Potassium dihydrogen phosphate (KDP) crystals are widely used in laser ignition facilities as optical switching and frequency conversion components. These crystals are soft, brittle, and sensitive to external conditions (e.g., humidity, temperature, and applied stress). Hence, conventional characterization methods, such as transmission electron microscopy, cannot be used to study the mechanisms of material deformation. Nevertheless, understanding the mechanism of plastic-brittle transition in KDP crystals is important to prevent the fracture damage during the machining process. This study explores the plastic deformation and brittle fracture mechanisms of KDP crystals through nanoindentation experiments and theoretical calculations. The results show that dislocation nucleation and propagation are the main mechanisms of plastic deformation in KDP crystals, and dislocation pileup leads to brittle fracture during nanoindentation. Nanoindentation experiments using various indenters indicate that the external stress fields influence the plastic deformation of KDP crystals, and plastic deformation and brittle fracture are related to the material’s anisotropy. However, the effect of loading rate on the KDP crystal deformation is practically negligible. The results of this research provide important information on reducing machining-induced damage and further improving the optical performance of KDP crystal components.

磷酸二氢钾（KDP）晶体广泛用作激光点火设备中的光学开关和频率转换组件。这些晶体柔软，易碎，并且对外部条件（例如湿度，温度和施加的应力）敏感。因此，常规的表征方法，例如透射电子显微镜，不能用于研究材料变形的机理。尽管如此，了解KDP晶体中塑性-脆性转变的机理对于防止加工过程中的断裂损伤很重要。通过纳米压痕实验和理论计算，探讨了KDP晶体的塑性变形和脆性断裂机理。结果表明，位错形核和扩展是KDP晶体塑性变形的主要机制，位错堆积导致纳米压痕过程中的脆性断裂。使用各种压头的纳米压痕实验表明，外部应力场会影响KDP晶体的塑性变形，塑性变形和脆性断裂与材料的各向异性有关。然而，加载速率对KDP晶体变形的影响实际上可以忽略不计。这项研究的结果为减少加工引起的损伤并进一步改善KDP晶体组件的光学性能提供了重要信息。使用各种压头的纳米压痕实验表明，外部应力场会影响KDP晶体的塑性变形，塑性变形和脆性断裂与材料的各向异性有关。然而，加载速率对KDP晶体变形的影响实际上可以忽略不计。这项研究的结果为减少加工引起的损伤并进一步改善KDP晶体组件的光学性能提供了重要信息。使用各种压头的纳米压痕实验表明，外部应力场会影响KDP晶体的塑性变形，塑性变形和脆性断裂与材料的各向异性有关。然而，加载速率对KDP晶体变形的影响实际上可以忽略不计。这项研究的结果为减少加工引起的损伤并进一步改善KDP晶体组件的光学性能提供了重要信息。