Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DUCTILITY”

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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Simultaneously improving mechanical properties and corrosion resistance of pure Ti by continuous ECAP plus short-duration annealing

Highlights: • Additional short-time annealing led to enhanced strength of UFG Ti due to texture strengthening. • UFG Ti showed improved corrosion resistance in artificial seawater compared with initial CG Ti. • Short-duration annealing enhanced corrosion resistance of UFG Ti due to stronger basal texture. - Abstract: This work investigated the effect of short-duration annealing on mechanical properties and corrosion behavior of bulk ultrafine-grained (UFG) pure Ti (grade 2) produced by high-efficiency equal-channel angular pressing (ECAP), serving the fast developing of marine industries. The initial coarse-grained (CG) Ti achieved higher strength after continuous ECAP at 420 °C for 4 passes, while additional short-duration annealing at 300 °C for 15 min of UFG Ti further led to extraordinary improvement of strength, which was associated with texture strengthening. The yield strength was increased from 362 MPa in as-received state to 561 MPa in post-ECAP annealed condition, and ultimate tensile strength from 450 MPa to 663 MPa. The ECAP-processed UFG Ti had better corrosion resistance in artificial seawater than the initial CG Ti. Short-duration annealing further improved the corrosion resistance of UFG Ti, which was related to stronger basal texture. The corrosion current density decreased from 68.37 nA cm{sup −2} for CG Ti in as-received condition to 41.77 nA cm{sup −2} for UFG Ti processed by ECAP plus short-duration annealing. The fraction of TiO{sub 2} within the surface oxide film for the post-ECAP annealed sample was increased. The bulk UFG Ti after post-ECAP short-duration annealing revealed an excellent combination of high strength, good ductility and superior corrosion resistance for marine applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The plastic flow machining: A new SPD process for producing metal sheets with gradient structures

Highlights: • A new process named Plastic Flow Machining is presented to produce thin sheets by an extrusion operation from bulk material. • The produced sheets present ultra-fine grain structures, good mechanical properties and high formability. • A deformation gradient was found across the thickness of the sheet regarding plastic strain, microstructure and texture. - Abstract: A new severe plastic deformation process is presented – the plastic flow machining – an extrusion process during which a sheet is formed through a lateral opening of the die in a single operation. The sheet is heavily deformed presenting an ultra-fine grain structure. Experimental results are presented for commercially pure aluminum concerning microstructures, textures and mechanical properties. A gradient structure was found across the thickness of the sheet concerning plastic strain, grain size and texture. Only simple shear textures were seen. The material strength increased by a factor of three with significant ductility and with relatively high Lankford parameter.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure evolution and properties of graphene nanoplatelets reinforced aluminum matrix composites

Highlights: • Lamellar structure of GNPs fibers and Al matrix was obtained in the rolling direction. • Stacking faults were observed in Al grains due to greatly increased GNPs/Al interfaces. • Strength of Al-0.2 wt% GNPs increased 36.8% with negligible electrical conductivity loss. - Abstract: Aluminum matrix composites reinforced with graphene nanoplatelets (GNPs) were prepared by continuous casting and subsequent rolling. Al-GNPs master alloy, prepared by ball milling and cold pressing, was added into Al melts to fabricate the composites. Microstructure evolution of the composites were observed using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). GNPs distributed uniformly in the as-cast specimen and then transformed into fibers in the rolling direction after deformation and finally a lamellar structure formed in the composites. Raman spectra showed that the structural damage of GNPs mainly came from ball milling. The interface between GNPs and Al was well combined in general while a few microcracks were observed, which reduced the ductility of the composites and no adverse aluminum carbide (Al{sub 4}C{sub 3}) was detected at the interface. Stacking faults were observed interior of the aluminum grain, which may due to the existence of plentiful interface introduced by GNPs. Fracture observation revealed that the load transferred from Al matrix to GNPs. The ultimate tensile strength of Al-0.2 wt% GNPs composites was about 36.8% higher than that of pure Al with the same casting and rolling process, which should result from the lamellar structure and load transfer, while the conductivity of the composites decreased slightly, indicating that interface scattering between Al and GNPs is very limited. The investigation results show that Al-GNPs composite is potential for high strength and high conductivity application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Microstructure evolution and mechanical properties of magnesium alloys containing long period stacking ordered phase

