Influence Of Thermal History Research Articles

In-situ preheating: Novel insights into thermal history and microstructure of directed energy deposition-arc of hot-work tool steels

Directed Energy Deposition-Arc (DED-Arc/M) represents a promising approach to the production of complex and medium-sized parts, eliminating the need for specific tooling and the minimization of resource use. However, the inherent thermal conditions of DED-Arc/M, characterized by high cooling rates and successive reheating cycles, result in microstructures distinctly different from those observed in traditional cast materials. Nevertheless, the influence of thermal history on DED-Arc/M processed hot-work tool steels remains an insufficiently addressed topic in previous studies. Therefore, this work systematically investigates the effects of heat input and accumulation through assessing the thermal history and resulting microstructural changes during DED-Arc/M processing of the hot-work tool steel AISI H13 (X40CrMoV5-1). Accordingly, layer-wise heat input results in heat accumulation, leading to high interpass temperatures, significantly impacting the solidification and, thus, the microsegregation as well as the overall chemical homogeneity. By employing an innovative statistical approach that incorporates quantitative EDS data, the distribution of chemical elements was investigated. Furthermore, a novel computational procedure through the utilization of empirical and thermodynamic calculations was used to identify microstructural effects on the thermodynamic stability of retained austenite. This research offers vital insights into the microstructural dynamics of tool steels processed through DED-Arc/M, underlining the pivotal role of precise thermal management in tailoring material microstructures and, consequently, influencing the properties for unlocking the full potential of additive manufacturing for industrial applications.

Influence of thermal history and consolidation force on wedge peel strength of CF/PEEK laminates manufactured by laser‐radiated in‐situ consolidation

AbstractProcessing parameters during the laser‐radiated in‐situ manufacturing process change the thermal history of the thermoplastic composite, which affects porosity and fiber‐resin interfacial bonding quality, and hence the wedge peel strength of the laminate. The effect of different laser powers and consolidation forces on the wedge peel strength of the specimens was investigated. Due to the fiber‐rich area on the tape surface during the laser heating phase as well as the insufficient consolidation force and consolidation length during the consolidation phase, the wedge peel strength decreased due to increased porosity and weak fiber‐resin bonding at the interlayer bonding interface. A conformable consolidation roller of lower hardness was used to improve the wedge peel strength of the laminates, which reduced the initial temperature of the cooling phase, thus inhibiting the void rebound and increasing the bonding strength at the fiber‐resin interface. The cross‐section and peeling surface were characterized by optical microscope and scanning electron microscope. The wedge peel strength of the laminates, with reduced voids and increased interfacial bonding strength between the fibers and the resin, is improved.Highlights Mechanism of void formation and evolution in different phases of laser‐radiated in‐situ consolidated laminate. Effect of consolidation roller hardness and deformation on wedge peel strength.

Engineering grain boundary energy with thermal profiles to control grain growth in SrTiO3

AbstractThis study investigates the influence of thermal history on grain boundary (GB) energy and the grain growth behavior of SrTiO3 at 1425°C. Two thermal profiles were explored: (1) a single‐step sintering at 1425°C for 1 h and (2) a two‐step profile with sintering completed at 1425°C for 1 h with an additional 10 h at 1350°C. Electron backscattered diffraction and atomic force microscopy were utilized to measure the grain size and GB energy distributions, respectively, for the samples before and after grain growth at 1425°C for 10 h. The two‐step profile exhibits fewer abnormal grains and a slower growth rate at 1425°C than the single‐step profile. Additionally, the two‐step sample comprises few high‐energy GBs and a narrow GB energy distribution, which suggests that it had a lower driving force for subsequent grain growth. The thermal profile was able to sufficiently change the growth rate such that the two‐step sample results in a finer grain size than observed for the single‐step sample after 10 h at 1425°C despite being exposed to elevated temperatures for almost twice as long. These results suggest that GB energy engineering through thermal profile modification can be used to control the grain growth rate and abnormal grain growth likelihood.

Revealing time-dependent behavior of asphalt binder at low-temperature by crystallization kinetics

To gain deeper insights into the influence of thermal history on wax crystallization and thermoreversible aging for enhanced asphalt pavement durability, this study employed the extended bending beam rheometer (ExBBR) test and modulated differential scanning calorimetry (MDSC) analysis. These techniques were utilized to analyze the crystallization kinetics of diverse asphalt binders under both isothermal and non-isothermal conditions. The ExBBR test results demonstrated that the cold-temperature performance of asphalt binders experiences continuous degradation with an increasing grade loss during conditioning. The Avrami isothermal crystallization kinetic theory proved to be an accurate descriptor of the thermoreversible aging tendency in asphalt binders. MDSC test findings revealed that distinct cooling rates exert an influence solely on specific asphalt varieties, with discrepancies in thermal signals arising from diverse oil sources. The Ozawa exponent, determined through the endothermic background area selected from the baseline, serves as a reliable guide for assessing the degree of thermoreversible aging in different asphalt binders. Crucially, the appearance of crystallizable fractions in asphalt binders with varying thermal histories can be effectively modeled using both isothermal Avrami and non-isothermal Ozawa theoretical frameworks. To conclude, the study undertook the separation of four components of asphalt, analyzing the microstructural evolution of these components under identical test conditions. The contribution of each component to the asphalt crystallization process is comprehensively expounded through considerations of glass transition temperatures, as well as endothermic and exothermic peaks associated with distinct components.

