Process strategy for crack-free production of diamond-reinforced metal matrix composites with minimal graphitization through laser powder bed fusion
Norman Schnell, Manuel Ferreira, Jan Wegner, Wolfgang Tillmann, Stefan Kleszczynski
Abstract
Laser powder bed fusion allows for creating novel material composites through dry-mixing additives into preexisting metal powder bases. One example is diamond-reinforced metal matrix composites. Production through powder bed fusion is a highly dynamic thermal process with temperature gradients ranging between room temperature and boiling point, as well as local cooling rates of up to 106-107 K/s. The addition of a hard phase, such as diamond particles, poses a challenge for the process design due to a susceptibility for residual stress and crack formation. Furthermore, the diamonds themselves experience a complex thermal history through repetitive remelting steps that can cause graphitization. In this publication, the effect of the applied energy, platform heating, and diamond coating on the processability is analyzed through light and scanning electron microscopy. This enables an in depth evaluation of causalities concerning part density, crack propagation, and diamond integrity. The findings are summarized in a stable process route that ensures crack-free parts with a relative density of 99.7 % and shows the effectiveness of titanium coating to limit thermally induced damage through graphitization.