Abstract
Laser cladding is a technique that allows the deposition of thick protective coatings on substrates. The process can be described as an addition of one material by cladding on the surface of the substrate, where the heat source is a high power laser beam. The resulting thickness of the clad is typically 50 m to 2 mm in one step. Once a thicker protection layer is needed, the process can be applied again.
The aim of the present work is to establish the capabilities of laser cladding process in the mould die repairing area for automotive industry. Influence of laser processing parameters (Power, Process Speed and Powder feed rate) as well as steel powder (AISI M2 and D2) and substrate influence were studied. The microstructure of the laser clad layer and substrate heat affected zone (HAZ) were characterized by Optical microscopy, Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD).
Results show that the process parameters (power, process speed, feed rate …) determine the dimensions of the clad layer and are related to the microstructure formation. Although it is simple to obtain geometrically acceptable clads (with the right shape and dimensions) in many cases occur some harmful effects as carbide dilution and non-equilibrium phases formation which modify the mechanical properties of the coating. Specifically, the presence of retained austenite in the substrate-coating interface is directly related to the cooling rate and implies a hardness diminution that must be avoided.
It has been checked that initial metallurgical state of the substrate as well as post-processing heat treatments have a big influence in the final result of the deposition. Tempered substrates imply higher laser absorption and heat accumulation than the ones in annealed condition.
Moreover, retained austenite is reduced as well as coating hardness increases with the proper tempering treatment after the repairing process. For this reason, it is necessary to optimize process conditions for each reparation in order to improve the working behaviour of the component.
Keywords: Laser Cladding, tool steel, microstructure, service behavior