Magnesium alloys containing rare earth (RE) in conjunction with other alloying elements, such as Zn, have drawn increasing interest due to their high strength, high ductility and high creep-resistance with the existence of long period stacking ordered (LPSO) phase. Although the LPSO phase has been studied over a decade, the question remains how it impacts the mechanical properties of Mg-RE-X alloys, where X represents a metallic element with its atomic radius smaller than Mg. This paper provides a tutorial review of the current status on the role of LPSO phase in manipulating the mechanical properties in Mg-RE-X based alloys, where some outstanding issues are also highlighted and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy

Highlights: • The grain size was continuously reduced with the increasing Sc content. • No evidence for the formation of the Cu-rich and Sc-containing W phase was observed. • Sc addition could promote the precipitation of S′ in the absence of pre-age stretch. • Sc addition would reduce the growth rate of δ′ and δ′-PFZs. • The highest combinations of strength and ductility were obtained in cast Al-Li alloys. - Abstract: In this work, the influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was investigated. It was found that the grain size of As-cast alloy was significantly reduced in steps with the increase of Sc addition, accompanied by the arising and increasing of cubic primary Al{sub 3}(Sc, Zr) phases. No evidence for the presence of the ternary W (Al{sub 8−x}Cu{sub 4+x}Sc) phase was obtained. The volume fraction of nanoscale Al{sub 3}(Sc, Zr) dispersoids was improved with the increase of Sc content, and the presence of Sc was observed to refine the S′ (Al{sub 2}CuMg) morphology during ageing. The addition of Sc lowered the growth rates of δ′ (Al{sub 3}Li) particles and δ′-Precipitate-free zones (δ′-PFZs) of the base alloy. The tensile property results showed that, with the increasing Sc content and ageing times, the yield strength (YS) and ultimate tensile strength (UTS) were continuously increased, and the highest elongation of 6.0% was obtained in the 0.2Sc-containing alloy aged for 32 h at 175 °C. The results indicated that the optimal Sc addition in cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was 0.2 wt%.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of in-process cryocooling on metallurgical and mechanical properties of friction stir processed Al7075 alloy

Highlights: • For in-process cryocooling (IPC) during FSP, an efficient cooling fixture was designed & fabricated. • FSP of Al7075 alloy with IPC setup suppressed precipitate coarsening as well as grain growth. • Nanosize η′ precipitates (20–30 nm) in IPC condition increased work hardening capacity & strength. • Simultaneous improvement in ductility & strength occurred for sample FSPed with IPC. - Abstract: Friction stir processing (FSP) of heat treatable aluminum alloys is reported to deteriorate strength and hardness properties in spite of huge grain size refinement. The improvement in strength due to the grain size refinement after FSP could not be able to offset the reduction in strength due to coarsening or dissolution of the strengthening precipitate(s). To overcome this, the present work investigates an effective way of heat rejection from the FSP zone to control the precipitate evolution besides the grain size refinement during FSP of Al7075 alloy. The FSP was carried out with standardized process parameters (i.e. 720 rpm, 65 mm/min traverse speed) under two different cooling environments: (i) at normal air cooling and (ii) by rushing a chilled mixture (−30 °C) of liquid nitrogen and methanol through the bottom of the backing plate. Microstructural evolution was examined through optical, scanning and transmission electron microscopy and electron backscatter diffraction to confirm the grain size and morphology of precipitate(s) formed. The in-process cryocooling during the FSP led to 65 and 72% improvement in the Vickers hardness and tensile strength, respectively, in comparison to the solutionized base metal. The results have been analyzed in terms of precipitate interface characteristics and its strengthening effect, Hall–Petch strengthening due to grain size reduction and tradeoff between them.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Annealing-induced microstructural evolution and mechanical anisotropy improvement of the Mg-Gd-Y-Zr alloy processed by hot ring rolling

