The influence of heat input on microstructure and porosity during laser cladding of Invar alloy

摘要

The Invar alloy coatings were prepared using laser cladding technology. The effects of heat input on the coatings size, microstructure and porosity of laser cladding layers were investigated by optical microscope (OM), scanning electron microscope (SEM) and electronic differential system (EDS). In this analysis, the microstructure of coatings consist of elongate cellular crystals and equiaxed cellular crystals. The results showed that the size, HAZ and crystals size of the samples clearly show a noteworthy increase by improving the heat input from 81.4 to 230 J/mm(2) . Meanwhile, an interesting phenomenon was discussed that the subgrain size near the layer line were extraordinarily distinct from the normal. The pores in the coatings are considered to be divided into two categories. The one is fusion lack porosity which is caused by the unfinished powders and rapid solidification. The other one, bubble porosity, is composed of trapped shielding gas and metal vapor. It is demonstrated that the porosity factors increase until a threshold heat input is reached and then decrease as the heat input increases. In this paper, the heat input of 126 J/mm(2) is more suitable to be applied in laser cladded Invar alloy.