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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Microstructural Characteristics, Mechanical Properties, and Corrosion Behavior of Field-Assisted Diffusion Welded Alloy 617

This study investigated the microstructural characteristics, mechanical response, and corrosion resistance of Alloy 617 diffusion welded by electric field-assisted sintering (EFAS). The microstructure exhibited good grain boundary (GB) migration across the interface and flat interface in the samples bonded at different conditions. Graded grain size was observed, with grain coarsening being more significant near sample surface due to EFAS-induced temperature gradient. Tensile testing revealed that the specimens fractured in the matrix away from the interface. The peak strength of 807 MPa was obtained in the samples welded at 1000°C. The materials obtained at 1100°C exhibited reduced tensile strength but improved ductility. Strain maps revealed by digital image correlation showed the flat interfaces were less ductile compared to the matrix. The hardness reduced near sample surfaces due to enlarged grains induced by temperature gradient. The interfaces with GB migration exhibited improved corrosion resistance in molten salt compared to the flat interfaces.

36 - MATERIALS SCIENCE↗
DOE OSTI2018

The Effects of Heat Treatment on Microstructure and Mechanical Properties of Tribaloy 400 Coatings Deposited by Laser Cladding

The effects of heat treatment on the microstructure, microhardness, nanohardness and wear resistance of Tribaloy 400 coatings prepared by laser cladding on 304 stainless steel were studied in this paper. The results show that the microstructures of Tribaloy 400 laser cladding layer are cobalt matrix dendrites and eutectic structure. After the heat treatment at 1250 °C for 1 h, the eutectic structure disappears and the strip-like Laves phase is formed on the Co matrix. Meanwhile, the hardness is obviously improved. After the heat treatment at 1250 °C for 1 h and then 900 °C for 4 h, a small amount of ε-Co appears, the strip-like Laves phases become coarser and blunter, and some of the strip structures combine together to form blocky structures, and the hardness is decreased. The wear resistance of the samples at 600 °C is better than that at RT since the hardness of the Laves phase increases with the rise in temperature.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Microstructure and mechanical properties of hip-consolidated Rene 95 powders

The effects of heat-treatments on the microstructure of P/M Rene 95 (a nickel-based powder metal), consolidated by the hot-isostatic pressing (HIP), were examined. The microstructure of as-HIP'd specimen was characterized by highly serrated grain boundaries. Mechanical tests and microstructural observations reveal that the serrated grain boundaries improved ductility at both room and elevated temperatures by retarding crack propagation along grain boundaries.

Shimanuki, Y.↗
DOE OSTI2023

Interfacial microstructure and mechanical properties of rotary inertia friction welded dissimilar 422 martensitic stainless steel to 4140 low alloy steel joints

In this work, dissimilar rotary inertia friction welds between 422 martensitic stainless steel and 4140 martensitic low-alloy steel were made to fabricate prototype heavy-duty diesel engine pistons. The influence of the inertia friction welding process and post weld heat treatment (PWHT) temperature on the interfacial microstructure evolutions and corresponding effects on mechanical properties of the 422/4140 welds were evaluated in detail. Carbon diffused from the 4140 side to the 422 side during PWHT at 650 °C for 1.5 h, causing the formation of a hard carbide-rich layer on the 422 side, and a softer but discontinuous C-depleted layer the 4140 side. PWHT at 700 °C for 1.5 h greatly accelerated C diffusion across the interface relative to 650 °C, resulting in a thicker hard carbide-rich layer and a relatively thick and continuous layer of coarse C-depleted grains (ferrite) on the 4140 side. In addition, the PWHT temperature greatly influenced the tensile properties and fracture behavior of the welds, with the 650 °C PWHT-ed samples failing predominately in a ductile manner in the 4140 heat affected zone during tensile testing. Conversely, the 700 °C PWHT specimens exhibited a strength reduction compared with the 650 °C PWHT specimens because of additional coarsening of the interfacial ferrite layer and softening of the base materials during PWHT, with brittle fracture between the hard and soft layers the predominate failure mechanism. Based on the findings, a reduced PWHT temperature and/or time, minimizing the hardness differential of the base metals, and pre-heating the 422 steel prior to welding are the potential pathways to achieve a more optimal balance between desirable tempering and stress relief of the weld microstructure and undesirable C migration across the weld interface, and to reduce the strength mismatch across the weld.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Influence of Rare Earth Ce Additions on Microstructure and Mechanical Properties of Experimental Pipeline Steels

