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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Effects of Annealing on the Microstructures and Mechanical Properties of Cold-Rolled TB8 Alloy

The microstructure and mechanical properties of TB8 cold-rolled plate with a thickness reduction of 50% during annealing at different temperatures are investigated. The results show that annealing for 1 h below 750 °C does not induce the recrystallization transition, remaining the main texture components of {001} <110>, {113} <110> and {112} <110>. The ellipsoidal ω phase is formed when the alloy is annealed at 400 °C. α phase is formed when the alloy is annealed from 450 to 750 °C. The size and volume fraction of α phase increases first and then declines in control of driving force of phase transformation and diffusion. The synergistic effect of the precipitation of ω phase and α phase and the disappearance of dislocation makes the tensile strength of the plate decrease first, then increase, and finally decrease with the increase in annealing temperature. The change in plasticity is opposite to that of strength.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure Characteristics and Comparative Analysis of Constitutive Models for Flow Stress Prediction of Inconel 718 Alloy

An accurate constitutive model is essential for analyzing deformation behavior of material and reliable numerical simulations in metal forming processes. In this study, hot tensile tests of Inconel 718 alloy have been conducted over a wide range of temperatures (300-973 K at an interval of 100 K), strains (0.01-0.3 at an interval of 0.01) and quasi-static strain rates (0.0001, 0.001, 0.01 s{sup −1}). Flow stress behavior is significantly affected by test temperatures and strain rates. Microstructure characteristics of deformed test specimens have been examined using scanning electron microscope and electron backscatter diffraction (EBSD). The fractography study revealed that fracture is mix-mode type, i.e., ductile and brittle. Subsequently, EBSD analysis shown that dynamic recrystallization mechanism is more pronounced at a higher temperature. Furthermore, four constitutive models, namely modified Cowper–Symonds, modified Johnson Cook, modified Zerillie-Armstrong and integrated Johnson Cook–Zerillie-Armstrong (JC-ZA) models have been investigated for flow stress prediction. Capability of models has been evaluated based on the correlation coefficient (R), average absolute error (Δ) and its standard deviation (δ). Accurate prediction of flow stress behavior is found by integrated JC-ZA model with R = 0.9873, Δ = 2.44 and δ = 4.08%.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Chemical Composition on the Microstructure and Properties of the Ag-Ga-Ge Alloys

This study presents a comparison of thermodynamically calculated phase compositions of Ag-Ga-Ge alloys at fixed temperatures with phase analysis results of alloys annealed at respective temperatures. Three isothermal sections of the Ag-Ga-Ge system at 25, 100 and 300 °C have been extrapolated using optimized thermodynamic parameters from the literature. An experimental analysis of the microstructure was carried out using optical microscopy, scanning electron microscopy and energy-dispersive spectrometry. Results obtained by x-ray powder diffraction methods (identified phases and lattice parameters) were compared with the results of the predicted phase equilibria. Good overall agreement between experimental and calculated values was obtained. The Brinell hardness and electrical conductivity of selected alloys were measured and obtained results were analyzed with respect to their overall compositions and phase constituents.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Corrosion Behavior of Cr Coating on M50 Steel Fabricated by Electrospark Deposition

Cr coatings are deposited on M50 steel by electrospark deposition with different parameters (100 V-60 μF, 100 V-90 μF, 100 V-120 μF, 150 V-60 μF, 150 V-90 μF and 150 V-120 μF). Influences of the depositing parameters on the microstructure and the corrosion behavior of the coatings were experimentally investigated. There is a linear trend of growth between the mass gain per area and the deposition cycles before reaching the maximum values. The voltage has more influence on the mass gain per area than the capacitance. The coatings display a splash-like pattern decorated with a few of micro-cracks. The micro-cracks are more sensitive to the voltage than the capacitance. The anti-corrosion ability of the coating is significantly better than the M50 steel. Local corrosion occurs in the coating when there are through-coating cracks. The coating deposited under 150 V-60 μF has the minimum defect density and the best anti-corrosion behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Heat Input on Microstructure, Residual Stress, and Corrosion Resistance of UNS 32101 Lean Duplex Stainless Steel Weld Joints

