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Wire arc additive manufacturing (WAAM) presents a highly promising alternative to conventional subtractive manufacturing methods to produce metallic components, particularly in the aerospace industry, where there is a demand for 17–4 precipitation-hardened (PH) stainless steel structures. This study focuses on investigating the microstructural characteristics, showing microhardness evaluations, and analyzing the tensile properties of the as-printed parts during the 17–4 PH manufacturing process at different locations and directions. The fabrication is carried out using gas metal wire arc additive manufacturing (GM-WAAM). As a result, it was found that the microstructure of the as-deposited part showed a complex configuration consisting of both finely equiaxed and coarsely formed δ-ferrite phases with vermicular and lathy morphologies. These phases were dispersed inside the martensitic matrix, while a small amount of retained austenite was also present. It was observed that the volume fraction of retained austenite (20–5%) and δ-ferrite phases (15.5–2.5%) decreased gradually from the bottom to the top of the as-deposited wall. This reduction in the fractions of these phases resulted in a progressive increase in both hardness (∼37%) and ultimate tensile strength (UTS) along the building direction. This study successfully fabricates a high-strength and ductile 17–4 PH as-printed part using WAAM. The findings provide evidence supporting the feasibility of employing WAAM for producing defect-free, high-strength components on a large scale while maintaining mechanical properties similar or better than wrought alloy 17–4 PH.
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Pulsed gas metal arc additive manufacturing of low-carbon steel: Microstructure observations and mechanical properties
Gas metal arc additive manufacturing (GMA-AM), also known as wire arc additive manufacturing (WAAM), uses an electric arc to melt a wire electrode and deposit objects layer by layer. This study focuses on creating single-pass wall structures using a low-carbon steel wire (ER70S-6) and examining the relationship between pulse frequency and weld geometry, microstructure, and mechanical properties. Microscopic observations showed a typical columnar microstructure with three distinct regions: acicular ferrite, bainite, and allotriomorphic ferrite in the first and last layers, while the mid-region exhibited homogenous polygonal ferrite grains with some pearlite at the grain boundaries. The tensile test results demonstrated a dependency of strength on the applied pulse frequency, with the highest strength (i.e., the ultimate tensile strength of 522 MPa and yield strength of 375 MPa with ductility of ∼52%) achieved in parts processed at a frequency of 100 Hz. Vickers microhardness values revealed uniform hardness in the middle region, consistent with the microstructure observation. Analyzing thermal cycles, coupled with microstructure analysis and continuous cooling transition diagrams, provided insight into how phase and microstructure evolution occurred in low-carbon low-alloy steels processed through PGMA-AM.
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- Award ID(s):
- 2050916
- PAR ID:
- 10476348
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Materials Today Communications
- Volume:
- 38
- ISSN:
- 2352-4928
- Page Range / eLocation ID:
- 107637
- Subject(s) / Keyword(s):
- Additive Manufacturing
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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This study aims to investigate surface roughness, microstructure, and mechanical properties of overhead thin-wall structures of stainless steel(SS316L) fabricated by cold metal transfer (CMT)-based wire + arc additive manufacturing (WAAM). In the first stage, single-layer bead experiments were carried out in flat and overhead positions utilizing Box-Behnken experimental design with a range of process parameters (i.e., wire feed rate, travel speed, and weave amplitude). To study the effect of individual process parameters on the bead geometry and identify a process window, analysis of variance(ANOVA) is performed using the bead cross-section measurement data. For single layer bead experiments in flat and overhead position, out of all process parameters, the weave amplitude is the most significant parameter on bead width, whereas travel speed is most significant parameter for bead height. Based on single-layer bead experiments, process parameters for thin wall deposition were identified. In the second stage, two thin-walls were deposited with wire feed rates of 1000 and 1500 mm/min in the overhead position. The surface roughness was measured using cloud point data acquired from the coordinate measuring machine(CMM). The deposited structure with the wire feed rate of 1500 mm/min resulted in better surface quality. It was also observed that, microstructure was composed of austenite and dendritic delta ferrite. The microstructure changed as the deposition height increased. The average microhardness value was measured 183 HV and 187.4 HV for the overhead structures. Average tensile properties of the SS316L overhead structures were comparable to that of SS316L fabricated by other WAAM processes.more » « less
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Abstract Bimetallic wire arc additive manufacturing (AM) has traditionally been limited to depositions characterized by single planar interfaces. This study demonstrates a more complex radial interface concept, with in situ mechanical interlocking and as-built properties suggesting a prestressed compressive effect. A 308 L stainless core is surrounded by a mild steel casing, incrementally maintaining the interface throughout the Z-direction. A small difference in the thermal expansion coefficient between these steels creates residual stresses at their interface. X-ray diffraction analysis confirms phase purity and microstructural characterization reveals columnar grain growth independent of layer transitions. Hardness values are consistent with thermal dissipation characteristics, and the compressive strength of the bimetallic structures shows a 33% to 42% improvement over monolithic controls. Our results demonstrate that biomimetic radial bimetallic variation is feasible with improved mechanical response over monolithic compositions, providing a basis for advanced structural design and implementation using arc-based metal AM.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.mtcomm.2023.107637