Highlights: • Growth of SRX grains in GBR is random, while that of TBR is anisotropic. • The new texture component in annealed MR weakens the anisotropy obviously. • T6 treatment leads to an excellent comprehensive mechanical property. - Abstract: Hot ring rolling (HRR) is widely used to fabricate large-size seamless ring-shape components. However, this process produces a severe mechanical anisotropy, which is not acceptable in practical industrial application and should be avoided. This paper reports the annealing-induced microstructural evolution and mechanical anisotropy improvement of HRRed Mg-8.12Gd-1.82Y-0.35Zr alloy ring. Results show that annealing treatment could improve the microstructural homogeneity of the ring owing to the occurrence of static recrystallization (SRX). SRX grains are preferentially formed at twin boundaries and initial grain boundaries due to high dislocation density, high level of stored energy, and stress concentration. Twin boundaries, to some extent, can suppress the migration of SRX grain boundaries. In addition, occurrence of SRX weakens the texture intensity and basal pole inclination, leading to a decrease in the mechanical anisotropy of the ring. Considering the weakened anisotropy, comparable strength, and improved ductility, annealing + aging (T6), compared with direct aging (T5), is a more suitable heat treatment schedule for the HRRed Mg-8.12Gd-1.82Y-0.35Zr alloy ring.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Friction stir welding of a carbon-doped CoCrFeNiMn high-entropy alloy

Highlights: • Friction stir welding of a CoCrFeNiMn HEA doped with C was successfully obtained. • M{sub 23}C{sub 6} carbides with d≈150 nm form in the HEA due to addition of 0.9 at.% C. • Friction stir welding resulted in a decrease in grain size from 9.2 μm to 4.6 μm. • Smaller grain size and increased fraction of M{sub 23}C{sub 6} increase strength by 84 MPa. - Abstract: Butt-joint seam of a high entropy alloy (HEA) of the CoCrFeNiMn system was successfully obtained by friction stir welding (FSW). The HEA was produced by self-propagating high-temperature synthesis. Along with the principal elements, a small amount (0.9 at.%) of C was added to the alloy. The as-cast alloy was cold rolled and annealed at 900 °C to produce refined microstructure. The structure of the annealed alloy consisted of a recrystallized face-centered cubic matrix with a grain size of 9.2 μm and fine Cr-rich M{sub 23}C{sub 6} carbides. FSW of the HEA resulted in microstructure refinement to d = 4.6 μm in the stir zone. A noticeable rise in strength and some decrease in ductility of the processed alloy in comparison with the initial condition can be associated with the microstructure refinement and some increase in the volume fraction of M{sub 23}C{sub 6} carbides.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Friction stir welding of multi-walled carbon nanotubes reinforced Al matrix composites

Highlights: • Al/MWCNT composites were successfully welded using friction stir welding. • After FSW, the composites possessed an excellent balance of mechanical properties. • High tensile strength and elongation over BM owing to MWCNTs after FSW. • Microstructures were investigated according to MWCNT contents and FSW conditions. - Abstract: In this study, we prepared composites between Al and multi-walled carbon nanotubes (MWCNTs) using the friction stir welding (FSW) method and investigated their microstructural evolution and mechanical properties by controlling the amount of MWCNT (1 and 3 vol%) and the plunging load (400 and 600 kg) used. After the FSW process, MWCNT showed slight coarsening of grain with random shear textures and accumulated dislocations; the differences obtained by varying the plunging load and MWCNT amount were insignificant. The friction-stir welded composite obtained using 3 vol% MWCNT and a plunging load of 600 kg possessed two-times better balance between strength and ductility than the base metal, due to the presence of both MWCNTs and the partially decomposed Al{sub 4}C{sub 3} in the composite.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of pre-cold rolling on the evolution of microstructure, microtexture, and mechanical properties of the mushy state rolled in-situ Al-4.5Cu-5TiB2 composite

