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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A Study on the Surface Composition and Migration of Materials and Their Effect on Surface Microhardness during Micro-EDM of Ti-6Al-4V

This study aims to investigate the effect of machining parameters on the surface topography and composition of Ti-6Al-4V after micro-EDM as well as the effect of elemental composition on the surface microhardness. The surface topography has been studied in terms of quality of machined surface, crater sizes, and the presence of surface defects. Statistical analysis was carried out to study the influence of micro-EDM process parameters, i.e., voltage, capacitance, discharge energy, electrode rotational speed, and the electrode coating, on the elemental composition of the machined surface. It was found that the crater size, and hence the surface finish, was dependent on the electrical parameters only, with more pronounced effect of capacitance over voltage. The 60 V and 30 pF combination resulted in crater size as small as 1 µm, whereas crater size of 12 µm was obtained using a combination of 4700 pF and 112 V. Although smaller capacitance resulted in smaller crater sizes, it also increased the chances of defects or deposition of debris on the machined surface. There was migration of material from the tool electrode, dielectric oil, and atmosphere to the workpiece surface, which influenced the surface topography, crater sizes, and surface microhardness. The effects of non-electrical parameters on the relative percentage of various elements were found to be statistically insignificant. The surface microhardness was found to increase slightly due to the surface modification after EDM. The reason for increase in surface microhardness was identified as the migration of tungsten from the tool electrode and carbon from the dielectric. The maximum surface microhardness of 455 HV was obtained at a surface composition after micro-EDM containing 7.96% C and 9.69% W, where non-machined Ti-6Al-4V surface does not have any carbon or tungsten on the surface.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microhardness Study of CdZnTeSe Crystals for X-ray and Gamma ray Detectors

A quaternary material Cd 1-x ZnxTe 1-y Sey (CZTS) is currently under investigation for its application as a material for hard X-ray and gamma ray detectors. The addition of selenium was found to be very effective in suppressing the formation of sub-grain boundaries and their networks. The CZTS crystals were grown by the THM technique at Brookhaven National Laboratory. The ingots are ~52 mm in diameter, weighting about 1.0-1.2 kg. In general, the ingots were crack-free except near the Te-CZTS interface. The goal of the presented work is to increase our understanding of key factors influencing the crystal quality and its suitability for radiation detection by a study of its mechanical properties, namely the microhardness and its dependence on crystal composition. Microhardness is closely connected to dislocations and their mobility. We report here on a detailed microhardness characterization and its correlation to the crystal composition of quaternary material Cd 1-x ZnxTe 1-y Se y . Measurements of the Vickers microhardness, resistivity mapping, photoluminescence, and Zn and Se composition analysis were employed along the crystal growth axis. The microhardness values, bandgap and Zn and Se composition along the crystal axis have been correlated. We also performed comparative study of a set of CdTe and CdZnTe samples prepared in the crystal growth laboratory of the Institute of Physics of Charles University or originating from commercial sources.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Vickers Microhardness Studies for SmBa{sub 2}Cu{sub 3}O{sub 7-δ} Added with NiO Nanosized Particles

The effect of nanosized particles NiO addition on the Vickers microhardness of polycrystalline SmBa{sub 2}Cu{sub 3}O{sub 7-δ} was investigated. Various amounts of nanosized particles NiO (x = 0.00, 0.02, 0.04, 0.08, and 0.12 wt%) were added to SmBa{sub 2}Cu{sub 3}O{sub 7-δ} prepared by the solid-state reaction method. Sample characterizations were carried out using X-ray powder diffraction (XRD), particle induced X-ray emission (PIXE), Rutherford backscattering (RBS), and scanning electron microscopy (SEM). The nanosized particle addition does not influence the orthorhombic structure of SmBa{sub 2}Cu{sub 3}O{sub 7-δ}, whereas it affects the oxygen content δ. The electrical and mechanical properties of (NiO){sub x}SmBa{sub 2}Cu{sub 3}O{sub 7-δ} samples were measured using four-standard probe technique and Vickers microhardness in order to investigate the effect of NiO nanosized particles on superconducting transition temperature and Vickers microhardness number H{sub v}. The Vickers microhardness data were analyzed using Hays and Kendall (HK), elastic plastic deformation (EPD), and modified proportional specimen resistance (MPSR) models. The analysis showed that the MPSR model was found to be the best to describe the behavior of H{sub v}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Peak microhardness recovery via T6 heat treatment with extremely soft annealed Al7075 feedstock in additive friction stir deposition

