Morphology of weld heat-affected zone liquation in cast alloy 718

Abstract

In this study, Direct Laser Metal Deposition (DLMD) technique is adopted for the additive manufacturing (AM) of Inconel 718 Superalloy. A 1 kW fiber laser with a coaxial nozzle head is used. The effects of scanning speed (2.5 and 5 mm/s) as well as powder feed rate (17.94 and 28.52 g/min) on the process were investigated. Characteristics of the 3D printed wall specimens such as the geometrical dimensions (width and height), microstructure observations, and the microhardness were obtained. To study the stability of the 3D manufactured walls, the height stability was considered for the investigation. Optical microscopy (OM), field emission electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and mapping analysis were performed to derive the microstructural features of the additively manufactured parts (AMP). Vickers microhardness test is used to evaluate the hardness distributions of AMP. Catchment concept of the powder in DLMD process is used for explaining different trends of the process. Results indicated that, by decreasing the scanning speed, the width and height of the deposited layer increase. The average width of AMP directly depends on scanning speed and the powder feed rate. Scanning speed has a reverse effect on the height stability; that is, the lower the scanning speed, the larger the stability. Microstructural results showed that because of the solidification process, the alloying elements will be accumulated in the grain boundaries. The non-uniform cooling rate and non-steady solidification rates of molten area in additive manufacturing process, the microhardness values of the AMP following a fluctuated trend.