The production and influencing factors of thermal stress in the connection between ceramic and metal

    When ceramic and metal are connected, due to the large difference in thermal expansion coefficient, when the joint is cooled from the connection temperature to room temperature or used in a different temperature range, residual stress will be generated in the joint. The formation and existence of residual stress directly affects the performance of the joint, and even causes the joint to be damaged during the cooling process. Therefore, analyzing and measuring the residual stress and taking mitigation measures on this basis is an effective way to improve the performance of the joints connected by dissimilar materials.

    The generation of thermal stress is mainly related to the physical properties of the material, the shape of the joint and the temperature distribution. Generally speaking, ceramic materials have a small thermal expansion coefficient and a large elastic modulus, while commonly used metal materials are just the opposite.

    The influencing factors of thermal stress are:

    (1) Material factors. Material factors mainly include thermal expansion coefficient, elastic modulus, Poisson's ratio, interface characteristics, and connected materials

    The porosity, the yield strength of the material and the work hardening coefficient. Among them, the poor thermal deformation between dissimilar materials, the ratio of elastic modulus, and Poisson's ratio are the main factors affecting thermal stress.

    (2) The influence of temperature distribution. Process parameters such as different heating methods, heating temperature, heating rate, and cooling rate will affect the distribution of thermal stress.

    (3) The shape factor of the joint. Joint shape factors mainly include plate thickness, plate width, length, the number of layers of connecting materials, the order of layer arrangement, the shape of the joint surface and the roughness of the joint surface. Among them, the ratio of the thickness of the two materials and the ratio of the length to the thickness of the joint are the main factors that affect the thermal stress.

    In the case of plate butt joints, the size of the interface thermal stress is related to the thickness of the two materials. When the thickness of the plate 1 is smaller than that of the plate 2, the interface stress is larger. When the thickness of the plate 1 is sufficiently small, the stress on the side of the plate 2 is close to zero , And the stress distribution on one side of the sheet 1 is relatively simple and can be regarded as a constant value.

(Huiputech)