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Results for “crack mitigation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Impact of polymer additives on crack mitigation of rod-coated fuel cell cathode catalyst layers

Cracks in catalyst layers (CLs) are a potential source of long-term failure in a fuel cell membrane electrode assembly (MEA). While modifications to the CL ink formulation can affect the degree of cracking, these changes may lead to lower initial performance than their cracked analogues due to the established link between formulation and performance. In this work, we explored the use of polymeric additives to mitigate CL cracks. Small quantities of poly (acrylic acid), poly (ethylene oxide), poly (methyl methacrylate), or poly (vinyl alcohol) - 5 wt% relative to ionomer mass - were added to the ink prior to its final mixing. Poly (vinyl alcohol) resulted in crack-free CLs, whereas the other polymers resulted in CLs with similar crack percentages as the control CL. Through a combination of transmission electron microscopy, X-ray computed tomography, and infrared spectroscopy, we ascribed the crack-mitigating mechanism of poly (vinyl alcohol) to its ability to hydrogen-bond with Nafion, the ion conducting polymer binder in the catalyst ink. Initial performance of this non-cracked electrode exhibited nearly identical electrochemical behavior to its cracked counterpart, demonstrating that PVA additives successfully reduce cracks while maintaining cell initial performance.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Influence of Process Parameters and Alloy Composition on Crack Mitigation in Selective Laser Melting

Microcracking and residual stresses are key limitations of laser powder bed fusion (LPBF), an additive manufacturing (AM) technique that uses a high power laser to consolidate successive layers of metal powder. For tungsten, these microcracks find their origin in the combination of a ductile-to-brittle transition (DBT) between 200°C and 400°C and high residual stresses. This work utilized in situ high speed video to capture the cracking mechanisms, and combined the experimental results with thermomechanical modeling to unveil correlations between crack network morphology and process parameter-related variables, such as the local temperature and residual stress distributions. Consequently, preheating and alloying with rare earth oxides were adopted as possible crack mitigation strategies, the efficacy of which was tested against the initial fundamental baseline results. Preheating temperatures above 500°C eliminated all cracking, though this threshold is expected to be higher when tungsten powder (higher oxygen content) is introduced. Alloying can serve as an active oxygen getter in the system, but the rare earth oxides in this work were too large to have significant contributions to crack-mitigation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Crack mitigation in additively manufactured AlCrFe 2 Ni 2 high-entropy alloys through engineering phase transformation pathway

The far-from-equilibrium solidification during additive manufacturing often creates large residual stresses that induce solid-state cracking. Here we present a strategy to suppress solid-state cracking in an additively manufactured AlCrFe 2 Ni 2 high-entropy alloy via engineering phase transformation pathway. We investigate the solidification microstructures formed during laser powder-bed fusion and directed energy deposition, encompassing a broad range of cooling rates. At high cooling rates (10 4 –10 6 K/s), we observe a single-phase BCC/B2 microstructure that is susceptible to solid-state cracking. At low cooling rates (10 2 –10 4 K/s), FCC phase precipitates out from the BCC/B2 matrix, resulting in enhanced ductility (~10 %) and resistance to solid-state cracking. Site-specific residual stress/strain analysis reveals that the ductile FCC phase can largely accommodate residual stresses, a feature which helps relieve residual strains within the BCC/B2 phase to prevent cracking. Our work underscores the value of exploiting the toolbox of phase transformation pathway engineering for material design during additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Crack mitigation and wear performance of high-strength steel coatings deposited by high-speed laser cladding

