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$\pm$0.7 and 19.2$\pm$1.2 J/m², 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.

本研究的目的是使用内能诱导开裂 (IEIC) 方法评估氮化钒 (VN) 硬质涂层的断裂韧性 (G _c )，并研究择优取向对断裂韧性的影响。VN 涂层通过不平衡磁控溅射沉积在 Si (100) 衬底上。使用两种不同的氮气流速来制备具有不同质地的涂层。使用 IEIC 方法评估试样的断裂韧性。结果表明，VN涂层的断裂韧性与织构有关，随机织构和(200)织构试样的_Gc值为11.2$\pm$0.7 和 19.2$\pm$分别为1.2 J/m ²，介于 TiN 和 ZrN 之间。较高的 G _c具有（200）织构的 VN 涂层与涂层中较高的残余应力一致。使用聚焦离子束和电子束系统检查断裂形态和裂纹扩展路径。无论是随机还是 (200) 纹理，涂层的断裂形态都是相似的，其中裂纹路径由水平 (R1) 和锯齿形 (R2) 区域组成。由于 VN 涂层具有相对均匀的应力梯度，由于边缘应力作用于局部缺陷，裂纹可能在试样边缘之前的涂层内部发生。与 ZrN 涂层的断裂行为类似，自由边缘效应引起的应力分布会随着裂纹前沿移动，从而推动主裂纹逐步扩展。