With standard T6 heat treatments, precipitate-hardened alloys such as Al7075 and Al6061 fabricated using Additive Friction Stir Deposition (AFSD) method restore to noticeablely different peak mechanical properties. Previous research observed similar results but did not provide a viable solution. This study proposes a new processing strategy, namely enhanced plastic deformation by subjecting the Al7075 feedstock to annealed softening treatments. Specifically, by annealing the standard T651-Al7075 feedstock and deposition substrate (179 HV), their Microhardness were first degraded to its lowest state (80 HV), which is called a Soft-to-Soft system. For the Soft-to-Soft system subjected to AFSD, after undergoing appropriate T6 heat treatment, the microhardness of the AFSD 7075 alloy was restored to its peak value (183.1 ± 1.8 HV). The results indicate that this softening strategy can effectively reduce the non-strengthening phase in the AFSD matrix, thereby increasing the strengthening phase (η′ phase). This addresses the issue of traditional AFSD-prepared aluminum alloys being unable to achieve peak performance through T6 heat treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Correlation of the Macrohardness and Microhardness

A method is developed for establishing a correlation between the microhardness and macrohardness at different loads. The method is based on comparison of the dimensions of the initial and reconstructed impressions. The diagonal of the initial impression (before elastic recovery) is determined analytically; that of the recovered impression is determined experimentally. It is possible to determine the macrohardness of thin films from microhardness measurements.

42 ENGINEERING↗
DOE OSTI2019

Surface Microhardness of Parts Machined by Asymmetric Uninterrupted Lapping

To improve the wear resistance of high-precision machine parts, a new technology has been developed: asymmetric uninterrupted lapping. The influence of its basic parameters on the surface microhardness is investigated. The optimal parameter values corresponding to maximum surface microhardness are determined.

42 ENGINEERING↗
DOE OSTI2026

Mapping the Microhardness of Al Matrix in U-7Mo/Al Dispersion Fuels at Medium and High Burn-up by in situ Nanoindentation

The mechanical degradation of the Al matrix in U-7Mo dispersion fuels was detected after irradiation in previous studies, but more details of the degradation mechanism are not clear yet to clarify the root cause. In this study, microhardness mapping in fresh and irradiated U-7Mo dispersion fuels coated with ZrN, with burn-up of 3.35 × 10 21 and 6.28 × 10 21 f/cm 3 , are measured to reveal the hardening of the Al matrix as a function of distance to fuel particles. Micro cubes were pulled by plasma focused ion beam scanning electron microscopy and tested by in situ nanoindenter with Berkovitch tip. Size effects are measured in medium and high burn-up samples. The higher burn-up specimen exhibits a more pronounced size effect when indent load is lower than 20 mN. Size effect correction models are also calculated by plots fitting, which predicts the true microhardness without size effect. Results shows that the hardness of the Al matrix near the ZrN coating has the highest value, then decreases moving away from the coating and become stable when the distance reaches ∼10 µm. The hardness starts increasing again getting closer to the next fuel particle, which makes the hardness distribution between two fuel particles to be “U” shape.

