Effect of the parametric optimization and heat-treatment on the 18Ni-300 maraging steel microstructural properties manufactured by directed energy deposition

Laser Deposited 18Ni300 Alloy Powder on 1045 Steel: Effect of Passes and Preheating on Microstructure

“…Maraging steel is one of the most frequent alloys used in the mould industry, mainly for repair purposes [ 15 ]. This alloy is composed of a large concentration of nickel, medium levels in cobalt and molybdenum, a small amount in titanium and a very low carbon concentration, i.e., the Ni (for 18–25 weight %) leads to reduce the start temperature of martensite transformation, Ms, to 150 °C, while austenite is not formed upon reheating until temperatures above 500 °C; this characteristic allows the alloy to be subjected to temperatures above 400 °C, leading to the precipitation of intermetallic phases which contribute to strengthening.…”

“…Maraging steels were also produced by the DED technique, the deposition of this alloy on AISI 304L stainless steel alloy was optimised, observing an increase for at least 170 HV in the heat-treated deposition, highlighting the production of almost 100% dense deposition by the application of energy densities over 180 J/mm 2 [ 22 ]. A recent study highlighted the significance of laser power on dilution, whereas the laser speed was very effective in the height, width, depth and porosity of deposited line beads [ 15 ]. Besides, a recent study revealed that the effectiveness of applying a deposition-pause strategy forming in-situ nano-precipitation led to an increase in hardness and yield strength, encouraging the possibility of eliminating postprocessing ageing treatment [ 23 ].…”

Automation of Property Acquisition of Single Track Depositions Manufactured through Direct Energy Deposition

“…• Ideal outputs established according to three characteristics: the ideal dilution values were set between 10% and 30% [12,37], as very low percentages lead to detached lines while larger values may result in worse claddings [38]; optimised wettability angles were established to be between 50 and 70º, as decreased wettability angles are associated with increased oxidation [3] and increased angles worsen overlapping beads while depositing three dimensional objects [38]; parameters that lead to the reduction of defects inherent to DED, such as pores, cracking and keyhole porosities. • Literature review: reviewed articles [27,28,39] suggest depositing lines, planes and/or specimens while maintaining energy densities above 65 J mm −2 , motivating an initial iteration orthogonal experiment L9 (3 × 3 Taguchi array) between the three most relevant parameters, namely the laser power P, scanning speed v s and feeding rate f r . This DOE varied the energy density between 66.1 ≤ E ≤238.1 J mm −2 and the ratio between the scanning speed and feeding rate by 0.012 ≤ v s / f r ≤0.1 m g −1 .…”

“…The optimised process parameters resulted in a ratio between the laser power and laser spot size of P/d s =720 W mm −1 and a specific energy of E =61.51 J mm −2 ; other research [29] deposited 18Ni300 tensile specimens using an orthogonal DOE between the laser power, scanning speed and feeding rate; the specimen produced with a specific energy of 67.7 J mm −2 achieved the highest ultimate tensile strength. Additional research [28] optimised process parameters for 18Ni300 processing, obtaining specific energy of 41.95 J mm −2 in the optimised parameters for dilution proportion. c1 A comparison between process variables the present work and the aforementioned research is visualised in Figure 13.…”

“…These alloys find application in the automotive, aerospace, military and tool die industries [26]. One of the advantages of this alloy, apart from its exceptional combination of high strength and toughness, is its printability: a recent research work [27] conducted 16 single tracks in which the energy density (expressed in Equation ( 1)) oscillated from 66.7 J mm −2 and 416.7 J mm −2 , returning beads with dilution proportions between 55% and 75%, values generally considered too excessive [12]; Additionally, researchers [28] developed processing maps for 18Ni300, concluding that laser powers larger than 1200 W with a laser spot size of 2.55 mm resulted in porosities below 0.7%, although speeds below 9 mm s −1 for the same power setting lead to dilution proportions (given by Equation ( 2)) below 12.5%.…”