Key Engineering Materials Vols. 353-358

Abstract: The evaluation of the interfacial adhesion of coating system has always been a rough task. In this paper, a special testing method of cross-sectional indentation is applied on a model coating system, i.e. electroplated chromium on a steel substrate which is generally regarded as an example of materials pair with strong adhesion. Based on fractography analysis with SEM and interfacial stress simulation with FEM, it is found that interfacial shear stress may induce coating spalling. More interestingly, spalling location is sensitive to substrate pretreatment process. This shows the feasibility of cross-sectional indentation to distinguish interfacial strength at a high level.

Abstract: Laser shock processing is an important surface treatment that induces compressive residual stress to components, where the coating plays an important role. This paper deduce a general formula of the optimum thickness of coating according to the law of energy conservation and analysis the influence of coating on residual stress of the titanium alloy in laser shock processing. Titanium alloy with black paint, silica acid black paint and without coating were shocked by laser system respectively. It was found that coating could increase shock pressure amplitude and laser density absorption. Compressive residual stresses at the surface of the sample with the black paint and silica acid black paint are about -212.2MPa and -264.2MPa respectively, while the surface stress on the uncoated specimen is very high tensile stress. The bare surface due to melting and vaporization, leads to a very rough surface. The depth of induced compressive stress could reduce stress corrosion cracking in titanium alloy and improve fatigue lifetime.

Abstract: Films were prepared on the steel (Q235) by means of vacuum vapor deposition through Al65Cu20Fe15 quasicrystal powders. Influence of ceria on the microstructure and properties of films were studied. TEM, SEM and XRD were used to observe the microstructure and morphology of films. The hardness and the modulus of the film were tested by MTS. The results showed that the films were formed through directly vapor deposited by Al65Cu20Fe15 quasicrystal. The films were constituted of many phases such as CuAl2, AlCu3 and I (Al65Cu20Fe15) phase. The composition of films was decided by the technology of deposition. After adding cerium, the microstructure of films did not radically change, however the hardness and modulus of films varied with the increase of cerium. When the cerium content was 5 wt%, the hardness of films was more than 9.0 GPa. Furthermore, adding cerium could improve obviously the corrosion resistance of films.

Abstract: Coating blade wears seriously in paper coating process. Wear mechanism was analyzed in this article. A new technology of surface coating process was introduced to increase the hardness of the edge of coating blade and thus to prolong its service life. Surface coating preparing process on blade was studied and metal-ceramic compound coating prepared successfully on the edge of coating blade with AT13 (Al2O3+13%TiO2) wear resistant material by plasma spraying process. NiCrAl alloy powder was used as under coat material. Microstructure of the coating is dense. The coating bonds well with the matrix and have high hardness. Results of grain-abrasion testing show that wear-resisting property of the metal/ceramic compound coating is about 7-8 times as that of steel blade.

Abstract: Abrasion mechanism of thermocouple cannula is studied in this article. For different working position and condition, different material should be selected to ensure the working characteristics of thermocouple cannula. Several protection methods were introduced to prolong the sevice life of thermocouple cannula. 1. M-Al series intermetallic compound coating protection method. 2. Metal/ceramic compound coating protection method. 3. Development of new abrasion-resisting material for high temperature according to some special work conditions of thermocouple cannula. With the adoption of those new technologies, thermocouple cannula’s service life can be prolonged to 3~5 times of that untreated.

Abstract: The plasma nitriding behaviors of nanocrystalline surface induced by surface mechanical attrition (SMA) and of conventional coarse-grained surface in 1Cr18Ni9Ti stainless steel were compared. Microstructure features of various sections in the surface layer, from the matrix to the nitriding surface, were systematically characterized by XRD, SEM and TEM. The thickness of compound layer and hardness distribution in the treated surface layer were investigated by means of metallographic observation and microhardness measurement. The subsequent nitriding kinetics of the treated steel with the nanostructured surface layer were greatly enhanced, the nitriding thickness was deeper than that of the conventional surface and the nitriding temperature could be as low as 300°C, which is much lower than conventional nitriding temperature.

Abstract: Based on the nonlinear theory of von Karman plate, axisymmetric nonlinear vibration of a functionally graded circular plate with clamped boundary condition is investigated under thermal loading. It is assumed that the mechanical and thermal properties of functionally graded materials vary continuously through the thickness of the plate and obey a simple power law related to the volume fraction of the constituents. Motion equations for the problem are derived. Existence of harmonic vibrations is assumed and then Ritz-Kantorovich method is used to convert the dynamic Von Karman equations to a set of nonlinear ordinary differential equations. Finally a shooting method is employed to numerically solve the resulting differential equations. Effects of amplitude A, thermal load parameter λ and material constant n on the vibration behavior of FGM plate are discussed in details.

Abstract: The tribological behaviors of Diamond-like carbon (DLC) films, prepared by the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method, were studied in the room temperature and the elevated temperature. The ball-on-disk tests with DLC films on steel specimens were conducted at a sliding speed of 60 rpm, a load of 10 N, and surrounding temperatures of 25°C and 75°C. The results show that the coefficients of friction and the amounts of wear of DLC films were decreased at higher temperature. After tests the wear tracks of hydrogenated DLC film were analyzed by Raman spectroscopy.

Abstract: Due to the environmental concerns, especially the greenhouse effect and GWP (Global Warming Potential), the carbon dioxide was investigated as an alternative natural refrigerant to replace HFCs (HydroFluoroCarbons) in refrigerator or air conditioning systems. To develop new compressor, especially rotary type, the friction and wear characteristics of sliding surfaces between vane and flange in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN and WC/C, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-flange type lubricated sliding tests were performed with a high pressure wear tester using HFC (R410A) and carbon dioxide. From the tests, wear volumes of vane surfaces applied with various coatings were compared each other.