Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Phase Transformation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Pressure-Induced Phase Transformations

The study of phase transitions in solids under high pressure conditions is a very active and vigorous research field. In recent decades, thanks to the development of experimental techniques and computer simulations, a plethora of important discoveries has been made under high-pressure conditions. Many of the achievements accomplished in recent years a affect various research fields, from solid-state physics to chemistry, materials science, and geophysics. They not only contribute to a deeper understanding of solid-sold phase transitions but also to a better understanding of melting under compression.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electron microscopic evidence for a tribologically induced phase transformation as the origin of wear in diamond

Tribological testing of a coarse-grained diamond layer, deposited by plasma-enhanced chemical vapor deposition, was performed on a ring-on-ring tribometer with a diamond counterpart. The origin of the wear of diamond and of the low friction coefficient of 0.15 was studied by analyzing the microstructure of worn and unworn regions by transmission and scanning electron microscopy. In the worn regions, the formation of an amorphous carbon layer with a thickness below 100 nm is observed. Electron energy loss spectroscopy of the C-K ionization edge reveals the transition from sp{sup 3}-hybridized C-atoms in crystalline diamond to a high fraction of sp{sup 2}-hybridized C-atoms in the tribo-induced amorphous C-layer within a transition region of less than 5 nm thickness. The mechanically induced phase transformation from diamond to the amorphous phase is found to be highly anisotropic which is clearly seen at a grain boundary, where the thickness of the amorphous layer above the two differently oriented grains abruptly changes.

36 MATERIALS SCIENCE↗
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↗
DOE OSTI2021

Magnetic ordering suppressed phase transformation of a TRIP-HEA during thermal cycling

Transformation-induced plasticity (TRIP) high-entropy alloys (HEAs) have drawn great attention as they present excellent mechanical properties, and their phase stability is critical for the underlying deformation mechanisms and the application temperature range. In this study, the kinetic phase transformation behavior of a dual-phase TRIP-HEA Fe 50 Mn 30 Co 10 Cr 10 (at. %) was probed by in situ neutron diffraction during thermal cycling between 293 and 425 K. Continuous austenitic and martensitic transformation were visualized through the evolution of hexagonal close-packed phase fraction during thermal cycling. Specifically, thanks to the magnetic sensitivity of neutron diffraction, it was found that the martensitic transformation under cooling became suppressed when the antiferromagnetic ordering started at ~326 K. This temperature was further confirmed as the Néel temperature by magnetization measurements. In this work, thermodynamic calculations revealed that the suppression effect on martensitic transformation is attributed to the consumption of the chemical driving force by the magnetic ordering. The magnetic ordering at such relatively high temperature is associated with the high Mn content. These findings shed light on a potential strategy to achieve better mechanical properties of Mn-containing alloys by manipulating the magnetic property through tuning the Mn content.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Selective Catalytic Behavior Induced by Crystal–Phase Transformation in Well–Defined Bimetallic Pt–Sn Nanocrystals

The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt–Sn phase. Colloidal chemistry offers a route for the synthesis of Pt–Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt 3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt 3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt 3 Sn/Al 2 O 3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L1 2 -ordered superlattice. Contrary to PtSn, H 2 cofeeding has no effect on the Pt 3 Sn deactivation rate. Finally, the results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure–performance relationship on emerging bimetallic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Phase transformation in multiferroic Bi{sub 5}Ti{sub 3}FeO{sub 15} ceramics by temperature-dependent ellipsometric and Raman spectra: An interband electronic transition evidence

Thermal evolution and an intermediate phase between ferroelectric orthorhombic and paraelectric tetragonal phase of multiferroic Bi{sub 5}Ti{sub 3}FeO{sub 15} ceramic have been investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Dielectric functions and interband transitions extracted from the standard critical-point model show two dramatic anomalies in the temperature range of 200–873 K. It was found that the anomalous temperature dependence of electronic transition energies and Raman mode frequencies around 800 K can be ascribed to intermediate phase transformation. Moreover, the disappearance of electronic transition around 3 eV at 590 K is associated with the conductive property.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Irradiation Tailoring of Deformation-Induced Phase Transformations

The objective of this project is to understand how irradiation enables deformation‐induced phase transformations in fcc metallic alloys. Low‐temperature deformation of face centered cubic (fcc) metals and alloys can occur through several modes, one of which is martensitic transformation, wherein fcc γ‐Fe austenite reverts to hexagonal close packed (hcp) ε‐ martensite or body centered cubic (bcc) α’‐martensite. Irradiation is believed to enhance the tendency for this transformation to occur, considering that irradiation similarly enhances other low‐temperature deformation modes such as dislocation channeling and deformation twinning. However, the mechanisms underlying the irradiation enhancement of martensitic transformations remain unknown.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Low-temperature solid-state phase transformations in 2H silicon carbide

Single crystals of 2H SiC were observed to undergo phase transformations at temperatures as low as 400 C. Some 2H crystals transformed to a structure with one-dimensional disorder along the crystal c axis. Others transformed to a faulted cubic/6H structure. The transformation is time and temperature dependent and is greatly enhanced by dislocations. Observations indicate that the transformation takes place by means of a slip process perpendicular to the c axis. Cubic SiC crystals were observed to undergo a solid state transformation above 1400 C.

