Abstract In order to understand the fracture resistance of nanocrystalline thin films, it is necessary to assess nanoscopic multiaxial stress fields accompanying crack growth during irreversible deformation. Here, a clamped cantilever with dimensions of 200 × 23.7 × 40 μm3 was machined by focused ion beam milling from a thin film composed of four alternating CrN and Cr layers. The cantilever was loaded to 460 mN in two steps and multiaxial strain distributions were determined by in situ cross-sectional X-ray nanodiffraction. Characterization in as-deposited state revealed the depth variation of fibre texture and residual stress across the layers. The in situ experiment indicated a strong influence of the residual stresses on the cross-sectional stress fields evolution and crack arrest capability at the CrN-Cr interface. In detail, an effective negative stress intensity of −5.9 ± 0.4 MPa m½ arose as a consequence of the residual stress state. Crack growth in the notched Cr layer occurred at a critical stress intensity of 2.8 ± 0.5 MPa m½. The results were complemented by two-dimensional numerical simulation to gain further insight into the elastic-plastic deformation evolution. The quantitative experimental and modelling results elucidate the stepwise nature of fracture advancement across the alternating brittle and ductile layers and their interfaces.

中文翻译：

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通过 X 射线纳米衍射和建模分析脆性-延性 CrN-Cr 夹紧悬臂梁裂纹扩展和停止过程中应力场的演变

摘要 为了了解纳米晶薄膜的抗断裂性，有必要评估不可逆变形过程中伴随裂纹扩展的纳米级多轴应力场。在这里，尺寸为 200 × 23.7 × 40 μm3 的夹紧悬臂是通过聚焦离子束铣削加工而成的，该薄膜由四个交替的 CrN 和 Cr 层组成。悬臂分两步加载至 460 mN，并通过原位横截面 X 射线纳米衍射确定多轴应变分布。沉积状态下的表征揭示了纤维质地和层间残余应力的深度变化。原位实验表明残余应力对 CrN-Cr 界面处的横截面应力场演变和裂纹止裂能力有很大影响。详细，由于残余应力状态，产生了 -5.9 ± 0.4 MPa m½ 的有效负应力强度。缺口铬层中的裂纹扩展发生在临界应力强度为 2.8 ± 0.5 MPa m½ 时。结果得到了二维数值模拟的补充，以进一步了解弹塑性变形演化。定量实验和建模结果阐明了在交替的脆性和韧性层及其界面上裂缝推进的逐步性质。结果得到了二维数值模拟的补充，以进一步了解弹塑性变形演化。定量实验和建模结果阐明了在交替的脆性和韧性层及其界面上裂缝推进的逐步性质。结果得到了二维数值模拟的补充，以进一步了解弹塑性变形演化。定量实验和建模结果阐明了在交替的脆性和韧性层及其界面上裂缝推进的逐步性质。