Laser beam profile modulation for microstructure control in laser cladding of an NiCrBSi alloy

A circular laser beam with a variable intensity profile was used to investigate the effects of beam intensity profile shaping on the microstructure formation within laser clad layers of an NiCrBSi type corrosion and wear resistant alloy. The raw beam profile output of a high power, fibre delivered laser was manipulated using a variable beam profile modulator. The beam profiles generated took the form of a focussed annular ring with a uniform intensity central fill. The relative intensities of the annular ring and central fill were varied by an adjustment of the optical elements in the variable beam profile modulator. Three of the generated beam profiles were used in the laser cladding of single track deposits of an NiCrBSi based corrosion and wear resistant alloy on Cr5 steel. The microstructure throughout the laser clad layers was examined using XRD, SEM and EDS. It was found that the variations in the scale and distribution of hard phases in the microstructure through the depth of the clad layer can be controlled by varying the laser beam profile. Using a traditional top-hat type beam profile, the microstructure varied from very coarse in the lower part of the clad layer to fine in the upper part. Creating beam profiles with a preferentially greater intensity at the outer edge than at the centre allowed clad layers to be produced with greater microstructural homogeneity throughout the depth of the layer and encouraged the growth of comparatively larger hard dendrite phases near the surface of the clad layer.