scholarly journals Heat Treatments for Stress Relieving AlSi9Cu3 Alloy Produced by Laser Powder Bed Fusion

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4184
Author(s):  
Jacopo Fiocchi ◽  
Chiara Colombo ◽  
Laura Maria Vergani ◽  
Alberto Fabrizi ◽  
Giulio Timelli ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Aluminum Matrix ◽  
High Strength ◽  
Eutectic Structure ◽  
Heat Treatments ◽  
Layer By Layer ◽  
Time Curve ◽  
Powder Bed ◽  
Stress Relieving ◽  
Elongation To Failure

The present work explores the effect of a stress relieving heat treatment on the microstructure, tensile properties and residual stresses of the laser powder bed fused AlSi9Cu3 alloy. In fact, the rapid cooling rates together with subsequent heating/cooling cycles occurred during layer by layer additive manufacturing production make low temperature heat treatments desirable for promoting stress relaxation as well as limited grain growth: this combination can offer the opportunity of obtaining the best compromise between high strength, good elongation to failure and limited residual stresses. The microstructural features were analysed, revealing that the high cooling rate, induced by the process, caused a large supersaturation of the aluminum matrix and the refinement of the eutectic structure. Microhardness versus time curve, performed at 250 °C, allowed to identify a stabilization of the mechanical property at a duration of 25 h. The microstructure and the mechanical properties of the samples heat treated at 25 h and at 64 h, considered as a reference for the conventionally produced alloy, were compared with the ones of the as-built alloy. Finally, it was shown that a 59% reduction of the principal residual stresses could be achieved after the 25 h-long treatment and such evolution was correlated to the mechanical behaviour.

scholarly journals Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments

2020 ◽  
Author(s):  
Giulio Marchese ◽  
Eleonora Atzeni ◽  
Alessandro Salmi ◽  
Sara Biamino
Keyword(s):  
Residual Stresses ◽  
Inconel 718 ◽  
Heat Treatments ◽  
Powder Bed Fusion ◽  
Stress Evolution ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
Sintering Mechanisms ◽  
Dendritic Structures

AbstractThe current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 °C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 °C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 °C involved the formation of δ phases, whereas 1065 °C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 °C did not trigger sintering mechanisms allowing to remove the powder from the inner channels.

scholarly journals A Review of Heat Treatments on Improving the Quality and Residual Stresses of the Ti–6Al–4V Parts Produced by Additive Manufacturing

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1006 ◽  
Author(s):  
Óscar Teixeira ◽  
Francisco J. G. Silva ◽  
Luís P. Ferreira ◽  
Eleonora Atzeni
Keyword(s):  
Fatigue Life ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Electron Beam Melting ◽  
Heat Treatments ◽  
High Melting Point ◽  
High Corrosion Resistance ◽  
Beam Source ◽  
Powder Bed ◽  
Metallic Parts

Additive manufacturing (AM) can be seen as a disruptive process that builds complex components layer upon layer. Two of its distinct technologies are Selective Laser Melting (SLM) and Electron Beam Melting (EBM), which are powder bed fusion processes that create metallic parts with the aid of a beam source. One of the most studied and manufactured superalloys in metal AM is the Ti–6Al–4V, which can be applied in the aerospace field due to its low density and high melting point, and in the biomedical area owing to its high corrosion resistance and excellent biocompatibility when in contact with tissues or bones of the human body. The research novelty of this work is the aggregation of all kinds of data from the last 20 years of investigation about Ti–6Al–4V parts manufactured via SLM and EBM, namely information related to residual stresses (RS), as well as the influence played by different heat treatments in reducing porosity and increasing mechanical properties. Throughout the report, it can be seen that the expected microstructure of the Ti–6Al–4V alloy is different in both manufacturing processes, mainly due to the distinct cooling rates. However, heat treatments can modify the microstructure, reduce RS, and increase the ductility, fatigue life, and hardness of the components. Furthermore, distinct post-treatments can induce compressive RS on the part’s surface, consequently enhancing the fatigue life.