In the present work, the influence of heat input on phase balance, residual stresses and corrosion resistance of UNS 32101 lean duplex stainless steel welds has been investigated. Three weldment types were obtained with different heat inputs by varying welding current, using gas tungsten arc welding process. The results revealed that increasing heat input caused a significant microstructural evolution with high austenite fraction in weld metals. The residual stresses were measured on the surface and through the sample’s thickness by x-ray diffraction technique based on Sin{sup 2}ψ method. The results showed an inversely proportional relationship between the heat input and the compressive residual stresses on the surface and through the thickness of the weld metal. Potentiodynamic polarization tests of the different welded joints evaluated in 3.5% NaCl solution exhibited high corrosion resistance of the weld metal produced with the low heat input.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of CeO{sub 2} on the Microstructure and Properties of Laser Cladding 316L Coating

Laser cladding was used to distribute a CeO{sub 2}-modified 316L powder coating onto a 316L stainless steel surface. The cladding layer phase composition was evaluated through x-ray diffraction. An analysis of the microstructure was conducted using an optical microscope and scanning electron microscope, while the micro-hardness was measured using a tester. The coating corrosion behavior in response to 3.5% NaCl solution was analyzed by polarization curves and electrochemical impedance spectroscopy. Finally, the overall performance of coatings with different CeO{sub 2} concentrations, 1, 2, and 3%, was compared. Results showed that adding CeO{sub 2} significantly refined the grains, reduced the coating porosity, and effectively limited the appearance of local corrosion. Also, additive CeO{sub 2} shifted the coating’s electrode potential in a positive direction, minimizing the current density of corrosion, creating a stable passivation film, and improving the coating’s corrosion resistance. The coating performance (hardness and corrosion behavior) was optimal when 2% CeO{sub 2} was employed as the powder mass.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Experimental Study on Microstructure and Hardness of Pure Titanium Subjected to Torsion Deformation at Different Temperatures

The studies of mechanical property, microstructure evolution and fracture analysis in pure titanium processed by torsion deformation at 298, 673 and 1073 K are conducted systematically. The variations of mechanical property of deformed pure titanium are shown through Vickers hardness evaluation. During torsion at 298 K, the grains are refined and elongated, but the α phase with different shapes precipitates for twisted samples at 673 and 1073 K. The fracture appearance indicates that the elongated dimples occur on fracture surface at 298 K. Besides, a large number of shear facets are arranged. However, typical intergranular fracture appearance with lots of blocks in polyhedral shape covers the fracture surface at 673 and 1073 K, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Nb Content on Microstructures and Mechanical Properties of Ti-xNb-2Fe Alloys

β-Type Ti-Nb-based alloys exhibit satisfactory biocompatibility and low Young’s modulus for biomedical applications. The microstructure and mechanical properties of a series of Ti-(14, 16, 18, 20, 22, 24)Nb-2Fe alloys fabricated by arc melting were investigated by XRD, optical microscopy, and tensile tests. Both ω and α″ phases existed in the Ti-14Nb-2Fe alloy, while just a single β phase existed in the other alloys. Twinning is an important deformation mechanism that causes work hardening and twinning-induced plasticity. It was found in the Ti-(14, 16, 18, 20)Nb-2Fe alloys and not in the Ti-22Nb-2Fe alloy. The Ti-14Nb-2Fe alloy exhibited the highest tensile strength and the highest Young’s modulus owing to the existence of the ω phase. The tensile strength decreased gradually from 830 MPa (highest) for the Ti-14Nb-2Fe alloy to 540 MPa (lowest) for the Ti-24Nb-2Fe alloy with an increase in the Nb content. The Young’s modulus decreased from 90 GPa for the Ti-14Nb-2Fe alloy to 63 GPa for the Ti-22Nb-2Fe alloy and then increased to 71 GPa for the Ti-24Nb-2Fe alloy. Elongation shows the same trend as the Young’s modulus. The Ti-22Nb-2Fe alloy, with a low Young’s modulus of 63 GPa, tensile strength of 570 MPa, and 15% elongation, was found suitable for biomedical applications. The Ti-20Nb-2Fe alloy also exhibits a high tensile strength, a Young’s modulus ratio of 9.24 × 10{sup −3}, and 18% elongation and is thus considered another valuable Ti alloy for biomedical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of FSW Repairing Process on the Microstructures and Mechanical Properties of Friction Stir-Welded 6082Al Alloy

