DEVELOPMENT OF A HIGH-TEMPERATURE REPETITIVE-IMPACT APPARATUS FOR EXHAUST VALVE MATERIAL TESTING

Some types of mating parts, such as exhaust valves and seats in diesel engines, must perform at elevated temperatures and in oxidizing environments, while at the same time resisting the effects of repetitive impacts and interfacial slip. The wear that takes place under such situations is the net result of a complex process that involves plastic deformation, tangential shear, and oxidation. Tribolayers form, are removed, and reform. An apparatus was designed to simulate the key aspects of elevated temperature wear of exhaust valves. Three degrees of motion: impact, slip, and rotation were taken into account. Two different test geometries were developed: (a) inclined cylindrical pins striking rounded corners, and (b) actual exhaust valve sealing surfaces striking the edges of flat blocks. The features of the high-temperature repetitive impact device are described, and examples of the wear scars produced by the two test configurations are presented.