灰铸铁件激光熔覆NiCuFeBSi合金的气孔行为

Pores distribution during laser-cladding NiCuFeBSi alloy on gray cast iron

通过对比分析45钢与HT250两种基体成形熔覆层内气孔形态,研究了熔覆层内气孔气体类型、分布规律以及影响因素.结果表明,熔覆层内气孔气体为CO,由石墨和氧或氧化物反应生成,气孔形状不规则、具有棱角状特征.气孔上浮形式并非垂直上浮,而是弥散式上浮.熔池内部强对流是影响气孔分布的内在因素.气孔运动幅度取决于熔池对流加速度,熔池温度越高,熔池表面张力梯度也越大,熔池对流的加速度越大.激光熔覆工艺是影响气孔分布的外在因素,适当降低激光功率和扫描速度、提高灰铸铁预热温度可有效消除熔覆层气孔缺陷,降低孔隙率.

With contrast of different kinds of pores characterization in cladding layers fabricated on the substrates of 45 steel and HT250,the composition,distribution and influence factors were investigated,respectively.The results show that the gas in pore was CO which was generated by the reaction of graphite and oxide.The shape of pores was irregular with many wedge angles.Furthermore,the floating path of pores was disperse instead of vertical due to the severe convection in molten pool.And the spread acceleration of pores was increased with the temperature as well as the surface tension gradient in the molten pool.However,the laser cladding parameters were the external factors affecting the distribution of pores.Enhancing the preheat temperature and reducing the laser power and laser scanning speed appropriately could avoid the generation of pores and decrease the porosity in the cladding layer.