When two 42-mm 6082Al plates were welded by friction stir welding (FSW), a discontinuously distributing groove defect is formed on the surface of the joint. Subsequently, the FSW repairing process was conducted at the defect location. The influence of the repairing process on the microstructures and mechanical properties of the joints were studied, and a description of the softening mechanism of the repaired joints is provided. The results show that TMAZ at the advance side is the weakest zone of the as-welded joints. The repairing process increases the heat input into the joints and thus promotes the coarsening and transformation of the precipitates in the joints, which further weakens the repaired joints. The average tensile strength of the joints repaired with a 24-mm pin is 205 MPa, which is 91% of that of the as-welded joint. The tensile strength generally increases when the size of the repaired pin decreases. The average tensile strength of the joints repaired with an 8-mm pin is 220 MPa, which is equivalent to the initial joints.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Heat Treatment on Microstructure Evolution and Mechanical Properties of Selective Laser Melted Inconel 718 Alloy

The microstructure characteristics of the selective laser melted Inconel 718 alloy under as-deposited, homogenization + solution + aging (HSA) and solution + aging (SA) conditions were studied. The anisotropy and heterogeneity of mechanical properties under different conditions were also investigated. Under the as-deposited condition, the morphology and size of the grains are heterogeneous. The dendrite structures which grow nearly perpendicular to the molten pool traces, accompanying interdendritic Laves phase, can be observed within the grains. The dendrite structure completely disappeared, and the Laves phases embedded in the interdendritic regions also dissolved into the matrix to precipitate γ′ and γ″ phases after heat treatments. Fully recrystallized grains were obtained under the HSA condition, while only incomplete recrystallized grains were obtained under the SA condition. However, the characteristics of γ′ and γ″ phases are very similar under the HSA and SA conditions. Significant improvement in strength after heat treatments was due to the dissolution of undesirable Laves phase and the precipitation of γ′ and γ″ phases. For all the three conditions, different tensile properties were observed depending on the orientation of the specimens. The scatter of mechanical properties is notable, and heat treatments increased the scatter of mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of Annealing Time on Microstructure and AC Corrosion Behavior of X80 Steel in Simulated Solution of Alkaline Soil

The alternating current (AC) corrosion behavior of X80 steels annealed for different times was investigated in an alkaline soil simulation solution by electrochemical measurement, immersion test and surface analysis technology. The results show that with or without AC interference, the steels annealed for various times have different corrosion resistance. The anticorrosion resistance of steel improves with an increase in annealing time. AC interference results in the evolution of the main cathodic reaction, and facilitates the corrosion of the steels. The steel annealed for 20 min presents a more severe corrosion degree with distinct pits. The corrosion behavior of the steels annealed for different times with AC application is closely related to the microstructure. A decrease in pearlite reduces the number of galvanic corrosion cells, decreasing the corrosion rate of steel. And the grain increase is beneficial for improving the corrosion resistance of the annealed steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Laser Weldability of AlSi{sub 10}Mg Alloy Produced by Selective Laser Melting: Microstructure and Mechanical Behavior

