Effect of CrB2 on the Microstructure, Properties, and Wear Resistance of Sintered Composite and the Diamond Retention in Fe–Cu–Ni–Sn Matrix

Abstract

Using the method of powder metallurgy, we studied the effect of CrB2 additives (0–8 wt %) on the formation of the structure of the diamond–matrix transition zone and the matrix material, microhardness, elastic modulus, and fixation of diamond grains in a Fe–Cu–Ni–Sn matrix and determined the wear resistance of sintered composite diamond-containing materials (DCMs). Micromechanical and tribological tests were carried out using composite samples 10 mm in diameter and 5 mm thick. The transition zone structure depends significantly on the concentration of CrB2 in the composite and has a different nature than the structure of the matrix material. The structure of the DCM transition zone based on the 51Fe–32Cu–9Ni–8Sn matrix consists of Cu, α-Fe, and Ni3Sn phases with graphite inclusions, and with the addition of CrB2, it consists of the α-Fe phase and Fe3C, Cr7C3, and Cr3C2 carbide layers without graphite inclusions. The hardness and elastic modulus of the matrix material of the sintered composites linearly increase with an increase in the concentration of CrB2 in their composition, while the wear rate decreases. The addition of 2 wt % of CrB2 to the 51Fe–32Cu–9Ni–8Sn composite increases hardness from 4.475 to 7.896 GPa and an elastic modulus from 86.6 to 107.5 GPa and decreases the wear rate from 21.61 × 10–6 to 10.04 × 10–6 mm3 N–1 m–1. The mechanism for improving the mechanical properties and decreasing the wear resistance of DCM samples containing CrB2 additive consists in grain refining of the matrix phases of iron and copper from 5–40 to 2–10 μm and in binding carbon released during graphitization of diamond grains into nanosized carbides Fe3C, Cr7C3, and Cr3C2. This, in turn, increases the ability of the matrix material to keep diamond grains from falling out during the operation of DCMs. The coarse-grained structure and the formation of graphite inclusions in the diamond–matrix transition zone explain poor mechanical and tribological properties of the initial (51Fe–32Cu–9Ni–8Sn) composite, causing its premature destruction and falling out of diamond grains from the DCM matrix.