This article investigates the fabrication of defect-free Rockit® 606, a high‑carbon, vanadium- and chromium-enriched precipitation-hardening martensitic steel coating, using high-speed laser cladding (HSLC). Compared to conventional laser cladding, HSLC offers higher deposition efficiency, improved coating quality, minimal thermal distortion, and a reduced heat-affected zone. Various HSLC parameters—including laser power, travel speed, powder feed rate, and overlap distance—were optimized to achieve superior coating properties. Microstructural analysis revealed solidification cracks in coatings deposited on carburized steel, regardless of processing parameters. However, preheating the substrate to 250 °C effectively eliminated cracking by reducing thermal gradients. The coatings exhibited a columnar dendritic microstructure, with coarser dendrites near the substrate and finer dendrites towards the surface. Hardness measurements confirmed that all coatings significantly exceeded the industry-specified threshold of 60 HRC, with preheating having minimal effect on overall hardness distribution. Reciprocating sliding wear tests demonstrated a substantial improvement in wear resistance for the defect-free HSLC coatings compared to baseline carburized steel. These findings underscore the potential of HSLC for producing high-performance, wear-resistant coatings suitable for industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Mitigating Crack Formation When Using High Oxygen Permeability Ionomer in PEMFC Catalyst Layers

High oxygen permeability ionomers (HOPIs) are being developed as an alternative to conventional perfluorosulfonic (PFSA) ionomers for cathodes in proton exchange membrane fuel cells (PEMFCs). HOPIs aim to reduce local oxygen transport resistance, improving performance and reducing degradation as the catalyst loses surface area. However, HOPIs' more rigid, 3D backbone leads to increased crack density in the cathode, potentially causing accelerated degradation. This study investigates crack formation in HOPI-based and PFSA-bound catalyst layers (CLs). We conducted a comprehensive parametric study to identify conditions and catalyst slurry components that minimize cracking. CLs were fabricated with various ionomer and catalyst types, under different relative humidity (RH) levels, solids weight percentages, solvent ratios, and ionomer-to-carbon ratios (I/C). Results show that HOPI-based CLs exhibit less cracking when fabricated under low RH conditions, with lower solids weight percentage, higher alcohol content, and lower I/C. Additionally, catalysts with low/medium surface area carbon supports show less cracking than those with high surface area carbon supports.

08 HYDROGEN↗
NASA NTRS2014

Mitigation of Crack Damage in Metallic Materials

A system designed to mitigate or heal crack damage in metallic materials has been developed where the protected material or component is coated with a low-melting temperature film. After a crack is formed, the material is heated, melting the film which then infiltrates the crack opening through capillary action. Upon solidification, the healing material inhibits further crack damage in two ways. While the crack healing material is intact, it acts like an adhesive that bonds or bridges the crack faces together. After fatigue loading damages, the healing material in the crack mouth inhibits further crack growth by creating artificially-high crack closure levels. Mechanical test data show that this method sucessfully arrests or retards crack growth in laboratory specimens.

Leser, Patrick E.↗
DOE OSTI2022

Phase-field modeling of crack growth and mitigation in solid oxide cells

Fracture and crack growth is one of the main degradation mechanisms in solid oxide cells (SOCs). However, the modeling of crack growth in SOCs is challenging due to their complex microstructures and possible plasticity development within the Ni particles in Ni-based SOC electrodes. In this study, a phase-field fracture model is developed, which incorporates the SOC microstructures and phase-dependent material properties, including yield strength, fracture toughness in the bulk and at the interphase boundaries. The model is employed to study crack initiation and growth under thermal and redox cycling on the hydrogen electrode side of SOCs. The simulation results demonstrate that under thermal cycling, work-zone cracking dominates in electrolyte-supported SOCs with cracks initiated at the triple-phase boundaries, while only minor mechanical degradation occurs in hydrogen-electrode-supported SOCs after hundreds of thermal cycles. Under redox cycling, through-cracking of yttria-stabilized zirconia (YSZ) in the hydrogen electrode and electrolyte layers dominates. Finally, the simulation results suggest several crack-mitigation strategies, including decreasing the porosity in the hydrogen electrode support layer and synchronizing thermal strain to balance oxidation strain.

