Wu Yixiong

Residual stresses in coating-based systems, part I: Mechanisms and analytical modeling

Thin films and multi-layered coatings comprised of different classes of materials are often used for various functional devices. The thermo-mechanical integrity of these systems is becoming a major concern and is strongly related to the residual stresses because of the fabrication processes. In this paper, the sources of the residual stresses in the coating-based systems and the concept of “misfit strain” were briefly reviewed. Analytical models were developed to predict the residual stresses in multi-layered film structures or coating-based systems using the force and moment balances. In addition, the residual stress distributions in the functionally and compositionally graded coatings were also analyzed.

Erosion-corrosion behaviors of high velocity arc sprayed Fe−Al/Cr3C2 coating

Iron aluminide intermetallic coatings were prepared from Fe−Al/Cr3C2 cored wires using High Velocity Arc Spraying (HVAS) technology. Erosion and corrosion properties of HVAS sprayed Fe−Al/Cr3C2 coatings were investigated. Results show that the erosion at impingement angle of 30° is more than that of 90°. The erosion resistance of coatings was enhanced with the increase of temperature. Coatings had a better erosion resistance than substrates. The erosion changed from ductile behaviors to brittle behaviors above 450°C. At high temperature, the erosion resistances were superior to those at low temperature and room temperature. Coatings had much higher corrosion properties than substrates. The temperature had a little effect on the corrosion resistance of coatings; The corrosion losing of coatings increased slowly with the increase of corrosion time. The HVAS-sprayed Fe−Al/Cr3C2 coatings exhibited a high bond strength and hardness.

Study on process stability and seam characteristics of high power laser welding with filling wire for high thickness steel

This paper focused on a systemic solution to high power laser welding for high thickness shipbuilding steel. The laser induced plasma not only absorbs laser energy but also affect welding process stability especially when laser power is higher than 10 kW. The electron density, electron temperature and plasma height are analyzed in paper with high speed camera and spectrometer in this paper. Laser Supported Combustion (LSC) result in instable laser welding process and cause bad seam quality. As an effective method to suppress plasma and keep stable welding process, flow rate of side blowing gas is analyzed. The relationship between Seam shape, its mechanical properties and welding parameters is studied. Experiments results showed that High power laser welding is a qualified and efficient method for high thickness shipbuilding steel.

Residual stresses in coating-based systems, part II: Optimal designing methodologies

In this part of the work, different cases are studied to illustrate the implementation of the analytical models that have been developed in Part I [Front. Mech. Eng. China, 2007, 2(1): 1–12]. Different topics are involved in the optimal design of coating-based systems. Some essential relations among material properties and dimensions of the coating and substrate and the residual stress variations are reflected. For the multilayered coating-based systems, some optimal design methodologies are proposed, such as the decrease in stress discontinuity at the interface between the adjacent layers, the curvature as a function of the coating thickness, the effect of the interlayer on the residual stress redistribution, and so on. For the single-layered coating-based systems, some typical approximations that are often used to predict the residual stresses in the coating-based system or bilayer structure are corrected. A simplified model for predicting the quenching stress in a coating is also developed.

Remanufacturing strategy for chemical equipment

Failure, especially induced by cracks, usually occurred in the service process of chemical equipment, which could cause the medium leakage, fire hazard and explosion and induced the personnel casualty and economic losses. To assure the long-term and safety service, it is necessary to apply the remanufacturing technology on the chemical equipment containing cracks. The recent research advances on the remanufacturing, the failure modes and the life extension technology for chemical equipment were reviewed. The engineering strategy of the remanufacturing for the chemical equipment was proposed, which could provide a reasonable and reliable technical route for the remanufacturing operation of chemical equipment. In the strategy, the redesign was also been considered.

The Development of a Microcomputer-based Control System of the Machine for Ultra Thin Sheets Welding

This paper describes a successfully developed CMC-80 microcomputer-based control system of GTAW welding machine for ultra thin sheets welding. ACMC-80 microcomputer is used to control a transsistor power source, a step motor and other equipments, thus the functions as position control, adaptive control, constant current control, current waveform modulation and selection of the welding sequences have been realized. This paper presents the constitution and the function of the system. It introduces also the used method against high frequence interference. The developed control system operates steadily and the welding quality has been obviously raised.