摘要
The objectives of this study were to evaluate the fracture toughness (G c ) of vanadium nitride (VN) hard coatings using internal energy-induced cracking (IEIC) method, and investigate the effect of preferred orientation on the fracture toughness. VN coatings were deposited on Si (100) substrates by unbalanced magnetron sputtering. Two different nitrogen flow rates were used to prepare coatings with different textures. The fracture toughness of the specimens were assessed using the IEIC method. The results showed that fracture toughness of the VN coatings was texture-dependent, and the G c values for specimens with random texture and (200) texture were 11.2±0.7 and 19.2±1.2 J/m 2 , respectively, which were in between those of TiN and ZrN. The higher G c for the VN coatings with (200) texture was consistent with the higher residual stress in the coatings. The fracture morphology and crack propagation path were examined using a focused ion beam and electron beam system. The fracture morphology of the coatings was similar regardless of random or (200) texture, where the crack path consisted of horizontal (R1) and zigzag (R2) regions. Since the VN coatings possessed a relatively uniform stress gradient, crack initiation may occur inside the coating ahead of the specimen edge due to the edge stress acting at local defects. Similar to the fracture behavior in ZrN coatings, the stress distribution due to free edge effect could move with the crack front and consequently drive the main crack to propagate stepwise.