08 HYDROGEN↗
DOE OSTI2025

Optimization of overhang printing in ceramic binder jetting additive manufacturing

Cylindrical-shaped horizontally-hanging overhangs with different heights on a solid cubic body were printed via binder jetting additive manufacturing with sililcon carbide powder feedstock. Cracking on the overhang neck and sagging on the overhang body were observed both pre- and post-curing, especially on printed design with a smaller particle size of 10 μm. Here, it was found that the width of cracking and depth of sagging were dependent on the height relative to the solid body in the powder bed, and elevated position of overhang with large volume of underneath loose powder led to increased extend of cracking and sagging. Overhang diameter and weight were varied, which were found with no apparent effects on its deformation extend. To mitigate cracking and sagging, contactless support was designed and tested, which could significantly improve the overhang stability and avoid any overhang deformations. Support gap and support distance were studied for their effects on support capability. The printing processes with and without contactless support were simulated by a finite element modeling approach to understand the stress distribution and evolution of the overhang structures, which revealed stress concentrations on the upper neck point of the designed overhang.

Binder jetting↗
DOE OSTI2025

Geometry and size dependent microstructure and crack formation in Rene 41 superalloy fabricated by laser powder bed fusion

This study provides a systematic investigation into the size and geometry-dependent microstructural evolution and cracking susceptibility of LPBF-fabricated Rene 41. By coupling experimental microstructural analysis with thermal modeling, this research uniquely identifies the relationship between geometry-specific thermal histories, carbide coarsening, and liquation cracking. Four different geometries with varying thickness were fabricated with the identical process parameters. It was found that the grain size and morphology are not affected by the part size. However, the thinner parts exhibited coarser sub-grain structures compared to the thicker ones. The crack formation was observed for the parts with cross-sections smaller than 1 mm, whereas thicker parts had high density without any defects. Further, the cracks were observed in the interdendritic regions, suggesting that liquation cracking was the active micro-crack formation mechanism. The detailed microstructural analysis combined with a thermal finite element analysis proved that the heat extraction efficiency was lower for thinner parts causing a lower cooling rate and coarser carbides, making them more susceptible to constitutional liquation. Microhardness measurements were conducted for each geometry and correlated with the observed microstructural variations. The findings highlight the critical need for geometry-specific optimization of LPBF process parameters to mitigate cracking and achieve microstructural uniformity, offering valuable insights into the fabrication of complex, high-performance aerospace components.

36 MATERIALS SCIENCE↗
NASA NTRS2019

A thin-ply composite with embedded metallic mesh for a spaceborne antenna

This study presents a technique developed for embedding a conductive metallic mesh into the layup of thin-ply carbon fiber reinforced polymer (CFRP) composite material. Thermal cycling and subsequent mechanical testing on fabricated samples has been used to evaluate thin-ply composites as a crack mitigation technique. Furthermore, the construction of thin-ply CFRP composite tubes has been demonstrated for both straight segments and curved segments utilizing a novel sacrificial ceramic molding method. These prototypes represent the building blocks for a 1 m scale radiating element and are the first test articles for the evaluation of thin-ply CFRP composites with an embedded metallic mesh. The successful implementation of a CFRP composite with an embedded metallic mesh would enable ultra-lightweight conductive structures for future applications, such as antennas, requiring survival in cryogenic temperatures.

Sakovsky, Maria↗
DOE OSTI2022

Quarterly Management Document – FY22, 1st Quarter, Multi-pass Hybrid Laser Arc Welding of Alloy 740H

