Microstrain Determination in Individual Grains of Laser Deposited Cladding Layers

The laser cladding technique makes the deposition of thick metallic, wear and corrosion resistant coatings feasible on weaker substrates. During the process, localized high thermal gradients generate internal stresses that may cause cracking when these overcome the fracture stress. To explain the formation and development of micro residual stresses the synchrotron 3DXRD microscopy technique was employed to investigate the strain tensor of individual grains of a Co based alloy cladding layer. The experimental method is based on the set of diffractions from a rotating specimen followed by indexing of reflections and identification of individual diffracting grains. The components of the strain tensor for these grains are calculated by a decomposition method applied to over-determined system of linear equations. The results of the individual strains tensor indicate modulation of the strains over neighboring grains. The final stress state depends on the solidification and cooling trajectory. Those groups of grains that solidify first are initially stress-free surrounded by molten material. The neighboring grains that solidify later will then assume the tensile character of the strain once the melt shrinks but limited by prior resolidified grains.