Papers by Keyword: Surface Self-Nanocrystallization

Abstract: Surface self-nanocrystallization (SSNC) is a new surface modification technology to develop new materials, which can obtain nanostructured layers with nanograins on the metals surface without changing the chemical composition of the metals. In this study, SSNC was introduced from the aspects of the preparation methods, microstructural mechanism, mechanical properties, surface roughness, corrosion resistance and applications. This paper will provide experience and reference for further comprehensive researches and industrial applications of SSNC.

Abstract: In this work, the effect of surface self-nanocrystallization on low-temperature gas carburizing for AISI316L austenitic stainless steel has been studied. The surface ultrasonic rolling processing (SURP) was used to prepare nanostructured surface layers, and then the un-SURP and SURP samples were treated by LTGC at 470 °C for 10 h, 20 h and 30 h. In order to analyze the effect of surface self-nanocrystallization on low-temperature gas carburizing, optical microscopy (OM), atomic force microscope (AFM), scanning electron probe micro-analyzer (EPMA) and nano-indentation analyzer were used. The results show depth of SURP-induced plastic deformation layer was about 330 μm. Meanwhile, the surface hardness and elastic modulus were increased but the surface roughness decreased obviously after SURP. After low-temperature gas carburizing, according to the results of the thickness, carbon concentration, nano-hardness and elastic modulus of the carburized layer, the conclusion is that surface self-nanocrystallization carried by SURP has a negative effect on the low-temperature gas carburizing for AISI316L austenitic stainless steel and with the increase of carburizing time, the greater the adverse effect on carburizing.

Abstract: Rapid low-temperature pack aluminizing was achieved on pipeline steel X80 through combined effect of surface refinement treatment and modification of pack powder. Self-nanocrystallization surface of pipeline steel X80 was obtained by surface mechanical attrition treatment (SMAT). In addition, zinc (Zn), which has lower melting point than that of Al, was added in the pack powder, to enhance the concentration of active aluminum (Al) atom. The mechanism of the low- temperature pack aluminizing was analyzed by examining the distribution of atoms and coating thickness using EDS and SEM. The study shows that aluminizing rate of as-SMATed pipeline steel with self-nanocrystallization surface is higher than that of non-SMATed pipeline steel under the same pack condition. The addition of Zn can increase the activity of diffusion atoms and accelerate the aluminizing by changing the state of pack powder from a single solid phase to a mixture of solid phase and liquid phase. The diffusion of atoms in this low-temperature pack aluminizing is considered as bulk diffusion which is driven by the activity of diffusion atoms in an unstable state following Fick law.