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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Influence of Thermomechanical Treatment on Structural-Phase Transformations and Mechanical Properties of the Cu–Al–Ni Shape-Memory Alloys

Using the methods of optical and electron microscopy and electron and X-ray diffraction analyses, the influence of thermomechanical treatment on the mechanical properties, average grain size, and structural and phase transformations is investigated in the Cu–Al–Ni triple alloys exhibiting a shape memory effect. In the alloys under study with a fixed content of 3wt% Ni the concentration of aluminum was varied from 9 to 14 wt%. It is shown that in the alloys subjected to thermal treatment, including forging and homogenizing annealing using controlled recrystallization in the austenitic state followed by quenching, the grain-boundary disintegration and segregation disappear. It is found out that the microstructure of the alloys in the hot-forged and hardened states with the content of aluminum 9–10 wt%. consists of the grains of the average dimensions within 60–80 μm, with the content of aluminum 10–12 wt% – 100–350 μm, while in the alloys with the content of aluminum up to 14 12 wt% the average grain size reaches 1 mm. According to the data of mechanical testing at room temperature, with a decrease in the content of aluminum the ultimate tensile strength (σ{sub UTS}), the yield strength (σ{sub М}) and the relative elongation (δ) increase. An improvement of the mechanical properties of the alloys is attributed to the grain structure refinement of the β{sub 2}-austenite and package substructure of the β'{sub 1}-and γ'{sub 1}-martensites as the content of aluminum in the alloys decreases. For instance, in the fine-grained alloys containing 9.2 and 9.5 wt% Al the value of relative elongation remains at a high level (>10%), while for the other alloys with 10–14 wt% Al it does not exceed 5%. As the content of aluminum in the alloys decreases, the character of the specimen fracture under uniaxial tension changes (from brittle to ductile).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

On the Influence of the Heat Treatment Temperature on the Superelastic Compressive Behavior of the Ni-Rich NiTi Shape Memory Alloy

In this paper, the relationship between the heat treatment temperature and the thermomechanical behavior of the Ni-rich NiTi shape memory alloy was experimentally investigated. Thermal analysis was performed through a differential scanning calorimetry experiments, and the NiTi superelastic effect was exhibited through loading/unloading compression cycle. It was found that the transformation temperatures and the compressive mechanical response are strongly affected by the heat treatment temperatures. The stress-induced phase transformation was characterized through the relationship between the heat treatment temperature and transformation stresses, elastic moduli and the deformation level upon loading. Subsequently, the evolution of the mechanical hysteresis loops and the mechanical dissipated energy was discussed. The obtained findings are supported by hardness measurements. To better understand the global tendency of the various phase transformation stages, the critical stress-temperature diagram was provided for different proposed heat treatment temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructures, Martensitic Transformation, and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti{sub 50−x/2}Ni{sub 50−x/2}Hf{sub x} (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti{sub 50−y/2}Ni{sub 50−y/2}Si{sub y} (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication and Properties of Composite Artificial Muscles Based on Nylon and a Shape Memory Alloy

This paper focuses on the design, fabrication and investigation of the mechanical properties of new artificial muscles formed by twisting and annealing. The artificial muscles designed by twisting nylon have become a popular topic in the field of smart materials due to their high mechanical performance with a large deformation and power density. However, the complexity of the heating and cooling system required to control the nylon muscle is a disadvantage, so we have proposed a composite artificial muscle for providing a direct electricity-driven actuation by integrating nylon and a shape memory alloy (SMA). In this paper, the design and fabrication process of these composite artificial muscles are introduced before their mechanical properties, which include the deformation, stiffness, load and response, are investigated. The results show that these composite artificial muscles that integrate nylon and a SMA provide better mechanical properties and yield up to a 44.1% deformation and 3.43 N driving forces. The good performance and direct electro-thermal actuation make these composite muscles ideal for driving robots in a method similar to human muscles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Integrating GLL-Weibull Distribution Within a Bayesian Framework for Life Prediction of Shape Memory Alloy Spring Undergoing Thermo-mechanical Fatigue

