Residual stresses in LENS ® components using neutron diffraction and contour method

Abstract

During manufacturing of components by laser engineered net shaping (LENS ®), a solid freeform fabrication process, the introduction of residual stresses causes deformation or in the worst case, cracking. The origin is attributed to thermal transients encountered during solidification. In the absence of reliable predictive models for the residual stresses, measurements are necessary. Residual stresses were measured in LENS ® samples of 316 stainless steel and Inconel 718 having simple geometrical shapes by both neutron diffraction and the contour methods. The results by the two methods are compared and discussed in the context of the growth direction during the LENS ® process. Surprisingly, the residual stresses are practically uni-axial, with high stresses in the growth direction.