Research On The Plastic Accumulation Of Cobalt-base/stainless Steel Gradient Coating Under Low Stress Repeated Impact

In engineering application, many key components can still be failure due to themacroscopic accumulated plastic deformation which work in the repeated impact loadand the stress is far less than the material yield limit.This kind load will be called lowstress repeated impact load in the paper.It is found that the plastic deformation of thematerial is mainly manifested in closer to the site from the collision surface.And thestrain decreases with increasing depth from the surface.The exponential relationshipbetween strain and layer deep.In addition, The so-called gradient material is a compositematerial that allows two different properties of the material showed a continuous changefrom side to side along the thickness direction.So that the function of the gradientmaterial also showed a gradient. Combination of materials of low stress repeated impactdeformation law and the characteristics of the graded material,the article was preparedby two specimens of the cobalt base/stainless steel linear gradient coating and indexgradient coating. Then study the law of its low stress repeated impact plasticdeformation and the establishment of a deformation model of cumulative macroscopicplastic strain.In this paper,the low stress repeated impact tests were in the same experimentalconditions.The paper selected three kinds of specimens.they were304stainless steel,instainless steel as matrix of linear gradient coating and index gradient coating.Researchmaterial fatigue strain and cumulative deformation law of the above materials,and thefollowing conclusions:①The plastic deformation of the all specimens is mainlymanifested in closer to the site from the collision surface.And the strain decreases withincreasing depth from the surface.When the depth reach a certain number,the specimenswill no longer be deformed.②In the initial stage of the impact,specimen strain is thebiggest.Then the strain will be getting smaller and smaller with the increase of the number of the impact.Finally,the strain tend to be stable,that means the specimens willno longer be deformed.③Index gradient coated specimen for resistance to low stressrepeated impact plastic deformation is more effective than stainless steel and the lineargradient coating.Its total cumulative deformation is only about1/3of304stainless steelspecimens.④Using the regression analysis method,the deformation models of gradientcoated specimen were established which showed the relationship among the strain ofthe low stress repeated impact,the impact times and the depth.⑤The deformation lawof gradient coating is similar to the typical creep,but it also has the the characteristics ofits own.The paper also has a preliminary analysis of the microstructure and deformationmechanism of the gradient coating,draw the following conclusions:①After the lowstress repeated impact,near the surface of the gradient coating has the grainfragmentation phenomenon.And the microstructure change is not more obvious withwith increasing depth from the surface.②The gradient coating has the deformationhardening or softening phenomenon after the repeated impact.And this phenomenononly occurred in a certain depth. Index gradient coating deformation hardening orsoftening phenomenon is the weakest,so the index gradient coating has the strongestability to resistance plastic deformation.