The purpose of this paper is to investigate the relationship between hydride morphology, in particular the presence of radial hydrides (RHs), stress state and failure mechanisms associated with the ring compression test (RCT). Samples of ZIRLO® cladding were pre-hydrided and subjected to thermo-mechanical treatments to precipitate long radial hydrides. The results show that the reorientation treatment was very successful. A considerable fraction of RHs was generated, the radial hydride continuity factor being around 80 to 90% of the wall thickness. The samples with reoriented hydrides were tested using the RCT at room temperature. Macroscopic brittle failure was observed with sudden load drops for displacements around 0.5 mm, with a calculated “offset strain” between 0.5 and 1%. Crack nucleation occurs in RHs located in regions with the highest values of hoop stress. These locations are the inner diameter of cladding at the vertical plane of the sample (12 and 6 o'clock positions) and the outer diameter at the horizontal plane (3 and 9 o'clock positions). Noticeable load drops in the RCT are associated with unstable crack propagation events through the radial hydride network, the crack front reaching up to 90% of the wall thickness in some cases. The failure micro-mechanism is quasi-cleavage in the hydrides and micro-void nucleation, growth and coalescence in the Zr matrix, with ductile tearing patches connecting neighboring hydrides. The main conclusion is that radial hydride metrics is not the only parameter that determines cladding failure in the presence of RHs, but the interaction between the location and continuity of RHs and the stress normal to the hydride (the hoop stress in this case). Consequently, if a radial hydride is located at a position within the cladding, where the hoop stress is small, a crack will not be initiated easily in the RCT.

本文的目的是研究氢化物形态之间的关系，尤其是径向氢化物（RHs）的存在，应力状态和与环压缩试验（RCT）相关的破坏机理。将ZIRLO®覆层样品进行预氢化，并进行热机械处理，以沉淀长的径向氢化物。结果表明，重新定向治疗非常成功。产生了相当大的相对湿度，径向氢化物连续性因子约为壁厚的80％至90％。使用RCT在室温下测试了带有重取向氢化物的样品。观察到宏观脆性破坏，位移突然下降，位移约为0.5 mm，计算出的“偏移应变”在0.5％至1％之间。裂纹形核发生在环向应力值最高的区域的RH中。这些位置是包层在样品的垂直平面上的内径（12点钟和6点钟位置）和在水平面的外部直径（3点钟和9点钟位置）。RCT中明显的载荷下降与通过径向氢化物网络的不稳定裂纹扩展事件有关，在某些情况下，裂纹前沿达到壁厚的90％。失效的微观机制是氢化物的准裂解和Zr基质中的微孔成核，生长和聚结，以及连接相邻氢化物的韧性撕裂斑块。主要结论是，在存在RH的情况下，放射状氢化物度量标准不是决定包层破坏的唯一参数，但是相对湿度的位置和连续性与垂直于氢化物的应力（在这种情况下为环向应力）之间的相互作用。因此，如果放射状氢化物位于包层内的环向应力小的位置，则在RCT中将不容易产生裂纹。