“…It is also noteworthy here that the dilution effect between adjacent layers has led to a slight deviation from the primary multi-material design, and the formation of a transition zone and a kind of gradation at the interface of the two alloys, which can be observed by EDS line analysis in Fig. 14 c and as reported in some previous studies 10 , 11 . Figure 13 The variations of ( a ) temperature gradient ( ) and solidification rate ( ) and ( b ) undercooling ( ) in the build direction.…”
Section: Resultssupporting
confidence: 85%
“…Shah et al 9 investigated the effect of laser direct metal deposition (LDMD) parameters on the development of SS316L/IN718 graded structure. Savitha et al 10 in a study on additive manufacturing of SS316/IN625 dual materials observed that the yield strength is always comparable to the weaker component (SS316), while Zhang et al 11 in a similar study obtained the yield strength and tensile strength of gradient samples close to IN625 and SS316L, respectively. Carroll et al 12 in determining the cause of cracking in a graded structure fabricated from SS304L and IN625 by DED, demonstrated the role of metal monocarbides in the form of (Mo, Nb)C using thermodynamic modeling by CALculation of PHAse Diagrams (CALPHAD) method.…”
In the present paper, the interrelated aspects of additive manufacturing-microstructure-property in directed energy deposition of SS316L-IN718 multi-material were studied through numerical modeling and experimental evaluation. The printability concept and solidification principles were used for this purpose. The printability analysis showed that the SS316L section is more susceptible to composition change and lack of fusion, respectively due to the high equilibrium vapor pressure of manganese and the more efficient heat loss in the initial layers. However, the IN718 section is more prone to distortion due to the formation of a larger melt pool, with a maximum thermal strain of 3.95 × 10−3 in the last layer. As the process continues, due to heat accumulation and extension of the melt pool, the cooling rate decreases and the undercooling level increases, which respectively result in coarser microstructure and more instability of solidification front in the build direction, as also observed in the experimental results. The difference is that the dendritic microstructure of the IN718 section, due to the eutectic reaction L → γ + Laves, is formed on a smaller scale compared to the cellular microstructure of the SS316L section. Also, the decrease in cooling rate caused the secondary phase fraction in each section (delta ferrite in SS316L and Laves in IN718) to increase almost linearly. However, the hardness calculation and measurement showed similarly, even though with the transition from SS316L to IN718 the hardness is significantly increased due to higher yield strength of the matrix and the presence of Laves intermetallic phase (~ 260 HV0.3), the hardness in each section decreases slightly due to the coarsening of the microstructure from the initial layer to the final.
“…It is also noteworthy here that the dilution effect between adjacent layers has led to a slight deviation from the primary multi-material design, and the formation of a transition zone and a kind of gradation at the interface of the two alloys, which can be observed by EDS line analysis in Fig. 14 c and as reported in some previous studies 10 , 11 . Figure 13 The variations of ( a ) temperature gradient ( ) and solidification rate ( ) and ( b ) undercooling ( ) in the build direction.…”
Section: Resultssupporting
confidence: 85%
“…Shah et al 9 investigated the effect of laser direct metal deposition (LDMD) parameters on the development of SS316L/IN718 graded structure. Savitha et al 10 in a study on additive manufacturing of SS316/IN625 dual materials observed that the yield strength is always comparable to the weaker component (SS316), while Zhang et al 11 in a similar study obtained the yield strength and tensile strength of gradient samples close to IN625 and SS316L, respectively. Carroll et al 12 in determining the cause of cracking in a graded structure fabricated from SS304L and IN625 by DED, demonstrated the role of metal monocarbides in the form of (Mo, Nb)C using thermodynamic modeling by CALculation of PHAse Diagrams (CALPHAD) method.…”
In the present paper, the interrelated aspects of additive manufacturing-microstructure-property in directed energy deposition of SS316L-IN718 multi-material were studied through numerical modeling and experimental evaluation. The printability concept and solidification principles were used for this purpose. The printability analysis showed that the SS316L section is more susceptible to composition change and lack of fusion, respectively due to the high equilibrium vapor pressure of manganese and the more efficient heat loss in the initial layers. However, the IN718 section is more prone to distortion due to the formation of a larger melt pool, with a maximum thermal strain of 3.95 × 10−3 in the last layer. As the process continues, due to heat accumulation and extension of the melt pool, the cooling rate decreases and the undercooling level increases, which respectively result in coarser microstructure and more instability of solidification front in the build direction, as also observed in the experimental results. The difference is that the dendritic microstructure of the IN718 section, due to the eutectic reaction L → γ + Laves, is formed on a smaller scale compared to the cellular microstructure of the SS316L section. Also, the decrease in cooling rate caused the secondary phase fraction in each section (delta ferrite in SS316L and Laves in IN718) to increase almost linearly. However, the hardness calculation and measurement showed similarly, even though with the transition from SS316L to IN718 the hardness is significantly increased due to higher yield strength of the matrix and the presence of Laves intermetallic phase (~ 260 HV0.3), the hardness in each section decreases slightly due to the coarsening of the microstructure from the initial layer to the final.
“…The results showed a gradual change of alloying elements at the interface due to the diffusion from the heat effect of the subsequent deposition process. Savitha et al [11] compared the composition variation and mechanical properties of laser-engineered net shaping (LENS) SS316-Inconel 625 dual alloy and graded material, and they pointed out that the elemental composition exhibited gradual changes near the transition region of the graded materials. In addition, a discrete change near the interface of the dual alloy was also evident, which contradicted Liang's result.…”
TA15/Ti2AlNb multiple-layer samples and a dual-alloy sample were fabricated by laser solid forming (LSF) in this study. The formation mechanism of the dilute region and microstructure evolution of the dual alloy were analyzed. The results confirmed a “step” distribution of the composition among several initial layers in the multiple-layer samples, which can be explained by calculating the ratio of the remelted zone to the deposited Ti2AlNb zone in each deposited layer. However, the “step” compositional distribution disappears, and the compositional variation tends to be more continuous and smooth in the TA15/Ti2AlNb dual-alloy sample, which is attributed to alloy elements’ diffusion at the subsequent multiple re-melting and the longer thermal cycle. The macrostructure of the TA15/Ti2AlNb dual-alloy sample consists of epitaxially grown columnar prior β grains at the TA15 side and equiaxed grains at the Ti2AlNb side, while the microstructure shows a transition of α+β→α+α2+β/B2→α2+β/B2→α2+B2+O with increasing amounts of Ti2AlNb, leading to the microhardness also changing significantly.
“…The fabrication of FGMs by AM technology has been studied previously, some of which are focusing on joining stainless steel/nickel-based alloys [25][26][27], Ti/TiC [6,28,29], and Ti6Al4 V/SS316 [5]. In [30], attempts have been made to fabricate discrete interface (DI) and compositionally graded (CG) SS316-IN625 dual materials using LENS. The microstructure of DI samples reveals a sharp transition from SS316 to IN625.…”
In this work, functionally graded materials of Stainless Steel 316L and Inconel 625 were fabricated using Directed Energy Deposition. Intermediate layers were built in between of SS316L and IN625. Pure SS316L and IN625 samples were also prepared. The results show microstructure varied sharply at the interface on pure SS316L and IN625 while changed gradually on gradient samples. Quantitative analysis reveals the consistence of designed and tested material composition at the gradient layers. Tensile testing shows the yield strength of graded samples is similar to that of pure IN625 while the ultimate tensile strength is approaching to that of pure SS316L due to the fracture at SS316L side. Microhardness measurements reveal the gradual change of hardness values over the gradient zone.
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