Effect of process parameters for selective laser melting with SUS316L on mechanical and microstructural properties with variation in chemical composition

Bang, Gyung Bae; Kim, Won Rae; Kim, Hyo Kyu; Park, Hyung-Ki; Kim, Chan Yun; Hyun, Soong‐Keun; Kwon, Ohyung; Kim, Hyung Giun

doi:10.1016/j.matdes.2020.109221

Cited by 48 publications

(18 citation statements)

References 31 publications

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“…An increase of grain size with decreasing cooling rates was already reported by Zitelli et al [1] and Keshavarzkermani et al [14]. Interestingly, Bang et al [58] recently investigated changes in microstructure and hardness i.a. of small 10 mm cubic L-PBF specimens of 316L over a broad range of parameter combinations of laser power (80 W to 480 W) and scanning velocity (493 mm•s −1 to 2958 mm•s −1 ).…”

Section: Subsumption Of the Results With Regard To Hardnessmentioning

confidence: 58%

“…As mentioned elsewhere, a direct comparison of VED values is not acceptable in its entirety and has to be done very carefully, see, e.g., [59,60]. However, when considering a comparison of the hardness values of Bang et al [58] with the values of the present study-its pre-study [5]-it becomes clear that Bang et al [58] used a much broader range of processing parameters (laser power and scanning velocity) than in the present study. Thereby, they provoked similar conditions in terms of resulting hardness and trends of increasing microstructural feature size at their 10 mm cubic specimens.…”

Section: Subsumption Of the Results With Regard To Hardnessmentioning

confidence: 99%

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Process Induced Preheating in Laser Powder Bed Fusion Monitored by Thermography and Its Influence on the Microstructure of 316L Stainless Steel Parts

Mohr

Sommer

Knobloch

et al. 2021

Metals

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Undetected and undesired microstructural variations in components produced by laser powder bed fusion are a major challenge, especially for safety-critical components. In this study, an in-depth analysis of the microstructural features of 316L specimens produced by laser powder bed fusion at different levels of volumetric energy density and different levels of inter layer time is reported. The study has been conducted on specimens with an application relevant build height (>100 mm). Furthermore, the evolution of the intrinsic preheating temperature during the build-up of specimens was monitored using a thermographic in-situ monitoring set-up. By applying recently determined emissivity values of 316L powder layers, real temperatures could be quantified. Heat accumulation led to preheating temperatures of up to about 600 °C. Significant differences in the preheating temperatures were discussed with respect to the individual process parameter combinations, including the build height. A strong effect of the inter layer time on the heat accumulation was observed. A shorter inter layer time resulted in an increase of the preheating temperature by more than a factor of 2 in the upper part of the specimens compared to longer inter layer times. This, in turn, resulted in heterogeneity of the microstructure and differences in material properties within individual specimens. The resulting differences in the microstructure were analyzed using electron back scatter diffraction and scanning electron microscopy. Results from chemical analysis as well as electron back scatter diffraction measurements indicated stable conditions in terms of chemical alloy composition and austenite phase content for the used set of parameter combinations. However, an increase of the average grain size by more than a factor of 2.5 could be revealed within individual specimens. Additionally, differences in feature size of the solidification cellular substructure were examined and a trend of increasing cell sizes was observed. This trend was attributed to differences in solidification rate and thermal gradients induced by differences in scanning velocity and preheating temperature. A change of the thermal history due to intrinsic preheating could be identified as the main cause of this heterogeneity. It was induced by critical combinations of the energy input and differences in heat transfer conditions by variations of the inter layer time. The microstructural variations were directly correlated to differences in hardness.

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Section: Subsumption Of the Results With Regard To Hardnessmentioning

confidence: 58%

Section: Subsumption Of the Results With Regard To Hardnessmentioning

confidence: 99%

Process Induced Preheating in Laser Powder Bed Fusion Monitored by Thermography and Its Influence on the Microstructure of 316L Stainless Steel Parts

Mohr

Sommer

Knobloch

et al. 2021

Metals

View full text Add to dashboard Cite

show abstract

“…In the CO 2 –SLM samples, the scan speed was slower than in the fiber laser one, and this implied higher energy input values and higher temperatures. Therefore, as there was more heat to evacuate, cooling was slower, and it favored the formation of delta ferrite [ 53 ] and grain growth [ 54 , 55 ]. The CO 2 –SLM samples showed greater porosity than other samples, which also resulted in a lower hardness value because of the reduced effective density of the material.…”

Section: Resultsmentioning

confidence: 99%

Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel

et al. 2021

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In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO2 laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO2 laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.

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“…In recent years, many researchers have made extensive studies on the microstructure and mechanical properties of SLM stainless steel materials around process parameters, such as laser power, scanning speed, and powder feeding rate. For example, optimizing the laser energy density can enhance the intensity of SUS316L material [11], and choosing a reasonable scanning speed can improve the surface quality and increase the hardness of 316L material [12]. Furthermore, the forming angle and scanning strategy also significantly affect the microstructure and tensile strength of SLM316L material [13,14].…”

Section: Introductionmentioning

confidence: 99%

Dynamic Mechanical Properties and Constitutive Model of Selective Laser Melting 316L Stainless Steel at Different Scanning Speeds

Lei

Liu

et al. 2021

Preprint

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A 316L stainless steel material is widely used in the design of impact-resistant structures. Using selective laser melting (SLM) technology to form 316L stainless steel to study its mechanical behavior under dynamic loading is vital to improve the service performance of this product. This study investigates the dynamic compression mechanical properties and the constitutive models of 316L stainless steel specimens formed at different scanning speeds. The quasi-static and dynamic compression mechanical properties of SLM316L stainless steel specimens formed at four scanning speeds were tested using an electro-hydraulic servo experimental system and split Hopkinson pressure bar experimental apparatus. Microstructure observation was used to analyze the differences in the mechanical properties of specimens with different forming parameters. Finally, the modified Johnson-Cook (J-C) constitutive model was established and compared with the experimental data to illustrate the applicability of the modified model in describing the dynamic mechanical properties of SLM316l stainless steel. In dynamic compression mechanics experiments, the results show that SLM316L stainless steel specimens exhibit typical viscoplastic characteristics and significant strain rate strengthening effects. Furthermore, the scanning speed significantly affects the stacking characteristics of SLM-formed specimens, and the yield strength in axial compression decreases with the loss of stacking characteristics. Finally, the modified J-C model can accurately describe the mechanical properties of SLM316l stainless steel. This study can provide a theoretical model and methodological support for the design and development of SLM316l stainless steel.

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Effect of process parameters for selective laser melting with SUS316L on mechanical and microstructural properties with variation in chemical composition

Cited by 48 publications

References 31 publications

Process Induced Preheating in Laser Powder Bed Fusion Monitored by Thermography and Its Influence on the Microstructure of 316L Stainless Steel Parts

Process Induced Preheating in Laser Powder Bed Fusion Monitored by Thermography and Its Influence on the Microstructure of 316L Stainless Steel Parts

Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel

Dynamic Mechanical Properties and Constitutive Model of Selective Laser Melting 316L Stainless Steel at Different Scanning Speeds

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