The present paper tackles an important but unmapped problem of the reliability estimations of smart materials. First, an experimental setup is developed for accelerated life testing of the shape memory alloy (SMA) springs. Generalized log-linear Weibull (GLL-Weibull) distribution-based novel approach is then developed for SMA spring life estimation. Applied stimulus (voltage), elongation and cycles of operation are used as inputs for the life prediction model. The values of the parameter coefficients of the model provide better interpretability compared to artificial intelligence based life prediction approaches. In addition, the model also considers the effect of operating conditions, making it generic for a range of the operating conditions. Moreover, a Bayesian framework is used to continuously update the prediction with the actual degradation value of the springs, thereby reducing the uncertainty in the data and improving the prediction accuracy. In addition, the deterioration of material with number of cycles is also investigated using thermogravimetric analysis and scanning electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Plane Strain Compression and Subsequent Recrystallization Annealing on Microstructures and Phase Transformation of NiTiFe Shape Memory Alloy

The effect of plane strain compression and subsequent recrystallization annealing on microstructures and phase transformation of NiTiFe shape memory alloy (SMA) is investigated. Inhomogeneous plastic deformation at various deformation degrees occurs in NiTiFe SMA during plane strain compression. Nanocrystalline phase and amorphous phase increase as the deformation degree increases. B2 austenite, B19′ martensite, nanocrystalline and amorphous phases coexist in the NiTiFe samples subjected to large plastic strain. The static recrystallization mechanisms depend on the microstructures of the deformed NiTiFe samples. The static recrystallization mechanisms deal with nucleation and growth of the recrystallized grains, growth of nanocrystalline phase and crystallization of amorphous phase. Grain size, subgrain boundaries, geometrically necessary dislocation density and Schmid factor are captured on the basis of electron backscattered diffraction data. The process of recrystallization annealing cannot eliminate the deformation texture completely. The slip direction [110] is the most favorable slip direction in the recrystallized NiTiFe sample. Plane strain compression along with subsequent recrystallization annealing changes the phase transformation path of as-rolled NiTiFe SMA, and it results in the decreasing martensite transformation start temperature. The three annealed NiTiFe samples exhibit the similar phase transformation behavior since complete recrystallization annealing leads to the similar microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2017

An origin of functional fatigue of shape memory alloys

Functional fatigue (FF) during thermal and mechanical cycling, which leads to the generation of macroscopic irrecoverable strain and the loss of dimensional stability, is a critical issue that limits the service life of shape memory alloys (SMAs). Although it has been demonstrated experimentally that such a phenomenon is related to microstructural changes, a fundamental understanding of the physical origin of FF is still lacking, especially from a crystallographic point of view. In this study, we show that in addition to the normal martensitic phase transformation pathway (PTP), there is a symmetry-dictated non-phase-transformation pathway (SDNPTP) during phase transformation cycling, whose activation could play a key role in leading to FF. By investigating crystal symmetry changes along both the PTPs and SDNPTPs, the characteristic types of defects (e.g., dislocations and grain boundaries) generated during transformation cycling can be predicted systematically, and agree well with those observed experimentally in NiTi. By analyzing key materials parameters that could suppress the SDNPTPs, strategies to develop high performance SMAs with much improved FF resistance through crystallographic design and transformation pathway engineering are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Giant and reversible room-temperature magnetocaloric effect in Ti-doped Ni-Co-Mn-Sn magnetic shape memory alloys

The practical applications of magnetocaloric materials for magnetic refrigeration require not only large magnitude but also reversibility, as well as room-temperature operating temperature, of the magneto caloric effect. However, it is a complex problem to simultaneously meet these demands in the Heusler-type Ni-(Co)-Mn-X (X = In, Sn, Sb, Ga) magnetic shape memory alloys which are a promising candidate for magnetocaloric materials, owing to the interdependence of magnetostructural transformation parameters. In this work, through synergic tuning of magnetostructural transformation parameters via alloying with Ti in Ni 42-x Ti x Co 9 Mn 39 Sn 10 alloys, we achieved a large reversible room-temperature magnetocaloric effect. By alloying with a proper amount of Ti, the martensitic transformation temperature was brought down to room temperature and the sensitivity of transformation temperature to magnetic field change was greatly enhanced with the transformation entropy change still remaining a large value, while the thermal hysteresis and the transformation interval only slightly increased. Thus, the field required to induce the complete and reversible transformation was significantly reduced. As a result, a large reversible room-temperature magnetic entropy change ΔS m of 18.7 J kg -1 K -1 under 5 T was achieved in the Ni 41 Ti 1 Co 9 Mn 39 Sn 10 alloy. This is the first report on reversibleΔS m in Ni-Mn-Sn-based Heusler alloys and the ΔS m we achieved represents the highest reversible ΔS m under 5 T reported heretofore in Ni-Mn-based Heusler alloys. Furthermore, the Ni 41 Ti 1 Co 9 Mn 39 Sn 10 alloy shows good compressive properties and stable martensitic transformation during thermal cycling, beneficial for potential magnetocaloric applications. This study is instructive for the development of high-performance magnetocaloric materials for room-temperature magnetic refrigeration.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Simultaneously achieved large reversible elastocaloric and magnetocaloric effects and their coupling in a magnetic shape memory alloy

