Laser Direct Metal Deposition Research Articles

Understanding thermal behavior in the LENS process

In direct laser metal deposition technologies, such as the laser engineered net shaping (LENS) process, it is important to understand and control the thermal behavior during fabrication. With this control, components can be reliably fabricated with desired material properties. This paper will describe the use of contact and imaging techniques to monitor the thermal signature during LENS processing. Development of an understanding of solidification behavior, residual stress, and microstructural evolution with respect to thermal behavior will be discussed.

Chemical and electrical insulation of fine iron and cobalt particles: A. Garreau, P.Latare. (CEA, France.)

Laser cladding of the high Co–Ni secondary hardening steel on the 18Cr2Ni4WA steel using the laser direct metal deposition (LDMD) technology was investigated. The hardness was measured with a Vickers indenter, and the microstructural evolution was analyzed using a SEM equipped with an EDS and X-ray diffraction. The results indicated that the wear resistance of the 18Cr2Ni4WA steel substrate could be greatly improved by the coating of laser cladded high Co–Ni secondary hardening steel. After laser cladding, the microstructure of the heat-affected zone in the 18Cr2Ni4WA steel substrate was typical martensitic structure transformed from the initial granular bainitic structure. Besides, Fe-based ferrite, martensite, lath retained austenite, and two types of precipitations dispersed in the matrix were observed in the laser cladded high Co–Ni secondary hardening steel coating. They were determined to be the needle-shaped Fe(Cr, Co, Ni)3C cementite with size of approximately 1–3 μm and rod-shaped fine-scale (less than 0.1 μm in length) M2C carbides, respectively.

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

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.