A STUDY ON THE FATIGUE RELIABILITY OF THERMALLY SPRAIED MATERIAL

由于热喷涂涂层具有很高的耐磨性、耐腐蚀性和耐热性，它被用于许多工程领域，用于表面强化和机械部件的修复，如造纸机轧辊、轴和大型轴承。随着这一工艺在多个行业的应用需求的增加，研究热喷钢的抗疲劳性能变得越来越重要。然而，热喷涂涂层的疲劳性能仍存在许多问题，本文研究了钴基自熔性合金热喷涂试件的疲劳寿命特征。研究了界面条件对喷塑试件疲劳强度的影响。通过旋转弯曲疲劳试验，研究了后热处理(熔融处理)对喷塑试件疲劳强度的影响。用扫描电子显微镜(Scan Electron…)研究了热喷涂试件的疲劳断裂机制结果表明：(1)熔融处理温度、加热速度和保温时间对喷涂层的组织形态、硬度和微孔体积分数(孔隙率)等性能有很大影响。(2)采用感应加热系统熔接的热喷涂试件的结合强度是由机械作用决定的。然而，在使用真空炉熔融喷雾试件的情况下，化学元素的扩散强烈地影响着界面特征和粘结强度。(3)火炬熔融试件的孔隙率值存在相当大的分散性。然而，通过使用感应加热系统很好地控制熔化，可以获得高质量的涂层。(4)热喷涂试件的疲劳断裂机制如下：(1)裂纹开始于界面处；(2)裂纹扩展到基材；(3)裂纹从喷涂层的界面扩展，整个涂层迅速失效；(4)基材的剩余部分失效。较少

Since a thermally sprayd coating has high wear, corrosion and heat resisance, it is used in many engineering fields for surface reinforcement and for repair of machine parts such as paper mill rolls, shafts and large bearings. With an increasing demand for the application of this process in several industries, it has become important to clarify the fatigue resistance of thermally sprayd steel. However, many problems remain unsolved concerning the fatigue properties of thermally sprayd coatings.In this study, the characteristics of the fatigue life of a thermally sprayd specimen with Co-based self-fluxing alloy were examined. The effects of the interface conditions on the sprayd specimen's fatigue strength were also studied. Rotational-bending fatigue tests were carried out to clarify the effect of post heat treatment (fusing treatment) on the fatigue strength of a sprayd specimen. The fatigue fracture mechanisms of thermally sprayd specimens were also examined using a Scanning Electron … More Microscope.The rusults are summarized as follows :(1) Fusing treatment temperature, heating rate and holding time strongly affect the characteristics of sprayd coatings such as configuration of microstructure, hardness and volume fraction of micro-pore (porosity).(2) Adhesion strength of thermally sprayd specimens which are fused by using a induction heating system is governed by mechanical interaction. Howver, in the case of a sprayd specimen fused by using a vacuum furnace, the diffusion of chemical elements strongly affects the characteristics of interface and adhesion strength.(3) There is considerable scatter in the value of porosity for torch-fused specimens. However, it is possible to achieve high quality coatings through well controlled fusing by using an induction heating system. In this case, the scatter of fatigue lives is much smaller than that of a torch-fused specimen.(4) The fatigue fracture mechanisms of thermally sprayd specimens are described as follows : (i) a crack start at the point of interface, (ii) the crack growth to the substrate (iii) the crack spreads from the interface in the sprayd coating and the entire coating fails rapidly (iv) the remaining part of substrate fails as a result of the coating failure. Less