Research Of Plastic Deformation Properties Of Iron-Nickel Graded Materials Under The Low And Repeated Stress

In the process of production, important parts under the low and repeated stress, often lead to failure because of the plastic deformation. Research shows that strain energy and stress in unit volume attenuate with layer depth. So strain rate decreases with the increase of collisions, and deformation are mainly concentrated on the surface of material and nearby. Based on this phenomenon, this paper adopts advanced technology-spark plasma sintering technology, to prepare three specimens1#the pure iron,2#iron by coating nickel,3#iron by graded coating nickel. After the low and repeated stress test, make an analysis of deformation rules and establish mathematical models under certain assumptions.With orthogonal test, prepare seven groups of sintering experiment, and find out the best sintering temperature, sintering time, and sintering pressure, to ensure the best comprehensive mechanics performance of the specimens. By micro-hardness testing, the hardness value of iron by graded coating nickel showed a trend of continuous gradient increases. Observation images under optical microscope and metallographic microscope show that the transition between each layer are inseparable, meeting the expectations.By coordinate grid method, the deformation of three specimens are analyzed. With the same condition (collision stress:σ=50Mpa, collision height:h=12.5mm, collision frequency:p=4Hz), specimen3#is better than the other two in cumulative strain and the maximum strain rate. At the same time, deformation area is significantly less than others. These fully reveal that the deformation resistance of gradient specimen is remarkably superior to specimen1#and specimen2#. Meanwhile, the strain-hardening is consistent with the conclusion above. After analysis of test data, and the establishment of mathematical model, we can come to the following conclusions:cumulative deformation and collision number are in exponential relationship; When the number of collision is definite, deep layer and the natural logarithm of the strain rate are linear. Using software, this paper carries on the regression analysis and inspection for the two model, to ensure the reliability.