Selective laser melting of Co-29Cr-6Mo alloy with laser power 180-360 W: Cellular growth, intercellular spacing and the related thermal condition

A feature of solidification during selective laser melting (SLM) is cellular growth. Thus, how growth direction and cell size may be affected and possibly be controlled by SLM parameters are important to be understood. Furthermore, intercellular spacing (lambda(1)) is suggestive of the thermal condition during solidification which needs to be known for advancing the understanding of SLM. In this work, grain solidification orientation and lambda(1) of a Co-Cr-Mo alloy produced by SLM over a range of laser power (P = 180-360 W) with other parameters kept unchanged have been evaluated. It has been found that the overall preferred growth of cellular solidification is not significantly affected by P. This is because, over the range of P values used, the shape of track did not change sufficiently to result in a significant variation of growth direction during epitaxial growth. It has also been found that P does not affect lambda(1). This suggests, since growth rate (R) relates to scan speed (v) which is unchanged, P does not significantly affect the temperature gradient of the solidification front (G). From the measured A., and estimated R, G and thus cooling rate (T) (over dot) can be estimated following the commonly used primary arm spacing model. The estimated G and T (over dot) which could not be directly measured will be compared with those predicted by simulation and the estimated T (over dot) will also be compared with those determined by using an emperical relationship from literature.