Investigation Of Relative Problems About Pure Iron Surface Mechanical Attrition Treatment And First-principles Calculations Of Carbon Monoxide Surface Absorption

Surface mechanical attrition treatment (SMAT), as an effective surface nanocrystallization approach, has been developed to fabricate a plastic deformation surface layer with the gradient distribution of grain sizes along the deformation depth and with the a certain depth of nanometer grains in the upper surface, which can effectively enhance the surface service properties. SMAT has been successfully applied in many material systems. The Interfacial structure and mechanical properties of the SMATed nanocrystalline surface layer have been reported, the mechanical of refinement of coarse grains from micrometer to nanometer scale has been understood fully and the intrinsic principle of the property transformation of surface nanocrystallization has been mastered basically. This technique is now increasingly used in many practical fields. Clear understanding the process, studying the microstructures and grasping the properties of the nanostructure surface layer is still absorbing much more deeper research.In this paper, the mechanical properties of the surface nanocrystalline had been studied experimentally and simulated. Based on the relationship of grain size, hardness and intensity, using the ANSYS code, the grads structure, the effect of nano surface layer on the intensity and hardness had been researched. The alloy technics based on SMAT had been improved, and higher depth of alloy layer had been acquired. The structure of alloy surface layer fabricated by adding Ni and ZrO2 powders respectively had been analyzed. Using the first principle, the carbon monoxide absorption on the iron (110) surface had been calculated by the molecule dynamical code MS. A model has been constructed to analyze the adsorption energy, the absorbing structure, the state and energy density, which will establish a base for further research the nano iron surface.The main conclusions are as follows.1. The existence of surface 25μm nano-layer on the iron can effectively enhance the sample whole tensile property. Compared with the coarse counterpart, the elastic modulus of the nanocrystallized specimen decreases, the yield strength and tensile strength of the sample increases, however elongation decreases. It is pleasure to find that the specimen's elastic modulus increased once more when the sample has been processed by a short time of low temperature anneal treatment. The anneal treatment may decrease the residual stress and density of defects. The refinememt of surface grains to nano-grade during SMAT is contribute to the improvement of yield strength and tensile strength. Accompany the SMAT process, multiply impacts rolled the Fe surface, the existence of remainder compress stress can effectively counteract the crack formation in the surface layer. Meantime, the development of the slippages of base metal can be effectively stopped owing the existence of nano-grains in the surface layer, which can also prevent the base metal rigid.2. The calculation of tensile model with the same sample size has confirmed the experimental conclusion. The tensile model, with a grade structure, based on the relationship of grain size, hardness and intensity can simulate the tensile process reliably. The estimated tensile value of nano iron surface layer is 400MPa. 3. Some alloy elements (Nickel powders has been used in this case) have been added to the sample container during SMAT, which has been concerted to be surface mechanical attrition alloy treatment (SMAAT). After SMAAT 100min+30min 600℃anneal, the welding of Ni powders into the Fe plates induced the formation of a homogeneous of Fe/Ni alloy with the depth of 30μm. The results of micro-structural research on the interface indicated that atomic diffusion was the main phenomena and an alloying layer was fabricated during the process. After three times of SMAAT 100min+30min 900℃anneal, the depth of the homogeneous layer of Fe/Ni alloy has been enhance to 60μm. The diffusion of atoms has been accelerated rapidly. The transition layer can be found evidently in the back dispersion morphology and line scan study, which is result of annealing treatment increasing the atoms diffusion. The intermetallic compound FeNi has been formed in the alloy layer. The strain energy coming from the continual ball peening may also serve to increase the diffusion driving force, and thus further enhance the diffusion kinetics of the atomic species. The hardness in the surface layer increased significantly and the values decrease with the increase of the depth from the surface to interior. The strengthening phases, the grain refining effect and work hardening effect make the surface hardness increases rapidly.4. For the sample added with ZrO2, after SMAAT 100min+30min 600℃anneal, the surface alloy layer is with 30～50μm depth is formed on the surface of Fe base. After three times of SMAAT 100min+30min 900℃anneal, an alloy layer with the depth of 100μm is formed on the Fe surface. The harder ZrO2 distributed in the alloy surface layer in its powder state, and the grains have been refined during SMAAT, which can contribute to the increase of hardness. A certain alloy ZrFe2 and Zr can be observed in the plastic deformation layer. The long time of SMAAT and anneal can offer the convenience of form of Zr and diffusion of atoms. 5. The carbon monoxide absorption on the iron (110) surface had been calculated by the molecule dynamical code MS which based on the first principle. The mechanical of absorption, ionization and chemical bond fabrication of carbon monoxide on the iron (110) surface had been studied by the constructed model, implied that the interaction of carbon monoxide and the iron (110) surface could be realized by the charge transformation form carbon monoxide to the iron (110) surface.