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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

In situ synchrotron X-ray diffraction analysis of ultrasonically assisted microstructure refinement during laser melting process

This work investigates the effect of ultrasonic treatment (UST) on the microstructure of AA4043 alloy during laser melting process. Here, the study utilizes in situ synchrotron X-ray diffraction (SXRD) and postmortem electron backscatter diffraction (EBSD) techniques to examine the ultrasonic grain refinement mechanism. The SXRD diffraction patterns exhibit higher continuity of major diffraction rings in the UST-test pattern, indicating a more refined grain structure. The presence of new diffraction spots in the post-test diffraction pattern with UST suggests the breakdown of epitaxial growth of columnar dendrites during solidification. Thermal profiles determined by analyzing the lattice parameter evolution show a faster cooling rate with UST. The inverse pole figures and aspect ratio distribution from EBSD reveal that the UST samples exhibit a refined, more equiaxed grain structure along the weld centerline. UST sample also develops more fine-sized low angle grain boundaries (LAGBs). These features offer better hot-cracking resistance in aluminum alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Operating Stresses and Their Effects on Degradation of LSM-Based SOFC Cathodes

The performance of solid oxides fuel cells (SOFCs) with four different Mn excess of lanthanum strontium manganite (LSM) -based cathodes were examined under different temperatures (1,000 °C, 900 °C), current densities (0, 380, and 760 mA cm -2 ), and cathode atmospheres (p O 2 )=0.1,0.15,0.21) for durations ranging from 58 to 1,008 h. Each yttria-stabilized zirconia (YSZ) electrolyte-supported “button” cell had a porous Ni/YSZ composite anode and a porous LSM/YSZ composite cathode. The cells’ output voltage versus time were recorded and electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements were performed every 24 hours. The total area specific resistance (ASR) was calculated from these measurements. The values of ASR from both EIS and LSV were comparable between each other but lower than that from durability test. Distribution of relaxation times (DRT) analysis was performed to investigate the electrochemical processes and their corresponding relaxation frequencies as well as their attributions to the total ASR. The series resistance and parallel resistance that obtained from the equivalent circuit fit of the Nyquist plot were higher at low temperature and low p O 2 regardless of LSM compositions. The area of the peaks derived from DRT analysis increased with time during individual tests. The microstructures of the tested cells were examined using scanning electron microscopy and energy-dispersive x-ray spectroscopy (SEM/EDS). Manganese oxide particles were observed near the cathode-electrolyte interface after prolonged (1,008 h) testing in air of a cell with LSM of 11% manganese excess, and after a short test (58 h) under low oxygen (p O 2 = 0.10) in a cell with LSM of 5% manganese excess. However, the role of MnOx in cell degradation is still unknown.

08 HYDROGEN↗
DOE OSTI2018

Atomic scale analysis of Nb3Sn on Nb prepared by a vapor-diffusion process for superconducting radiofrequency cavity applications

We report an atomic-scale analysis of the microstructure of Nb3Sn coating on Nb prepared by vapor diffusion process for superconducting radiofrequency (SRF) cavity application using transmission electron microscopy (TEM). Epitaxial growth of Nb3Sn on the Nb substrate is found and four types of orientation relationships at the Nb3Sn/Nb interface are identified by electron diffraction or high-resolution scanning transmission electron microscopy (STEM) analysis. Thin Nb3Sn grains are observed in regions with low Sn flux and they have the specific orientation relationship, Nb3Sn (1-20)//Nb (-111) and Nb3Sn (002)//Nb (0-11). The Nb3Sn/Nb interface of thin grains had a large lattice mismatch, 12.3 at.%, and a high density of misfit dislocations was observed by HR-STEM. Based on our microstructural analysis of the thin grains, we conclude that the thin regions are probably a result of a slow interfacial reaction with this particular orientation relationship at the interface. The Sn-deficient regions are seen to form initially at the Nb3Sn/Nb interface and remain in the grains due to the slow diffusion of Sn in bulk Nb3Sn. The formation of Sn-deficient regions and the effects of strain and interfacial energies on the formation of Sn-deficient regions at various interfaces were also estimated by first-principle calculation. The finding of orientation relationships at the Nb3Sn/Nb interface provides important information about the formation of defects in Nb3Sn coatings such as large thin regions, Sn-deficient regions, which are critical to the performance of Nb3Sn superconducting radiofrequency cavities for accelerators.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Integrity assessment of the ferritic / austenitic dissimilar weld joint between intermediate heat exchanger and steam generator in fast reactor

