Effect of the CrB2 Additive Content on the Structure, Mechanical Properties, and Performance Characteristics of Diamond-Containing Cdiamond–(WC–Co) Composite Materials Formed by Spark Plasma Sintering

Abstract

The structure and mechanical properties (hardness Н, elasticity modulus Е, estimative parameters for determining the resistance to elastic H/E and plastic Н³/Е² deformations, ultimate bending R_bm and compression R_cm strength) of diamond-containing С_diamond–WC–Co–CrB₂ composite materials (DCM) formed by spark plasma sintering and the ability of their hard-alloy matrix to retain diamond grains from falling out have been studied as a function of the chromium diboride content (within a range from 0 to 10 wt %). It has been established that the addition of CrB₂ at a concentration of 4 wt % to 25C_diamond–70.5WC–4.5C leads to an increase in the ultimate bending R_bm (from 2040 ± 20 to 2375 ± 50 MPa) and compression R_cm (from 5100 ± 30 to 5650 ± 70 MPa) strengths and in the estimative parameters for determining the resistance to elastic H/E (from 0.043 to 0.051) and plastic Н³/E² (from 0.062 ± 0.0040 to 0.080 ± 0.0070 GPa) deformations. A further increase in the CrB₂ concentration (to 10 wt %) in a specimen leads to a gradual decrease in the ultimate bending R_bm (to 1840 ± 80 MPa) and compression R_cm (to 5100 ± 100 MPa) strengths with a growth in Н/E (to 0.054) and Н³/Е² (to 0.088 GPa). As a criterion for estimating the hard-alloy matrix ability to retain diamond grains from falling out, it is proposed to use the state of the surface relief of fracture in a DCM specimen. Under such a condition, the relief surface of diamond is indicative of strong adhesion between diamond grains and a hard-alloy matrix. The destruction of a DCM specimen along the diamond–matrix interface indicates that the adhesion between diamond grains and a hard-alloy matrix is weak to worsens the performance characteristics of such DCMs. It has been shown that the mentioned mechanical and performance characteristics of DCM specimens can be attained by adding 4 wt % of CrB₂ into DCMs to decrease the growth rate of WC grains and, as a consequence, to form a homogeneous fine-grained microstructure in their hard-alloy matrix.