Large reversible caloric effects covering a broad temperature region are essential for high-efficiency and environment-friendly solid-state caloric refrigeration that can potentially replace the traditional vaporcompression-based cooling technology. Here, we report the simultaneously achieved large reversible magnetocaloric and elastocaloric effects in a Ni 43 Co 6 Mn 40 Sn 11 magnetic shape memory alloy. A reversible near-room-temperature magnetic entropy change Δ S m of as high as 19.3 J kg –1 K –1 under 5 T was experimentally obtained and the corresponding adiabatic temperature change Δ T ad was estimated to be 7.7 K. Meanwhile, a large reversible elastocaloric effect with a directly measured Δ T ad up to 7.1 K was attained. The elastocaloric effect exhibits high cyclic stability with no apparent degradation during 380 cycles of loading and unloading. Furthermore, we propose and demonstrate the utilization of the multicaloric approach under the coupled uniaxial stress and magnetic field to enlarge the refrigeration temperature region of reversible caloric effects. By combining the reversible magnetocaloric and elastocaloric effects and the reversible multicaloric effect under the coupling of uniaxial stress and magnetic field in the hysteresis region, large reversible caloric effects covering a broad temperature region from 257 K to 383 K can be obtained. Finally, this study may pave the way for designing advanced caloric materials with cyclically stable and reversible large caloric effects and wide refrigeration temperature region for solid-state refrigeration.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of composition and crystallographic ordering on the ferromagnetic transition in Ni–Co–Mn–In magnetic shape memory alloys

In the present study, the effects of composition and the level of crystallographic ordering were studied in Ni 45 Co 5 Mn 50-X In X magnetic shape memory alloys with X = 13.55, 13.71 and 13.92, in order to reveal the relationship between the Curie temperature (T C ) of the austenite phase and the degree of L2 1 ordering. Various samples were prepared using secondary heat treatments at different temperatures below the order-disorder transition temperature and for different durations, after solution heat treatment, in order to control the degree of ordering. T C s were determined using calorimetric and magnetometry measurements. The relationship between the T C and the degree of order was used to predict the evolution of the order during selected heat treatments. It was shown that the T C of austenite exhibits a monotonous non-linear dependence on the fraction of the L2 1 phase. This relationship was corroborated via ab initio numerical calculations within a mean field approximation. Dependence of the crystallographic order parameter on temperature and duration of secondary heat treatments showed that ordering kinetics is fast, the total degree of order depends only on the annealing temperature and cooling rate for long enough treatments, and maximum achievable degree of order is limited by the low thermal energy available for atomic diffusion at low temperatures. Lastly, small changes in composition were observed to have a significant impact on martensitic transformation temperatures, and a significant but smaller effect on the ferromagnetic transition in these systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Role of microstructure on the actuation fatigue performance of Ni-Rich NiTiHf high temperature shape memory alloys

Here, the focus of the present study was to systematically investigate the influence of microstructure on the actuation fatigue performance of a Ni-rich NiTiHf high temperature shape memory alloy (HTSMA). Different aging heat treatments led to the formation of H-phase nano-precipitates with different sizes and morphology within the matrix, enhancing thermo-mechanical stability and enabling control of transformation temperatures. The actuation fatigue testing of specimens was performed until failure through thermally-induced reversible martensitic transformation under a constant stress (300 MPa) with two distinct upper cycle temperatures (UCT) of 300 °C and 350 °C. Consequently, the specimens heated to 700 °C and furnace cooled to 100 °C in 48 h, with relatively large precipitates, failed at average fatigue life of 15,500 cycles and exhibited 1.0% average actuation strain in the 300 °C UCT experiments, while those aged at 550 °C for 3 h, with the precipitate sizes less than 20 nm, attained an average fatigue life of 10,800 cycles and an actuation strain of 2.5%. Samples with intermediate precipitate sizes after aging at 600 °C for 10 h failed at the shortest average fatigue life of 8,200 cycles with an intermediate average actuation strain of 2.0%. Furthermore, increase in UCT decreased the fatigue life and resulted in larger average actuation strains for all samples. Overall, the current findings constitute the first systematic results demonstrating the microstructure dependence of the evolution of actuation strain, irrecoverable strain, and transformation temperatures during actuation fatigue, and actuation fatigue life of the Ni-rich Ni 50.3 Ti 29.7 Hf 20 HTSMA, demonstrating the importance of controlling the H-phase precipitate size.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Acoustic emission analysis of cyclically loaded superelastic shape memory alloy fiber reinforced mortar beams

