where X is the residual indentation coefficient, P is the applied
load and C is half of the indentation crack length. X depends on
hardness to modulus ratio (H/E) of the boride, equaling to 0.016(E/
H)
1/2, where E and H are the Young's modulus and microhardness,
respectively. And the value of E is approximately 290 GPa [37–41]