Papers by Author: Xin Min Fan

Abstract: Nanostructured surface layer was synthesized on 316L stainless steel by means of high-speed rotation wire-brushing deformation (HRWD). The refined microstructure features were systematically characterized by optical microscopy (OM), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) observations. Furthermore, the microhardness was examined by microhardness tester. After HRWD treatment, obvious grain refinement was observed and a nanocrystalline surface layer was formed on 316L stainless steel. It was found that a gradient microstructure with grain size from nanoscale to microscale was obtained along the depth of its surface layer. The thickness of the nanocrystalline surface layer varies from a few to about 20μm depending upon the treatment duration and compressive stress. The microhardness of nanostructured surface layer was enhanced significantly, and along the depth from the top surface, the microhardness in the surface gradually decreased to that of the matrix. Besides, the grain refinement mechanism and behaviors were discussed.

Abstract: As an active metal, chromium is easy to form oxides film on the surface, which acts as an obstacle to the nitrogen diffusion in plasma nitriding. Rare earth (RE) was introduced into the conventional plasma nitriding (CPN) to improve the nitriding behavior. Chromium coatings were treated by CPN and rare earth plasma nitriding (REPN) at 620°C for 5 and 10 hours respectively. Comparative study showed that the addition of RE prompted greatly the formation of higher nitrogen containing phase CrN, rather than Cr2N. It created a crack-free, much denser and thicker nitrides layer, which contributed to the increase of hardness. The dynamic ultra micro hardness of the samples treated by REPN was nearly 1600GPa, which was much higher than the original and the CPN treated samples. The conclusion could be drawn that compared to CPN, REPN are more efficient for chromium coating nitriding.

Abstract: A nanostructure surface layer was produced on low carbon steel and commercially pure titanium using high-speed rotating wire-wheel deformation (HRWD). The microstructural features of the surface layer were systematically characterized by cross-sectional optical microcopy observations, transmission electron microscopy, and microhadness measurement was conducted along the depth from top surface layer to matrix of the samples. The results show that nearly equiaxed nanocrystalline layer is formed on the surface of the low carbon steel and pure titanium, in which the average grain size is about 8 nm and 15 nm respectively. The microhardness of the top surface is enhanced obviously compared with that of the coarse-grained matrix.

Abstract: Plasma arc, a kind of high energy density beam, is proposed as one kind of surface treatments in this paper to improve the adhesive properties of the chromium coatings to the steel substrate. Scratch tests are used to obtain the critical load (Lc) of the coatings. The wear behaviors are evaluated by a reciprocating ball-on-flat wear machine and the wear tracks of the coating were characterized by scanning electronic microscope (SEM). Results show that plasma arc treatment could promote the adhesive and the wear performances of the chromium coatings. Optimal value of Lc and the wear resistance of the treated coatings could be obtained when the average output energy density of the plasma arc (E) grow to 1.05×105J/m2. The comparative study indicates that the promotion of the adhesion could be attributed to the formation of the inter-diffused alloyed layer and the improved hardness distribution. This promotion then contributes to the improvement of the wear performance, which makes up, even exceeds the loss of it caused by the drop of the coatings hardness.

Abstract: Nanostructure surface layer was fabricated on a low carbon steel cylinder specimen by means of circulation rolling plastic deformation (CRPD), and the effect of annealing temperature on microstructure and properties of surface nanocrystalline structure was studied. The microstructure of the surface layer on the samples was observed by transmission electron microscopy and the microhardness variation along the depth was measured on the cross-sectional samples by using microhardness instrument. After CRPD treatment for 250min, the average grain size was about 10nm in the top surface layer and increased with an increment of the distance from the top surface. The surface nanocrystallization samples were annealed at 200°C, 300, 400°C and 500°C for 30min respectively. The nanocrystallization grain of surface layer did not grow for samples after annealed at 200°C and 300°C. After surface nanocrystallization by CRPD treatment the microhadness of top surface obviously increase from 220HV0.1 to 520HV0.1.

Abstract: The tribological properties of Zr-based and Cu-based bulk metallic glasses (BMGs) sliding against discs of SUS 304 and Si3N4 at room temperature under dry and lubrication of fresh plasma, distilled water, and physiological distilled water were investigated on a pin-on-disc testing machine. The results demonstrated the influences of counterface materials, lubrication conditions and the characteristics of BMGs on the frictional behaviors of the Cu- and Zr-based BMGs. It is found that the steady state friction coefficients and the wear rates sometimes are not consistent, and the wear resistance was been improved when the counterface change from SUS304 to Si3N4. Otherwise, wear rates of the BMGs under lubrication conditions are much lower than that of under dry sliding conditions, and the Cu-based BMGs exhibits higher wear resistance than Zr-based BMGs under same experimental conditions because it is a nanocrystalline amorphous alloy and has the higher glass transition and crystallization temperatures.

Abstract: In this paper, the circulation rolling plastic deformation(CRPD) surface nanocrystallization technology is proposed based on the idea that the severe plastic deformation can induce grain refinement. The equipment of CRPD is designed and manufactured. A nanocrystallization surface layer was successfully obtained in a column sample of low carbon steel. The average grain size in the top surface layer is about 18 nm, and gradually increases with the distance from the surface. The hardness increases gradually from about 200HV0.1 in the matrix to about 600HV0.1 in the surface layer.