boron nitride(cBN)is a new generation of super-hard materials because of the second only to the hardness of the diamond and better thermal stability of not occurring oxidation in the atmosphere until the temperature above 900?,The cBN phase addition as super hard second phase could modify contradictions between hardness and toughness of cemented carbide.Furthermore,the compound could integrate advantages of these two materials and posess good comprehensive performance,which probably makes it to become a promising excellent tool materials.Binder metal has a great influence on the performance of cBN reinforced cemented carbide composite.Its mechanical properties can be changed by the kind and content of the binder metal.Co was traditionally used as binder metal of cemented carbide,however it is expensive element,scarce resource and even reducing the corrosion resistance of cemented carbide.In this study,metal Ni was introduced partially to replace Co as binder metal,and WC-Co-Ni-cBN composite was prepared by spark plazma sintering(SPS)and hot pressing(HP)methods,respectively.The effect of Ni content,sintering temperature,holding time on microstructures and properties of WC-Co-Ni-cBN composite was investigated.Meanwhile,In order to improve the interface bonding of cBN particles and cemented carbide matrix and without increasing the binder content,we adopted chemical nickel-plating in the surface of cBN particles.It could generate a pyknotic metal membrane in cBN surface to promote the densification and improve the comprehensive performance of the WC-Co-Ni-cBN composite.The experimental results were shown as follows.(1)When binder metal Co-Ni ratio was 2:3,the WC-4Co-6Ni-cBN composite shows the best comprehensive performance prepared by SPS.The relative density of WC-4Co-6Ni-cBN is 98%,of which the hardness and fracture toughness are 22.4 GPa and 14.8 MPa·m1/2,respectively.(2)The corrosion resistance of composite was improved by using Ni replacing Co in WC-Co-Ni-cBN composite.(3)The best sintering temperature is 1280? in the preparation of WC-Co-Ni-cBN composite by SPS,the relative density,hardness and fracture toughness of composite are 98.9%,23.4 GPa,14.8 MPa·m1/2,respectively.(4)With the increase of the holding time,the hardness and flexural strength of WC-Co-Ni-cBN show the trend of increase first and then decrease,while the fracture toughness decrease first and then increase.The composite prepared by holding time of 15 min has the best performance,of which the relative density,hardness,fracture toughness and flexural strength are 98.1%,18.2 GPa,13.3 MPa·m1/2,1095 MPa,respectively.(5)The optimum parameter and condition of chemical nickel-plating for cBN particle:pH=10,T=8 0? and plating 10 min,plating solution(5 g/l Na3C6H507·5.5H2O+5 g/l CH3COONa+30 g/l NiSO4·6H2O+30 g/l NaH2PO2·H2O).A pyknotic metal membrane in cBN surface could be obtained.(6)Interface bonding between cBN and cemented carbide matrix has been modified by using coated cBN particles.The mechanical properties of WC-Co-Ni-cBN(coated)composite have also been improved,of which the relative density,hardness,fracture toughness and flexural strength are 98.4%,18.8 GPa,14.2 MPa·m1/2,1190 MPa,respectively.