Quench Temperature Research Articles

Reversed austenite for enhancing ductility of martensitic stainless steel

The novel heat treatment concept, “quenching and partitioning” (Q&P) has been developed for high strength steels with enhanced formability. This heat treatment involves quenching of austenite to a temperature between martensite start and finish, to receive a several amount of retained austenite. During the subsequent annealing treatment, the so called partitioning, the retained austenite is stabilized due to carbon diffusion, which results in enhanced formability and strength regarding strain induced austenite to martensite transformation. In this study a Q&P heat treatment was applied to a Fe-0.45C-0.65Mn-0.34Si-13.95Cr stainless martensite. Thereby the initial quench end temperature and the partitioning time were varied to characterize their influence on microstructural evolution. The microstructural changes were analysed by dilatometer measurements, X-ray diffraction and scanning electron microscopy, including electron back-scatter diffraction. Compression testing was made to examine the mechanical behaviour. It was found that an increasing partitioning time up to 30 min leads to an enhanced formability without loss in strength due to a higher amount of stabilized retained and reversed austenite as well as precipitation hardening.

Minimum film-boiling quench temperature increase by CuO porous-microstructure coating

Increase in the minimum film-boiling quench temperature, TMFB, is achieved with microstructured CuO particles, and attributed to local cooling (fin effect) by the microstructure causing liquid–solid contact. A periodic structure is obtained using electrochemical deposition of 1 μm diameter particles on brass sphere diameter 15 mm forming unit-cell porous cones of average height L = 100 μm and base diameter D = 20 μm. Fin analysis predicts the cone tip cooling to the homogeneous nucleation temperature of water (∼330 °C), while the base temperature is at 600 °C. This causes liquid–solid contact during quenching, and analysis suggests the fin effective thermal conductivity ⟨k⟩ and fin characteristic length L2/D are key to this liquid–solid contact that influences TMFB.

Heat transfer during quenching of high temperature surface by the falling cryogenic liquid film

Contact between a liquid and an extremely superheated solid surface is restored during quenching. The cryogenic experiment and numerical simulation were performed to study the peculiarities of heat transfer during quenching of hot vertical copper plate being much higher than the Leidenfrost temperature by the falling film of liquid nitrogen. An anomalous behavior of heat transfer has been found in the vicinity of the quench front. The results revealed that the maximum heat flux into the liquid during quenching is significantly higher than the average in the quasi-stationary conditions. The dynamic pattern of quench front propagation has been obtained in the numerical experiment. It was found that the quench front initialization occurs after lowering the surface temperature to the thermodynamic limit of superheat for liquid nitrogen. The correlation to determine the time of quench front stagnation is proposed. The numerical model allows us to quantify the quench front velocity and temperature fields in the heater, which are variable in space and time. The reliability of the simulation results has been confirmed by direct comparison with the experimental data on the quench front geometry and velocity as well as on the surface temperature change over time.

Chemical Vapor Deposition Growth of Few-Layer MoTe2 in the 2H, 1T', and 1T Phases: Tunable Properties of MoTe2 Films.

Chemical vapor deposition allows the preparation of few-layer films of MoTe2 in three distinct structural phases depending on the growth quench temperature: 2H, 1T', and 1T. We present experimental and computed Raman spectra for each of the phases and utilize transport measurements to explore the properties of the 1T MoTe2 phase. Density functional theory modeling predicts a (semi-)metallic character. Our experimental 1T films affirm the former, show facile μA-scale source-drain currents, and increase in conductivity with temperature, different from the 1T' phase. Variation of the growth method allows the formation of hybrid films of mixed phases that exhibit susceptibility to gating and significantly increased conductivity.

Kinetics of polymer collapse: effect of temperature on cluster growth and aging.

Using state of the art Monte Carlo simulations of a bead-spring model we investigate both the equilibrium and the nonequilibrium behavior of the homopolymer collapse. The equilibrium properties obtained via multicanonical sampling recover the well-known finite-size scaling behavior of collapse for our model polymer. For the nonequilibrium dynamics we study the collapse by quenching the homopolymer from an expanded coiled state into the globular phase. The sequence of events observed during the collapse is independent of the quench depth. In particular, we focus on finding out universal scaling behaviors related to the growth or coarsening of clusters of monomers, by drawing phenomenological analogies with ordering kinetics. We distinguish the cluster coarsening stage from the initial stage of primary cluster formation. By successful application of a nonequilibrium finite-size scaling analysis we show that at all quench temperatures, during the coarsening stage, the cluster growth is roughly linear and can be characterised by a universal finite-size scaling function. In addition, we provide evidence of aging by constructing a suitable autocorrelation function and its corresponding dynamical power-law scaling with respect to the growing cluster sizes. The predicted theoretical bound for the exponent governing such scaling is strictly obeyed by the numerical data irrespective of the quench temperature. The results and methods presented here in general should find application in similar phenomena such as the collapse of a protein molecule preceding its folding.

Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist

The origin of intermediate-depth seismicity has been debated for decades. A substantial fraction of these events occurs within the upper plane of Wadati–Benioff double seismic zones believed to represent subducting oceanic crust. We deformed natural lawsonite-rich blueschist samples under eclogite-facies conditions (1.5<P<3.5 GPa; 583 K<T<1121 K), using a D-DIA apparatus installed at a synchrotron beamline continuously monitoring stress, strain, phase changes, and acoustic emissions (AEs). Two distinct paths were investigated: i) heating during deformation at pressures >2.5 GPa to maximum temperatures ranging from 762 to 1073 K, during which lawsonite and glaucophane became gradually unstable while entering the stability field of lawsonite–eclogite and the breakdown reaction of lawsonite was only crossed in case of the highest final temperature; ii) heating while deforming at a pressure <2 GPa to a maximum temperature of 1121 K associated with crossing the breakdown reaction of lawsonite and successively entering the stability fields of epidote–blueschist and eclogite–amphibolite but not of lawsonite–eclogite. Upon entering the Lws-Ecl stability field samples exhibited brittle failure, accompanied by the radiation of AEs. In-situ X-ray diffraction and microstructural analysis demonstrate that fractures are topologically related to the formation of omphacite. Amorphous material was detected along the fractures by transmission-electron microscopy without evidence for free-water. Since the newly formed omphacite crystals are small compared to the initial grains, we interpret the observed mechanical instability as a transformation-induced runaway under stress triggered during the transition from lawsonite–blueschist to lawsonite–eclogite. In contrast, we find no microstructural evidence that the breakdown of lawsonite, and hence the liberation of water leads to the fracturing in samples that experienced the highest quench temperatures of 1073 and 1121 K, although some AEs were detected during an experiment performed at 1.5 GPa. Our experimental results challenge the concept of “dehydration embrittlement”, which ascribes the genesis of intermediate-depth earthquakes to the breakdown of hydrous phases in the subducting oceanic plate. Instead we suggest that grain-size reduction (transformational faulting) during the transition from lawsonite–blueschist to lawsonite–eclogite leads to brittle failure of the deviatorically loaded samples.

Experimental investigation of quench and re-wetting temperatures of hot horizontal tubes well above the limiting temperature for solid–liquid contact

Quench cooling of a hot dry surface involves the rapid decrease in surface temperature resulting from bringing the hot surface into sudden contact with a coolant at a lower temperature. Quench temperature is the onset of the rapid decrease in surface temperature and corresponds to the onset of destabilization of a vapor film that exists between the hot surface and the coolant. Situations involving quench cooling are encountered in a number of postulated accidents in Canada Deuterium Uranium CANDU reactors, such as the quench of a hot calandria tube in certain Loss of Coolant Accidents LOCA. If the calandria tube temperature is not reduced by initiation of quench heat transfer, then this may lead to subsequent fuel channel failure and for this accident knowledge of quench heat transfer characteristics is of great importance. In this study, a Water Quench Facility WQF has been designed and built at the Thermal Processing Laboratory TPL at McMaster University and a series of experimental tests were carried out to investigate the quench of hot horizontal tubes using a vertical rectangular water multi-jet system. The tubes were heated to a temperature between 380 and 780°C then cooled to the jet temperature. The temperature variation with time in tube circumferential and axial directions was measured. The two-phase flow behavior and the propagation of the re-wetting front around and along the tubes were simultaneously observed using a high-speed camera. The effects of initial surface temperature, water subcooling (in the range 15–80°C) and jet velocity (in the range 0.15–1.60m/s) on the quench process were investigated. The quench and the re-wetting temperature (the temperature at which the liquid establishes wet contact with the solid) were found to greatly depend on water subcooling. One of the main findings in this study is the existence of a critical water subcooling range within which any small change in water subcooling has a considerable effect on both the quench and the re-wetting temperatures. Empirical correlations have been developed and provided good fit of the experimental data and agreed well with correlations developed by other researchers for curved surfaces. The quench temperature was found to decrease by increasing surface curvature and solid thermal conductivity. However, the re-wetting temperature is a weak function of both variables. Effect of spatial location on the surface of the tube was also studied. The stagnation point showed higher quench and re-wetting temperatures compared to other locations on the tube surface.

