Fatigue Assessment of Inconel 625 Produced by Directed Energy Deposition from Miniaturized Specimens

In recent years, the industrial application of Inconel 625 has grown significantly. This material is a nickel-base alloy, which is well known for its chemical resistance and mechanical properties, especially in high-temperature environments. The fatigue performance of parts produced via Metallic Additive Manufacturing (MAM) heavily rely on their manufacturing parameters. Therefore, it is important to characterize the properties of alloys produced by a given set of parameters. The present work proposes a methodology for characterization of the mechanical properties of MAM parts, including the material production parametrization by Laser Directed Energy Deposition (DED). The methodology consists of the testing of miniaturized specimens, after their production in DED, supported by a numerical model developed and validated by experimental data for stress calculation. An extensive mechanical characterization, with emphasis on high-cycle fatigue, of Inconel 625 produced via DED is herein discussed. The results obtained using miniaturized specimens were in good agreement with standard-sized specimens, therefore validating the applied methodology even in the case of some plastic effects. Regarding the high-cycle fatigue properties, the samples produced via DED presented good fatigue performance, comparable with other competing Metallic Additive Manufactured (MAMed) and conventionally manufactured materials.

FID-calibrated simultaneous multi-slice fast spin echo with long trains of hard pulses

Objective: To develop a novel, free-induction-decay (FID)-calibrated single-shot simultaneous multi-slice fast spin echo (SMS-FSE) with very long hard pulse trains for high encoding efficiency and low energy deposition. Approach: The proposed single-shot SMS-FSE employs a mixed pulse configuration in which a long excitation pulse that is spatially multi-band (MB) selective is used in conjunction with short spatially nonselective refocusing pulses. To alleviate energy deposition to tissues while reducing signal modulation along the echo train, variable low flip angles with signal prescription are utilized in the refocusing pulse train. A time-efficient FID-calibration and correction method is introduced before aliased voxels in the slice direction are resolved. Simulations and experiments are performed to demonstrate the feasibility of the proposed method as an alternative to conventional HASTE for generating T2-weighted images. Main results: Compared with conventional HASTE, the proposed method enhances imaging speed effectively by an MB factor up to 5 without apparent loss of image contrast while successfully eliminating FID artifacts. Significance: We successfully demonstrated the feasibility of the proposed method as an encoding- and energy-efficient alternative to conventional HASTE for generation of T2-weighted contrast.

In-situ Synthesis and Characterization of Ceramic Reinforced Inconel 718 Coatings Using B4C-Inconel 718 Powders by Laser Directed Laser Energy Deposition

Inconel 718 has been widely used in aerospace, nuclear and marine industries due to excellent high-temperature mechanical properties and corrosion resistance. In recent years, laser directed energy deposition (DED) become a competitive method in the fabrication of Inconel 718 coatings. Compared with other surface coating processes, laser DED has the advantage of extremely fine-grained structures, strong metallurgical bonding, and high density. However, the hardness and wear resistance of Inconel 718 coatings still need to be improved. To further improve these properties, ceramic reinforced Inconel 718 coatings have been investigated. Compared with ex-situ ceramic reinforcements, the in-situ synthesized reinforcements have the advantage of refined ceramic particle size, uniform distribution, and low thermal stress. B4C was a preferable additive material to fabricate in-situ synthesized multi-component ceramic reinforced Inconel 718 coatings. The addition of B4C could form a large number of borides and carbides as ceramic reinforcements. In addition, the in-situ reactions between Inconel 718 and B4C could release heat during the fabrication, thereby promoting the melting of material powders. However, there are currently no investigations on the in-situ synthesis mechanisms, microstructure, and mechanical properties of laser DED fabricated B4C-Inconel 718 coatings. In this study, the effects of B4C on the properties of Inconel 718 coatings were investigated. Results show that Ni3B, NbB, and Cr3C2 phases were formed. With the addition of B4C, the size of Laves phase was refined and the porosity was decreased. The hardness and wear resistance of B4C reinforced coatings were improved by about 34% and 28%, respectively.