In-situ strain observation in high power laser cladding

The modern experimental technique – so called Digital Image Correlation – is applied during high power laser surface treatments for in-situ observation of displacements and strains near the processing area during and a short time after laser processing. An experimental setup has been designed and tested to measure in-situ the strain during treatment with a high power 2 kW CW Nd:YAG laser, i.e. laser hardening, surface remelting, and laser cladding with Nanosteel, Eutroloy 16012 and MicroMelt 23 powders, on C45 steel and 301 stainless steel plates using the commercial 3D digital image correlation system. The in-situ strain was measured at the bottom surface of the 5 mm thick plate using a mirror located under the plate. Experimental measurements allow discrimination between thermal and residual strains. The strain build-up in the direction parallel and perpendicular to the laser cladding direction were measured for different laser surface treatment setups and for laser cladding of all three powders. The observation provides very useful information concerning laser surface treatment (surface hardening and surface remelting) and laser cladding. Analysis of these measurements could help to optimize the laser cladding parameters with an aim to suppress the formation of high level internal strains.