Research On Comprehensive Evaluation Method Of The Quality Of CBN Coating On The Surface Of Titanium Alloy Parts

Laser cladding is widely used in surface modification of materials, and this technology has been very mature. But there are only a few researches on the comprehensive evaluation of surface quality of the coating. In this paper, construction and application of the comprehensive evaluation system of coating's quality are described in detail by cladding CBN coating on the surface of TC11. The comprehensive evaluation of surface quality of cladding layer is a kind of process which is multi-factor, multi-level, nonlinear, and even dynamic disturbance. The quality grades are determined through establishment of multi-level models,definition of standard levels, and contrast between calculation results of the models and standard levels.Surface defects of coating are analyzed in sub-model 1. Crack defect, dilution rate defect,smoothness defect, pore defect, morphology defect and particle defect are mainly considered.Firstly, boundary of benchmark coupon is made according to the specific circumstances of various types of defects. Then the coupons are randomly selected and quality grade of the coupons is determined through applying fuzzy evaluation theory and AHP for analyzing defect information, and calculating possible degree matrix and priority vector.Mechanical properties of the coating are researched in sub-model 2. Microhardness and abrasive resistance are mainly considered according to the purpose of the research. But the main purpose of the research is to improve the wear resistance of titanium alloy.In order to reflect this characteristic,important influence of abrasive resistance is highlighted by choosing max product fuzzy operator and using a typical F distribution to solve each index membership functions for each standard level.Finally,the quality of coupon is determined by calculating and correcting model.The most immediate purpose of application-level model is to feedback the information of the two sub-models to the final evaluation.Dynamic weight is used to achieve the purpose of this feedback.The dynamic weight is considered as a kind of synthetic weight: the objectiveweight and the subjective weight.Eventually they are integrated into a comprehensive weights after solving objective weight by using entropy method and subjective weight by using AHP and theory of consensus degree.The standard level of products quality must be defined to achieve the purpose of comprehensive evaluation of the coating.Four levels of product quality are defined according to the specific circumstances of each secondary indicator,and each level is decided by three parts, which are the district zone, the disturbance zone and the prohibition zone.Eigenvalues of standard level are also given for each level.Dynamic weights of secondary indicators are calculated after selecting coupons,and then surface quality level of coupons are given by comparing eigenvalues of coupons' quality level with eigenvalues of standard level.