Papers by Keyword: Laser Cladding

Abstract: An in-situ synthesized TiC gradient coating was prepared on a Ti600 substrate. .Results indicated that the microstructure and chemical compositions of the gradient coating exhibited a continuous gradient distribution. The most outer coating has an excellent comprehensive properties. The gradient coating has a good wear resistance, under dry sliding wear condition. The granular wear is the main way for the coating wear. The hardening mechanism for gradient coating are second phase strengthening, grain refining strengthening and solid solution strengthening.

Abstract: In the whole process of micro-forging regulation laser cladding layer, the microstructure structure of cladding layer would change. In order to establish the microstructure evolution of the whole process, firstly re-crystallization model was set up based on Avrami equation and experimental data, and various material constants were gained with regress; secondly calculation for the model was carried out on DEFORM-2D,then the results were compared with experimental data, which showed that calculation results of this model kept good consistency with experimental data, and proved that the model could be applied in a full size finite element simulation of the micro forging process.

Abstract: Micro-plastic deformation was produced on the surface of the laser cladding layer by micro-forging, thus cracks were healed in cladding layer; in order to reduce the thermal stress, preheating the substrate was needed to reduce the temperature gap between cladding layer and substrate. In this paper, temperature field by micro-forging on laser cladding Ni60 layer was simulated on software named DEFORM-2D. Compared the width of cracks, the results showed that reasonable and effective preheating temperature could ensure to reduce or eliminate cracks on laser cladding layer.

Abstract: The aim of this work was to improve the surface layer properties of the Mg-Al-Zn cast ZM5 magnesium alloys by melting and preplaced Al powder or Al+Y₂O₃ powder on the surface. Laser processing was carried out using high power continuous wave CO₂ laser. The resulting surface layers were examined using metallographic light microscopy, scanning electron microscopy, X-ray diffraction. The corrosion resistance was detected by potendiodynamic polarization test. The morphology of the Al cladding coatings are dendrities. And the coatings have excellent corrosion resistance compared to the untreated ZM5 substrate. The enhanced corrosion resistance coating doped with Y2O3 was attributed to the refined microstructure induced by Y₂ O₃

Abstract: The Ni-based WC alloy coatings were successfully fabricated on NAK80 mold steel by Nd:YAG and CO2 lasers. The microstructure and properties of the laser cladded coatings were analyzed by SEM, EDS, XRD and microhardness tester. The results show that phase constituents of both coatings are mainly composed of tungsten carbide (WC+W2C), Cr23C6, NiCr, CrB2 and γ-Ni. The excellent metallurgical bondings have formed at the interface between the substrate and the laser cladded coatings. Dendrite and white and block WC phase were observed in two kinds of laser cladded coatings, but the dendrite in Nd:YAG laser cladded coating is more fine. The microhardness of NAK80 mold steel is greatly improved by laser cladding, however the microhardness of the CO2 laser cladded coating is even higher than the Nd:YAG laser cladded coating.

Abstract: According to the microstructure defects of laser claded nickel alloy, such as crack and nets brittle phase, the friction stir processing (FSP) method is utilized in this paper to modify microstructure defects by the coupled effect of thermal and stress of FSP. For this purpose, two key scientific problems of large deformation condition and microstructure evolution theory during FSP, are proposed in this paper. Based on this, the following issues are highlighted in this work. Firstly, obtain the friction condition of larger deformation by continuous dirved friction experiment. Secondly, study on the temperature (T), stress (σ), and strain velocity under different processing parameters via self-developed physical simulation apparatus. Thirdly, disclose the effects of T、σ、 on the microstructure evolution and then obtain the microstructure evolution equation by dynamic re-crystallization. The above work could provide theory support for the new technique of laser cladding and FSP for preparing high performance coating.

Abstract: Laser surface cladding of Ti-6Al-4V alloy by Ti+C+Al powders (Titanium and carbon powders with an atomic ratio of 1:1 were mixed with 20-40wt.% aluminum powders) was investigated. TiC particles were in situ formed mainly during the solidification. Effect of Al content on the porosity and microstructure of the cladding layer was studied. The resultant microstructure in the modified surface layer was characterized and the micro-hardness on the cladding layers was measured, as well as the wear rates. The results show that the coating had good metallurgical bonding with substrate when the Al mass fraction in Al-Ti-C system is 30 %. The micro-hardness of coating is 802HV0.5 which is 2~3 times as that of the Ti-6Al-4V alloy approximately.

Abstract: The temperatures inside the gas turbine reach up to 1000°C, alloys used for gas turbine components must be oxidation, and corrosion resistant, and stable in structure under high temperature circumstances. A Co-based alloy was cladded on the 1Cr18Ni9Ti stainless steel surface using a high power carbon dioxide laser. The microstructure evolution and hot corrosion properties of samples in 75%Na₂SO₄+25%NaCl saline were investigated. The results show that the microstructures of the cladded layer is fine, and the hot corrosion resistance of the cladded layer was significantly improved because of the formation of a protective oxide film of CoO and CoO•Cr₂O₃. Under high temperature corrosive atmosphere, the high content of Co promoted the formation of the protective oxide film. The refinement of dendritic structures and the formation of Co-based alloy oxides lower the penetration rate of the sulphur ions that induce the intergranular corrosion.

Abstract: Titanium alloys which exhibit excellent material properties like a high strength to weight ratio and good corrosion resistance have become the important structural materials in the applications of the aerospace. However, it’s quite difficult to repair the damages of the titanium alloy parts such as fatigue crack and erosion resulted from poor working environment using the traditional manufacturing technology while the problem can be easily solved with the help of laser cladding technology. For the excellent quality of the fixed parts, it is extraordinarily significant to obtain the rule of the temperature and thermal stress distribution in the cladding process. To investigate the influencing rule of cladding coating's temperature and stress on laser cladding process parameters, the model of laser cladding based on TC4 titanium alloy is built by the way of finite element method (FEM). This model encompasses the effects of the temperature-dependent thermal conduction and radiation as well as the latent heat of fusion. Different laser processing parameters are chosen to calculate the temperature and stress of cladding layer.The result shows that the temperature of the clad coating is positive correlation with the raise of laser power and the depth of the powder layer, and negative correlation with the raise of scanning speed and the laser spot diameter. In addition, the transient stress of clad coating is augmented with the increase of laser scanning velocity, laser spot diameter and the depth of the clad coating while it’s negative correlation with the raise of laser power. The numerical results provide the theoretical guidance for optimization of the laser cladding parameters on TC4 titanium alloy.

Abstract: In order to enhance the performances of laser remanufacturing part, we combined laser cladding with active screen plasma nitriding duplex treatment to repair metal part. The microstructure, phase structure and micro-hardness of duplex treated coating were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and micro-hardness tester. Wear tests were carried out on reciprocating wear tester under dry sliding condition. The results show that the white layer and the nitrogen diffusion layer were formed after nitriding treatment. The duplex treated coating consists mainly of γ-Fe, CrN, Fe₄N and Fe₃N. The duplex treated coating improved not only surface hardness but also wear resistance.