“…Based on the literature reported in recent years [31][32][33][34][35][36] , diborides which possess a (0 0 1) growth texture have a higher hardness than that of massive films that do not possess such a structure in the hexagonal crystal structure [5,7,37] ; (vi) the possible solid solution hardening effect of nitrogen atoms. When P N2 exceeds 0.006 Pa, the volume fraction of the soft amorphous BN phase at the grain boundary is increased, resulting in the sharp reduction of both hardness and elastic modulus.…”