Highlights: • Microstructure-Microtexture evolution study of the mushy state rolled composite (MRC) and MRC with pre-cold rolling (PCMRC). • The Microstructure and microtexture were characterized using SEM, EBSD, and TEM. • Exactly opposite trends in micro-hardness variation across the thickness of MRC and PCMRC were discussed. • The PCMRC exhibited the best combination of hardness, strength, and ductility. • A proper microstructure-microtexture-property correlation was established with experimental evidence. The mushy state rolling has been found as a promising technique for near-net forming of the cast Al-4.5 wt% Cu-5 wt% TiB{sub 2} in-situ composite to obtain microstructural refinement and moderate mechanical properties. Cold rolling with 30% reduction in thickness was carried out before mushy state rolling, for achieving a relatively more homogeneous distribution of CuAl{sub 2}-TiB{sub 2} particles as well as an appropriate microstructure to enhance the mechanical properties. A comparative investigation on the microstructural and microtextural evolution, along with mechanical properties of both the mushy state rolled composite (MRC) and pre-cold rolled mushy-state rolled composite (PCMRC) was performed, and the microstructure-property correlation was established. The PCMRC exhibited the lowest homogenized lengthscale parameter (L{sub H} 29 μm) indicating the maximum uniformity of particle distribution, computed with the help of multi-scalar analysis of area fractions (MSAAF) technique. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) studies revealed the presence of fine sub-grains within centrally located deformed Al grains due to dynamic recovery, as well as the particle stimulated nucleation of equiaxed fine Al grains by dynamic recrystallization or rapid solidification of liquid near edges for both the investigated composites. The PCMRC displayed a superior combination of hardness (96.82 ± 4.5 HV{sub 5kgf}), 40% higher ultimate tensile strength (301.4 ± 1.8 MPa), and 68% more uniform elongation (30.8% ± 0.5%), compared to the MRC. The improvement in mechanical properties is attributed to the uniform particle distribution and presence of both higher density of low angle boundaries and recrystallized grains adjacent to the particles, obtained from prior cold rolling.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microstructure and mechanical properties of an ultrafine Ti–Si–Nb alloy

In this study, Nb-modified ultrafine Ti–Si eutectic alloy was made by cold crucible levitation melting, tested in compression at room temperature, and characterized by electron microscopy. Compression tests of (Ti 86.5 Si 13.5 ) 97 Nb 3 specimens measured an ultimate compressive strength of 1180 MPa and a compressive plastic strain of 12%, both of which are higher than in eutectic Ti 86.5 Si 13.5 alloy. Electron microscopy showed that the Ti–Si–Nb alloy had a bimodal microstructure with micrometer-scale primary α-Ti dendrites distributed in an ultrafine eutectic (α-Ti + Ti 5 Si 3 ) matrix. The enhanced ductility is attributed to the morphology of the phase constituents and to the larger lattice mismatches between α-Ti and Ti 5 Si 3 phases caused by the Nb addition. The crystallographic orientation relationship of Ti 5 Si 3 with α-Ti is ($1\bar{1}00$)[$\overline{11}$26]Ti 5 Si 3 ∥($01\bar{1}1$)[5$\overline{143}$] α–Τi.

