冷热搭接对激光熔覆涂层组织及性能的影响

Effects of Hot Overlapping and Cold Overlapping on Microstructure and Properties in Laser Cladding

通过热搭接和冷搭接两种方法,在45#钢表面激光熔覆自熔性镍基碳化钨粉末,原位自生硬质涂层,探究两种搭接方法对熔覆层组织和性能的影响。实验所采用的激光熔覆工艺参数为离焦量3mm,送粉电压7V,扫描度2mm/s,搭接率25.47%,激光功率1200W,冷搭接中每一道熔覆完成后停留20min再进行下一道加工,热搭接则一次性完成多道激光熔覆,每道间无加工停留时间;使用洛氏硬度机(HR-150DT)测量熔覆层表面硬度,通过金相显微镜对熔覆层金相组织进行观察分析,并利用显微硬度计(HVS-1000)分析熔覆层截面硬度。热搭接熔覆层洛氏硬度沿多道熔覆方向逐渐降低,而冷搭接熔覆层的平均洛氏硬度几乎保持不变,约为基体材料(HRC:22)的2.5倍;热搭接熔覆层与基体交界处存在气孔等缺陷,晶粒尺寸逐渐增大,而冷搭接熔覆层与基体冶金结合比较牢固,沿交界处垂直方向晶粒由枝状晶到等轴晶,组织性能良好;冷搭接熔覆区显微硬度分布较均匀,与基体相比提高约3倍。多道激光熔覆采用冷搭接方法,所得到的熔覆层组织和性能较好。

Through hot lap and cold lap two ways ,by using laser cladding fluxed nickel-based tungsten carbide powder on the surface of 45# steel, it becomes a layer after the chemical reaction. Researchs the effect of cladding layer organization and performance by using the two methods. The experiment uses the laser cladding, and the process parameters are ＆focus amount（ 3mm ） ,powder feeding voltage（ 7V ） , scanningspeed （2mm/s）, overlapping rate（ 25A7% ） and the laser power（12OOW ）. In the cold lap, before the next process, it should last 20 minutes after completing each cladding But in hot lap, it can complete multi-channel laser cladding in a one-time, and between every process dosent need last one time. By using Rockwell hardness machine （HR-150DT）to measure the surface hardness of the cladding layer,and through advanced microscope to analysis microstructure of cladding, Micro Hardness Tester （HVS-1000） measures cross-section of the cladding layer. The rockwell hardness of hot overlapping cladding showing decreases alongthe direction of multi-track cladding, but the Rockwell hardness of hot overlapping cladding remains almost unchanged and the overage rockwell hardness of cladding is 2.5 times of the matrix （HRC：22）. The junction of hot lap cladding layer and the substrate hove holes and other defects and the size of grains gradually increases. But the metallurgical bond of cold lap cladding layer and the substrate is strong. Between cladding layer and the substrate, the grains begin to grow outward and the organization presents columnar crystals and equiaxed and good organizational performance. Microhardncss of cold lap cladding region is uniformly distributed and it is 3 times of the matrix. Microstructure and properties of the cladding layer is better by the way of multi-channel laser clad cold overlapping.