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Fig. 9. The macro-morphology and the corresponding microstructure from traverse cross-section built with different technological parameters. V s and V f refer to the laser scanning speed and the powder feeding rate, respectively. The laser power P is 2 kW for all the specimens.creased, the duration of the laser beam interaction on the powder and the substrate becomes shorter, which results in less heat input of the laser cladding. After certain a threshold of the laser scanning speed, energy available will be insufficient to fuse the powder to the substrate, and an incomplete fusion appears. A relatively weak bonding between the layer and the substrate will be formed. This phenomenon is undesired. By adjusting the processing parameters, this phenomenon will be eliminated. Similarly, under a given laser scanning speed, the powder feeding rate also exists a threshold. When the powder feeding rate is higher, the powder flux shields the laser beam. The energy which melts the substrate mostly comes from that of permeated from the cladding powders is so small that it causes insufficient substrate melting, the metallurgical bonding between the cladding layer and the substrate can't also achieved. The laser cladding process doesn't realize. In a word, on condition that other technological parameters hold immutable, a given laser scanning speed corresponds with a critical powder feeding rate and a given powder feeding rate also corresponds with a critical laser scanning speed. Furthermore, the critical powder feeding rate decreases accompanying the increase of the laser scanning speed at the same technological condition. Similarly, the critical laser scanning speed decreases with the increase of the powder feeding rate. In practice, the adjustment of the powder feeding rate should limit within the critical powder feeding rate at a given scanning speed and the adjustment of the scanning speed should limit within the critical scanning speed at a given powder feeding rate. A good matching of the scanning speed and the powder feeding rate is necessary in laser cladding. The Microhardness of Cladding LayersThe microhardness is an important index to evaluate the material properties. It is possible to understand the mechanical properties of the cladding layer by means of the microhardness across the layer, at least on a rough scale. The microhardness measurement across the transverse cross-section of the sample was carried out using microhardness tester. Figure 10 exhibits the effects of the laser scanning speed and the powder feeding rate on microhardness distribution of the transverse section of the sample. Horizontal ordinate represents the vertical distance from the substrate to the measuring point of the sample and vertical ordinate represents the Vickers hardness of the measuring point. From Fig. 10, it can be observed that with the increasing of the distance, the hardness profiles all present increasing trend. It is apparent that the microhardness of the laser cladding layer is much higher than that of the substrate and...

Thin wall was formed by multi-layer overlapping laser cladding. The results showed that the surface of thin wall presents granular. Laser remelting could obviously improve the surface finish of the thin wall because of the melt of small granules. Match between the laser beam and the powder stream is very important and directly affects the forming quality. The microstructure of the thin wall presented obviously and continuously grown dendrite. Individual layers form metallurgic bonding and ensure whole properties of the cladding thin wall.