Microstructural Evolution Of LPBF AlSiMg – Effect Of Water Quenching Vs Furnace Cooling Vs Direct Aging

2021 ◽  
Author(s):  
Dheepa Srinivasan ◽  
Dayananda Narayana
Keyword(s):  
Heat Treatment ◽  
Microstructural Characterization ◽  
Heat Treatments ◽  
Water Quenching ◽  
Powder Bed ◽  
Part Geometry ◽  
Stress Relieving ◽  
Direct Aging ◽  
Potential Applications ◽  
Lower Elongation

Abstract The heat treatment response of AlSi10Mg via laser powder bed fusion (LPBF) has been studied via detailed microstructural characterization. The effect of solutioning (S) and water quenching (WQ) vs furnace cooling (FC), and direct aging (DA) vs solutioning and aging (SA), has been analysed, for microstructure and tensile properties. 11 heat treatments were carried out to map the partitioning of Si, starting with stress relieving at 200 °C vs 300 °C, followed by solution heat treatment at 430°C vs 530 °C, water quenching vs furnace cooling, aging at 160 °C vs direct aging at 160 °C, to establish the microstructure of LPBF AlSi10Mg alloys for potential applications. The microstructure at 430 °C and 530 °C shows Si precipitate fractions of 25% and 14%, respectively. Room temperature mechanical properties, revealed the 300 °C, 2 h stress relieved sample with the highest strength and ductility (YS of 230 MPa and 16%). At 430 °C, both water quenching and furnace cooling showed similar strengths and 16% elongation, while at 530 °C, there was a much lower elongation (8–9%) with the T6 (53 °C, WQ, SA) showing higher strength and elongation. This study brings out the importance of being able to choose the heat treatments suitable to AlSiMg part geometry, via LPBF additive manufacturing for various applications.

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.

Effects of Residual Stresses on the Fatigue Performance of Welded Steels with Longitudinal Stiffeners

2013 ◽  
Vol 768-769 ◽  
pp. 636-643 ◽  
Author(s):  
Jonas Hensel ◽  
Thomas Nitschke-Pagel ◽  
Klaus Dilger ◽  
Steffen Schönborn
Keyword(s):  
Fatigue Strength ◽  
Residual Stresses ◽  
Stress Ratio ◽  
Fatigue Testing ◽  
High Strength ◽  
Fatigue Loading ◽  
X Ray ◽  
Initial Residual Stress ◽  
Stress Relieving ◽  
Longitudinal Stiffeners

Residual stresses may affect the behavior of welded steels under fatigue loading. However, for design of welded structures the height and distribution of residual stresses from welding are often not known so that tensile residual stresses in the order of the yield strength are conservatively assumed. Here presented results focus on the influence of residual stresses on the fatigue strength of longitudinal stiffeners made from a mild steel S355NL and a high strength steel S960QL. The initial residual stress conditions were measured using X-ray and neutron diffraction. In order to characterize the influence of residual stresses on the fatigue strength, specimens were tested in the as-welded condition and after a stress relieving heat treatment. The fatigue testing was conducted under alternating constant amplitude loading with a stress ratio of R=-1.

Theoretical study of the prestressing strand's stress by computer modeling methods

2020 ◽  
Vol 76 (11) ◽  
pp. 1139-1148
Author(s):  
A. G. Korchunov ◽  
E. M. Medvedeva ◽  
E. M. Golubchik
Keyword(s):  
Residual Stresses ◽  
High Strength ◽  
Pearlitic Steel ◽  
Internal Stresses ◽  
Steel Microstructure ◽  
Compressive Stresses ◽  
Wide Range ◽  
Prestressing Strands ◽  
Increasing Temperature ◽  
Wire Strand

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

Effect of diamond burnishing parameters on the state of the processed surface layer of billets made of high-strength "30ХГСН2А-ВД" steel

2020 ◽  
pp. 82-86
Author(s):  
A.N. Shvetsov ◽  
D.L. Skuratov
Keyword(s):  
Surface Layer ◽  
Residual Stresses ◽  
Strain Hardening ◽  
Processing Speed ◽  
Synthetic Diamond ◽  
High Strength ◽  
The State ◽  
Diamond Burnishing

The influence of the burnishing force, tool radius, processing speed and feed on the distribution of circumferential and axial residual strses, microhardness and the depth of strain hardening in the surface layer when pr ssing of "30ХГСН2А-ВД" steel with synthetic diamond "ACB-1" is considered. Empirical dependencies determining these parameters are given. Keywords diamond burnishing, strain hardening depth, circumferential residual stresses, axial residual stresses, microhardness. [email protected], [email protected]

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