36 - MATERIALS SCIENCE↗
DOE OSTI2022

Microhardness Distribution of Long Magnesium Block Processed through Powder Metallurgy

Powder metallurgy is a popular method of making raw powders into specific shaped samples. However, the pressure distribution and the microhardness difference within the sample are nonnegligible and unclear when the sample is long or exceeds a specific size. In this study, the long magnesium blocks, with a ratio of about 2.8 between the sample height and the sample side length, are successfully synthesized under three uniaxial and two biaxial conditions. Then, the sample hardness values on the outer surface and the center plane are tested to study the microhardness distribution. The modified analytical expression indicates that the normal pressure exponentially decreases along the compression direction, which is consistent with the hardness distribution trend. Because higher pressure leads to a more compact arrangement of the powders, more metal bonds are formed after sintering. During the first pressing, the sidewall pressure makes the surface hardness higher. The secondary reverse compression mainly improves the bottom and core hardness due to the re-orientation and re-location of the powders. The obtained relationship between the applied pressure and the hardness distribution is instructive in predicting and improving the sample quality.

Wang, Jiaying↗
DOE OSTI2019

Effect of Friction Stir Processing on the Microhardness, Wear and Corrosion Behavior of Al6061 and Al6061/SiO{sub 2} Nanocomposites

An effect of the friction stir processing (FSP), its pass numbers and addition of the SiO{sub 2} nanoparticles on microhardness, wear behavior and corrosion performance of the Al6061 aluminum alloy was investigated. Scanning electron microscopy (SEM) and optical microscopy were utilized to characterize the microstructure of the alloy, FSPed and composite samples. SEM observations revealed that the SiO{sub 2} particles were not uniformly dispersed in the matrix after two passes of FSP. However, increasing the pass number more than two passes resulted in a great improvement in the distribution of the SiO{sub 2} particles. The application of FSP led to overall softening compared to the base metal. Softening of the Al6061 alloy was probably attributed to the coarsening of Mg{sub 2}Si. Corrosion resistance of the FSPed samples found a significant reduction compared to the base metal. Applying higher pass number of the process and also addition of the SiO{sub 2} nanoparticles improved the wear behavior of the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Solution Treatment on the Microstructure, Micromechanical Properties, and Kinetic Parameters of the β → α Phase Transformation during Continuous Cooling of Ti-6Al-4V Titanium Alloy

The aim of this study is to examine the effect of solution treatment temperature (STT) on the microstructure, the micromechanical properties, and the kinetic parameters of the β → α phase transformation during continuous cooling of the dual phase titanium alloy Ti-6Al-4V. Increasing the STT from 1050 to 1200 °C delays the formation of the α phase during cooling and increases the value of its activation energy. The microstructural analysis reveals the emergence of α{sub W} platelets from protuberances on the α{sub GB}/α{sub W} interface. The investigation of the morphology of the α{sub W} platelets reveals the presence of ledges on their longest side showing a sharp extremity. The micromechanical properties determined by nanoindentation and microhardness tests are almost insensitive to the cooling rate but are strongly affected by the STT; the higher the STT, the lower the overall microhardness of the Ti-6Al-4V alloy. In addition, the STT affects the microhardness and the Young’s modulus of both α and β phases differently; when the STT increases, the microhardness and the Young’s modulus of the α phase decrease, whereas those of the β phase increases.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Determining the Effects of Neutron Irradiation on the Structural Integrity of Additively Manufactured Heat Exchangers for Very Small Modular Reactor Applications, DOE Final Report (Project # 19-16980)

