Thermal fatigue test of PVD coating
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There is no corresponding standard for the fatigue test of PVD coating. Instead, it can refer to the fatigue test method of existing thermal barrier coating (e.g., heat-resistant coating on the surface of aero-engine blades).
In addition to the general requirements for the coating, the PVD coating must also meet some special requirements. Thermal fatigue resistance is an important index for this channel.Because sometimes PVD coating often works at a higher temperature, repeatedly experiencing the effects of high and low temperature, enduring the role of thermal fatigue stress.Such as coating on the surface of the aluminum alloy die casting mould, if under normal temperature to 700 ℃ alternating temperature, need to coating has higher thermal fatigue resistance is not fall off.Several methods have been used to measure the thermal fatigue resistance of thermal barrier coating, including induction heating - compressed air cooling, induction heating - water gas cooling and electric furnace heating - water cooling.The specimens used are cylindrical, rectangular and physical.In terms of the proximity between the test conditions and the actual working environment of components and parts, the induction heating and compressed air cooling mode is relatively close to the actual working environment. However, the test equipment is complex, the test time is long, and the test cost is high.Electric heating - water cooling is the opposite way;The advantages and disadvantages of induction heating and water vapor cooling are in between.Considering that this kind of test is mainly used for the comparison of thermal fatigue properties of different coating materials and different processes, the electric furnace heating and water cooling method can completely achieve this purpose.In addition, another advantage of the electric furnace heating and water cooling method is that the test process can partly refer to the standard hb6660-1992 and be carried out on the existing test machine, which brings convenience to the test work.
Sample design is a key work in coating test. Whether the sample design is reasonable or not will greatly influence the test results. Previous tests have shown that the coating is usually destroyed first around the corner of the rectangular plate specimen due to the large stress concentration at the corner of the specimen and the thermal stress caused by the uneven heat at various parts of the specimen during the test. The cylindrical sample can avoid the above problems and is a reasonable sample.