scholarly journals Electron Backscattered Diffraction to Estimate Residual Stress Levels of a Superalloy Produced by Laser Powder Bed Fusion and Subsequent Heat Treatments

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4643
Author(s):  
Mathieu Terner ◽  
Jiwon Lee ◽  
Giulio Marchese ◽  
Sara Biamino ◽  
Hyun-Uk Hong
Keyword(s):  
Residual Stress ◽  
Elevated Temperatures ◽  
Heat Treatments ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Electron Backscattered Diffraction ◽  
Significant Drop ◽  
Powder Bed ◽  
Stress Relieving ◽  
Stress Levels

Metal Additive Manufacturing and Laser Powder Bed Fusion (LPBF), in particular, have come forth in recent years as an outstanding innovative manufacturing approach. The LPBF process is notably characterized by very high solidification and cooling rates, as well as repeated abrupt heating and cooling cycles, which generate the build-up of anisotropic microstructure and residual stresses. Post-processing stress-relieving heat treatments at elevated temperatures are often required in order to release some of these stresses. The effects of 1 h–hold heat treatments at different specific temperatures (solutionizing, annealing, stress-relieve and low-temperature stress-relieve) on residual stress levels together with microstructure characterization were therefore investigated for the popular Alloy 625 produced by LPBF. The build-up of residual stress is accommodated by the formation of dislocations that produce local crystallographic misorientation within grains. Electron backscattered diffraction (EBSD) was used to investigate local misorientation by means of orientation imaging, thereby assessing misorientation or strain levels, in turn representing residual stress levels within the material. The heavily constrained as-built material was found to experience full recrystallization of equiaxed grains after solutionizing at 1150 °C, accompanied by significant drop of residual stress levels due to this grains reconfiguration. Heat treatments at lower temperatures however, even as high as the annealing temperature of 980 °C, were found to be insufficient to promote recrystallization though effective to some extent to release residual stress through apparently dislocations recovery. Average misorientation data obtained by EBSD were found valuable to evaluate qualitatively residual stress levels. The effects of the different heat treatments are discussed and suggest that the peculiar microstructure of alloys produced by LPBF can possibly be transformed to suit specific applications.

scholarly journals Optimization of the Post-Process Heat Treatment of Inconel 718 Superalloy Fabricated by Laser Powder Bed Fusion Process

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 144
Author(s):  
Eslam M. Fayed ◽  
Mohammad Saadati ◽  
Davood Shahriari ◽  
Vladimir Brailovski ◽  
Mohammad Jahazi ◽  
...  
Keyword(s):  
Inconel 718 ◽  
Mechanical Performance ◽  
Solution Treatment ◽  
Heat Treatments ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Homogenization Treatment ◽  
Powder Bed ◽  
Post Process ◽  
High Fraction

In the present study, multi-objective optimization is employed to develop the optimum heat treatments that can achieve both high-mechanical performance and non-distinctive crystallographic texture of 3D printed Inconel 718 (IN718) fabricated by laser powder bed fusion (LPBF). Heat treatments including homogenization at different soaking times (2, 2.5, 3, 3.5 and 4 h) at 1080 °C, followed by a 1 h solution treatment at 980 °C and the standard aging have been employed. 2.5 h is found to be the homogenization treatment threshold after which there is a depletion of hardening precipitate constituents (Nb and Ti) from the γ-matrix. However, a significant number of columnar grains with a high fraction (37.8%) of low-angle grain boundaries (LAGBs) have still been retained after the 2.5 h homogenization treatment. After a 4 h homogenization treatment, a fully recrystallized IN718 with a high fraction of annealing twins (87.1%) is obtained. 2.5 and 4 h homogenization treatments result in tensile properties exceeding those of the wrought IN718 at both RT and 650 °C. However, considering the texture requirements, it is found that the 4 h homogenization treatment offers the optimum treatment, which can be used to produce IN718 components offering a balanced combination of high mechanical properties and adequate microstructural isotropy.

scholarly journals The Importance of Subsurface Residual Stress in Laser Powder Bed Fusion IN718

