A study on the residual stress during selective laser melting (SLM) of metallic powder

Liu, Yang; Yang, Yongqiang; Wang, Di

doi:10.1007/s00170-016-8466-y

Cited by 402 publications

(174 citation statements)

References 26 publications

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“…To more accurately predict the residual stress development, finite element analysis coupling thermal aspects and powder/mechanical properties are preferred [101,[103][104][105]. Experimental measurements using X-ray [105][106][107] or neutron diffractometer [101,108] have been reported, but the results are unable to present the residual stress profile within the whole component, since these measurements were performed on sporadic spots on the superficial region. Note that the residual stress might be relaxed and re-distributed if the component is directly removed from the base plate after the process, and experimental measurement on this kind of sample would probably give artificial results.…”

Section: Residual Stressmentioning

confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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Linköping 2018Cover image: A fracture surface of EBM IN718 after tensile test at room temperature.During the course of research underlying this thesis, Dunyong Deng was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Dunyong Deng AbstractAdditive manufacturing (AM), also known as 3D printing, has gained significant interest in aerospace, energy, automotive and medical industries due to its capabilities of manufacturing components that are either prohibitively costly or impossible to manufacture by conventional processes. Among the various additive manufacturing processes for metallic components, electron beam melting (EBM) and selective laser melting (SLM) are two of the most widely used powder bed based processes, and have shown great potential for manufacturing high-end critical components, such as turbine blades and customized medical implants. The futures of the EBM and SLM are doubtlessly promising, but to fully realize their potentials there are still many challenges to overcome.Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties and low cost. Though IN718 is being mostly used as a turbine disk material now, the initial introduction of IN718 was to overcome the poor weldability of superalloys in 1960s, since sluggish precipitation of strengthening phases γ ′ /γ ′′ enables good resistance to strain-age cracking during welding or post weld heat treatment. Given the similarity between AM and welding processes, IN718 has been widely applied to the metallic AM field to facilitate the understandings of process-microstructure-property relationships.The work presented in this licentiate thesis aims to better understand microstructures and mechanical properties EBM and SLM IN718, which have not been systematically investigated. Microstructures of EBM and SLM IN718 have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the process conditions. Monotonic mechanical properties (e.g., Vickers microhardness and tensile properties) have also been measured and rationalized with regards to the microstructure evolutions before and after heat treatments.For EBM IN718, the results show the microstructure is not homogeneous but dependant on the location in the components, and the anisotropic mechanical properties are probably attributed to alignment of porosities rather than texture.iii Post heat treatment can slightly increase the mechanical strength compared to the as-manufactured condition but does not alter the anisotropy. SLM IN718 shows significantly different microstructure and mechanical properties to EBM IN718. The as-manufactured SLM IN718 has very fine dendritic microstructure and Laves phases in the interdendrites, and is "work-hardened" by the residual strains and dislocations present in the material. Mechanical properties are different between horizontally and vertically built samples, and heat treatment can m...

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Section: Residual Stressmentioning

confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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“…As the consolidation process in L-PBF is characterised by competitive grain growth at the solid-liquid interface [37], local differences in stress state are inevitable. Moreover, with successive laser passes, regions of the material experience repeated heating and cooling such that residual stress of different extent is generated along the build direction [38]. Since the relaxation of residual stress during heat treatment is accompanied by elastic recovery of various regions in the bulk material, it promotes the opening of high stress concentration areas [33] such as pre-existing defects, in this case grain boundaries or gas pores.…”

Section: Mechanisms Of Defect Formationmentioning

confidence: 99%

Effect of heat treatment on fatigue crack initiation of laser powder bed fusion stainless steel 316L

et al. 2018

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Abstract. Laser powder bed fusion (L-PBF) is an emerging additive manufacturing technique for building structural components. L-PBF processing defects, such as lack of fusion pores, promote fatigue crack initiation and shorten the fatigue life. With well-controlled processing, critical pores can be avoided such that the microstructure-driven intergranular crack initiation mode becomes operative. In this work, the fatigue crack initiation behaviours of as-built and solution annealed L-PBF stainless steel 316L were studied. Crack initiation of the as-built samples is driven by de-bonding of the dendritic grain boundaries. High temperature annealing results in the formation of thermally-induced defects, possibly via the reheat cracking mechanism and the nucleation of pre-existing gas pores. As heat treating could have led to recrystallization and annihilation of the original grain boundary defects, the thermally-induced defects became the new sites for crack initiation. In addition, heat treatment incurred significant reduction in yield strength, such that the interaction of fatigue and ratcheting strain accumulation dominated the deformation behaviour of the material. The resulting fatigue strength in the finite life regime was reduced by about 13% but the fatigue endurance limit was not affected.

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“…First principles models, both simple and complex, were proposed by Patterson et al [35,36] and Fergani et al [61], all of which were demonstrated and verified using various numerical experiments and comparisons to published experimental data. Examples of computational studies that were verified using various simple part deformation experiments were those performed by Vrancken et al [62], Zinovieva et al [63], Liu et al [64] and Safronov et al [65]. Stress models built using ANSYS include those models developed by Zaeh and Branner [66] and Gu and He [67].…”

Section: Stress and Distortion Modelsmentioning

confidence: 99%

Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

2017

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Abstract:A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce full-density metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of the literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging and design-of-experiments), support structure optimization and overhang feature design; approximately 143 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs and potential future research directions are discussed in-depth in light of the present review.

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A study on the residual stress during selective laser melting (SLM) of metallic powder

Cited by 402 publications

References 26 publications

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Effect of heat treatment on fatigue crack initiation of laser powder bed fusion stainless steel 316L

Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

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