Residual stress measurements in additively manufactured pure copper processed with different laser intensity profiles

Due to an outstanding electrical and thermal conductivity copper is the material of choice in numerous applications, e.g., electric wiring or heat-exchanging units. However, conventional manufacturing becomes extremely challenging and cost-intensive when machining of complex, high-precision components, such as cooling channels in heat transfer elements is required. Powder bed-based additive manufacturing processes, particularly laser-based powder bed fusion (PBF-LB/M), represent promising candidates to overcome the challenges related to conventional production. However, the specific thermal histories in PBF-LB/M often lead to anisotropic microstructures with large, elongated grains. Hence, the application of the established sin2Ψ method for evaluating residual stress states becomes challenging.
The presented comparative study focuses on the determination of residual stresses in PBF-LB/M copper, based on application of the sin2Ψ method. As a first step, two different microstructures, arising from a Gaussian and a Top Hat laser intensity profile applied within the PBF-LB/M process, were characterized by X-ray diffraction (XRD) measurements and electron backscatter diffraction (EBSD). Based on the XRD texture measurements stress factors were determined to compensate the influence of texture on residual stress measurements. Likewise, the XRD measuring strategy was adapted to the present microstructure, e.g., by increasing the number of tilt angles. Results obtained are critically discussed.