36 MATERIALS SCIENCE↗
DOE OSTI2011

On deformation twinning in a 17.5%Mn-TWIP steel: A physically-based phenomenological model

TWinning Induced Plasticity (TWIP) steel is a typical representative of the 2nd generation of advanced high strength steel (AHSS) which exhibits a combination of high strength and excellent ductility due to the twinning mechanisms. This paper discusses the principal features of deformation twinning in faced-centered cubic austenitic steels and shows how a physiscally-based macroscopic model can be derived from microscopic considerations. In fact, a dislocation-based phenomenological model, with internal state variables such as dislocation density and micro-twins volume fraction representing the microstructure evolution during deformation process, is proposed to describe the deformation behavior of TWIP steels. The contribution of this work is the incorporation of a physically-based twin’s nucleation and volume fraction evolution model in a conventional dislocation-based approach. Microstructural level investigations, using scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques, for the TWIP steel Fe–17.5 wt.% Mn–1.4 wt.% Al- 0.56 wt.% C, are used to validate and verify modeling assumptions. The model could be regarded as a semi-phenomenological approach with sufficient links between microstructure and overall properties and therefore offers good predictive capabilities. Its simplicity also allows a modular implementation in finite element-based metal forming simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Microstructure Optimization of Austenitic Alloy 800H (Fe-21Cr-32Ni)

The microstructural evolution, specifically of grain boundaries, precipitates, and dislocations in thermomechanically processed (TMP) Alloy 800H samples was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The TMP not only significantly increased the fraction of low-{Sigma} coincidence site lattice boundaries, but also introduced nanoscale precipitates in the matrix and altered the distribution of dislocations. Statistical analysis indicates that the morphology and distribution of grain boundary precipitates were dependent on grain boundary types. The microstructure optimization played a synergistic effect on the significantly increased strength with comparable ductility and enhanced intergranular corrosion resistance and creep-fatigue life compared to the as-received samples.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Brittle nature and the related effects of zirconium hydrides in Zircaloy-4

The use of zirconium alloys such as Zircaloy-4 in nuclear reactors is limited by brittle hydride formation, for example in harsh reactor operating conditions such as those in the pressurized water reactors. Even though much research has studied this phenomenon, a more systematic, in-depth study of the effects of hydrides on the properties of Zircaloy-4, using various analytical techniques, can add more details to the understanding of these effects. In the current study, hydrogen charging was performed on Zircaloy-4 at different levels compatible with commercial reactor operating conditions and conditions in accident scenarios. Effects of hydriding on the Zircaloy-4 (α-(hcp)-Zr) tensile properties, together with an in-depth study of any relationship between tensile and the microstructural properties of the material, are discussed. While a moderate pinning effect on the equiaxed α-Zr grain size was observed, no significant change in bulk texture of the Zry-4 was revealed as the hydrogen level increased up to nominally 1230 wppmH. At a nominal value of 490 wppmH, Zircaloy-4 fractured at a low strain value just above the yielding point, and brittle tensile fracture was observed in a sample H-charged to nominally 1230 wppmH. The low ductility and brittle fracture of the samples were attributed to the presence of brittle inter-grain boundary hydrides. Finally, it was observed that brittle fracturing was also supported by intra-grain boundary hydrides that were affected by the tensile deformation of the sample.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Irradiation effects in tungsten—From surface effects to bulk mechanical properties

Advanced materials such as tungsten fibre-reinforced composites allow to overcome severe weaknesses of the baseline materials for plasma-facing components — copper and tungsten. The effect of the fusion environment on the mechanical properties of these materials, e.g. the embrittlement by neutron irradiation, plays a key role for the development of future fusion reactors. To simulate this effect, high-energy ions are used as a substitute for the displacement damage by neutrons. We propose the use of very fine tungsten wire as a possibility of studying the influence of irradiation damage on the mechanical properties. This is possible as they allow full-depth irradiation of almost the entire volume despite the limited penetration depth of ions. Geometrical size effects are mitigated due to the nanoscale microstructure of the wire. In addition, similar wire is used in tungsten fibre-reinforced composites. Thus, the investigation of irradiated wire can directly be used for the prediction of the bulk composite properties. For the proof of this concept tungsten wire with a diameter of 16 μm was electrochemically thinned to 5 μm and irradiated with 20.5 MeV W 6+ ions. The mechanical properties were subsequently determined by macroscopic tensile testing. Irradiation to 0.3, 1 and 9 dpa did not lead to a change of the mechanical behaviour. Both strength and ductility, the latter indicated by the reduction of area, were similar to the as-fabricated state.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Scuffing initiation in metals sliding against copper under non-lubricated conditions

