Extreme High-Speed Laser Material Deposition (EHLA) of AISI 4340 Steel

Abstract

A variant of conventional laser material deposition (LMD), extreme high-speed laser material deposition (German acronym: EHLA) is characterized by elevated process speeds of up to 200 m/min, increased cooling rates, and a significantly reduced heat affected zone. This study focuses on the feasibility of using EHLA to apply material onto Fe-based substrate materials with AISI 4340 as a filler material. We studied how three different build-up strategies-consisting of one, three, and five consecutive deposited layers and hence, different thermal evolutions of the build-up volume-influence the metallurgical characteristics such as microstructure, porosity, hardness, and static mechanical properties. We propose a thermo-metallurgical scheme to help understand the effects of the build-up strategy and the thermal evolution on the microstructure and hardness. The tensile strength of the build-up volume was determined and is higher than the ones of forged AISI 4340 material.Coatings 2019, 9, 778 2 of 16 layer and substrate. The applied powder particles bond to the substrate by mechanical clamping, which leads to tensile residual stresses and reduces the fatigue life of the deposited layers. Wu et al. [7] studied the feasibility of repairing AISI 4340 components through friction stir processing (FSP). In this study filling blocks were used as filling material. The filler blocks were first fixed to the substrate by electron beam welding, then the filler blocks were joined to the material to be repaired using a friction stirrer. The results showed no defects in the repaired zone. The measured maximum tensile strength was 91.8% compared to that of a forged structure and a ductile-brittle fracture was observed.LMD has also widely been used to repair parts made of this low-alloy steel. LMD can be used to repair and functionalize surfaces thanks to its advantages, such as the metallurgical bonding between the deposited layer and the substrate [8], the defined and well controlled energy deposition [9], and the reduced heat affected zone (HAZ) [10]. Shi et al. [11] used laser cladding as a repair process for AISI 4340. They investigated the tensile strength of the samples after cladding. The specimens were prepared by adding a notch with the dimensions of 13.73 mm in length and 0.7 mm in thickness to the center of a plate-shaped substrate, and filling the notch with the AISI 4340 filler by LMD. Then, the excess cladded layer was removed by a CNC machine to generate a flat surface finish. The specimens were taken out from the plate and machined by wire cutting. Tensile test results indicated that the elongation of the specimen was 0.6%. An explanation for the brittleness was given by the detection of untempered martensite in the cladded area and the HAZ zone, which leads to high hardness and low ductility and toughness. Chew et al. [12] investigated the fatigue performance after cladding AISI 4340 on substrates out of the same material. The authors prepared the specimens by adding a pre-clad groove, filling the groove with AISI 43...

A coupled multiphase Lagrangian-Eulerian fluid-dynamics framework for numerical simulation of Laser Metal Deposition process

“…This type of outcomes is therefore intended to pave the way to improvements in the set up of printing process, by predicting the stand-off distance, i.e., the nozzle base vs. substrate distance, necessary to reach the complete fusion of the particles. As recently argued in [15], such an information can lead to a considerable decrease of the thermal gradients that characterize the cooling of the molten pool and also to accelerate the deposition process of the metallic material, optimizing the whole printing process both in terms of time and costs.…”

“…The current literature shows that several numerical strategies have been implemented to aid the design of LMD set-ups, leading to possible optimal conditions of minimizing thermal gradients and speeding up the whole deposition process [15], but a comprehensive numerical tool, modeling the various multiphysics phenomena involved in fluid-particles interaction, still lacks.…”

“…Such a percentage increases non linearly with the laser power, highlighting a sort of plateau for high laser powers, reached sooner as the inclination angle decreases. Considering high laser powers (1200, 1700, and 2200 W), values at least of 85% of the liquid mass fraction are reached at the focal plane for any inclination angles ∈ [15,35] degrees. On the other hand, by increasing , a reduction of liquid mass fraction is observed for any value of laser power, three percentage points for P = 2200W , and about seven points for the other values of P. However, by accepting suboptimal percentages of molten material at the focal point, the laser power can be significantly diminished by suitably decreasing the inclination angle: about 97% of liquid fraction can be obtained either by laser powers P = 2200W with = 35 • , or by laser powers P = 1200W with = 15 • .…”

A coupled multiphase Lagrangian-Eulerian fluid-dynamics framework for numerical simulation of Laser Metal Deposition process

“…This type of outcomes is therefore intended to pave the way to improvements in the set up of printing process, by predicting the stand-off distance, i.e., the nozzle base vs. substrate distance, necessary to reach the complete fusion of the particles. As recently argued in [39], such an information can lead to a considerable decrease of the thermal gradients that characterize the cooling of the molten pool and also to accelerate the deposition process of the metallic material, optimizing the whole printing process both in terms of time and costs.…”

High-Speed Laser Cladding on Thin-Sheet-Substrates—Influence of Process Parameters on Clad Geometry and Dilution

“…Typically, laser cladding is performed on substrates with thicknesses of multiple millimeters, such as cylinders [11,12] or plates [13,14]. The application of laser cladding on thin-sheet substrates was first reported by Burmester et al [15] and has only been scarcely studied in the literature for sheets with a thickness below 10 mm [16,17], as well as below 1 mm [15,18,19].…”