Integrity of the modified 9Cr-1Mo / alloy 800 dissimilar joint welded with Inconel 182 electrodes has been assessed under creep condition based on the detailed analysis of microstructure and stress distribution across the joint by finite element analysis. A hardness peak at the ferritic / austenitic weld interface and a hardness trough at the inter-critical heat affected zone (HAZ) in ferritic base metal developed. Un-tempered martensite was found at the ferritic / austenitic weld interface to impart high hardness in it; whereas annealing of martensitic structure of modified 9Cr-1Mo steel by inter-critical heating during welding thermal cycle resulted in hardness tough in the inter-critical HAZ. Creep tests were carried out on the joint and ferritic steel base metal at 823 K over a stress range of 160-320 MPa. The joint possessed lower creep rupture strength than its ferritic steel base metal. Failure of the joint at relatively lower stresses occurred at the ferritic / austenitic weld interface; whereas it occurred at inter-critical region of HAZ at moderate stresses. Cavity nucleation associated with the weld interface particles led to premature failure of the joint. Finite element analysis of stress distribution across the weld joint considering the micro-mechanical strength inhomogeneity across it revealed higher von-Mises and principal stresses at the weld interface. These stresses induced preferential creep cavitation at the weld interface. Role of precipitate in enhancing creep cavitation at the weld interface has been elucidated based on the FE analysis of stress distribution across it. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2013

Cyclic CO{sub 2} chemisorption–desorption behavior of Na{sub 2}ZrO{sub 3}: Structural, microstructural and kinetic variations produced as a function of temperature

A structural, microstructural and kinetic analysis of the Na{sub 2}ZrO{sub 3}–CO{sub 2} system was performed over 20 chemisorption–desorption cycles. Different cyclic experiments were performed between 500 and 800 °C. Although the best results were obtained in Na{sub 2}ZrO{sub 3} sample treated at 550 °C, all the samples treated between 500 and 700 °C presented good CO{sub 2} chemisorption efficiencies and stabilities. On the contrary, Na{sub 2}ZrO{sub 3} sample treated at 800 °C presented a continuous decrement of the CO{sub 2} chemisorption. After 20 cycles all the samples presented a partial Na{sub 2}ZrO{sub 3} decomposition, determined by the ZrO{sub 2} formation, which was associated to sodium sublimation. Additionally, the Na{sub 2}ZrO{sub 3} microstructural analysis showed a systematic morphological evolution. It was microscopically observed that Na{sub 2}ZrO{sub 3} particles tend to fracture due to the Na{sub 2}CO{sub 3} formation. Later, after several cycles these tiny fractured particles sinter producing new polyhedral and dense Na{sub 2}ZrO{sub 3}–ZrO{sub 2} particles. Finally, an exhaustive kinetic analysis showed a high CO{sub 2} chemisorption–desorption stability at different temperatures. - Graphical abstract: A CO{sub 2} chemisorption–desorption analysis was performed in the Na{sub 2}ZrO{sub 3}–CO{sub 2} system. Different cyclic experiments were performed between 500 and 800 °C and the results showed high CO{sub 2} chemisorption efficiencies. Nevertheless the Na{sub 2}ZrO{sub 3} composition and microstructure evolved during the cycles. Highlights: • Different CO{sub 2} chemisorption–desorption cycles were performed in the Na{sub 2}ZrO{sub 3} phase. • Na{sub 2}ZrO{sub 3} presents interesting microstructural changes depending on temperature. • At T≤550 °C, Na{sub 2}ZrO{sub 3} presents the best cyclability due to microstructural factors. • At T≥600 °C, Na{sub 2}ZrO{sub 3} presents a partial decomposition after 20 cycles. • Na{sub 2}ZrO{sub 3} presents excellent CO{sub 2} cyclability properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Precipitation behavior of the sigma phase with Ni and Mn content variations in superaustenitic stainless steel weld metal