Superelastic shape memory alloys (SMAs) are metallic alloys that can recover their nonlinear deformations upon unloading. The use of SMAs in cementitious composites as fibers can enable crack recovery and re-centering capabilities. In this study, the crack recovery characteristics of SMA fiber reinforced mortar specimens subjected to flexural cyclic loading are studied through acoustic emission analysis. SMA fiber reinforced mortar specimens with fiber volume ratios of 0.3%, 0.5% and 1.0% are tested under cyclic flexural loads. Acoustic emissions (AE) signals are captured and analyzed to characterize the crack formation and crack width development at each cycle of loading. In addition, the crack width propagation of the specimens is monitored by Digital Image Correlation measurement system and is used as a basis in AE analyses. Results show that the SMA fiber reinforced mortars exhibit considerable re-centering and crack recovery characteristics at large deformation amplitudes.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Parallel projection—An improved return mapping algorithm for finite element modeling of shape memory alloys

Here, we present a novel finite element analysis of inelastic structures containing Shape Memory Alloys (SMAs). Phenomenological constitutive models for SMAs lead to material nonlinearities, that require substantial computational effort to resolve. Finite element analysis methods, which rely on Gauss quadrature integration schemes, must solve two sets of coupled differential equations: one at the global level and the other at the local, i.e. Gauss point level. In contrast to the conventional return mapping algorithm, which solves these two sets of coupled differential equations separately using a nested Newton procedure, we propose a scheme to solve the local and global differential equations simultaneously. In the process we also derive closed-form expressions used to update the internal/constitutive state variables, and unify the popular closest-point and cutting plane methods with our formulas. Numerical testing indicates that our method allows for larger thermomechanical loading steps and provides increased computational efficiency, over the standard return mapping algorithm.

42 ENGINEERING↗
DOE OSTI2020

On the elastocaloric effect in CuAlBe shape memory alloys: A quantitative phase-field modeling approach

We report the reversible stress-induced phase transformation in shape memory alloys (SMAs) is a dissipative process during which heat is absorbed or released. The inherent temperature variations inside the material has an elastocaloric effect (eCE) with appealing applications in solid-state cooling technology such as compact and efficient on-board refrigeration system for eletronic devices. In this manuscript, we conduct the first study of eCE of CuAlBe SMAs utilizing phase-field modeling. For an applied stress of 500 MPa, the results for polycrystalline Cu-Al11-2Be (at. %) show a minimum adiabatic unloading temperature change of -10 K over a pseudoelastic window of 40 K. In the absence of plastic deformation, the material demonstrates good reproducibility of the eCE over a few loading–unloading cycles. The presence of plastic deformation is found to cause functional fatigue that deteriorates the cooling capacity; however, the coefficient of performance only decreases from 9.04 to 8.03, which is still a very good value. These results place CuAlBe as a frontrunner SMA for solid-state cooling compared to the expensive NiTi.

36 MATERIALS SCIENCE↗
DOE OSTI2026

PET waste- and bio-derived imine vitrimers for shape-memory, intrinsic flame-retardant, and recyclable carbon fiber composites

