Control of asymmetric track geometry in printed parts of stainless steels, nickel, titanium and aluminum alloys

In powder bed fusion, distorted temperature fields and deposit dimensions, undesirable surface features, and defects have been attributed to asymmetry in track geometry. It is also thought to affect sensing and control. While data on the asymmetry have been widely reported in the literature for many commonly used alloys, the origin of the asymmetry and the role of alloy composition and process variables are not known. Here we examine the role of local differences in heat transfer from the fusion zone as the origin of asymmetry in the track geometry. We use a mechanistic model of heat transfer and experimental data to examine the role of main process variables and alloy composition on the extent of asymmetry and provide easy-to-use process maps. We show that high laser power and slow scanning speed decreases asymmetry. Marangoni, Fourier and Peclet numbers can be used for controlling asymmetry. Among the four alloys examined, stainless steel 316 and AlSi10Mg are the most and least susceptible to asymmetry because of their lowest and highest thermal diffusivity, respectively.