This report summarizes the progress made on the project during the first quarter of FY22. The model for deep penetration laser welding continues to be developed to understand and mitigate cracking issues associated with laser welding Alloy 740H. The effects of laser wobble on laser welding of this alloy are also being developed. Additionally, the short-term creep behavior of welds made by various hybrid laser arc parameters has been obtained and the results indicate they are comparable to welds made by conventional gas tungsten arc welding which is a factor 2 slower than the hybrid welds. Additionally, the creep behavior of laser-only welds is also consistent with conventional gas tungsten arc welds as well as the hybrid laser arc welds made under this project. However, the creep rate of the laser-only welds is much higher than that observed in the hybrid laser arc welded specimens. This is most likely due to the narrower weld produced by laser-only welding compared to hybrid laser arc welding and, thus, the higher creep rate of laser-only welded creep specimens is likely a result of the increased fraction of base metal (which exhibits a higher creep rate than weld metal) contained within the gage section of the creep specimen. Creep rupture lifetimes were all about the same for both laser-only and hybrid laser arc welded specimens and consistent with the creep rupture lifetime of conventional gas tungsten arc welded creep specimens.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mitigate Stress Corrosion Cracking (SCC) in High-Strength Al castings (CRADA 508)

This project will develop approaches to overcome the barriers to simultaneous high-strength and high resistance to stress corrosion cracking (SCC) in Al casting alloys. Thus, success in this project will enable fabrication of light-weight components that are otherwise made of either heavier cast iron, or lower-strength Al alloys which need to be oversized (and hence, are heavier) to compensate for lower strength. This project will leverage the availability of advanced analytical instruments and scientific expertise available only through the LightMAT Consortium. If successful, this project has the potential to enable light-weighting of multiple components in light-duty cars and trucks across all makes and models.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Mitigate Stress Corrosion Cracking (SCC) in High-strength Al Castings (CRADA 508)

Development of high strength, corrosion resistant, aluminum alloys is important to a number of industries, including automotive, aerospace, power, etc. Understanding how processing methods such as casting, chemistry, additives and recycle content affect an alloy’s microstructure and performance in real world environments is crucial to their implementation. One major concern is how the repeated exposure to saline solutions can be detrimental to the structural integrity of aluminum alloy components. This study was undertaken as a collaboration between Eck Industries and PNNL to investigate the stress corrosion cracking (SCC) and corrosion behavior of aluminum alloys. This work examines the SCC response of three different materials set. First is cast A206 Al alloy produced by three different casting techniques (i.e., permanent mold, and sand casting with and without chill) and with or without nano forming additives as potential grain refiners. The second materials set comprises Al alloy tubes extruded by PNNL’s ShAPE process and produced using raw material with three different ratios of twitch and pre-consumer Al 6061 scrap. Finally, the third materials set comprises two Al-Si-Mg-Fe alloys with controlled Si% and Fe% to mimic recycle grade Al alloys. The corrosion behavior of these materials was characterized using SCC testing and scanning electrochemical cell microscopy (SECCM) technique; mechanical behavior was characterized using tensile testing, and microstructure was characterized using optical and electron microscopy techniques. Of the A206 Al alloys, the samples with nano forming additives performed poorly compared to those without. The best SCC performance (i.e. least degradation in mechanical properties) was demonstrated by A206 alloy sand cast with chill while the permanent mold sample showed the worst SCC performance. The SECCM was performed on A206 alloy sand cast with chill to understand the effect of microstructure and determine the location-dependent corrosion properties on grain boundaries (GB) and inside grains (IG) on the sample. The corrosion potential and current measured on GB and IG at various points on the sample established that the GB locations are more cathodic and corrosive than the IG locations. Further work needs to be conducted to investigate the mechanisms behind the observed dependence of SCC on casting technique and nano forming additives. Among the ShAPE extruded tubes, SECCM data suggests the decreasing order of tendency to corrode as follows: 100% twitch > 75% twitch > 50% twitch. Finally, both variants of the Al-Si-Mg-Fe alloys showed a large volume fraction of Fe- and Si-containing intermetallics and additional work is needed to discern differences in their respective corrosion responses. In summary, correlating local electrochemical behavior (e.g. via SECCM) with micro/nanostructure, in conjunction with bulk mechanical behavior, can help identify the right fabrication method and alloy chemistry to minimize SCC issues in Al alloys.

36 MATERIALS SCIENCE↗