2021 ◽  
pp. 2100895
Author(s):  
Itziar Serrano-Munoz ◽  
Alexander Evans ◽  
Tatiana Mishurova ◽  
Maximilian Sprengel ◽  
Thilo Pirling ◽  
...  
Keyword(s):  
Residual Stress ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed

Residual Stress Measurements in a 316l Uniaxial Fatigue Sample Manufactured by Laser Powder Bed Fusion

2021 ◽  
Author(s):  
Catrin Mair Davies ◽  
Paul Sandmann ◽  
Tobias Ronneberg ◽  
Paul A Hooper ◽  
Saurabh Kabra
Keyword(s):  
Residual Stress ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Stress Measurements

EXPLORATORY INVESTIGATION ON RESIDUAL STRESS AND DISTORTION OF 20MnCr5 CARBURIZING STEEL PROCESSED BY LASER POWDER BED FUSION

2021 ◽  
Author(s):  
Lucas Robatto ◽  
Ronnie Rego ◽  
Anderson Vicente Borille ◽  
José Maria Mascheroni ◽  
Arthur Raulino Kretzer
Keyword(s):  
Residual Stress ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Exploratory Investigation

scholarly journals The residual stress in as-built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Itziar Serrano-Munoz ◽  
Tatiana Mishurova ◽  
Tobias Thiede ◽  
Maximilian Sprengel ◽  
Arne Kromm ◽  
...  
Keyword(s):  
Residual Stress ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Scanning Strategy ◽  
Powder Bed

scholarly journals Analytical Modeling of Residual Stress in Laser Powder Bed Fusion Considering Part’s Boundary Condition

Crystals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 337 ◽  
Author(s):  
Elham Mirkoohi ◽  
Hong-Chuong Tran ◽  
Yu-Lung Lo ◽  
You-Cheng Chang ◽  
Hung-Yu Lin ◽  
...  
Keyword(s):  
Residual Stress ◽  
Thermal Stress ◽  
Kinematic Hardening ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Repeated Heating ◽  
Powder Bed ◽  
Heating And Cooling ◽  
Body Load ◽  
Point Body

Rapid and accurate prediction of residual stress in metal additive manufacturing processes is of great importance to guarantee the quality of the fabricated part to be used in a mission-critical application in the aerospace, automotive, and medical industries. Experimentations and numerical modeling of residual stress however are valuable but expensive and time-consuming. Thus, a fully coupled thermomechanical analytical model is proposed to predict residual stress of the additively manufactured parts rapidly and accurately. A moving point heat source approach is used to predict the temperature field by considering the effects of scan strategies, heat loss at part’s boundaries, and energy needed for solid-state phase transformation. Due to the high-temperature gradient in this process, the part experiences a high amount of thermal stress which may exceed the yield strength of the material. The thermal stress is obtained using Green’s function of stresses due to the point body load. The Johnson–Cook flow stress model is used to predict the yield surface of the part under repeated heating and cooling. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Experimental measurement of residual stress was conducted using X-ray diffraction on the fabricated IN718 built via laser powder bed fusion to validate the proposed model.

Residual Stress Measurements in a 316L Uniaxial Samples Manufactured by Laser Powder Bed Fusion

2020 ◽  
Author(s):  
C. M. Davies ◽  
P. Sandmann ◽  
T. Ronneberg ◽  
P. A. Hooper ◽  
Saurabh Kabra
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Cross Section ◽  
316L Stainless Steel ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Stress Measurements ◽  
Compressive Stresses ◽  
Central Cross Section

Abstract Uniaxial samples have been manufactured for tension/compression testing from 316L stainless steel by laser powder bed fusion (LPBF). Samples manufactured by LPBF are known to contain high levels of residual stresses. These uniaxial samples were built from a solid cylindrical rod and subsequently machined to reduce the central cross section of the sample to the required gauge diameter and improve the surface finish. Finite element (FE) models have been developed to simulate the LPBF process of the rods, their removal from the build plate and subsequent machining into the tension/compression samples. High tensile residual stresses were predicted at the surface of the samples, balances by similar magnitude compressive stresses along their axis. Post machining however, these stresses were reduced by around 80% or more. Residual stress measurements were performed on the samples post machining using the neutron diffraction techniques. These measurements confirmed that negligible residual stresses remained in the samples post removal from the build plate and machining.

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