Herein, the effect of Ce additions ranging from 57 to 263 ppm is evaluated for an experimental pipeline steel. Compared to the Ce-free steel, progressive Ce additions result in a slightly refined microstructure, significantly improve transverse impact properties, and slightly increase strength. All these observations can be attributed to the gradual transformation of Mn sulfide and Mn–Si–Al oxide inclusions to Ce-containing oxide/sulfides. In particular, the inclusions consist exclusively of sub-5 μm spherical Ce 2 O 2 S particles upon near-stoichiometric additions of Ce, considering the oxygen and sulfur impurity level of the steel. In conclusion, the results suggest that Ce is a potentially promising alloying addition for next-generation pipeline steels by replacing overtly deleterious inclusions with potentially beneficial ones.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Trajectory of Additively Manufactured Titanium Alloys with Superior Mechanical Properties and Engineered Microstructures

Additive manufacturing (AM) plays a crucial role in the manufacturing and development of advanced materials including titanium alloys for engineering applications. During the last two decades, a great deal of effort has been devoted to print titanium parts with desired properties. However, due to presence of non-equilibrium/metastable phases, anisotropic microstructure, and various porosities in the printed titanium alloys, achieving an excellent combination of mechanical properties has been challenging. Here this review paper aims to provide a comprehensive overview of multiple post-process and in-process approaches to achieve enhanced strength-ductility combinations by microstructure engineering. Approaches such as addition of alloying elements/nucleants, multi-step post heat treatment, in-situ heat treatment, forced inter-pass cooling, in situ peening/rolling, hybridizing microstructure, high-intensity acoustic vibration, thermo-hydrogen refinement of microstructure, deliberately introducing lack of fusion defects with subsequent hot isostatic pressing are discussed in detail. Finally, we conclude by highlighting the challenges associated with each method and potential areas of improvement that can pave the way to develop reliable components with enhanced performance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Improvement of Microstructure and Mechanical Properties of CoCrCuFeNi High-Entropy Alloys By V Addition

V element had positive effect in improving the strength of many alloys, so it was possible that V had potential to strengthen CoCrCuFeNi high-entropy alloys (HEAs) with face-centered cubic (FCC) crystal structure, which was relatively weak in strength and had outstanding ductility. In this paper, we studied the alloying effect of V on the phase evolution, microstructure and the mechanical properties of the (CoCrCuFeNi){sub 100−x}V{sub x} (x = 0-16, atomic ratio, hereafter in at.%) HEAs systematically. The results showed that V element had capacity to induce sigma phase precipitation. The volume fraction of sigma phase increased from 0 to 12%; the compressive yield stress of (CoCrCuFeNi){sub 100−x}V{sub x} HEAs increased from 300 to 613 MPa with V content increasing from 0 to 16% (atomic ratio, hereafter in at.%). However, the compression fracture strain decreased from 50 to 28%. V addition was beneficial in improving the strength of CoCrCuFeNi HEA, and the increase in sigma phase volume fraction was the key factor for the improvement of the (CoCrCuFeNi){sub 100−x}V{sub x} HEAs in yield stress.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Corrosion Properties of Laser-Welded SAF 2507 Super Duplex Stainless Steel Joints