Will, H. A.↗
DOE OSTI2018

Effects of Heat Treatment on Phase Transformation and Corrosion Resistance of Boride Layer on Austenitic Stainless Steel AISI 304

The austenitic stainless steel AISI 304 was thermochemically surface treated using a powder-packed boronizing process at a temperature of 950 °C for about 4 hours. Double-phase boride layer (FeB and Fe{sub 2}B) was detected and then investigated for the corrosion resistance compared with the untreated one. Heat treatment was performed at a temperature range of 800 to 900 °C for 2 hours on the boronized austenitic stainless steel AISI 304 to diminish the double-phase boride layer. Afterward, corrosion tests were performed to clarify the effects of heat treatment as well as phase transformation on the corrosion resistance of the boronized austenitic stainless steel AISI 304. The results of this study showed that the formation of single-phase Fe{sub 2}B layer offers the best corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterising the polymorphic phase transformation at a localised point on a Cu6Sn5 grain

Highlights: • A single-targeted Cu{sub 6}Sn{sub 5} grain adjacent to Sn-rich sites and Cu{sub 3}Sn was investigated using HVTEM. • Phase transformation from hexagonal to monoclinic in a single-targeted Cu{sub 6}Sn{sub 5} grains. • A time-temperature transformation (TTT) diagram was constructed using the HVTEM results. - Abstract: Cu{sub 6}Sn{sub 5} is an important intermetallic for electric interconnects and anode material of Li-ion batteries, with a polymorphic transformation from hexagonal eta-Cu{sub 6}Sn{sub 5} at temperatures higher than 186 °C to monoclinic eta′-Cu{sub 6}Sn{sub 5} at lower temperatures. The polymorphic transformation of Cu{sub 6}Sn{sub 5} has the potential to generate internal stresses in soldered joints during both the soldering process and subsequent device operation involving thermal cycling. Here we developed a systematic method to characterise the polymorphic transformations at localised points in a single grain of Cu{sub 6}Sn{sub 5} that is in intimate contact with adjacent Sn rich and Cu{sub 3}Sn phases to establish a time–temperature transformation (TTT) diagram of the eta to eta′-Cu{sub 6}Sn{sub 5} transformation. The method involves in situ temperature-controlled high-voltage transmission electron microscopy (HVTEM) of a single-targeted Cu{sub 6}Sn{sub 5} grain with observation of diffraction patterns during multiple heating and cooling experiments on a 0.5 μm thick sample made by focused ion beam milling (FIB). The results are compared to previously reported powder X-ray diffraction data. It is concluded that there is good agreement between both techniques and the transformations observed in the powder are representative of those in individual grains present in polycrystalline structures. Based on the newly developed TTT, it was established that the high-temperature eta-Cu{sub 6}Sn{sub 5} could be stablised down to room temperature if the cooling rate exceeded 20 °C min{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Phase transformation and fluorescent enhancement of ErF 3 at high pressure

In this study, pressure-induced phase transformation and fluorescent properties of ErF 3 were investigated here using in-situ synchrotron X-ray diffraction and photoluminescence up to 32.1 GPa at room temperature. Results showed that ErF 3 underwent a reversible pressure-induced phase transition from the β-YF 3 –type to the fluocerite LaF 3 -type at 9.8 GPa. The bulk moduli B 0 for low- and high-pressure phases were determined to be 130 and 208 GPa, respectively. Also, photoluminescencent studies showed that new emission lines belonging to the transition of 2 H 11/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 , and 4 F 9/2 → 4 I 15/2 appeared during phase transition, suggesting pressure-induced electronic band splitting. Remarkably, significant pressure-induced enhancement of photoluminescence was observed, which was attributed to lattice distortion of the material under high pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

FEM modeling of plastic flow and strain-induced phase transformation in BN under high pressure and large shear in a rotational diamond anvil cell

In this study, combined three-dimensional plastic flow and strain-induced phase transformation (PT) in boron nitride (BN) under high pressure and large shear in a rotational diamond anvil cell (rotational DAC or RDAC) are investigated. Geometrically nonlinear frameworks including finite elastic, transformational, and plastic deformations and finite element method (FEM) are utilized. Quantitative information is obtained on the evolutions of the stress tensor, plastic strain, volume fraction of phases in the entire sample, and slip-cohesion transitions, all during torsion under a fixed compressive load in RDAC. The effects of the applied compressive stress and the sample radius on PT and plastic flow are discussed. In comparison with DAC, the same amount of the high-pressure phase can be obtained at a much lower pressure in RDAC, which reduces the required force and the risk of diamond fracture. Also, RDAC has a potential to complete PT during torsion under pressure close to the minimum possible. A quasi-homogeneous pressure can be obtained in a transforming sample in RDAC under a proper choice of properties and parameters of a gasket. A number of experimental phenomena, including the pressure self-multiplication and quasi-homogeneous pressures in DAC and RDAC, are reproduced and interpreted. Finally, the simulation results provide a significant insight into coupled PTs and plastic flow in material in RDAC, and are important for the optimum design of experiments and the extraction of material parameters for PT, as well as for the optimization and control of PTs by the variation of various parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of niobium and phase transformation temperature on the microstructure and texture of a novel 0.40% C thermomechanically processed steel

