Assessment of Additive Manufactured IN 625’s Tensile Strength Based on Nonstandard Specimens

Abstract

The study aimed to evaluate the tensile strength of additively manufactured (AMed) IN 625 using sub-sized test pieces and compare them to standard specimens. Cylindrical round coupons of varying diameters were manufactured along the Z-axis using the laser powder bed fusion technique and subjected to heat treatment. The simulation of the alloy solidification predicted the formation of several intermetallics and carbides under equilibrium conditions (slow cooling), apart from the γ phase (FCC). Sub-sized tensile specimens with different gauge diameters were machined from the coupons and tensile tested at ambient temperature. The results showed that sub-sized specimens exhibited lower tensile and yield strengths compared to standard specimens, but still higher than the minimum requirements of the relevant ASTM standard for AMed IN 625. The lower strength was attributed to the “size effect” of the test specimens. Fracture surfaces of the sub-sized test specimens exhibit a mixed character, combining cleavage and microvoid coalescence, with improved ductility compared to standard test pieces. The study highlights the importance of adapting characterization methods to the particularities of manufactured parts, including reduced thicknesses that make sampling standard-size specimens impractical. It concludes that sub-sized specimens are valuable for quality control and verifying compliance with requirements of AMed IN 625 tensile properties.

Assessment of Residual Stresses in Laser Powder Bed Fusion Manufactured IN 625

“…This establishes a clear correlation between these variables and the deformations observed in IN 625 parts produced through PBF-LB/M. Nevertheless, in the current study, the process parameters were selected for the manufacturing of bridge-type test pieces based on their excellent results in terms of density, microstructure, and mechanical properties, as demonstrated in previous studies [33][34][35][36]. This approach was intentionally adopted to facilitate a more precise understanding of the isolated impact of scanning strategies on results, independent of other variables.…”

“…To determine the impact of stress-relieving heat treatment in reducing residual stress, careful consideration must be given to the selection of temperature and duration, particularly about the microstructure and mechanical properties of additively manufactured parts. The choice of temperature and conditions for the heat treatment was guided by previous studies conducted by the authors [33][34][35] on additively manufactured IN 625 alloy, specifically examining its effects on microstructure and properties. However, a stress-relief heat treatment typically ranges from 650 to 870 • C [43], and the selection of 870 • C for IN 625 aligns with industry standards [44].…”

“…Also, the samples were built with no contour strategy. Prior studies conducted by the authors [33][34][35][36] demonstrated that these parameters are optimal in terms of the density, microstructure, and mechanical properties of the IN 625 alloy manufactured using the same Lasertec 30 SLM machine. This approach was adopted to facilitate a more precise understanding of the isolated impact of scanning strategies on the results, independent of other variables.…”

Simulation of 316L Stainless Steel Produced the Laser Powder Bed Fusion Process

“…Paraschiv et al [31] investigated the tensile strength of additively manufactured undersized samples made of IN 625 material and compared them with standard samples. They used round sample shapes produced using the LPBF method as samples, while for the final form they used non-standard-shaped samples due to material consumption and production time.…”