High-density direct laser deposition (DLD) of CM247LC alloy: microstructure, porosity and cracks

Abstract

Nickel-based alloys are known as non-weldable materials due to their complex characteristics. Consequently, additive manufacturing of these alloys is particularly challenging. In this paper, the influence of process parameters on the porosity, crack formation and microstructure of additively manufactured CM247LC nickel-based alloy is analysed. The feasibility of the direct laser deposition (DLD) process to manufacture crack-free and low-porosity CM247LC samples is studied. CM247LC samples were built on Inconel 718 that has similar chemical composition, to form hybrid superalloy parts. It was shown that crack-free and high-density CM247LC samples can be obtained through DLD without significant substrate preheating for certain parameter combinations: laser power in the range of 800–1000 W and powder feed rates between 6 and 8 g/min. High-cost and complex preheating was avoided that was commonly reported as necessary to achieve similar densities. For hybrid parts, a large beam diameter and slow scan speeds were employed to achieve optimal conditions as it was evident from the achieved bonding between the Inconel 718 substrate and the deposited layers. It was observed that good bonding between the two materials can be obtained with laser power values between 800 and 1000 W, scanning speed higher than 300 mm/min and powder flow rates of 6–8 g/min.

Surface integrity of hybrid CM247LC/Inconel 718 components produced by laser-directed energy deposition

“…A typical structure suffering from such potential heat accumulation and draining between the blades is shown in Fig. 6, in spite of the fact that it was built utilising optimised process parameters for building dense walls free of cracks as reported earlier [43]. The figure indicates that the heat accumulation was excessive during the L-DED deposition and the nucleation of solidification cracks was enhanced [8].…”

“…The L-DED parameters used were as follows: laser power 800 W, scan speed 240 mm/min and powder flow rate of 9.8 g/min. More information about the selected process parameters is provided in another study [43].…”

Designs, advancements, and applications of three-dimensional printed gyroid structures: A review

“…[162][163][164] Surface irregularities in the gyroid Many researchers who investigated, lattices have been particularly prone to manufacturing problems due to their intricacy, which pushes the limitations of additive manufacturing methods. The SLM and EBM 3D printed metals parts (Al-Si10-Mg, 165 Ti6Al4V, 166 hybrid CM247LC/Inconel 718 167 ) have observed surface roughness to be a big issue and attached many unmelted particles or bonded particles, gas porosity, lack of fusion, balling phenomenon, staircase, microvoids, and narrow short cracks. It is believed due to the existence of large residual stresses during the process.…”

Pore evolution mechanisms during directed energy deposition additive manufacturing

“…Porosity is a common feature in DED-produced components and has been observed in various alloys 5 – 7 , including titanium alloys 6 , 8 , 9 , nickel-based superalloys 7 , 10 and aluminium alloys 11 . Porosity mainly consists of gas porosity and lack of fusion features, categorised by their formation mechanisms 12 .…”