Selective laser melting (SLM) allows 3D complex parts to be produced with integrated functionalities but does not permit to realize large dimension parts, as the building chamber volume of commercial SLM systems is limited. Therefore, the possibility of joining SLM-built parts by welding appears as extremely valuable. In this work, laser weldability of SLMed AlSi{sub 10}Mg parts has been investigated. The cooling rates induced by the welding process are lower than the ones of SLM; therefore, typical eutectic silicon network of SLM-built parts appears broken in both the melted zone and part of the heat-affected zone, as confirmed by calorimetric measurement. This microstructural evolution caused a local decrease of hardness from 132 HV to 73 HV and a reduction of ductility caused by porosity formation in the weld bead. Moreover, the thermal treatment, performed at 320°C, can limit the gap of tensile response among welded bead and base SLM material.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructural Characterization and Simulation of High Temperature Inelastic Deformation and Fracture of Al-Li 2070

A combined experimental and simulation investigation is carried out to characterize the high temperature deformation behavior of a recently developed Al-Li alloy, AA2070, over a temperature range including typical forging temperatures. Focus is placed on providing explanations for the temperature-dependent plastic and fracture behavior observed for this material using macroscale tensile tests, microscale imaging and analysis, and physics-based micromechanical modeling. It is shown that AA2070 experiences non-monotonic elongation to failure with a rise in temperature. Detailed fractography and microstructural analysis, including dynamic recrystallization analysis, provide insight into this interesting and practically useful behavior. In addition, a validated crystal plasticity model is called upon to explain the unique texture observed in the necked region of the ductile tensile specimen. The insights provided by this investigation will allow improved design of high temperature forming operations for AA2070 and similar alloys which can extend the application of third generation Al-Li alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Three-Point Bending Fatigue Behavior of Al-Cu-Mg-Ag Alloys with Various Mg Contents

This paper presents an investigation on the influence of Mg content on the microstructures, tensile properties and three-point bending fatigue behavior of Al-Cu-Mg-Ag alloys. The results indicate that the alloy containing 0.70 wt.% Mg possesses lower tensile properties and higher fatigue performance compared to the one with 1.15 wt.% Mg. Increasing Mg content in Al-Cu-Mg-Ag alloys can enhance the nucleation and precipitation of Ω phase, as well as increase the volume fraction and number density of constituent particles. The investigation of the fatigue crack initiation and growth behavior of Al-Cu-Mg-Ag alloy using interrupted fatigue tests suggests that micro-cracks mainly nucleate on Al{sub 2}Cu constituent particles and the fatigue life is mainly associated with the density of constituent particles.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Significant Contribution to Strength Enhancement from Deformation Twins in Thermomechanically Processed Al{sub 0.1}CoCrFeNi Microstructures

Strengthening mechanisms from thermomechanical processing treatments were explored in single-phase FCC high-entropy alloy Al{sub 0.1}CoCrFeNi. Cold work offers substantial strengthening in this low stacking fault energy material owing to the resultant high work hardening rates. An enormous increase in yield strength of ~ 275% was obtained in 40% rolled material, but was accompanied by a steep drop in ductility. Recovery and recrystallization annealing treatments were investigated for improving elongation and obtaining better balance of strength–ductility combinations. Formation of novel microstructures from the different processing routes was examined. X-ray diffraction peak broadening and mechanical test results were coupled to estimate micro-strain in the different conditions and understand micro-strain’s correlation to strength. Retention of large-scale deformation twins formed during cold rolling is shown to play a key role in elevation of yield strength after heat treatments.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Uncertainty quantification of microstructural properties due to variability in measured pole figures