SAF 2507 super duplex stainless steel has been welded using laser beam (LB) welding and laser/gas metal arc hybrid (LGH) welding processes. The pitting and intergranular corrosion properties of the welding joints have been tested using electrochemical testing and microstructure observations. The volume fraction of the ferrite phase reaches 70% in the weld zone of the LB welding joint, while the volume fraction of the ferrite phase is 60% for the welding joint of LGH due to the introduction of Ni from welding wire. The pitting corrosion resistance of the welding joint for LB is better than that of LGH. The pitting corrosion is easily conceived in the heat-affected zone (HAZ) because of the formation of Cr{sub 2}N in the HAZ during welding.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Three-Layer TIG-Welded 2219 Aluminum Alloys with Dissimilar Heat Treatments

2219-C10S and 2219-CYS aluminum alloys are 2219 aluminum alloys with different heat treatment processes, and they have been widely used in the aerospace industry. In the present study, 2219-C10S and 2219-CYS aluminum alloys were butt-welded by three-layer tungsten inert gas arc welding (with the welding center of the third layer shifted toward the CYS side), and the microstructure characteristics and mechanical properties of the welded joint were investigated. The lamellar θ′ phases, the bulk or rod θ phases, and the coarse rod-shaped or pancake-shaped Al-Cu-Fe-Mn phases coexisted in the two aluminum alloys. The Cu content of the α-Al matrix and the distribution of eutectic structures of different welding layers in the weld zone (WZ) were varied, implying that the segregation degrees of the Cu element were different due to the different welding thermal cycles in different welding layers. The microhardness values of the CYS side were much higher than those of the C10S side in each region on both sides of the joint. The tensile test deformation was concentrated mainly in the regions of WZ and the over aged zone (OAZ), where the microhardness values were relatively low. The main deformation concentrated region was transferred from the CYS side to the C10S side with the increase in the tensile load during the tensile test. The fracture behavior of the tensile test showed that the macroscopic crack initiated near the front weld toe had gone through the crack blunt region, the shear fracture region of the partially melted zone (PMZ), and the shear fracture region of OAZ. Meanwhile, the fracture characteristics gradually evolved from brittle to ductile. The concentrated stress and the dense eutectic structure in the region near the front weld toe of the C10S side contributed to the fracture of the joint. The shift of the welding center of the third layer to the CYS side resulted in two effects: (i) the microhardness values from the middle layer to the top layer in the PMZ of the CYS side were the most significantly increased and (ii) the distance between the front weld toe and the fusion line of the CYS side was significantly larger.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Thermal Exposure on the Microstructure and Mechanical Properties of Al-Si-Cu-Ni-Mg-Gd Alloy

The present study focused on the effect of thermal exposure on the phase evolution and properties of the cast-T6 Al-12Si-4Cu-2Ni-0.8Mg-xGd (x = 0, 0.1, and 0.2) alloy used for cast piston.The thermal stability of the alloys was studied in the temperature range of 200-300 °C for exposure duration up to 500 h, thus obtaining the relationship between the microstructural evolution and its impact on the mechanical properties. The fine Al{sub 2}Cu phase grew into the coarse θ-Al{sub 2}Cu phases during the thermal exposure, resulting in a decrease in the mechanical strength of the alloy. The thermal stability and stiffness of the Al-Si-Cu-Ni-Mg alloys were improved with the increase in Gd content from 0 to 0.2%.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electric field enhanced diffusion welding of alloy 617: Microstructural characteristics and mechanical properties

