Research Of The Measurement For Bond Strength Of Coating Using Stress Wave

Coating is kind of surface treatment technique to improve properties of materials surface, which are better than the materials themselves. Many ways of different technics can be used to improve the surface qualities of materials, such as friction-resistance, causticity-resistance, high temprature resistance and so on. The bond strength between coating and body is one of the most important targets to satisfy the mechanical, physical and chemical properties for coatings in applicatuion. Lots of methods are being applied to measure the bond strength of coatings, but they are all in the stage of being studied and far from perfact in actual application. Based on the application background and engineering purpose, a new method of measuring bond strength using stress wave is developed in this paper. In the way of this paper, Fe-base-alloy-coating or Ni-base-alloy-coating film is coated on the surface of the free end of a steel bar by oxygen-acetylene spraying. When a compressive stress pulse is generated by an impact on the other end, the pulse reflected from the free end will become a tensile one. The tensile stress will act on the coating interface, and if its amplitude is large enough the coating can be pulled apart. Then, the stress pulses can be automatically collected by computer data acquisition system via strain gauge stuck on the middle of the bar. From the one-dimension linear theory of stress wave, the reason for stress wave to pull apart coating is analysed particularly, and some mathematic expressions are obtained. In order to prove the validity of the method, some experiments are made for measuring the tensile bond strength of Fe-base-alloy-coating and Ni-base-alloy-coating, and the magnitudes of tensile bond strength between coating and 45# steel are obtained. However,it should be pointed out that the work in this paper is the beginning stage. There are still some factors, such as the length of specimen, the sorts and thickness of coating and so on, should be considered farther. The disadvantage of the method is that the specimen must be a straight bar.