An official website of the United States government
Recovery plays distinct roles in nanostructured and coarse-grained metallic materials. While static and dynamic recovery usually soften work-hardened, coarse-grained materials, static recovery has been shown to strengthen nanostructured metals. This study extends this understanding by demonstrating that dynamic recovery can also strengthen nanostructured metals under deformation. Tensile, creep, and plane strain compression tests on nanostructured aluminum reveal a trend of increasing strain-hardening with decreasing strain rate and increasing temperature. Molecular dynamics simulations further indicate that sudden strain rate reductions lead to an initial drop in flow stress, followed by strain hardening. These findings suggest that dynamic recovery could serve as an effective strengthening mechanism for nanostructured metals, offering improvements in uniform elongation.
more »
« less
Electrochemical Healing of Fractured Metals
Abstract Repairing fractured metals to extend their useful lifetimes advances sustainability and mitigates carbon emissions from metal mining and processing. While high‐temperature techniques are being used to repair metals, the increasing ubiquity of digital manufacturing and “unweldable” alloys, as well as the integration of metals with polymers and electronics, call for radically different repair approaches. Herein, a framework for effective room‐temperature repair of fractured metals using an area‐selective nickel electrodeposition process refered to as electrochemical healing is presented. Based on a model that links geometric, mechanical, and electrochemical parameters to the recovery of tensile strength, this framework enables 100% recovery of tensile strength in nickel, low‐carbon steel, two “unweldable” aluminum alloys, and a 3D‐printed difficult‐to‐weld shellular structure using a single common electrolyte. Through a distinct energy‐dissipation mechanism, this framework also enables up to 136% recovery of toughness in an aluminum alloy. To facilitate practical adoption, this work reveals scaling laws for the energetic, financial, and time costs of healing, and demonstrates the restoration of a functional level of strength in a fractured standard steel wrench. Empowered with this framework, room‐temperature electrochemical healing can open exciting possibilities for the effective, scalable repair of metals in diverse applications.
more »
« less
- PAR ID:
- 10419014
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 35
- Issue:
- 24
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Combining a retrogression heat treatment with simulta- neous warm forming can increase the formability of peak-aged, high-strength aluminum alloys while allowing peak-aged strength to be recovered through a single reaging heat treatment after forming. This process is termed retrogression-forming-and-reaging (RFRA). This study investigates the applicability of RFRA to AA6013- T6 sheet material. Elevated-temperature tensile tests were performed at temperatures from 230 to 250 °C and strain rates from 3.2 10 −3 to 10 −1 s −1 . Tensile tests were followed by reaging with a simulated paint-bake heat treatment. Flow stress at a true strain of 0.10 ranges from 230 MPa (250 °C and 3.2 10 −3 s −1 ) to 290 MPa (230 °C and 10 −1 s −1 ), significantly lower than the room-temperature yield strength of 360 MPa in the T6 condition. The average elongation to rupture and reduc- tion in area from elevated-temperature tests are 22% and 56%, respectively, which are similar to the room- temperature values for the T4 condition. Elevated- temperature testing reduced material hardness compared to the original T6 condition. Subsequent reaging with a simulated paint-bake raised hardness to 96% of the T6 condition in un-deformed material, but slightly decreased the hardness of the deformed material. Recommendations for implementing RFRA of AA6013-T6 are presented.more » « less
-
Abstract This study demonstrates the simultaneous achievement of high strength and excellent corrosion resistance in a Ni-free, high N austenitic stainless steel fabricated by laser powder bed fusion (PBF-LB). The formation of a single-phase austenitic structure was confirmed through X-ray diffraction analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic potentiodynamic polarization tests conducted in 0.6 M NaCl solution at room temperature revealed high breakdown potential (1187 ± 31 mVSCE), indicating excellent corrosion resistance for the additively manufactured Ni-free austenitic stainless steel compared to wrought 316L stainless steel. These findings were further supported by immersion tests in FeCl3solution. The additively fabricated alloy’s yield strength and ultimate tensile strength exceeded 800 MPa and 1 GPa, respectively. The results highlight the potential for developing highly corrosion-resistant, high-strength Ni-free austenitic stainless steel by PBF-LB for possible applications for biomedical implants and structures relating to nuclear energy.more » « less
-
Abstract The demand for effective de-bondable adhesive technology enabling substrate separation under small loads has grown in recent years. Thermally Expandable Particles (TEP) can be embedded in structural adhesives to promote mechanical separation of the adherends. However, the activation of TEP additives in joints with non-metallic adherends is challenging and can result in substrate thermal damage and poor de-bonding performance, due to the low thermal conductivity and dielectric loss factor typical of plastics and polymer-matrix composites. In this study, the effect of bondline stainless steel inserts on fully composite (Carbon Fiber Reinforced Polymer, or CFRP) bonded Single Lap Joints (SLJ) mechanical and de-bonding performance is evaluated. A centrifugal mixer is used to disperse the TEP in the adhesive. TEP additives are activated using induction heating of the bondline insert, which also helps control crack initiation and propagation. SLJ de-bonding tests are run under a constant 20 lb (89 N) load, and substrate temperature is recorded with thermocouples and an infrared thermometer. Joint strength is evaluated with quasi-static lap shear tests on a servo-hydraulic tensile test apparatus. Preliminary de-bonding testing is performed on a broad initial set of 316 stainless steel insert designs. Out of those, the four best-performing insert geometries are chosen for the complete study. Two TEP enrichment levels (10% and 20% wt.) are investigated. The mechanical and de-bonding performance of SLJs with steel inserts is compared to TEP-only baseline fully-composite and multi-material (AA 6061 Aluminum Alloy + CFRP) joints. The results show that bondline inserts enable fast de-bonding of fully-composite SLJs. Insert geometry and thickness affect joint de-bonding time and reliability, and can be optimized to allow for a partial recovery of lap shear strength. 100% de-bonding reliability is achieved with “block”-type inserts, with de-bonding performance similar to TEP-enriched metallic joints. Visual inspection of the fracture surfaces shows the relationship between TEP activation and crack propagation path. Discussion and conclusions are provided.more » « less
-
Unalloyed nickel aluminide has important applications but lacks ductility at room temperature. In this study, iron-added nickel aluminide alloys exhibit plasticity enhancement. The nickel aluminide alloys are prepared with different iron contents (0, 0.25, and 1 at%) to study their plasticity. The indentation-induced deformed areas are mapped by the synchrotron X-ray diffraction to compare their plastic zones. A complimentary tight binding calculation and generalized embedded atom method demonstrate how the Fe-addition enhances the plasticity of the iron-added nickel aluminide alloys.more » « less
