激光熔覆层中孔隙、裂纹缺陷的形成机制及抑制方法研究进展

Research progress on formation mechanism and inhibition methods of porosity and crack defects in laser cladding layer

激光熔覆是以高能量密度的激光为热源在基体材料表面熔覆合金实现熔覆层与金属基体冶金结合的技术。激光熔覆技术控制精度高、输出功率恒定、没有电弧接触固熔池大小深度一致性好。并且激光熔覆具有效率高、热输入集中、热影响区小等特点是一种很有发展前景的金属表面改性技术。但因其冷却速度较快在熔覆层中易产生缺陷。熔覆层中的缺陷主要有裂纹、孔隙、固体夹杂、未熔合、形状缺陷等。基于国内外对熔覆层中缺陷的研究发现对熔覆层影响最大的是孔隙和裂纹。通过模拟和实验研究者们发现了孔隙、裂纹的形成原因,并通过改变加工工艺和粉末类型成功的减少了孔隙、裂纹的产生。本文从激光熔覆层中孔隙、裂纹两个缺陷出发,归纳了孔隙的生成原因及扩散方式,并从加工工艺、粉末材料出发总结了孔隙的抑制方法。其次说明了裂纹的产生原因,描述了几种影响裂纹产生的因素,总结了减少裂纹的加工工艺和一些辅助措施。最后指出了目前激光熔覆层缺陷研究中尚未解决的问题并对其未来发展方向进行了展望。

The laser cladding technology used a high energy density laser as a heat source to clad the alloy layer on the surface of the base material to achieve metallurgical bonding between the cladding layer and the metal substrate.Since the laser cladding technology has high control precision,constant output power and no arc contact,the molten pool width and depth have good consistency.Furthermore,laser cladding is a promising metal surface modification technology,becauseof high efficiency,concentrated heat input,and small heat affected zone,etc.However,due to its faster cooling rate,defects are easily generated in the cladding layer.The defects in the cladding layer mainly include cracks,porosity,solid inclusions,unfused,and shape defects.Based on the research on defects in the cladding layer at home and abroad,it is found that cracks and porosity have the greatest influence on the cladding layer.Through simulations and experiments,the researchers discovered the form causes of porosity and cracks,and successfully reduced porosity and crack generation by changing processing techniques and powder types.This paper started from the two defects of porosity and cracks in the laser cladding layer.Firstly,the causes of the formation of porosity and the way of diffusion were summarized.The method of porosity inhibition was summarized from the processing technology and powder materials.Secondly,the causes of cracks were explained,several factors affecting the cracks were described,and the processing techniques for reducing cracks and some auxiliary measures were summarized.Finally,the unsolved problems in the current research of laser cladding defects were pointed out and the future development direction was prospected.