Contact-mode high-speed atomic force microscopy (HS-AFM) has been utilised to measure in situ stress corrosion cracking (SCC) with nanometre resolution on AISI Type 304 stainless steel in an aggressive salt solution. SCC is an important failure mode in many metal systems but has a complicated mechanism that makes failure difficult to predict. Prior to the in situ experiments, the contributions of microstructure, environment and stress to SCC were independently studied using HS-AFM. During SCC measurements, uplift of grain boundaries before cracking was observed, indicating a subsurface contribution to the cracking mechanism. Focussed ion beam milling revealed a network of intergranular cracks below the surface lined with a thin oxide, indicating that the SCC process is dominated by local stress at oxide-weakened boundaries. Subsequent analysis by atom probe tomography of a crack tip showed a layered oxide composition at the surface of the crack walls. Oxide formation is posited to be mechanistically linked to grain boundary uplift. This study shows how in situ HS-AFM observations in combination with complementary techniques can give important insights into the mechanisms of SCC.

接触模式高速原子力显微镜（HS-AFM）已用于在侵蚀性盐溶液中以纳米分辨率测量AISI 304型不锈钢的原位应力腐蚀开裂（SCC）。在许多金属系统中，SCC是重要的故障模式，但其机制复杂，使得故障难以预测。在原位实验之前，使用HS-AFM独立研究了微观结构，环境和应力对SCC的贡献。在SCC测量过程中，观察到开裂前晶界的隆起，表明地下对开裂机理的贡献。聚焦离子束铣削显示在衬有薄氧化物的表面下方的晶间裂纹网络，这表明SCC过程主要受氧化物弱化边界处的局部应力支配。随后通过原子探针断层摄影术对裂纹尖端进行分析，结果表明在裂纹壁表面形成了一层层状氧化物。氧化物的形成被认为与晶界隆起在机械上相关。这项研究表明，原位HS-AFM观察与补充技术的结合如何能够对SCC的机制提供重要的见解。