Preparation of polypropylene microspheres for selective laser sintering via thermal‐induced phase separation: Roles of liquid–liquid phase separation and crystallization

ABSTRACTAlthough selective laser sintering (SLS) has been widely applied in many fields, more research work is needed to develop proper polymer microspheres for SLS. Thermal‐induced phase separation (TIPS) is a facile way but rarely reported to prepare the polymer microspheres. The roles of liquid–liquid phase separation (LLPS) and crystallization in the TIPS process are not clear. In this study, proper polypropylene (PP) microspheres for SLS are successfully prepared via TIPS with xylene. The diameters and morphologies of these PP microspheres can be regulated easily by changing the PP concentration and the quench temperature. The large undercooling drives the solution into the metastable LLPS region and produces PP microspheres with smooth surfaces. The PP crystallization occurs both on the LLPS interface and inside the polymer‐rich phase when the solution is quenched to a temperature near the binodal line, and the tiny bent lamellae are formed on the microsphere surface. At higher temperature only PP crystallization occurs, which results in the formation of PP particles consisting of packed lamellae. The PP microspheres prepared here are suitable for SLS and promote the development of SLS potentially. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 320–329

Fabrication of rigid poly(lactic acid) foams via thermally induced phase separation

Rigid poly(lactic acid) (PLA) foams were prepared by thermally induced phase separation followed by solvent exchange and vacuum drying. A novel tetrahydrofuran (THF)/water solvent system was used for the induction of liquid-liquid phase separation of PLA solution at three different temperatures; 24 °C, 4 °C and −20 °C. PLA gels obtained were mechanically stabilized by replacing THF/water solvent mixture with ethanol nonsolvent. Characterization of rigid PLA foams was obtained by scanning electron microscopy, mercury intrusion porosimetry, x-ray diffractometry, infrared spectroscopy and differential scanning calorimetry analyses. Effects of fabrication parameters on the morphology and pore structure were systematically examined. The parameters investigated included; (i) polymer concentration, (ii) THF/water ratio and (iii) quench temperature. Results showed that degree of porosity and the morphology of the pores, such as the pore size and shape could be controlled by tuning the fabrication parameters. By controlling the degree of phase separation of PLA solution, foams with dual micro and nano structures were obtained.

Effects of bath temperature on the morphology and performance of EVOH membranes prepared by the cold‐solvent induced phase separation (CIPS) method

ABSTRACTThe development and characteristics of porous EVOH membranes by cold‐solvent induced phase separation (CIPS) process were investigated. Binary dopes of 1,3‐propandiol/EVOH prepared at 80 °C were immersed in 1,3‐propandiol at a lower temperature to engender polymer precipitation. The quench temperature affects phase separation modes, and hence structure and performance of resulting CIPS membranes. When the bath temperature was set below the crystallization line and above the binodal (e.g. 45 °C), the formed membrane was dominated by a packing of semicrystalline EVOH globules. When the bath was set at a temperature just below the spinodal (e.g. 20 °C), spinodal decomposition (SD) dominated the precipitation process to give a lacy‐like bicontinuous structure; yet there is also a clear imprint from polymer crystallization. When the bath temperature was set deeply within the spinodal dome (e.g. 5 °C), polymer crystallization affected only little the SD‐derived bicontinuous morphology. Water permeation flux, wettability, tensile strength, and ultra‐filtration experiments of the membranes were conducted. The results indicated that those properties were closely correlated with the porosity level, pore size, and membrane morphology. Moreover, X‐ray diffraction and DSC analyses indicated that the formed membranes had a crystallinity of 38 to 42%, consistent with the literature data. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2016,133, 44553.

Energy dissipation at the silica glass/compressed aerogel interface: The fate of Wild 2 mineral grains and fragments smaller than ~100 nm

Allocation FC6,0,10,0,26 from Stardust track 10 shows a slightly wavy silica glass/compressed silica aerogel interface exposing a patchwork of compressed silica aerogel domains and domains of silica glass with embedded Wild 2 materials in ultra-thin TEM sections. This interface is where molten silica encountered compressed silica aerogel at temperatures <100 °C, and probably near room temperature, causing steep thermal gradients. An Mg, Fe-olivine grain, and a plagioclase-leucite intergrowth survived without melting in silica glass. A Mg-, Al-, Ca-, K-bearing silica globule moved independently as a single object. Two clusters of pure iron, low-Ni iron, and low-Ni, low-sulfur Fe-Ni-S grains also survived intact and came to rest right at the interface between silica glass/compressed silica aerogel. There are numerous Fe-Ni-S nanograins scattered throughout MgO-rich magnesiosilica glass, but compositionally similar Fe-Ni-S are also found in the compressed silica aerogel, where they are not supposed to be. This work could not establish how deep they had penetrated the aerogel. Iron nanograins in this allocation form core-ring grains with a gap between the iron core and a surrounding ring of thermally modified aerogel. This structure was caused when rapid, thermal expansion of the core heated the surrounding compressed aerogel that upon rapid cooling remained fixed in place while the iron core shrank back to its original size. The well-known volume expansion of pure iron allowed reconstruction of the quench temperature for individual core-ring grains. These temperatures showed the small scale of thermal energy loss at the silica glass/compressed silica aerogel interface. The data support fragmentation of olivine, plagioclase, and iron and Fe ± low-Ni grains from comet 81P/Wild 2 during hypervelocity capture.