Field emission scanning electron microscopy, electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) have been employed to investigate the effect of niobium and phase transformation temperature on the evolution of microstructure and texture in a novel thermomechanically processed, medium‑carbon, low-alloy steel intended for slurry pipeline applications. Thermomechanical processing consisted of hot-rolling in the austenitic region with deformation both above the recrystallization limit temperature and below the recrystallization stop temperature. Immediately after rolling, specimens were directly quenched in water to two different temperatures of 560 °C and 420 °C and subsequently furnace cooled from those temperatures to simulate the cooling of coiled strip on a hot strip mill. The microstructure of samples quenched to 560 °C mostly comprised of upper bainite, whereas the samples quenched to 420 °C mainly consisted of lath-type lower bainite. The transformation texture of all samples at the mid-thickness position consisted of α, γ and ε-fibers with high intensities close to the transformed copper, transformed brass and rotated cube components. The addition of 0.013 wt% Nb refined the microstructure and sharpened the texture. The texture of the small fraction of retained austenite present in the final microstructures indicated that the main bcc texture components result from the brass and copper components in the parent austenite.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High-temperature phase transformation and topochemical nature in ferroelastic (NH{sub 4}){sub 2}SO{sub 4}

The electrical conductivity of ferroelastic ammonium sulfate (NH{sub 4}){sub 2}SO{sub 4} revealed an anomaly at around 130 °C (=403 K, T{sub P}) on heating with large and irreversible thermal hysteresis through thermal cycle. Ferroelastic domain walls and surface morphology of (NH{sub 4}){sub 2}SO{sub 4} were investigated by hot-stage polarizing microscopy. Structural phase transition from an orthorhombic ferroelastic phase to a hexagonal paraelastic phase was not identified at T{sub P} upon heating. On further heating above T{sub P}, microscopic spots appeared and grew on the crystal surface, suggesting that the high-temperature anomaly at T{sub P} was an indication of an onset of thermal decomposition controlled by topochemical factors. The increase of electrical conductivity above T{sub P} was attributed to proton migration. - Graphical abstract: Surface morphology of the (100) face of (NH{sub 4}){sub 2}SO{sub 4} on heating, showing chemical reaction at the surface. - Highlights: • We investigate the high-temperature phase transformation of ammonium sulfate. • The increasing conductivity upon heating is attributed to proton migration. • Structural phase transition from orthorhombic to hexagonal phase is not confirmed. • High-temperature anomaly is related to an onset of thermal decomposition. • The nature of the high-temperature anomaly is topochemical controlled by defects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Tracing Phase Transformation and Lattice Evolution in a TRIP Sheet Steel under High-Temperature Annealing by Real-Time In Situ Neutron Diffraction

Real-time in situ neutron diffraction was used to characterize the crystal structure evolution in a transformation-induced plasticity (TRIP) sheet steel during annealing up to 1000 °C and then cooling to 60 °C. Based on the results of full-pattern Rietveld refinement, critical temperature regions were determined in which the transformations of retained austenite to ferrite and ferrite to high-temperature austenite during heating and the transformation of austenite to ferrite during cooling occurred, respectively. The phase-specific lattice variation with temperature was further analyzed to comprehensively understand the role of carbon diffusion in accordance with phase transformation, which also shed light on the determination of internal stress in retained austenite. These results prove the technique of real-time in situ neutron diffraction as a powerful tool for heat treatment design of novel metallic materials.

Yu, Dunji↗
DOE OSTI2026

Spatially resolved phase transformation mapping in 410 stainless steel during additive manufacturing visualized via real-time infrared data

Here, in this study, we demonstrate that spatially resolved cooling curves derived from real-time infrared (IR) thermography during additive manufacturing (AM) can capture spatial variations in phase transformation temperatures through cooling curve analysis (CCA). Using this approach, we show that during laser hot-wire deposition of 410 stainless steel (410SS), the martensite start temperature (M s ) evolves dynamically throughout the build. The M s temperature is spatially nonuniform, ranging from 185 °C to 348 °C, with the lowest values toward the build center and higher values toward the upper region of the deposit. In the lower portion of the build, no M s inflection is detected via CCA, consistent with transformation occurring earlier during thermal cycling followed by tempering during subsequent thermal cycles. These trends in M s are corroborated by characterizing the microstructure by electron backscatter diffraction (EBSD). Traditionally, M s is assumed to be constant, and a single interpass temperature is applied during both deposition and residual stress modeling. Our results demonstrate that IR-derived cooling curves provide a route to spatially and temporally resolved transformation temperature tracking for dynamic interpass control and improved residual-stress modeling.

Additive manufacturing↗
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↗