AbstractThe 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 Rbm and compression Rcm strength) of diamond-containing Сdiamond–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 25Cdiamond–70.5WC–4.5C leads to an increase in the ultimate bending Rbm (from 2040 ± 20 to 2375 ± 50 MPa) and compression Rcm (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 Rbm (to 1840 ± 80 MPa) and compression Rcm (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.