Developing circular multifunctional vitrimers and carbon fiber–reinforced polymers (CFRPs) that are simultaneously recyclable, mechanically robust, and intrinsically flame retardant remains a major challenge. Here, in this study, we report multifunctional vitrimers and their carbon fiber–reinforced vitrimer (CFRV) composites, where the vitrimer design integrates closed-loop recyclability, enhanced interfacial adhesion, and intrinsic flame retardancy within a single materials platform. The vitrimer matrix is synthesized from post-consumer polyethylene terephthalate (PET) waste and a vanillin-derived phosphorus-containing crosslinker, forming an imine-based network. The resulting vitrimer resin exhibits high tensile strength, thermal healability, repeated reprocessability, programmable shape memory, and rapid chemical depolymerization under mild conditions. Amine-functionalized carbon fibers significantly improve fiber–matrix interfacial bonding, yielding CFRVs with tensile strengths up to 789 MPa and complete recovery of structurally intact fibers after chemical recycling. The phosphorus-rich aromatic network further imparts intrinsic flame retardancy, enabling self-extinguishing behavior without external additives. This work advances a materials design paradigm for next-generation multifunctional, sustainable vitrimers and CFRVs, while simultaneously addressing the recycling challenges associated with both plastic and CFRP waste.

Bio-derived crosslinker↗
DOE OSTI2025

HydroEcoLSTM: A Python package with graphical user interface for hydro-ecological modeling with long short-term memory neural network

Machine learning (ML) is emerging as a promising tool for modeling hydro-ecological processes due to the increasing availability of large environmental data. However, the use of ML requires sufficient programming knowledge due to a lack of a graphical user interface (GUI). In this study, we introduced a GUI package, named HydroEcoLSTM, with the long short-term memory network (LSTM) as the core model, that allows non-ML experts to utilize their domain knowledge to construct complex ML models. We demonstrated the functionalities of HydroEcoLSTM with two practical examples, including (1) predictions of streamflow in both gauged and ungauged catchments and (2) predictions of multiple outputs (i.e., streamflow and isotope transport from two catchments). The simulation results obtained in both case experiments are satisfactory. In the first example, the average Nash–Sutcliffe Efficiency (NSE) for streamflow simulation during the testing period is 0.79 while the application of the trained model in two assumed ungauged catchments also achieves the average NSE of 0.68. In the second example, the average NSE for streamflow and instream isotope simulation during the testing period is 0.71. Ultimately, applications of HydroEcoLSTM with real-world examples demonstrate its potential use for practical applications and research without requiring extensive coding skills.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Transformation-induced fracture toughening in CuAlBe shape memory alloys: A phase-field study

Stress-induced transformation ahead of a crack tip can relax the stress concentration and produce fracture toughness in shape memory alloys (SMAs). In this manuscript, we utilize a nonisothermal phase-field model (PFM) to study the martensitic transformation induced crack tip toughening in CuAlBe SMA. The force-displacement curve, transformation zone and high stress zone in single crystalline samples show high dependency on the grain orientation with respect to the crack alignment. Comparison between isothermal and non-isothermal simulations reveals that the transformation-induced self-heating decreases the toughening capability by increasing the critical transformation stress. Investigating the high stress zones in CuAlBe and the nontransforming CuAl alloy shows that the toughening is obtained by redistributing the stress concentration far from the crack tip, as the high stress zone follows the tip of the transformation zone. Increasing the acuity of the crack tip is found to generate more symmetric martensite wings on both side of the crack axis and a more localized high stress zone. The polycrystal specimen displays higher toughening due to the internal constraints related to the presence of various grains with difference orientations. Depending on the orientation of the grain inclosing the crack tip, the toughening can be lower or higher. Finally, coincidence of the crack tip with a triple junction is found to improve the toughening behavior.

42 ENGINEERING↗
DOE OSTI2019

In-situ TEM analysis of the phase transformation mechanism of a Cu–Al–Ni shape memory alloy

We report that minimizing phase transformation (PT) hysteresis is of crucial importance for reliability of shape memory alloy (SMA)-based devices, where the lattice strain/stress caused by thermal hysteresis leads to functional degradation. As a result, understanding structural factors that control PT pathway is critical for development of materials with high reversibility. In this study, two distinct PT mechanisms (from γ$'\atop{1}$ martensite to β 1 austenite phase) in Cu–Al–Ni SMAs were revealed by in-situ TEM observation. A growth-dominant conventional PT mechanism shows in the fast quench sample, whereas a nucleation-dominant PT mechanism that suppresses interface propagation and induces high thermal hysteresis displays in the slow quench sample. By characterizing the atomic scale composition and microstructure we discover that slow quenching induces nanoprecipitation that changes chemistry of the matrix alloy, which in turn causes the higher PT hysteresis and temperature, while fast quenching avoids the formation of these nanoprecipitates. Lastly, our finding provides valuable insights into the fabrication of SMAs with better reliability.

36 MATERIALS SCIENCE↗