“…Chouhan et al observed gas porosities formed at both low and high energy densities due to particle arrestment in the melt pool and the small formation of bubbles. Stagnant melt-pool zones were found to increase the porosity due to the inability of bubbles to escape during the solidification process [34]. The 2500 s −1 tested L-DED material exhibited a similar fracture surface with both large void solidification defects and fractured particles, as observed in Figure 8.…”
Quasi-static and high-rate tensile experiments were used to examine the strain rate sensitivity of laser-directed energy deposition (L-DED)- and additive friction stir deposition (AFSD)-formed AerMet 100 ultrahigh-strength steel-additive manufactured builds. Electron backscattered diffraction (EBSD) revealed similar as-deposited grain sizes between the two AM processes at approximately 24 μm and 17 μm for the L-DED and AFSD samples, respectively. The strain hardening rate, θ, revealed little change in the overall hardening observed in the L-DED and AFSD materials, with a consistent hardening in the quasi-static samples and three identifiable regions in that of the high-rate tested materials. The L-DED deposited materials displayed average ultimate tensile strength values of 1835 and 2902 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively and the AFSD deposited materials displayed ultimate tensile strength values of 1928 and 3080 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively. Overall, the strength for both processes displayed a positive strain rate sensitivity, with increases in strength of ~1000 MPa for both processes. Fractography revealed significant solidification voids in the laser DED material and poor layer adhesion in the AFSD material.
“…Chouhan et al observed gas porosities formed at both low and high energy densities due to particle arrestment in the melt pool and the small formation of bubbles. Stagnant melt-pool zones were found to increase the porosity due to the inability of bubbles to escape during the solidification process [34]. The 2500 s −1 tested L-DED material exhibited a similar fracture surface with both large void solidification defects and fractured particles, as observed in Figure 8.…”
Quasi-static and high-rate tensile experiments were used to examine the strain rate sensitivity of laser-directed energy deposition (L-DED)- and additive friction stir deposition (AFSD)-formed AerMet 100 ultrahigh-strength steel-additive manufactured builds. Electron backscattered diffraction (EBSD) revealed similar as-deposited grain sizes between the two AM processes at approximately 24 μm and 17 μm for the L-DED and AFSD samples, respectively. The strain hardening rate, θ, revealed little change in the overall hardening observed in the L-DED and AFSD materials, with a consistent hardening in the quasi-static samples and three identifiable regions in that of the high-rate tested materials. The L-DED deposited materials displayed average ultimate tensile strength values of 1835 and 2902 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively and the AFSD deposited materials displayed ultimate tensile strength values of 1928 and 3080 MPa for the 0.001 s−1 and 2500 s−1 strain rates, respectively. Overall, the strength for both processes displayed a positive strain rate sensitivity, with increases in strength of ~1000 MPa for both processes. Fractography revealed significant solidification voids in the laser DED material and poor layer adhesion in the AFSD material.
“…distinct cause. Such pores may be related to the entrapment of gasses during deposition regardless of shielding type [18], with bubbles unable to escape to the surface due to strong Marangoni flow in the meltpool [21].…”
Section: Resultsmentioning
confidence: 99%
“…Finally, very fine pores (<1μm) were also found with both shielding types, but do not appear to have a distinct cause. Such pores may be related to the entrapment of gasses during deposition regardless of shielding type [18], with bubbles unable to escape to the surface due to strong Marangoni flow in the meltpool [21]. Figure 3. Common defects in the repaired samples including, (a) filled and (b) unfilled pores related to unmelted powders, (c) very large gas pores found in the fracture surfaces of a locally shielded fatigue samples [16] and (d) very fine pores found with both shielding types.…”
Laser-directed energy deposition (L-DED) is a key enabling technology for the repair of high-value aerospace components, as damaged regions can be removed and replaced with additively deposited material. While L-DED repair improves strength and fatigue performance compared to conventional subtractive techniques, mechanical performance can be limited by process-related defects. To assess the role of oxygen on defect formation, local and chamber-based shielding methods were applied in the repair of 300M high strength steel. Oxidation between layers for locally shielded specimens is confirmed to cause large gas pores which have deleterious effects on fatigue life. Such pores are eliminated for chamber shielded specimens, resulting in an increased ductility of ∼15%, compared to ∼11% with chamber shielding. Despite this, unmelted powder defects are not affected by oxygen content and are found in both chamber- and locally shielded samples, which still have negative consequences for fatigue.
“…Production of functional prototypes is another possibility, alongside small series production [8,9]. However, some problems still need to be fixed, such as microstructure monitoring, porosity which can lead to bad mechanical behaviour [10], geometrical accuracy inducing the need of post-process rectification [11], and crack events during manufacturing, either at substrate-deposit interface or in the clad [12].…”
Within the large Additive Manufacturing (AM) process family, Directed Energy Deposition (DED) can be used to create low-cost prototypes and coatings, or to repair cracks. In the case of M4 HSS (High Speed Steel), a reliable computed temperature field during DED process allows the optimization of the substrate preheating temperature value and other process parameters. Such optimization is required to avoid failure during the process, as well as high residual stresses. If 3D DED simulations provide accurate thermal fields, they also induce huge computation time, which motivates simplifications. This article uses a 2D Finite Element (FE) model that decreases the computation cost through dividing the CPU time by around 100 in our studied case, but it needs some calibrations. As described, the identification of a correct data set solely based on local temperature measurements can lead to various sets of parameters with variations of up to 100%. In this study, the melt pool depth was used as an additional experimental measurement to identify the input data set, and a sensitivity analysis was conducted to estimate the impact of each identified parameter on the cooling rate and the melt pool dimension.
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