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Investigation of 0Cr18Ni9 Stainless Steel Supersonic Fine Particles Bombaeding(SFPB) Surface Nanocrystallization’s Mechanism and Property

Author: LiuZhongLiang
Tutor: JingXiaoTian；GeLiLing
School: Xi'an University of Technology
Course: Materials Science and Engineering
Keywords: Supersonic Fine Particles Bombarding (SFPB) Surface nanocrystallizaion 0Cr18Ni9 stainless steel Low stacking fault energy Deformation twins Martensite transformation Low temperature gas nitriding
CLC: TB383.1
Type: Master's thesis
Year: 2008
Downloads: 110
Quote: 1
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Abstract


The surface nano process is the surface layer of a certain thickness is formed in the surface of the bulk material nanocrystalline tissue. By surface nanometer process, not only the unique properties of nanomaterials gives traditional materials to improve its overall performance, optimize traditional surface treatment processes, access to the surface has a unique structure and superior performance, as well as in the nanoscale system research process, the relationship between structure and properties of the ideal sample. This selection has a wide application background and stacking faults 0Cr18Ni9 can lower stainless steel as an object of study, the use of the supersonic particle bombardment process (SFPB) technology to achieve surface nano; metallurgical microscope, X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) samples on the surface of the nano structure characterization; assessment and analysis of a the surface nanocrystallization hardness, wear resistance, corrosion resistance, and low-temperature nitriding behavior. Low stacking fault energy of material SFPB process nano-mechanisms and 0Cr18Ni9 stainless steel penetration mechanism of low-temperature nitriding discussed the following main conclusions: 1. Supersonic particle bombardment 0Cr18Ni9 stainless steel surface nano. After 30 minutes SFPB, 0Cr18Ni9 stainless steel surface formed about 30μm thick the nanocrystalline tissue surface, the surface grain size of about 18nm, with the increase in the processing time, the grain size continues to decrease and then gradually stabilized; With from the surface depth increases, the grain by the random orientation of the equiaxed nanocrystalline gradually becomes irregular shape having a preferential orientation of submicron grain, grain refinement gradually becomes nonuniform. Strain-induced martensitic transformation was 2.0Cr18Ni9 stainless SFPB process. The content of the surface layer of martensite with the increased processing time of growth tends to 100% by of 30 minutes SFPB processing 0Cr18Ni9 stainless steel surface, the martensite content: martensite content is gradually reduced with the depth from the surface increase, while the Austrian Golgi content increases. 3 low stacking fault energy 0Cr18Ni9 Stainless SFPB process of deformation twins as the main deformation way. Organizational structure along the depth from the surface to be treated as follows: surface nanocrystalline mostly the twins, the monophyletic twins, flat-type dislocation arrays, no stress matrix; grain refinement of this material by deformation twins split, segmentation process as close to the treated surface gradually getting smaller and smaller scales; near the surface, with a multi-system deformation twins nanoscale grain division of nanoscale structural units; gradually so that the orientation of these structural units of the repeated impact of the projectile into a random distribution. 4. Surface nano nitrogen 0Cr18Ni9 stainless steel sample surface diffusion speed, thus optimizing the low-temperature nitriding effect of such a material, and of multiplying the low-temperature diffusion layer thickness. Surface nanocrystallization sample was 400 ° C, 450 ° C for 9 hours nitriding formed nitride layer thickness is twice the size of the coarse-grained samples under the same conditions; ε-phase and γ 'phase structure is formed in the surface layer, improve the layer hardness gradient greatly improving the hardness of the specimen surface.

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