No abstract

No abstract

No abstract

Measuring temperatures in the material during laser metal deposition (LMD) has an inherent challenge caused by the laser. When thermocouples are radiated by the high intensity laser light overheating occurs which causes the thermocouple to fail. Another identified difficulty is that when the laser passes a thermocouple, emitted light heats the thermocouple to a higher temperature than the material actually experience. In order to cope with these challenges, a method of measuring temperatures during LMD of materials using protective sheets has been developed and evaluated as presented in this paper. The method has substantially decreased the risk of destroying the thermocouple wires during laser deposition. Measurements using 10 mm 2 and 100 mm 2 protective sheets have been compared. These measurements show small variations in the cooling time (∼0.1 s from 850°C to 500°C) between the small and large protective sheets which indicate a negligible effect on the temperature measurement.

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.