Metallic components in sliding contact are sometimes subjected to high-loads with little or no lubrication. Such starved conditions can lead to a phenomenon called scuffing. Various definitions exist for this term, but in the present case, three criteria were used to signal its onset: changes in friction, vibrations, and noise, coupled with surface examination. On this basis, scuffing initiation was determined for seven technically pure metals (Al, Mo, Nb, Ta, Ti, W, Cu) and stainless steel, all rubbing against Cu. A flat-ended pin-on-disk test configuration was used with normal loads of 1-3 N, and with step-wise increases in sliding speed from 0.16 to 2.56 m/s. Al was only weakly resistant to scuffing, presumably due to its solubility in Cu, its high ductility and its relatively low elastic modulus. Niobium provided satisfactory sliding behavior at low speeds and loads, presumably due to protective oxides; however, it scuffed at higher loads when the oxide broke through. Stainless steel, Mo, and Ta had higher friction coefficients than Al and Nb, presumably because the relatively high strengths of the former prevented severe wear even when their oxide films failed. Like Al, Ti scuffs on Cu, probably because of its high relative solubility; however, Ti's higher elastic modulus resists the more severe forms of surface damage than does Al. Of all the materials slid against Cu, W displayed the least scuffing, even under maximum speed and load. Tungsten's negligible solubility in Cu may have reduced its adhesion, and W's high elastic modulus resisted shear-deformation, even at high frictional heating. Self-mated Cu couple scuffed when the speed was increased. The oxides on the Cu surface serve as solid lubricant avoiding scuffing at lower speeds.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effects of helium implantation on the tensile properties and microstructure of Ni₇₃P₂₇ metallic glass nanostructures

We report fabrication and nanomechanical tension experiments on as-fabricated and helium-implanted ~130 nm diameter Ni₇₃P₂₇ metallic glass nano-cylinders. The nano-cylinders were fabricated by a templated electroplating process and implanted with He⁺ at energies of 50, 100, 150, and 200 keV to create a uniform helium concentration of ~3 at. % throughout the nano-cylinders. Transmission electron microscopy (TEM) imaging and through-focus analysis reveal that the specimens contained ~2 nm helium bubbles distributed uniformly throughout the nano-cylinder volume. In-situ tensile experiments indicate that helium-implanted specimens exhibit enhanced ductility as evidenced by a 2-fold increase in plastic strain over as-fabricated specimens, with no sacrifice in yield and ultimate tensile strengths. This improvement in mechanical properties suggests that metallic glasses may actually exhibit a favorable response to high levels of helium implantation.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Finite Element Modeling of a Non-Isothermal Superplastic-Like Forming Process

Conventional superplastic forming (SPF) has been modified to increase the productivity and reduce some of the drawbacks, such as high forming temperature and high percentage thinning, to suit the automotive industries. One of the modifications was to combine between the conventional SPF and the use of a mechanical preformed blank to form the non-superplastic grade aluminum alloy (AA5083-O). The requirement of high temperature usually results in microstructural defects during forming process. In this paper, finite element modeling was adopted to investigate the superplastic-like forming process using the non-isothermal heating system. In the simulation, two phases (mechanical pre-forming and gas blow for ming) of the process were conducted under different temperatures, where the material was mechanically drawn into the die cavity at 200 deg. C in the first phase, and it formed with gas pressure applied at a global temperature increasing from 400 deg. C to 500 deg. C. Because of the non-isothermal heating of material, it was found that it had enough ductility to flow more easily in the specific zones (die corners and radius). Additionally, FEM results showed that a better formed part can be obtained by the increasing temperature forming, compared to the stable temperature phase.

36 MATERIALS SCIENCE↗