This study investigated the microstructural characteristics and mechanical behavior of diffusion welded nickel-based Alloy 617 obtained by electric field-assisted sintering (EFAS) using various parameters. The interfacial microstructure exhibited different characteristics including good grain boundary (GB) migration across the interface in the samples diffusion-welded at 1100 °C and a flat interface in the samples joined at 1000 °C and 1050 °C. The interface consisted of fine Al 2 O 3 oxides, while precipitation of interfacial M 23 C 6 carbides was not observed. Grain boundaries migrated across the Al 2 O 3 oxides, leaving these oxides within the grains. Graded grain size was observed, with grain coarsening being more significant near the sample surface due to the temperature gradient induced by EFAS. Tensile testing revealed that the specimens fractured in the matrix away from the interface, indicting strong diffusion-welded joints. Further, the peak tensile strength of 807 MPa was obtained in the samples welded at 1000 °C due to minimal grain growth. The materials obtained at 1100 °C exhibited reduced tensile strength but improved ductility. Strain maps revealed by digital image correlation showed alternating high and low strain segments in the samples produced at 1000 °C and 1050 °C, indicating that the flat interfaces with no GB migration were less ductile compared to the matrix. A greater strain uniformity was observed along the bond interfaces with improved GB migration. The hardness reduced near the sample surfaces due to enlarged grains induced by temperature gradient. This study demonstrates that GB migration and enhanced mechanical strength can be achieved in diffusion-welded Alloy 617.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of Solidification Cooling Rates on Microstructures and Physical Properties of Fe-6.5%Si Alloys

Compared to the widely used Fe-3.2wt%Si steel, Fe-6.5wt%Si has superior electric and magnetic properties, including higher electrical resistivity, lower iron loss, higher permeability, and near zero magnetostriction. However, Fe-6.5wt%Si sheet is difficult to produce using traditional manufacturing processes as the high silicon content favors the formation of ordered phases that embrittle the material. Fortunately, these ordered phases can be suppressed if the alloy is cooled fast enough from a high temperature kinetically trapping the disordered solid solution or amorphous state. Planar flow casting is known for its rapid solidification rate. In order to consider it as a viable method to manufacture ductile Fe-6.5wt%Si sheets, the effect of cooling rate on physical properties of Fe-6.5wt%Si alloy are systematically investigated. In this work, various cooling rates are achieved by changing melt-spin wheel speeds, which significantly affect the solidification temperature profile and have profound effects on ordering, microstructures, textures, hardness, and magnetic properties. High cooling rates result in refined grains, reduced ordering, enhanced <100> out of the plane texture, decreased hardness, and increased coercivity. This study demonstrates a critical cooling rate at ~1.7 × 10 5 K/s, corresponding to a tangential wheel speed of 5-7 m/s, below which the hardness significantly increases in agreement with the sudden increase of the ordered phases that causes the material embrittlement.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure and creep properties of cast near-eutectic Al–Ce–Ni alloys

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al 11 Ce 3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al 3 Ni and Al 11 Ce 3 fibers, (iii) large ternary eutectic colonies, where the binary Al 3 Ni and Al 11 Ce 3 phases are alternating or intertwining within the individual, fine fibers (diameters of ~60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al 3 Ni and Al 11 Ce 3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. Additionally, the alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al 3 Ni particles which engulf finer, more stable Al 11 Ce 3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al 3 Ni and Al 11 Ce 3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Low-Activation Fe-Cr-V Multicomponent Single-Phase Alloys

A ternary equiatomic and nearly equiatomic alloy composed of the low-activation elements Fe, Cr, and V was designed for potential application as low-activation structural materials for the first wall of fusion reactors. The optimal composition of the multicomponent alloy was determined by minimizing the Gibbs free energy for solid-solution formation. The microstructure, phase stability, and mechanical properties of the equiatomic and optimized Fe-Cr-V alloys were studied. The equiatomic alloy consisted of a body-centered-cubic (BCC) solid-solution phase with a small amount of a face-centered-cubic (FCC) solid-solution phase, whereas the optimized alloy consisted of a single BCC solid-solution phase in the as-cast state. The crystal grains of both alloys were equiaxial. No phase transition was observed in the optimized alloy after homogenization; however, for the equiatomic alloy, the FCC solid-solution phase disappeared and surface relief was observed. The Vickers microhardness and yield strength of the Fe-Cr-V alloys increased after homogenization compared with those of the as-cast alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Ti-4Al-1Mn Titanium Alloy