Auburn University (AU) teamed with the University of Missouri Research Reactor (MURR) and Kansas State University (KSU) to determine how to best use laser-powder bed fusion (L-PBF) additive manufacturing (AM) methods for generating radiation resistant nickel-based superalloys, Inconel alloy 625 and 718, for special purpose reactor (SPR) or very small modular reactor (vSMR) heat-exchangers (HeXs). Compact, conformal, and durable HeXs that are tolerant of extreme environments are needed for supporting the technical maturity of next-generation, portable compact reactors. AM is an enabler for realizing this new wave of HeXs – providing a means to make customizable hot and cold stream architectures with novel flow path geometries (e.g., tortuous channels with non-uniform, asymmetric cross-sections) and reduced layer-to-layer contact resistance (i.e., no separate bonding procedure required). AM further enables a more time/cost efficient means for fabricating SPRs by reducing the number of suppliers required for HeX assembly and allowing for on-site HeX fabrication. The project aim has been to better understand how neutron irradiation affects the microstructure and properties of additively manufactured nickel-based superalloys, to accelerate their safe, reliable use in the modular reactor industry. The major objective was to qualify/quantify the microstructure and microhardness of nickel-based superalloys (including Inconel 718 and 625) additively manufactured via the L-PBF process in the neutron-dosed (irradiated) and non-irradiated states over a course of 3 years. Effects of build orientation during L-PBF and post-AM heat treatments on neutron resistance, microstructure and mechanical properties were also investigated. Neutron damage mechanisms via hardening were characterized. This project combined subject-matter experts in AM, mechanical/microstructure metallic part characterization, and neutron irradiation, as well as unique assets and capabilities at AU and MURR at MU, to ensure project results translated to effectively addressing known gaps in nuclear science and engineering. Parts were fabricated using L-PBF systems readily available at AU. Specimens were then irradiated using MURR facilities; a manipulator equipped hot cell was also used to measure material hardness after dosing. MURR, a 10 MW, light-water nuclear reactor, is the largest, highest powered, highest-flux university owned research reactor in the U.S. The major findings in this project provide evidence that AM can serve as an alternative way to build structural components for future advanced small modular reactors using advanced materials like Inconel 625 (IN625) or Inconel 718 (IN718). After full spectrum neutron irradiation, vertically as-built AM IN625 samples were observed to display better resistance towards radiation-induced-hardening defects relative to traditionally machined metals. A Vickers microhardness tester, using settings of 1 kgf and dwell time of 15 seconds per indentation, was used to measure hardness in this study. The as-built, vertically printed samples experienced 1.2% of radiation hardening vs. 5.25% radiation hardening observed in wrought IN625. Another set of IN625 and IN718 samples were exposed to fast neutron irradiation. It was observed that IN718 showed more resistance towards radiation hardening compared to IN625 samples indicating IN718 had a better performance. Results showed that the IN718 samples experienced less change (-2.5 to 3.24 %) in microhardness. On the other hand, IN625 samples underwent more (0.9 to 7.21%) change in microhardness after fast neutron irradiation. AM IN625 samples were irradiated using an ion (proton) beam in cyclotron. The mechanical properties of AM samples post irradiation were compared with wrought samples. The irradiated region on the samples were tested using nano-hardness indention. It was observed that the beam current and time used in this study generated an annealing effect and thus reduced the hardness of the samples. The sum of the project results provide precious insight into how one may minimize radiation hardening in AM materials while maintaining material property constraints. Results should assist engineers in selecting an appropriate heat treatment for AM nickel-based superalloys for increased radiation resistance. Results should increase confidence levels for adopting AM for building nuclear reactor components which perform the same or better than conventionally manufactured components. Fast neutron irradiation testing provided an accelerated means of obtaining radiation effects without making materials radioactive and difficult to handle.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2019

The Effect of Zinc on the Structural, Electrical, and Mechanical Properties of YBCO-123 Superconducting Nanoparticles Prepared by an Acetate-Based Sol-Gel Process

In this study, zinc (Zn)-doped YBaCuO (YBCO)-123-based high-temperature superconducting samples were produced using the sol-gel method, which is commonly used for preparing nanosize materials. Zn ions were substituted by Cu ions (YBa{sub 2}Cu{sub 3-x}Zn{sub x}O), and Zn doping effects on structural, electrical, and mechanical properties of the YBCO-123 superconductors were examined in detail. Undoped sample was prepared under same conditions. X-ray diffraction analysis (XRD) was used to determine phase analysis and lattice parameters of the superconducting samples. To analyze the microstructure properties, scanning electron microscope (SEM) measurements were performed. Resistivity and microhardness measurements were also carried out for superconducting and mechanic properties, respectively. Vickers microhardness, young modulus, fracture toughness, and yield strength values of the samples were calculated. Microhardness measurements were analyzed using the Kick’s law, proportional sample resistance (PSR) model, EPD model, the Hays-Kendall (HK) approach, and indentation-induced cracking (IIC) model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructure Evolution of Ultra-Fine-Grained AZ31 B Magnesium Alloy Produced by Submerged Friction Stir Processing

