Basic Experimental Investigations Of Multi-laser Cladding

Laser cladding is an advanced surface modification technology which has been widely used to improve the performance of material’s surface and repair broken components. In recent years, It is employed to conduct additive manufacture more and more widely. Cracks during laser cladding are considered to be the major problem that confines the wider applications of this technology. Heat treatment is an effective method to reduce the cracking susceptibility of laser cladding. But the heat input of conversional heat treatment methods is very high and that will lead to deformation and performance degradation of substrate material. In2012, a patent entitled "Preparing three-beam laser cladding non-crack coating with preheating and after-heating function by dividing emitted laser beam into preheating laser beam and after-heating laser beam, blowing alloy powder, and after-heating formed coating" is published. It is reported in the patent that the technology is capable of producing crack-free coatings with very high efficiency. To promote understanding and application of this technology, basic experimental investigations of multi-laser cladding were conducted in this work. The main work done and the conclusions obtained are as follows:(1) The conversional mental solidification theory and the characteristics of molten pool generated by laser are combined to elaborate and analyze the solidification process of molten pool and the resultant material micro-structure in both single laser cladding process and multi-laser cladding process, for the requirements of theory guidance in experimental results interpretations in terms of coatings’micro-structure and micro-hardness followed. The cracking mechanism of material during laser cladding is elaborated and analyzed from the angle of stress and strain, in order to guiding the experimental method design and results interpretation followed.(2) The initial experimental investigation of laser heat treatment is performed using controlled variables method. The effects of laser power and scanning speed on coatings’ micro-structure and micro-hardness are investigated. The results indicate that the remolten depth of coating and the grain size in the remolten zone of the coating are increased with laser power and decreased with scanning speed; as the increase of laser power or the decrease of scanning speed, the micro-hardness of coating’s cross section is not varied uniaxially, but the fluctuation range of micro-hardness is decreased, which indicated that the material organization is more uniform; the appropriate laser power for heat treatment during multi-laser cladding process is between300to400watt when the scanning speed is6mm/s.(3) The effects of two parameters "lead time"(time interval between pre-heat treatment and cladding) and "delay time"(time interval between cladding and post-heat treatment) in multi-laser cladding on the residual stress of coating’s surface and, micro-hardness and micro-structure of coating’s longitudinal section are investigated experimentally by equivalently simulating the process of multi-laser cladding. The experimental results indicate that lead time and delay time have strong influences on the surface residual stress of coatings and there exist the lead time and delay time that lead to minimal residual stress of coating’s surface, the effect of lead time on the micro-structure and-hardness is not apparent, the effect of delay time on the micro-structure and-hardness is significant:as the increase of delay time, the remolten depth of coating is increased and the micro-hardness30μm blow remolten line is increased first, then decreased and remained steady eventually.Some patterns and knowledge about multi-laser cladding are uncovered in this work and that facilitated the understanding of the technology and laid a certain foundation for the further research of multi-laser cladding.