Highlights: • Precipitation behaviors in the superaustenitic stainless steel welds were researched. • The fraction and size of the sigma phases decreased with addition of both Ni and Mn. • The Ni addition induced the increase of Mo content in a sigma phase. • The Mn prevented the Mo increase in the sigma, and consequently the Mo depletion. • Ni addition elevated the Mo activity, which induced clustering of Mo in the sigma. - Abstract: In this study, precipitation behavior of the sigma phase with variations of the Ni and Mn in superaustenitic stainless steel weld metal was evaluated focused on microstructure and thermodynamic analysis. Experiments were conducted with variation of Ni and Mn based on a 23Cr-17Ni-6Mo superaustenitic stainless steel weld. And GTAW welding was performed on the casted specimens for simulating the weld metal. The weld metal consisted of γ-dendrite and an amount of sigma phases at interdendritic boundaries. And the sigma phase fraction showed decreasing behavior inversely according to addition of the Ni and Mn in the weld metal. From the microstructural analysis, the Ni addition induced increase of Mo content in the sigma phase, which caused the Mo depletion zone around the sigma phase. Whereas, the Mn addition induced replacement of Mo in sigma phase by Mn, so that the Mo depletion zone was not formed. Also, from the Thermo-Calc analysis, it was revealed that Ni addition caused increase of Mo activity, which induced Mo clustering in the sigma phase, while the Mn addition showed opposite effect of the Mo activity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Dissimilar Metal Weld Joints of P91/Ni Alloy: Microstructural Characterization of HAZ of P91 and Stress Analysis at the Weld Interfaces

Microstructure evolution and hardness were evaluated at the interface of two friction-welded transition joints between P91 and AISI 304 fabricated applying Inconel interlayers, viz. single-interlayer weld (P91/IN600/AISI304) and three-interlayer weld (P91/IN625/IN600/IN800H/AISI304). The welds were subjected to post-weld heat treatment at 1023 K for 1 h followed by air cooling and a long-term exposure at 973 K for 100, 250, and 500 h. A soft zone with the absence of lath martensite was noticed in both the welds which was located at the intercritical heat-affected zone of the welds. This zone was found to be extending with time toward the fine grain heat-affected zone by carbide precipitation and coarsening at the grain boundaries. Soft zone formation at the interface of the welds was found to be due to carbon diffusion. The presence of high-nickel-content alloy at the interface was proven to be beneficial in stopping carbon diffusion at the interface. Though soft zones existed in both the welds, better creep rupture life was observed for three-interlayer welds. Finite element analysis of these weld joints was performed for thermal loading followed by tensile loading. The results from this analysis indicated that thermal expansion also plays an important role in the failures of these dissimilar weld joints by creating high stress at the interface due to incompatibility.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microstructural and micro-mechanical analysis of 14YWT nanostructured Ferritic alloy after varying thermo-mechanical processing paths into tubing

Microstructural analyses and micro-pillar compression were conducted on 14YWT nanostructured ferritic alloy (NFA) to compare different processing pathways: hydrostatic extrusion and Pilger processing with varying annealing temperatures into thin walled tubing, and after hot extrusion and cross-rolling into a plate. Hydrostatic extrusion at 815 °C resulted in the smallest grain sizes and highest yield strength of 1.20 GPa. Pilger processing with annealing at 800 °C had fine grained regions and bands of coarse grains, leading to a large variation in yield strength of 0.9–1.40 GPa. Higher annealing temperatures of 1200 °C after pilger processing significantly increased the grain size and lowered the yield strength to 1.01 GPa. These tubes showed a stronger (111) crystallographic texture in the normal direction and elongated grains in the extrusion direction. Characterization of the nano-oxides using TEM reveals more numerous, smaller oxides present in tubing processed at lower temperatures. Overall, this work shows NFA tubing after hydrostatic extrusion and pilger processing can lead to fine grained microstructures and texturing leading to higher yield strengths at lower annealing temperatures (e.g. 800 °C).

