Water Cavitation Peening And Contact Fatigue Properties Of Camshaft Materials

The surface of materials is strengthened by conventional shot peening, and thereby the fatigue life of components can be improved, which gets extensive applications. However, it makes the large surface damage, the surface hardening layer is not required to generate the zero component of the surface roughness is difficult to achieve effective strengthening treatment. However, it makes damage to the surface of components, it is difficult to achieve efficient strengthening treatment that the surface hardened layer is required to generate while the surface roughness of the components is not changed, and it is hard to strengthen the surface of components of complex structure. The first domestic water cavitation peening machine is developed by the research group, according to mechanism of cavitation and cavitation erosion, the surface of components produces a uniform residual compressive stress layer with little damage due to the cavitation impacts. WCP can be described as a green technology which makes up for the shortcomings of conventional shot peening.In this paper, both 20Cr and 50Mn were tested using water cavitation peening equipment in different time. Utilizing optical microscope, scanning electron microscope, microhardness instrument and residual stress measuring equipment, the test specimens were analyzed which were processed by WCP in different time. The samples of different process parameters were tested and analyzed comparatively through contact fatigue testing machine.Results indicated that the surface of 20Cr treated in different WCP time appeared various different degree of corrosion pits, the degree increased with the increase of treatment duration. The surface came out the coterminous pits in 120min of WCP, and the surface layer appeared the flaw in 120min, of which the depth was about 15μm using SEM. The morphology of the surface and the surface layer of 50Mn in 60min was similar to the same process of 20Cr.The microhardness of the surface after WCP enhanced obviously in contrast with undisposed surface of 20Cr. The surface hardness enlarged with the increasement of WCP time, but the time is too long to increase the hardness. The hardness amplitude reached the maximum in WCP 90min, while the hardness began to decrease in 120min.In addition the surface layer hardness test results showed that the hardened layer depth of 20Cr with WCP was 20-40μm.Combining with analysis of both the morphology and the hardness, which included that cavitation bubbles collapse caused the surface damage close to the saturation of 20Cr in 120min. Through comprehensive analysis,90min of water cavitation peening was the best time for 20Cr.The surface of 20Cr obtained higher residual compressive stress than that of not WCP, the difference value of residual compressive stress was smaller than that of not WCP in X and Y. It indicated that WCP effect is obvious, and the distribution of surface residual compressive stress was well-proportioned. In contact fatigue test, the fatigue life of specimens after WCP was higher than the life of the samples with not WCP, and with the increase of WCP time, the life was augmented, which showed that WCP had good strengthening feature again.