Ten-millimeter-thick strain-hardened AZ31B-H24 magnesium sheets were subjected to friction stir processing (FSP) in air and submerged friction stir processing (SFSP) under water to investigate their microstructures and microhardness properties. Different rotational speeds of 500, 630, 800, and 1000 rpm and traverse speeds of 50, 100, 200, and 350 mm/min were employed for processing the materials. For SFSPed samples, the rotational speed of 500 rpm and 200 mm/min of traverse speed resulted in an ultra-fine-grained structure with a minimum grain size of about 400-500 nm, which is half compared to that of FSPed. It was found that both processes led to variation of crystallographic orientation, and enhancing the rotational speed and lowering the traverse speed promoted the development of a {0002} basal texture. The microhardness of SFSPed material increased significantly up to 110% (~ 95 Hv), while the microhardness was 45% (~ 65 Hv) higher than the base metal (~ 45 Hv) for FSPed material.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Cyclic Thermal Oxidation Evaluation to Improve Ti6Al4V Surface in Applications as Biomaterial

Thermal oxidation treatments are widely used to modify titanium surfaces. Thermally oxidized titanium alloys are used as biomaterials due to their better surface properties, such as corrosion resistance. However, the use of cyclic thermal treatment for this purpose has not yet been reported. This paper’s objective was to compare roughness, microhardness and corrosion resistance after cyclic and conventional isothermal heat treatments in a Ti6Al4V alloy. The heat treatments were performed over a period of 24 h with a maximum temperature of 650 °C, and cyclic conditions were executed from 200 to 400 °C for 48 cycles, each lasting 0.5 h. After the thermal treatments, roughness was measured through profilometer and atomic force microscopy, Vickers microhardness was evaluated, and polarization corrosion tests were performed in simulated body fluid. All treatments increased surface roughness, microhardness and corrosion resistance at 500 mV above open-circuit potential in polarization tests, compared to the material without oxidation. These results are associated with rutile formation, observed through XRD analysis. Although the isothermal and cyclic treatments presented similar behaviors, the 650-200 °C cyclic heat treatment provided an intermediate roughness and produced a slightly better corrosion resistance, demonstrating that cyclic thermal treatments are a viable alternative for improving titanium alloy surface properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructural Evolution and Properties of 24CrNiMoY Alloy Steel Fabricated by Selective Laser Melting

24CrNiMoY alloy steel samples were fabricated by selective laser melting (SLM), and a phase transformation model was established to study the alloy steel microstructural evolution. Meanwhile, microhardness and tensile properties of 24CrNiMoY alloy steel prepared by different laser energy densities (E{sub v}) were investigated. Results indicate that the microstructural evolution of 24CrNiMoY alloy steel is consistent with the phase transformation model. The main microstructure changed from martensite to bainite with the increase in thermal cycle numbers. In addition, a suitable E{sub v} plays an important role in refining the bainite structure and improving the alloy steel properties. When the E{sub v} decreases from 210 to 140 J/mm{sup 3}, the bainite lath width reduces from 1.7 to 0.6 μm. Simultaneously, the relative density, tensile strength and microhardness of the fabricated samples increase first and decrease later. 24CrNiMoY alloy steel sample prepared by 160 J/mm{sup 3} has fine mechanical properties: The tensile strength is 850 MPa and microhardness is 360 HV{sub 0.2}.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of Annealing on the Properties of AW5754 Aluminum Alloy-AZ31B Magnesium Alloy Explosively Welded Bimetals