14YWT↗
DOE OSTI2019

Transmission EBSD (t-EBSD) as Tool to Investigate Nanostructures in Superconductors

The transmission electron backscatter diffraction (t-EBSD) technique has proven to be an indispensable tool for the analysis of microstructures of superconducting samples, both high-T{sub c} samples (YBa{sub 2}Cu{sub 3}O{sub y}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}) as well as MgB{sub 2} or iron-based materials. The knowledge of the grain boundary properties (misorientation, length, width) is essential for the further optimization of sample performance. Any addition of secondary phase(s) to improve the flux pinning properties is required to be of nanometer dimensions, so the higher achievable resolution and the better imaging properties are important to obtain reasonably high image quality to enable automated orientation mapping. The orientation maps reveal not only the location and the shape of the inclusions within the superconducting matrix or at the grain boundaries but also their influence on the surrounding superconducting matrix, which also plays an important role in flux pinning. In the case of sintered MgB{sub 2} bulk samples, the demand for higher critical current densities leads to MgB{sub 2} grains in the 100-nm range, which is already difficult to be studied by means of conventional EBSD. Furthermore, t-EBSD is useful for the analysis of specific microstructures of unconventional superconductors like superconducting foams or superconducting nanowire networks.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Using and Developing Novel Data Analytics for Digitalized Microstructures. Draft

The primary goal of this work is to develop and implement analytic methods for quantitative analysis of microstructure. These analytic methods are demonstrated on microstructures generated by the Sandia kinAic Monte Carlo code SPPARKS. This report documents progress to that end as well as incremental work towards larger aspirations of making process-structure-property connections for complex processes such as welding and additive manufacturing.

42 ENGINEERING↗
DOE OSTI2015

Studies on densification, mechanical, micro-structural and structure–properties relationship of magnesium aluminate spinel refractory aggregates prepared from Indian magnesite

The present work intends to study the development of magnesium aluminate spinel aggregates from Indian magnesite in a single firing stage. The raw magnesite has been evaluated in terms of chemical analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. The experimental batch containing Indian magnesite and calcined alumina has been sintered in the temperature range of 1550 °C–1700 °C. The sintered material has been characterized in terms of physico-chemical properties like bulk density, apparent porosity, true density, relative density and thermo-mechanical/mechanical properties like hot modulus of rupture, thermal shock resistance, cold modulus of rupture and structural properties by X-ray diffraction in terms of phase identification and evaluation of crystal structure parameters of corresponding phases by Rietveld analysis. The microstructures developed at different temperatures have been analyzed by field emission scanning electron microscope study and compositional analysis of the developed phase has been carried out by energy dispersive X-ray study. - Highlights: • The studies have been done to characterize the developed magnesium aluminate spinel. • The studies reveal correlation between refractory behavior of spinel and developed microstructures. • The studies show the values of lattice parameters of developed phases.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Morphology and structure features of ZnAl{sub 2}O{sub 4} spinel nanoparticles prepared by matrix-isolation-assisted calcination