Mechanical behavior of Ti-4Al-1Mn titanium alloy has been studied in annealed, cold-rolled and heat-treated conditions. Room temperature tensile strength as well as % elongation has been found to be low with increasing amount of cold rolling. Lowering of strength in cold worked condition is attributed to premature failure. However, the same has been mitigated after heat treatment. Significant effect of cooling media (air and water) from heat treatment temperature on microstructure was not found except for the degree of fineness of α plates. Optimum properties (strength as well as ductility) were exhibited by samples subjected to 15% cold rolling and heat treatment below β transus temperature, which can be attributed to presence of recrystallized microstructure. In cold worked condition, the microstructure shows fine fragmented α plates/Widmanstätten morphology with high dislocation density along with a large amount of strain fields and twinning, which gets transformed to recrystallized equiaxed microstructure and with plate-like morphology after near β heat treatment. Prior cold work is found to have a significant effect on mechanical properties supported by evolution of microstructure. Twinning is found to be assisting in deformation as well as in recrystallization through the formation of deformation and annealing twins during cold working and heat treatment. Fracture analysis of the tested sample with prior cold work and heat-treated condition revealed quasi-ductile failure as compared to only ductile failure features seen for samples heat treated without prior cold work.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Microstructure and tensile properties of Fe-40 at. pct Al alloys with C, Zr, Hf, and B additions

The influence of small additions of C, Zr, and Hf, alone or in combination with B, on the microstructure and tensile behavior of substoichiometric FeAl was investigated. Tensile properties were determined from 300 to 1100 K on powder which was consolidated by hot extrusion. All materials possessed some ductility at room temperature, although ternary additions generally reduced ductility compared to the binary alloy. Adding B to the C- and Zr-containing alloys changed the fracture mode from intergranular to transgranular and restored the ductility to approximately 5 percent elongation. Additions of Zr and Hf increased strength up to about 900 K. Fe6Al6Zr and Fe6Al6Hf precipitates, both with identical body-centered tetragonal structures, were identified as the principal second phase in these alloys. Strength decreased steadily as temperature increased above 700 K, as diffusion-assisted mechanisms became operative. Although all alloys had similar strengths at 1100 K, Hf additions significantly improved high-temperature ductility by suppressing cavitation.

Gaydosh, D. J.↗
DOE OSTI2018

Effect of Heat Treatment and Combination of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Titanium Alloy Ti6Al2V2Zr1.5Mo

The heat treatment and cold rolling combinations have been carried out on titanium alloy Ti6Al2V2Zr1.5Mo, and microstructure evolution and mechanical behavior have been studied. Solution treatment below the β-transus temperature, followed by air cooling, resulted in higher microhardness/strength as compared to the same with water quenching. A sudden drop in microhardness/strength is observed in sample solution heat-treated above β-transus temperature followed by air cooling. The former is attributed to the additional presence of fine secondary α-phase formed by dynamic aging during air cooling as compared to water-quenched samples which did not have fine secondary α-phase. Solution treatment above β-transus temperature resulted in Widmanstatten microstructure with no significant fine secondary α in air-cooled samples. Among the studied conditions of cold rolling (CR), gain in strength of the alloy from annealed condition is significant with first 15% reduction and thereafter it is marginal for 30% reduction. Initiation of cracks at the edges has been observed in 30% CR. The microstructure of cold-rolled samples confirms the fragmentation of α-plates with the presence of high dislocation density. Heat treatment of cold-rolled samples resulted in significant reduction in strength from the as-cold-rolled conditions. The marginally lower strength than the as-received (annealed) or heat-treated alloy samples is due to the recrystallization in CR samples and the formation of Widmanstatten microstructure in air-cooled samples. The alloy does not have fine secondary α or regions with large dislocation density in this condition. The microstructure in the samples heat-treated (with air cooling) below as well as above β-transus temperature (after CR) is similar to air-cooled samples (without prior CR) with heat treatment above β-transus temperature. This indicates the reduction in recrystallization temperature with cold working, which is substantiated with the reduction in strength as well.

36 MATERIALS SCIENCE↗