Xu Xiaolei

Characteristics of low pressure plasma arc source ion nitrided layer on austenitic stainless steel at low temperature

Abstract Samples of the AISI 304 austenitic stainless steel nitrided at low temperature and low pressure by low pressure plasma arc source ion nitriding have been examined by cross-sectional transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy and microhardness tester. A high nitrogen content layer with a thickness of approximately 10 μm which is very hard and f.c.c. phase was obtained by nitriding at ∼420°C for 70 min at pressure of 0.4 Pa. The results of XPS suggest that the nitrogen induced by nitriding process be in the state of solid solution. The transmission electron microscopy results are consistent with that of previous X-ray diffraction observations.

Low pressure plasma arc source ion nitriding compared with glow-discharge plasma nitriding of stainless steel

Abstract The nitrided layers produced by low temperature conventional d.c. glow discharge plasma nitriding and low pressure plasma arc source ion nitriding on AISI 304 austenitic stainless steel were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness testing. The surface nitrogen content was determined by electron probe microanalysis (EPMA) and energy dispersive X-ray analysis (EDX). The nitrogen content in the nitrided layer obtained using a low pressure plasma arc source is higher than that in the nitrided layer obtained by d.c. glow discharge plasma nitriding at 420°C. Microstructural analyses by XRD show that both treatments at the same temperature of ∼400°C lead to predominant formation of the f.c.c. nitrogen [N] solid solution phase γ N . However, the concentrations of N and the layer thickness of this phase are clearly different for the various treatments. There are substantial differences in microstructures and phases detected by TEM, which showed that the pure expanded austenite phase with a f.c.c. structure was formed in the nitrided layer for the low pressure plasma arc source, but for glow discharge plasma nitriding, the CrN+γ mixture was present in the nitrided layer even when nitriding at temperatures below 450°C. The reason for this is not clear. When the temperature was increased to 480–500°C, there was no evident difference in the microstructures and phases in nitrided layers obtained by both treatments. The nitrided layers all consisted of CrN+α-Fe phases. Both nitriding methods are able to harden the surface of austenitic stainless steel by nitrogen diffusion forming nitrided layers.

Low temperature nitriding and carburizing of AISI304 stainless steel by a low pressure plasma arc source

Abstract This paper presents results on the nitriding and carbrizing of AISI 304 stainless steel by a low-pressure plasma arc source at 420°C in ArN 2 H 2 or ArH 2 CH 3 COCH 3 (acetone) gas mixtures. The working pressure was 0.3–0.4 Pa and the negative voltage applied to the samples was 0.8–1 kV. The phase of nitrided layer formed on the surface was confirmed by X-ray diffraction. The hardness of the samples was measured by using a Vickers microhardness tester with the load of 100 g. X-Ray photoelectron spectroscopy and Auger electron spectroscopy were also carried out to elucidate the chemical states and N concentration of the nitrided layer. The surface properties were investigated by wear and corrosion measurements.

Microstructures and properties of PVD aluminum bronze coatings

Abstract Aluminium bronze coatings were deposited by the hollow cathode discharge (HCD) ion plating technique. The thickness of coatings were over 20 μm with excellent adhesion to the substrate. The structures of the coatings deposited on QAL10-4-4 aluminum bronze were studied by cross-sectional transmission electron microscopy (X-TEM) and X-ray diffraction (XRD). The results show that coating consists of different morphology zones. There are more γ2(Cu9Al4)and β(NiAl) phase in the coating than in the bulk material. The wear test and practical application showed that after deposit the wear resistance evidently improved.

XTEM and XPS studies of plasma nitrocarburising layers on 0.45% C steel

Abstract A characterisation study of the phases formed during nitrocarburising of 0.45% C steel at 540±20°C for 4 h in a d.c. glow discharge was performed by X-ray diffraction, cross-sectional electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show a compact surface layer with columnar morphology composed of γ′-Fe4N and e-Fe2–3N with some α-Fe existing at the interfaces between columns. There are three different kinds of column, which consist of a mixture of e with γ′ precipitations, single γ′ and single e, respectively. A transition layer is present between compound layer and diffusion layer. This layer is mainly composed of γ′ phases with sphere morphology. In the diffusion layer γ′ phases and larger carbides were observed.

Formation of molybdenum boride cermet coating by the detonation spray process

The effects of the powder particle size and the acetylene/oxygen gas flow ratio during the detonation spray process on the amount of molybdenum phase, porosity, and hardness of the coatings using MoB powder were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The results show that the presence of metallic molybdenum in the coating results from decomposition of MoB powder during thermal spray. The compositions of the coatings are metallic Mo, MoB, and Mo2B, which are different from the phases of the original powder. The amount of molybdenum phase increases monotonously with the oxygen/acetylene ratio, but the increasing rate for the fine powder is faster than that for the coarse powder. The porosity and hardness of the coating are related to the amount of molybdenum phase. The phase constitution of the coating is discussed.