Quenching effects for piezoelectric properties on lead-free (Bi1/2Na1/2)TiO3 ceramics

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5)TiO3 (BNT), were fabricated by a quenching procedure after sintering, and then their electrical properties were investigated with the aim to increase their depolarization temperature Td. From the measurement of the temperature dependence of dielectric properties, Td increased with increasing quench temperature. The Td of a BNT sample quenched from 1100 °C was 223 °C, which was almost 50 °C higher than that prepared by the ordinary cooling process. From the measurement of P–E hysteresis loops, both the remanent polarization Pr and the coercive field Ec of BNT samples prepared by ordinary firing were almost the same as those quenched from 1100 °C. Additionally, from the measurements by a resonance–antiresonance method, the electromechanical coupling factor k33 of ordinarily fired BNT was 0.45, and that of the quenched BNT was 0.46. From these results, it is clarified that the quenching procedure is an effective way to increase the Td of BNT ceramics without deteriorating ferroelectric and piezoelectric properties.

Optimization of heat-treatment parameters in hardening of titanium alloy Ti-6Al-4V by using the Taguchi method

Titanium alloys are widely applied in aircraft, nuclear, and military parts because of their high strength-to-density ratio, high toughness, and high corrosion resistance. However, achieving excellent mechanical properties of these alloys relies on appropriate heat-treatment processes. In this research, the prevalent alloy Ti-6Al-4V was used to investigate the optimization process parameters of heat treatment by using the Taguchi method. Hardness after aging and tensile strength (TS) were chosen as quality characteristics. Eight controllable factors were selected, comprising fan, solution temperature, duration time of solution treatment, protective gas, quench delay time, cooling rate, temperature, and duration time of aging treatment. The experiment was performed using orthogonal arrays of L18(21 × 37). The best combination condition of process parameters was obtained after a Taguchi quality analysis. The quality reproducibility was verified to be excellent through confirmation experiments. The results showed that the hardness after aging was higher than HRC 43 ± 0.5, the TS of rod material higher than 169 ksi, and the TS of plate material higher than 157 ksi while using the best heat-treatment condition. The quality characteristics all met the AMS 4965 specifications of quality requirements for alloy Ti-6Al-4V.

Kinetic modeling of near-interface defect segregation during thermal annealing of oxygen-conducting solid electrolytes

Solid electrolytes are widely employed in devices for energy storage and conversion. Extended defects (grain boundaries, surfaces and dislocations) can generate substantial resistance to ionic transport due to defect segregation. When synthesized through solid state reaction or sintered from powders, solid electrolytes go through thermal annealing processes at high temperatures. It is during these annealing phases that cation transport becomes fast enough to affect the distribution of cation defects near the interface. We developed a kinetic model of the annealing process as it affects the near-interface defect behavior based on the Poisson-Cahn model for predicting defect segregation behavior in concentrated solid solutions. Taking the fluorite-structured solid solution CeO2-Gd2O3 as a model system, results reveal that dopant profiles approach equilibrium on a timescale of seconds at 1300°C and 20%, 1% and 0.1% dopant cation concentration. At lower temperatures, the dopant profile developed much more slowly. The quench temperature is predicted to be around 900°C, where it requires >15h for the dopant profile to reach equilibrium.

Aging and related scaling during the collapse of a polymer

We present results showing aging during the collapse of a polymer chain quenched from an expanded state to the globular phase via Monte Carlo dynamics of a model homopolymer. The constructed two-time correlation function, an analogue of the density- density autocorrelation, shows a power-law scaling with respect to the size of monomer clusters formed during the collapse. The numerical estimates obtained at different quench temperatures are in agreement with a theoretically predicted bound for the decay exponent governing the scaling behavior.

