涂层断裂韧性的声发射辅助拉伸测量方法

An Acoustic Emission-Based Uniaxial Tensile Test Method for Evaluation of Fracture Toughness of a Coating on Its Substrate

涂层的断裂韧性与界面结合强度是表征涂层/基体材料体系力学性能的重要指标。但如何准确地测量涂层的断裂韧性和强界面结合的涂层/基体材料体系的界面结合强度至今仍存在困难。以铬涂层/钢基体材料为对象,采用声发射和显微镜实时动态检测技术与拉伸实验相结合的方法,探索了铬涂层的断裂韧性以及铬涂层/钢基体的界面剪切强度。根据相关力学模型和实验测量结果,得到铬涂层在室温下的断裂韧性为27.41 J/m2.同时,发现在铬涂层裂纹饱和后界面开裂都未发生,获得了该种材料体系界面剪切强度的一个下限值。

Fracture toughness and interracial adhesive strength of coating on its substrate are the crucial parameters characterizing the performance and reliability of coating-substrate system. In this paper, a tensile experiment with acoustic emission signals inverse analysis and in situ observation of the cracking of the coating and interface was proposed to evaluate the fracture toughness and interracial shear strength of the hard and brittle electroplated chromium coating on ductile steel substrate. The acoustic emission detector was attached to the specimen to check the signals of the cracking of chromium coating or interface and whether the crack density became saturated or not. The experimental results show that the strong signals belonged to the periodic cracking of the chromium coating. A mechanical model can be used to determine the fracture toughness. When the crack density of chromium coating became saturated, the steel substrate exhibited plastic deformation; however, the interface cracking could not be observed. This indicates the yield shear flow stress of the substrate can be exerted along the interface through the ductile substrate undergoing plastic deformation, and the yield shear flow stress level of the ductile steel substrate can only serve as a lower bound estimate of the ultimate shear strength of the interface.