Study On Structure And Properties Of C-BN/Cu Composite Materials By Spark Plasma Sintering Method

Cubic boron nitride has a number of attractive physical and chemical properties, such as high hardness that only less than diamond,high wearing resistance,low friction coefficient, high thermal conductivity, favourable thermal stability and antioxygenic property under high temperature and it does not react with molten ferrous materials,very suitable for precision finishing of steel product.It is comprehensively applied to produce various tools or superabrasive against abrasion in the field of auto manufacture, mechanical processing, precision processing, stone materials processing, constructional materials, aviation, new materials processing, and so on.The range and field of application for c-BN are restricted due to the bad processing property of c-BN superhard material. As an abrasive material, which is used to manufacture various tools or superabrasive coats, the processing of c-BN is mainly produced by means of vapor deposition, resin bond, vitrified bond, metal bond, electroplating and brazing, et al. The efficiency of c-BN produces prepared by using vapor deposition processing is low. When the c-BN is prepared to be a coat or a wearable component by means of sinter processing, c-BN would be knocked down which was operated as the function of wearability. The lifespan of c-BN coat with electroplated processing is short, and it contaminates the environment in processing. In the production prepared by brazing, the alloy bonding can be formed in the interface between filler substrate and c-BN. But the filler freezes to be molten structure, which decreases its own wearability and makes c-BN to be uneven in the substrate.In this paper, the design of bionic structure is adopted. The c-BN/Cu-based composite materials are prepared by SPS that uses the c-BN grain as strengthened phase and the CuNiSnTi alloy as substrate. The spark plasma sintering is an advanced technology for materials synthesis and one of effective methods for preparation plasticmetal-ceramic composite.As a newly developed process,compared to traditional ones,SPS has the superiority of short sintering time,low sintering temperature and the good ability to prepare high compacted mass.Then, the influence of compactablitiy and wearability of the c-BN/Cu composite materials is investigated by adjusting of c-BN granularity ,volume percentage and SPS parmeters (sintering temperature, pressure and the keeping time). Also, the influence of abrasion versus load on wear resistance of composite materials is studied. Microstructure and abrasion mechanism of c-BN/Cu composite materials is analysised, The joining of c-BN/Cu composite materials and carbon steel using brazed welding and SPS is primary investigated,including miccrostructure and properties of the joints using different methods.Experiments indicate that CuNiSnTi active alloy exhibits a good wettability on c-BN. During the process of SPS, titanium atoms in active alloys segregated preferentially to the surface of the c-BN to form TiN and TiB2 by reaction between titanium atoms and nitride and boron atoms, strong chemical joining was formed in the interface between c-BN and active alloy.Coming within the designed SPS parameters, the density and compactness of c-BN/Cu compiste materials increase with the increase of sintering temperature and keeping time,firstly increase and then hold the line with the increase of pressure.The regression equations shows that, at the sintering temperature of 800℃, the pressure of 30 Mpa and the keeping time of 5 min, the composite materials have good compactness.The friction coefficient and wear mass loss of compiste materials decrease with the increase of compactness.While the volume percentange of c-BN is 25%-35%,c-BN/Cu composite materials have good wearing quality. The 120～150μm c-BN and nom-smooth units can form micron-micron coupling,and comppsite materials have biggish friction coefficient and lesser wear mass loss. The wear of coposite materials is adhesive wear at the beginning,due to chipping off of c-BN, abrasive wear begin to predominate, accompanied fatigue wear.Using brazed welding, the shear-strength of c-BN/Cu composite materials and carbon steel joints is 158 MPa, and the tensile strength is 44MPa.Using SPS to join c-BN/Cu composite materials and carbon steel,the joints have higher ensile strength, fracture happen to c-BN/Cu.