Xu Jiujun

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.

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.

Elastic-plastic deformation analysis of multi-layer surface coating under sliding contact

Abstract The sliding contacts of gradient layer, sandwich layer and ordinary multi-layer coatings subjected to the same surface load have been investigated under elastic-plastic deformation in this paper. The result shows that the positive gradient layer coating, in which the elastic modulus reduced gradually from the top layer to the substrate, can improve the strain and stress fields near the layer-substrate interface greatly and its stress contour in the vertical direction is very smooth. The coating has as well a small stress on the layer-substrate interface and in the substrate. The sandwich layer coating can greatly reduce the maximum shear stress on the interface of the layer-substrate and the stress at the crack tip, but the stress and the strain gradients near the interface are very large. The stress and strain distributions of the ordinary layer have not evidently improved compared to those of single layer. Known from the analysis of the stress and strain distributions and the crack stress fields for the four kinds of coatings, the gradient layer coating has more advantages in these aspects. The results of this paper can provide the reference for the selection and design of coatings.

Dy2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

(Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 (BCTZ)+ xwt%Dy2O3(x = 0–0.20) ceramics were prepared by conventional solid-state process, and the effects of Dy2O3 on the microstructure and the electrical properties were investigated. X-ray diffraction pattern confirmed that the BCTZ ceramics exhibit tetragonal structure, and stable solid solutions between BCTZ and Dy2O3 were well established in the range investigated. SEM images show that the addition of Dy2O3 restrains abnormal grain growth and leads to the formation of homogeneous microstructures during sintering. Dy3+ occupies B-site at x = 0–0.15, and A-site at x = 0.20 respectively. A-site occupation of Dy3+ into BCZT ceramic facilitates the ferroelectric domains reorientation and thus improves the piezoelectric properties significantly from 315pC/N(x = 0) to 425pC/N(x = 0.20). The corresponding planar electromechanical coupling factor at x = 0.20 was 49.1%. The A-site occupation(x = 0.2) also exhibits superiority to the improvement of dielectric properties and ferroelectric properties for BCZT ceramics (ϵ33 = 3264 at 1 kHz, 2Pr = 28.4μC/cm2, 2Ec = 5.28 kV/cm).

Preparation of Bi3.15Dy0.85(Ti3-xFex)O12(x = 0-0.3) Ceramics and Their Electrical Properties

Bi3.15Dy0.85(Ti3-xFex)O12(x = 0−0.3) lead-free piezoelectric ceramics were prepared by a solid-state reaction method. The effects of the amount of Dy2O3 and Fe2O3 on the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction shows that the introduction of Dy and Fe does not change the layered perovskite structure of Bi4Ti3O12. SEM images indicated that Bi3.15Dy0.85(Ti3-xFex)O12 ceramics with nearly pore-free microstructures and high densities were obtained. The dielectric constant decreases with the addition of Dy2O3, but remarkably increased with the amount of Fe2O3, and it decreases with frequency, showing a diffuse phase transition behavior.