Experimental pole figures are an important input for microstructure homogenization models. In this paper, we derive an exact analytical formulation to quantify the uncertainties in homogenized properties due to uncertainty in the experimentally measured pole figures. The pole figures are acquired from a set of Ti-7Al alloy samples. These samples were obtained from the same process: by compressing a beta forged ingot at room temperature followed by annealing. The samples were taken from different regions of the original ingot, and this created variability in the resulting pole figures. The joint multivariate probability distributions of the computed orientation distribution function (ODF) is then found using the method of characteristic functions based on a Gaussian model of the pole figures. Engineering properties such as elastic modulus can be obtained by volume averaging over the ODF. We also show that uncertainty in elastic properties can be analytically obtained using direct transformation of random variables in the homogenization approach.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The effect of carbon on the microstructures, mechanical properties, and deformation mechanisms of thermo-mechanically treated Fe 40.4 Ni 11.3 Mn 34.8 Al 7.5 Cr 6 high entropy alloys

We investigated the effects of cold rolling followed by annealing on the mechanical properties and dislocation substructure evolution of undoped and 1.1 at. % carbon-doped Fe 40.4 Ni 11.3 Mn 34.8 Al 7.5 Cr 6 high entropy alloys (HEAs). X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT) were employed to characterize the microstructures. The as-cast HEAs were coarse-grained and single phase f.c.c., whereas the thermo-mechanical treatment caused recrystallization (to fine grain sizes) and precipitation (a B2 phase for the undoped HEA; and a B2 phase, and M 23 C 6 and M 7 C 3 carbides for the C-doped HEA). Carbon, which was found to have segregated to the grain boundaries using APT, retarded recrystallization. The reduction in grain size resulted in a sharp increase in strength, while the precipitation, which produced only a small increase in strength, probably accounted for the small decrease in ductility for both undoped and C-doped HEAs. For both undoped and C-doped HEAs, the smaller grain-sized material initially exhibited higher strain hardening than the coarse-grained material but showed a much lower strain hardening at large tensile strains. Wavy slip in the undoped HEAs and planar slip in C-doped HEAs were found at the early stages of deformation irrespective of grain size. At higher strains, dislocation cell structures formed in the 19 μm grain-sized undoped HEA, while microbands formed in the 23 μm grain-sized C-doped HEA. Conversely, localized dislocation clusters were found in both HEAs at the finest grain sizes (5 μm). The inhibition of grain subdivision by the grain boundaries and precipitates lead to the transformation from regular dislocation configurations consisting of dislocation-cells and microbands to irregular dislocation configurations consisting of localized dislocation clusters, which further account for the decrease in ductility. Our investigation of the formation mechanism and strain hardening of dislocation cells and microbands could benefit future structural material design.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Quantitative characterization of gradient microstructures: A study on friction stir spot processing of pure cobalt

Heterogeneous microstructures in polycrystalline metals can enhance the strength and ductility, outperforming homogeneous structures of similar composition. This study investigates deformed cobalt via friction stir spot processing with varying dwell times to uncover the effects of plastic deformation and heat generation on the formation of morphological, phase, and grain boundary character gradients. A new approach to quantify the morphological gradients in materials, which describes grain morphology in terms of density followed by parametric regression, enables direct quantification of processing depth and gradient sharpness. Results show that longer processing times increase the steepness of morphological gradients and reduce the deformation depth for friction stir spot processing with low plunge depths and high tool rotational speeds. The amount of retained FCC is increased in the shorter processing conditions, primarily due to refined grain size, increased defect content, and reduced heat generation. Crystallographic texture analysis of the HCP phase indicated a dominant B-fiber described by (0001) ∥ shear plane normal in the extreme processing conditions and the formation of a P-fiber, shear direction ∥ ⟨11$\bar2$0⟩ for intermediate dwell times. The texture of the FCC phase for low processing times was a C texture {100}⟨011⟩ where longer processing times were dominated by a [001] fiber texture with a main {110}⟨100⟩ orientation and emergence of a slight [111] fiber in the longest processing condition. The approaches outlined in this work give insight into quantifying gradients and improve the understanding of highly deformed cobalt.

36 MATERIALS SCIENCE↗

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