Graphical abstract: The substrate ZnO as the isolation medium is effective in preventing the sintering and agglomeration of ZnAl{sub 2}O{sub 4} nanoparticles, and it also prevents their contamination. High purity, well-dispersed, and single-crystal ZnAl{sub 2}O{sub 4} nanoparticles with 3.72 eV band gap were obtained. - Abstract: Well-dispersed ZnAl{sub 2}O{sub 4} spinel nanoparticles with an average crystalline size of 25.7 nm were synthesized successfully and easily by polymer-network and matrix-isolation-assisted calcination. The product microstructure and features were investigated by X-ray diffractometry, thermogravimetric and differential thermal analysis, Fourier transform-infrared spectroscopy, N{sub 2} adsorption–desorption isotherms, and energy dispersive X-ray spectra. The morphology and optical performance of the as-prepared ZnAl{sub 2}O{sub 4} nanoparticles were characterized by scanning electron microscope, transmission electron microscopy, and photoluminescence spectrometer. Experimental results indicate that excess ZnO acted as the isolation medium is effective in preventing the sintering and agglomeration of ZnAl{sub 2}O{sub 4} nanoparticles, and it also prevents their contamination. Then, high purity and well-dispersed ZnAl{sub 2}O{sub 4} nanoparticles with single-crystal structure were obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructural-Level Fuel Performance Modeling of U-Mo Monolithic Fuel

As the physics that governs the microstructural evolution of nuclear fuel span various time and spatial scales, to fully understand the fuel behavior inevitably involves atomic to mesoscale resolution that can be difficult to determine experimentally. Microstructural-level modeling and simulations can be used to develop physics-based materials models that can provide physical understanding to inform fabrication process control, as well as a valuable feedback mechanism between post-irradiation examination (PIE) results and fabrication parameters. In accordance with the program schedule, the primary goals of the microstructure modeling effort are to: 1. Address critical microstructural questions and provide practical guidance to the fabricator via the fuel product specification; 2. Provide mechanistic inputs for the existing fuel performance code to improve its descriptive and predictive capability at the macroscopic scale. In fiscal year (FY)-21, the work scope consisted of six main facets: (1) the effect of carbides on fuel performance; (2) gas diffusivity in different phases; (3) integration of microstructural fuel performance modeling; (4) property degradation; (5) irradiation creep; and (6) historical analysis of microstructure data. Brief summaries of each are included below.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Applying high resolution SyXRD analysis on sulfate attacked concrete field samples

High resolution synchrotron X-ray diffraction (SyXRD) was applied for a microstructural profile analysis of concrete deterioration after sulfate attack. The cement matrices consist of ordinary Portland cement and different amounts of supplementary cementitious materials, such as fly ash, natural pozzolana and granulated blast furnace slag. The changes of the phase composition were determined along the direction of sulfate ingress. This approach allows the identification of reaction fronts and zones of different phase compositions and conclusions about the mechanisms of sulfate attack. Two reaction fronts were localized in the initial 4 mm from the sample surface. The mechanism of deterioration caused by the exposition in the sulfate-bearing soil is discussed. SyXRD is shown to be a reliable method for investigation of cementitious materials with aggregates embedded in natural environments.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys

Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 Degree-Sign C for the titanium-based filler and 900-990 Degree-Sign C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr{sub 2}Cu, Ti{sub 2}Cu and (Ti,Zr){sub 2}Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 Degree-Sign C for Ti-based and 990 Degree-Sign C for Zr-based) resulted in an acicular Widmanstaetten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. - Highlights: Black-Right-Pointing-Pointer Temperature or time was the main factors of controlling braze joint strength. Black-Right-Pointing-Pointer Developing a Widmanstaetten microstructure generates equal strength to base metal. Black-Right-Pointing-Pointer Brittle intermetallic compounds like (Ti,Zr){sub 2}Ni/Cu deteriorate shear strength. Black-Right-Pointing-Pointer Ti and Zr base filler alloys were the best choice for brazing Ti-6Al-4V.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Comparative Analysis of Radial and Random Microstructures of Mesophase Pitch Carbon Fibers

