Laser Powder Bed Fusion of Inconel 718: Residual Stress Analysis Before and After Heat Treatment

Residual stresses (RS) of great magnitude are usually present in parts produced by Laser Powder Bed Fusion (PBF-LB), mainly owing to the extreme temperature gradients and high cooling rates involved in the process. Those “hidden” stresses can be detrimental to a part’s mechanical properties and fatigue life; therefore, it is crucial to know their magnitude and orientation. The hole-drilling strain-gage method was used to determine the RS magnitude and direction-depth profiles. Cuboid specimens in the as-built state, and after standard solution annealing and ageing heat treatment conditions, were prepared to study the RS evolution throughout the heat treatment stages. Measurements were performed on the top and lateral surfaces. In the as-built specimens, tensile stresses of ~400 MPa on the top and above 600 MPa on the lateral surface were obtained. On the lateral surface, RS anisotropy was noticed, with the horizontally aligned stresses being three times lower than the vertically aligned. RS decreased markedly after the first heat treatment. On heat-treated specimens, magnitude oscillations were observed. By microstructure analysis, the presence of carbides was verified, which is a probable root for the oscillations. Furthermore, compressive stresses immediate to the surface were obtained in heat-treated specimens, which is not in agreement with the typical characteristics of parts fabricated by PBF-LB, i.e., tensile stresses at the surface and compressive stresses in the part’s core.

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Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion

Materials ◽

10.3390/ma14206157 ◽

2021 ◽

Vol 14 (20) ◽

pp. 6157

Author(s):

Matteo Vanzetti ◽

Enrico Virgillito ◽

Alberta Aversa ◽

Diego Manfredi ◽

Federica Bondioli ◽

...

Keyword(s):

Heat Treatment ◽

Precipitation Hardening ◽

Solution Treatment ◽

Heat Treatments ◽

Point Of View ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Heat Treated ◽

Direct Aging

Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 °C followed by water quenching and subsequently by an artificial aging at 170 °C for 2–8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 °C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 °C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry.

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Microstructure and Selective Corrosion of Alloy 625 Obtained by Means of Laser Powder Bed Fusion

Materials ◽

10.3390/ma12111742 ◽

2019 ◽

Vol 12 (11) ◽

pp. 1742 ◽

Cited By ~ 4

Author(s):

Marina Cabrini ◽

Sergio Lorenzi ◽

Cristian Testa ◽

Fabio Brevi ◽

Sara Biamino ◽

...

Keyword(s):

Heat Treatment ◽

Intergranular Corrosion ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Alloy 625 ◽

Heat Treated ◽

Selective Corrosion ◽

Corrosion Susceptibility ◽

Acid Test

The effect of microstructure on the susceptibility to selective corrosion of Alloy 625 produced by laser powder bed fusion (LPBF) process was investigated through intergranular corrosion tests according to ASTM G28 standard. The effect of heat treatment on selective corrosion susceptibility was also evaluated. The behavior was compared to commercial hot-worked, heat treated Grade 1 Alloy 625. The morphology of attack after boiling ferric sulfate-sulfuric acid test according to ASTM G28 standard is less penetrating for LPBF 625 alloy compared to hot-worked and heat-treated alloy both in as-built condition and after heat treatment. The different attack morphology can be ascribed to the oversaturation of the alloying elements in the nickel austenitic matrix obtained due to the very high cooling rate. On as-built specimens, a shallow selective attack of the border of the melt pools was observed, which disappeared after the heat treatment. The results confirmed similar intergranular corrosion susceptibility, but different corrosion morphologies were detected. The results are discussed in relation to the unique microstructures of LPBF manufactured alloys.

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Unravelling the multi-scale structure–property relationship of laser powder bed fusion processed and heat-treated AlSi10Mg

Scientific Reports ◽

10.1038/s41598-021-85047-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

P. Van Cauwenbergh ◽

V. Samaee ◽

L. Thijs ◽

J. Nejezchlebová ◽

P. Sedlák ◽

...

Keyword(s):

Heat Treatment ◽

Grain Refinement ◽

Rapid Solidification ◽

Material Properties ◽

Mechanical And Thermal Properties ◽

Powder Bed Fusion ◽

Structure Property ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Heat Treated

AbstractTailoring heat treatments for Laser Powder Bed Fusion (LPBF) processed materials is critical to ensure superior and repeatable material properties for high-end applications. This tailoring requires in-depth understanding of the LPBF-processed material. Therefore, the current study aims at unravelling the threefold interrelationship between the process (LPBF and heat treatment), the microstructure at different scales (macro-, meso-, micro-, and nano-scale), and the macroscopic material properties of AlSi10Mg. A similar solidification trajectory applies at different length scales when comparing the solidification of AlSi10Mg, ranging from mould-casting to rapid solidification (LPBF). The similarity in solidification trajectories triggers the reason why the Brody-Flemings cellular microsegregation solidification model could predict the cellular morphology of the LPBF as-printed microstructure. Where rapid solidification occurs at a much finer scale, the LPBF microstructure exhibits a significant grain refinement and a high degree of silicon (Si) supersaturation. This study has identified the grain refinement and Si supersaturation as critical assets of the as-printed microstructure, playing a vital role in achieving superior mechanical and thermal properties during heat treatment. Next, an electrical conductivity model could accurately predict the Si solute concentration in LPBF-processed and heat-treated AlSi10Mg and allows understanding the microstructural evolution during heat treatment. The LPBF-processed and heat-treated AlSi10Mg conditions (as-built (AB), direct-aged (DA), stress-relieved (SR), preheated (PH)) show an interesting range of superior mechanical properties (tensile strength: 300–450 MPa, elongation: 4–13%) compared to the mould-cast T6 reference condition.

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Heat treatment of aluminium alloys produced by laser powder bed fusion: A review

Materials & Design ◽

10.1016/j.matdes.2021.109651 ◽

2021 ◽

pp. 109651

Author(s):

J. Fiocchi ◽

A. Tuissi ◽

C.A. Biffi

Keyword(s):

Heat Treatment ◽

Aluminium Alloys ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed

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Laser Powder Bed Fusion Processing of Fe-Mn-Al-Ni Shape Memory Alloy—On the Effect of Elevated Platform Temperatures

Metals ◽

10.3390/met11020185 ◽

2021 ◽

Vol 11 (2) ◽

pp. 185

Author(s):

Felix Clemens Ewald ◽

Florian Brenne ◽

Tobias Gustmann ◽

Malte Vollmer ◽

Philipp Krooß ◽

...

Keyword(s):

Heat Treatment ◽

Crack Formation ◽

Microstructural Analysis ◽

Tensile Load ◽

Grain Structure ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Cyclic Heat Treatment ◽

Powder Bed ◽

Cyclic Heat

In order to overcome constraints related to crack formation during additive processing (laser powder bed fusion, L-BPF) of Fe-Mn-Al-Ni, the potential of high-temperature L-PBF processing was investigated in the present study. The effect of the process parameters on crack formation, grain structure, and phase distribution in the as-built condition, as well as in the course of cyclic heat treatment was examined by microstructural analysis. Optimized processing parameters were applied to fabricate cylindrical samples featuring a crack-free and columnar grained microstructure. In the course of cyclic heat treatment, abnormal grain growth (AGG) sets in, eventually promoting the evolution of a bamboo like microstructure. Testing under tensile load revealed a well-defined stress plateau and reversible strains of up to 4%.

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