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Research on Surface Modification of Commercial Pure Iron Processed by Surface Self Nano-crystallization

Author: WangYueTian
Tutor: ShengGuangMin
School: Chongqing University
Course: Materials Science and Engineering
Keywords: Surface self- nanocrystallization Pure iron High energy shot peening Proliferation Alloying
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 24
Quote: 0
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Abstract


Stainless steel having a good corrosion resistance, heat resistance, low-temperature strength and mechanical properties, in various fields are widely used, but its price is also much more expensive than ordinary steel materials; in actual use, the material failure occurs mostly in the surface of the material, such as material corrosion and wear; Therefore, in some occasions only need to reach the surface of the stainless steel performance using certain methods produce good mechanical properties and corrosion resistance of the surface structure than all can save a lot of stainless steel alloy dosage, which considerably lower production costs. This article is based on the basis of this theory, penetrate the from nano chemical industry pure iron surface by the surface of Cr, Ni elements, the ingredients of pure iron surface layer at or near the level of the stainless steel, the center remains pure iron, so that not only satisfy stainless steel needs of the environment, but also saves a lot of costs and resources, practical engineering applications. By the energetic shot peening, in the end surface of pure iron bars prepared had a layer structure of the surface of the nano-grain size. Atom diffusion due to surface since the nano nano tissues containing a high volume fraction of grain boundaries, be able to provide a large number of channels for the diffusion of atoms, nano organization has a higher Gibbs free energy, reduce the activation energy, which will help improve the diffusion The coefficient of diffusion of atoms in the process. Characterization of pure iron surface nano-layer nano layer relationship between thermal stability and deformation depth peening time. Of the sample after the shot peening at a temperature of 600 ° C to 850 ° C within a single diffusion of Ni and Cr-Ni diffusion treatment in order to achieve a pure iron surface alloying. The structure of the sample before and after the proliferation characterized by optical microscopy, X-ray diffraction and scanning electron microscopy were used to characterize the sample after the diffusion of the concentration distribution of the alloying elements to be measured by energy dispersive spectroscopy. The hardness and corrosion resistance of the surface of the alloy layer after diffusion can also studied. As the peening time is increased, the thickness of the deformable layer of the pure iron surface increasing shot peening time reaches 6min sample the surface of the grain is refined to nanometers, the thickness of the deformed layer is about 135 μm, the grain size from surface to the increasing depth with increasing depth, the shot peening treatment time exceeds 6min, the thickness of the deformed layer is no longer significantly increased. The pure iron energetic peening tissue is annealed at a temperature of below 600 ℃, there is a relatively good thermal stability. After treatment in 600 ℃ ~ 850 ℃ diffusion of Ni or Cr-Ni sample the outermost layer of nanocrystals and deformation layer grain have varying degrees of growing up, the impact of the positive role of the nanocrystals atomic diffusion; in between relatively good intermediate temperature of the diffusion effect, the formation of an alloy layer of about 10μm. The hardness of the surface of the sample after the diffusion process has greatly improved, and declined rapidly within the range of 40 μm up to the hardness of the matrix. Energetic shot peening lower than the original sample of the corrosion resistance of the surface of the pure iron specimen, and then after the diffusion process, have greatly improved corrosion resistance, and higher than the original sample.

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