Carbon fibers (CF) with radial and random microstructures are produced. Here, these fibers are subjected to identical treatment before being mechanically tested and analyzed with Weibull analysis, with the results revealing a statistically significant difference in tensile strengths of 2.23 GPa for random CF and 1.69 GPa for radial CF. Raman mapping probed the crystalline structure perpendicular to the fiber axis and found a uniform structure, while wide‐angle X‐ray diffraction showed a significant difference of 7.5 Å in the crystallites’ basal lengths parallel to the fiber. Small‐angle X‐ray scattering is completed parallel to the fiber for the first time. A cross‐section Guinier plot of the 1D azimuthal integration is generated assuming symmetric scattering, and the parallel scatterers are found to have a similar length scale to the crystallite's length, validating the testing method. Finally, transmission electron microscopy is completed on the longitudinal cross‐section of each fiber. The radial carbon fiber is found to have a core–shell structure, as evidenced further by fast Fourier transform images. Through all studies, it is shown that the structure developed during mesophase pitch spinning altered the microstructure, thus impacting the mechanical properties, confirming a direct relationship between processing, structure, and properties.

Scherschel, Alexander [Univ. of Virginia, Charlott↗
DOE OSTI2024

Voltage and temperature effects on low cobalt lithium-ion battery cathode degradation

Degradation of low cobalt lithium-ion cathodes was tested using a full factorial combination of upper cut-off voltage (4.0 V and 4.3 V vs. Li/Li + ) and operating temperature (25 °C and 60 °C). Half-cell batteries were analyzed with electrochemical and microstructural characterization methods. Electrochemical performance was assessed with galvanostatic cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) supported by distribution of relaxation times (DRT) analysis. Electrode microstructure was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray absorption near edge structure (XANES) imaging. Higher cut-off voltage cycling shows presence of NiO x formation, a low diffusivity rock-salt phase, in both CV and XRD data. XRD patterns confirmed that the rock-salt phase was beginning to form at the low cut-off voltage at high temperature, but in much lower intensity than at the high cut-off voltage. Higher temperature accelerates degradation processes at both voltages. Degradation factors at high temperature include NiO x formation, cathode material dissolution, and electrolyte decomposition. SEM analysis suggests that supporting phases may isolate and disconnect active material particles reducing capacity retention and battery life cycle. DRT analysis and XANES imaging show that both high temperature samples revealed a NiO x phase based on an increased diffusive impedance and a visible shift in the XANES spectra. The low cut-off voltage, high temperature sample showed a split peak and shift to lower energies indicating early formation of the NiO x phase. The diffusive impedance, which hinders intercalation and deintercalation, is driven by the formation of the NiO x phase. While primarily driven by cut-off voltage, elevated temperature also contributes to this degradation mechanism.

electrochemical impedance spectroscopy↗
DOE OSTI2017

Effect of Joining Atmosphere in Transient Liquid Phase Bonding of Inconel 617 Superalloy

In the present paper, transient liquid phase (TLP) bonding of Inconel 617 alloy under the different furnace atmospheres of vacuum, argon gas, and air was investigated. The experiments were carried out at 1408 K (1135 °C) for 300 minutes by using BNi-1 filler metals with different thicknesses of 50 and 100 µm. The microstructure, chemical analysis, shear strength, and microhardness of the resultant joints were studied. After 300 minutes, complete isothermal solidification was obtained for both the interlayers having 50 and 100 µm thicknesses under all the furnace atmospheres. The specimens bonded under vacuum condition showed the highest shear strength, failure energy, and ductility. Also, the joint produced under argon gas atmosphere using 100-µm-thick filler metal showed a good strength and may be acceptable in many applications. However, the specimens bonded under air atmosphere were weak, due to their further cavities and non-dissolved carbides. The presence of non-dissolved carbides in the diffusion-affected zone resulted in increasing the hardness of the base metal near the interface. The carbides were dissolved and the hardness of the diffusion-affected zone was reduced under vacuum condition compared to argon and air atmospheres. The best result was obtained for the specimen joined using the 50-µm-thick interlayer under vacuum atmosphere, with about 95.8 pct joint efficiency.

36 MATERIALS SCIENCE↗