Understanding the viscosity of supercooled liquids and the glass transition through molecular simulations

We discuss a potential energy landscape (PEL) approach to calculate the characteristically sluggish viscous behaviour of supercooled liquids. This phenomenon is central to the theoretical understanding of the liquid-to-glass transition, a long-standing challenge in non-equilibrium statistical mechanics of amorphous states of matter. Experimentally, the shear viscosity of supercooled glass-forming liquids shows strong variations with the quench temperature. In particular, two types of behaviour are observed, Arrhenius and highly super-Arrhenius. Conceptually, the molecular description of the structural and dynamical processes underpinning the viscosity behaviour has become a topic of interest because of general implications for the kinetics of slow relaxation in the glassy state. We regard the supercooled liquid as an assembly of interacting particles undergoing thermal fluctuations such that the system evolves in space and time by crossing a series of potential energy barriers. To find these barriers and their corresponding atomic configurations, we apply an energy landscape sampling algorithm that maps out the evolution trajectories in the form of alternating sequences of local energy minima and saddle points. The energy sequences and the atomic coordinates constitute a body of atomic-scale data which we then process using two distinct methods. One is based on an effective activation barrier extracted from the transition-state pathway data, and the other is based on the linear response theory of statistical mechanics. The former is heuristic by being more physically transparent, while the latter is theoretically more rigorous. Through these two complementary calculations, an understanding of the temperature variations of shear viscosities of supercooled liquids, as well as the nature of fragile and strong behaviour of the glass transition, emerges. Our calculation provides a molecular-level account of the viscosities of supercooled liquids in a unified and consistent manner without invoking ad hoc assumptions. Relative to the nature of the glass transition, the usefulness of the PEL perspective is demonstrated, along with the concept of crossover between strong and fragile behaviour. In terms of advancing atomistic simulation capability, we believe the time-scale limitations of traditional molecular dynamics may be significantly extended through the use of metadynamics algorithms for sampling transition-state pathways.

Modified Methodology for the Quench Temperature Selection in Quenching and Partitioning (Q&amp;P) Processing of Steels

The original method to select the optimum quench temperature for quenching and partitioning (Q&P) processing aims to determine the quench temperature which yields a maximum volume fraction of retained austenite. In the present study, the original method was reviewed and refined by comparison with experimental results. The proposed methodology is based on the use of a modified Koistinen–Marburger equation for the kinetics of the athermal martensite transformation of steels containing C, Mn, Si, Cr, and B.

Thermal-Hydraulic Analysis of the Low- &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$T_{c}$&lt;/tex-math&gt; &lt;/inline-formula&gt; Superconductor (LTS) Winding Pack Design Concepts for the DEMO Toroidal Field (TF) Coil

Three design concepts, namely, WP#1, WP#2, and WP#3, for the low- $T_{c}$ superconductor DEMO toroidal field coil was proposed in 2014. This paper is focused on the thermal-hydraulic analysis of all the designs using simplified models, which includes: 1) hydraulic analysis—calculation of the mass flow rates in each conductor at operating conditions during the dwell time; 2) heat removal analysis—calculation of the steady-state mass flow rates and temperature profiles in each conductor as functions of the nuclear heat deposition rate; and 3) estimation of the maximum quench temperature and pressure in each conductor assuming the extreme scenario for the maximum pressure. The detailed analysis of the WP#1 design in burn and in quench conditions using the THEA code was also carried out. It took into account the expected electromagnetic and heat load maps along each conductor and different quench initiation scenarios leading to the maximum hot spot temperature or to the maximum pressure. Our analysis shows that the temperature margin in the WP#1 and WP#3 conductors is sufficiently large, but it is too small in some WP#2 conductors. The hot spot temperatures in some WP#1 cables calculated with THEA are too high. These results provide information for further improvements of the conductors' design.

A comparative analysis of reticular crack on ceramic plate driven by thermal shock

Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been studied and investigated. Experimental tests were carried out to characterize the reticular crack that has been found in the Ge Kiln, which is a famous art of the ancient Chinese culture. After comparative analysis between thermal-shock cracks and the glaze crack patterns of the Ge Kiln porcelain, it is found that this study is expected to provide a powerful tool for recurrence of the long-lost firing and cooling process of the Ge Kiln porcelain.

Microstructure-mechanical properties relationships for quenching and partitioning (Q&P) processed steel

The quenching and partitioning (Q&P) processing of advanced high strength steels has been shown to result in a distinct improvement of their strength and ductility. The selection of the quench temperature during Q&P processing makes it possible to obtain a wide range of mechanical properties for the final martensite-austenite microstructures. In the present study, a physically-based model describing the relationship between the microstructure and the mechanical properties of Q&P processed steels is developed. The model is applied to the mechanical properties of a Q&P processed medium Mn steel.