| Laser cladding is used to form a kind of surface coating, which has a good metallurgical bonding with the substrate, without gas holes and crack, by using a high energy laser beam to melt coating material and a thin layer base metal. It has been becoming one of new techniques that have infinite development future and characteristic very much in the modern surface technique system, and bigger application foreground in "remanufacturing engineering in the 21st century".With the researches on development-of laser cladding technology in the world, and with the analyses to problems faced in the industrial application process of this technology, we have carried out mangy experiments and mechanism analysis on the laser cladding materials, the exploration of laser cladding technique and the equipments used in laser cladding. The main topics and achievements of this thesis are as follows:1. The Advancement in Laser CladdingThe advancement in laser cladding was summarized, in the five aspects of theories, techniques, materials, equipments and applications. The main problems blocking the industrial applications were discussed. The trends of the development in laser cladding technology were putted forward. The most difficult problems, which have to be settled in current, are cracks and other defects emerged in the layers of laser cladding.2. Effects of Three Types of WC on The Laser Cladding Layers of G112 AlloyDifferent effects of nickel-wrapped WC, single crystal WC and cast WC on laser clad G112 layers are compared. In the condition of adding 30wt.% WC to G112 alloy, it is shown that there are different heat damage fashions on the different types of WCs by the heating of high power laser beam. And the three types of WCs distribute differently in the clad layers at lower laser scanning speed, Cast WC particles stacking at the bottom, sintered WC dispersing homogeneously while nickel-wrapped WC particles being in between. The micro-hardness of the layers are greatly improved no matter what type of WC is added, and the micro-hardness of G112+WC layers change with laser scanning speed, which get the biggest numbers when V=4mm/s. And about tribological properties,after adding WC to G112 alloy, the improving extent is in the order of nickel-wrapped WC >single crystal WC >cast WC. As a result based on all the above investigates, the synthetical effects of adding nickel-wrapped WC or single crystal WC to G112 is better than that of cast WC. 3. Effect of Y2O3 on the Multi-track-joined Ni-WC Alloy Coatings by Laser CladdingHigh quality nickel based WC coatings by laser cladding are obtained with addition of proper amount of Y2O3. Compared to the coatings without Y2O3, the coatings with Y2O3 possess a much finer and more uniform microstructure, higher micro-hardness and much better tribological properties. Its friction coefficient remains constant during wear test while that of the coatings without Y2O3 increases quickly. We attribute the quality improvement by Y2O3 to the crystalline refinement, clarifying and strengthening effect of Y3+. In our experiment, we find the best technique condition is that: V=1.4mm/s, P=1.8kw, adding 0.2wt.%Y2O3 to Gil2+10wt.%WC(nickel-wrapped WC). At the same time, we have done some experiments of adding few MgO to G112+10wt%WC, and also gotten better effects. 3.Design of a New Powder Feeder for laser claddingFinding and analyzing the problems occurring in our experiments of using some powder feeding equipments for laser cladding, we have developed a new type powder feeder by ourselves, which use rolling screw to feed powder. This equipment has a simple structure and is convenience for use. We processed experiment of laser cladding by using it and acquired a better effect. |
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