Effect of Process Parameters on the Crack Formation in Laser Metal Powder Deposition of Alloy 718

Cracking in Alloy 718 using laser metal powder deposition has been evaluated in this study. It is found that the material is susceptible to cracking when the laser power is high, the scanning speed is high, and the powder-feeding rate is low. Almost all the cracks are located close to the center of the deposited wall and propagate in the normal direction to the substrate. Evidence of liquation are found at the cracked surfaces, and since all cracks reside in regions which are reheated several times, the cracks are determined to most likely be heat-affected zone liquation cracks. The influence of respective process parameter was evaluated using a design of experiment approach. It is shown that, when the powder-feeding rate is incorporated as a variable, the heat input is not a suitable indicator for the hot cracking susceptibility in laser metal powder deposition of Alloy 718. A combinatory model using the power density together with the heat input is therefore proposed.