Papers by Author: Chang Jun Chen

Abstract: Retracted article: In this paper, epitaxial growth on Ni-based single crystals was achieved by using spark deposition and laser powder deposition. Different Ni-based substrates, such as CMSX-4, TMS 138A as well as deposition materials: NiCrAl, Rene N4 and modified 4.5^th generation single crystal alloys were used. The deposited layers were analysed by laser confocal microscopy, FEG-SEM, X-ray and electron backscatter diffraction (EBSD), had very little dilution and epitaxial growth was confirmed for the deposits made using Rene N4 electrodes. The deposition time at 100 V voltage, 850 W power and 110 Hz frequency was 3min and the layer thickness varied from 0.3 to 0.5 mm. Cracks were observed in certain areas with the formation of stray grains. In order to investigate the influence of the laser processing during multiple build up, specimens with one and ten layers were manufactured. The total layer thickness on substrates was 0.3 mm and 2 mm, respectively. The processing parameters were: laser power of 500 W, laser beam diameter of 0.6 mm and the z displacement was equal to 80% of the layer height. The laser deposition also resulted in successful epitaxial growth and minimal defects (pores or cracks), however the clads presented high dilution.

Abstract: In this paper, epitaxial growth on Ni-based single crystals was achieved by using spark deposition and laser powder deposition. Different Ni-based substrates, such as CMSX-4, TMS 138A as well as deposition materials: NiCrAl, Rene N4 and modified 4.5th generation single crystal alloys were used. The deposited layers were analysed by laser confocal microscopy, FEG-SEM, X-ray and electron backscatter diffraction (EBSD), had very little dilution and epitaxial growth was confirmed for the deposits made using Rene N4 electrodes. The deposition time at 100 V voltage, 850 W power and 110 Hz frequency was 3min and the layer thickness varied from 0.3 to 0.5 mm. Cracks were observed in certain areas with the formation of stray grains. In order to investigate the influence of the laser processing during multiple build up, specimens with one and ten layers were manufactured. The total layer thickness on substrates was 0.3 mm and 2 mm, respectively. The processing parameters were: laser power of 500 W, laser beam diameter of 0.6 mm and the z displacement was equal to 80% of the layer height. The laser deposition also resulted in successful epitaxial growth and minimal defects (pores or cracks), however the clads presented high dilution.

Abstract: In this research work, ProCAST software is employed to study the sand casting process of a box-type part for wind turbine. The casting part is big in size, non-uniform in wall thickness, and heavy in some local positions. Shrinkage cavity and porosity are very likely to from at these locations. By numerical simulation, the influence of the parameters such as pouring temperature, chills, riser on mold filling and solidification is analyzed. Simulation researches reveal that with appropriate pouring temperature, correct number, size and location of chills and risers, a smooth mold filling, reduced shrinkage and other defects are available and desired sound castings can be produced.

Abstract: Mg-RE electrode was used for deposition of micro-arc coatings on AZ31 magnesium alloy upon variation in there different processing parameters(high, low and middle pulsed discharges). Mass transfer trends from electrode to substrate and microstructure of Mg-RE coating on AZ31 substrate were observed. Characterization has been performed by using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The microstructure, properties (continuity, thickness) were investigated. It is found that an increase in the energy mode above a certain threshold value leads to an increase in mass gain from electrode to substrate.

Abstract: A 3-D modeling based on the numerical resolution of fluid flow and heat transfer for laser-cladding processes of In718 Superalloy is proposed. The implementation of developed procedures allowed us to treat the problem with specific and complex boundary conditions. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam diameter and scanning speed. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. The computational results present good coincidences with the corresponding experiments of laser cladding process.

Abstract: An attempt has been made to fabricate Ni-base alloy layer on the surface of TC2 titanium alloy substrate by laser repair cladding technology for repairing the worn surface of TC2 alloy after in service. Laser cladding is carried out by melting the preplaced Ni-base alloy powder using a continuous wave CO₂ laser and using Ar as shielding gas. Microstructure and chemical composition of the cladding coating was revealed by optical microscope (OM), scanning electron microscope (SEM), together with the energy dispersive X-ray spectroscope (EDS). A clad layer with low dilution and metallurgically bonding coating to the substrate could be obtained. A significant improvement in microhardness is achieved in the cladding layer and at the interfacial region. The results showed that laser repair cladding is highly promising technology to restore damaged Ti alloy parts.