Explosive welding of AW5754 aluminum alloy to AZ31B magnesium alloy was performed. AW5754 was proposed as a flyer plate. A parallel setup was used during explosive welding. The annealing of AW5754/AZ31B composite plate at 250, 300 and 350 °C for 2, 3, 4 and 5 h was performed after explosive welding. Bimetals were characterized by regular wavy interface. Annealing resulted in the creation of intermetallic compounds (IMCs). The increase in the thickness of IMC interfacial layer was observed with increasing of annealing temperature and time. IMC layer of highest thickness was recorded after annealing at 350 °C for 5 h and averaged 67 µm. EDS analysis showed that the interfacial layer close to AW5754 alloy was formed by Al{sub 3}Mg{sub 2} IMC, and interfacial layer adjacent to the AZ31B alloy consisted of Mg{sub 17}Al{sub 12} IMC. Bright particles were spread at the AW5754-Al{sub 3}Mg{sub 2} IMC interface. Rise in the microhardness at the interface of produced bimetal was associated with work hardening. Microhardness values increased to 218 HV0.025 after annealing process due to IMCs present at the interface. Decrease in microhardness in locations close to the IMC interfacial layer was found after heat treatment due to recrystallization. The bimetal tensile strength reached 120 MPa. The annealing resulted in decrease in the bimetal tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multi-scale investigation on mechanical behavior and microstructural alteration of C-S-H in carbonated Alite paste

Carbonation treatment is a promising option to enhance recycled concrete aggregate (RCA) quality and eventually improve concrete performance. This study investigated the multi-scale mechanical properties of calcium silicate hydrates (C-S-H) in a mature alite paste subjected to accelerated carbonation treatment by testing macro compressive strength, microhardness and nanoindentation. The results show that, carbonation treatment resulted in a heterogeneous distribution of carbonation products in the alite sample. Reinforcement of C-S-H by the randomly precipitated calcite and vaterite crystals prevailed over the nano-structural and compositional alteration of C-S-H induced by carbonation, leading to an increase of nano-indentation modulus at the edge of the sample. Also, the microhardness at the edge zone was markedly higher than that at the core of the carbonated sample. The carbonated peripheral zone with improved nano-scale modulus and microhardness was likely serving as a “hard shell”, contributing to the improved macro compressive strength. The new insights into the multi-scale mechanical properties of carbonated C-S-H contribute to further understanding of the enhanced properties of RCA after carbonation treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructure and mechanical properties of hypoeutectic Al–6Ce–3Ni-0.7Fe (wt.%) alloy

Here, a hypoeutectic, Fe-modified Al–Ce–Ni alloy (Al–6Ce–3Ni-0.7Fe, wt.%) is studied in terms of microstructure, thermal stability, ambient temperature strengthening, and creep resistance. The as-cast microstructure consists of primary Al dendrites and interdendritic binary eutectic regions (Al–Al11Ce3 and/or Al–Al9(Fe,Ni)2), with micron/submicron lamellar spacing, depending on the location along the height of the ingot. The cast alloy exhibits excellent coarsening resistance at 400 °C, with mostly unchanged microstructure and microhardness after 6 weeks of aging, indicating good thermal stability of Al11Ce3 and Al9(Fe,Ni)2. Orowan strengthening and load transfer are identified as strengthening mechanisms at ambient and elevated temperature. A high volume fraction of the intermetallic phases (providing load transfer) and relatively coarse eutectic spacing (for modest Orowan strengthening) result in a moderate as-cast microhardness of 566 ± 32 MPa. Creep resistance at 300 and 350 °C is similar to a binary Al-12.5Ce eutectic alloy (with twice the Ce content) because of two countering effects: Al–6Ce–3Ni-0.7Fe shows a higher volume fraction of strengthening intermetallic phases, but it also exhibits a large fraction of primary Al dendrites which weaken the alloy. By contrast, the alloy, when laser-remelted at the surface, has a fully eutectic microstructure without primary aluminum dendrites achieved by high undercooling on solidification, with a refined network of eutectic phases that doubles the microhardness as compared to the cast alloy. Whereas coarsening is faster due to the shorter diffusion distances between the eutectic phases, hardness remains ~30% higher than the as-cast alloy after ~6 weeks aging at 400 °C.

36 MATERIALS SCIENCE↗