Particle size dependence of the microsegregation and microstructure in the atomized Ni-based superalloy powders: Theoretical and experimental study

The microstructure and microsegregation of atomized powder, which depend on their sizes, are of great importance to the mechanical properties of the consolidated bulk materials. Therefore, it is necessary to reveal the relationship between particle size and powder attributes. The effects of particle size on the solidification characterization of the atomized Ni-based superalloy powders were studied via finite element simulation. Based on the simulations, a model was developed to predict the microsegregation and microstructure of atomized powders with different sizes and study the influence of thermal history on the powder attributes during the atomization processes. The radiation heat transfer and temperature gradient within the rapid solidification alloy powders were taken into account in this model. For validating the accuracy of the model, the predictions of the present model were compared with the microsegregation and microstructure of the specific size powder close to the screen mesh size. The results showed that microstructure depended primarily on the temperature gradient within the powder, while the solidification rate had a more significant effect on the microsegregation. The model predicted microstructure features in agreement with the experiment, and for microsegregation, the deviations of prediction for most elements were less than 10%. This work provides a new model to precisely predict the microsegregation and microstructure of the atomized alloy powders and sets a foundation to control the powder features for various engineering applications.

Influence of thermal history on the crystallization behavior of high-Bs Fe-based amorphous alloys

Influence of thermal history on the crystallization behavior of high-Bs Fe-based amorphous alloys

Temperature‐mediated transgenerational plasticity influences movement behaviour in the green algae Chlamydomonas reinhardtii

Abstract A prerequisite for the survival and reproduction of organisms is to successfully navigate thermal environmental conditions that unfold over time and space. While effective movement behaviour has been highlighted as a key mechanism by which organisms and populations may persist amidst the backdrop of directional environmental warming, it remains unclear how behavioural plasticity may mediate such effects, particularly across time‐scales that span multiple generations. Here, we examine the capacity for transgenerational plasticity to alter the movement behaviour of the motile green algae Chlamydomonas reinhardtii in response to changes in thermal conditions. We first acclimated C. reinhardtii populations to thermal environments near (25°C), below (12.5°C) or above (37.5°C) the temperature range that maximizes population growth rate. Subsequently, we assayed the micro‐spatial scale movement behaviour of these populations in thermally homogeneous environments across a period of 2 weeks in each respective environment, with the goal of evaluating the influence of thermal history on movement behaviour in a novel thermal environment. Our results indicate that thermal history can mediate the movement patterns of C. reinhardtii individuals for up to 10 generations and that the trajectory by which phenotypes converge on their acclimated values can be highly nonlinear. Subsequently, we demonstrated—using a dispersal assay in spatially variable environments—that thermal acclimation history can additionally alter movement patterns at ecologically relevant scales. Collectively these findings indicate the possibility for transgenerational plasticity to modify behaviour across extended time‐scales and converge on acclimated states via nonlinear trajectories. Understanding the efficacy of behaviour for navigating novel thermal environments, such as environments anticipated amidst environmental warming, may thus require considering past as well as present environmental conditions. Read the free Plain Language Summary for this article on the Journal blog.

Evolution of microstructure and mechanical property of Ti-47Al-2Cr-2Nb intermetallic alloy by laser direct energy deposition: From a single-track, thin-wall to bulk

The complex thermal history during the laser direct energy deposition (L-DED) can result in the inhomogeneous microstructure of the Ti-47Al-2Cr-2Nb (TiAl) alloy. This work investigates the grain structure and metastable microstructure evolution of L-DED TiAl samples with different deposit shapes of single-track, thin-wall, and bulk. Numerical simulations were performed for all samples to reveal the influence of thermal history on microstructural evolution. Among the three samples, the single-track sample has unique dendritic and cellular structures due to the highest cooling rate. Meanwhile, incompletely precipitated lamellar γ was found at the boundary and inside the α2 grains. And residual B2 phase is also present in the single-track sample. As for the thin-wall and bulk samples, they exhibit fully lamellar structure, and contain only γ and α2 phases at room temperature. During the L-DED process, the temperature gradient and cooling rate inside both samples decreased with the elevation of the deposition height. However, due to the different thermal histories, the temperature gradient and cooling rate do not change in the same way. This leads to a large difference in grain structure and metastable microstructure between the thin-wall and bulk samples. Also, these changes affect the mechanical properties of TiAl alloys. In summary, this study can provide potential guidance for a tailored microstructure in L-DED TiAl alloy.

Accurate Three-Dimensional Thermal Dosimetry and Assessment of Physiologic Response Are Essential for Optimizing Thermoradiotherapy.

Simple SummaryMany clinical trials have shown benefit for adding hyperthermia (heat) treatment to radiotherapy. Despite overall success, some patients do not derive maximum benefit from this combination treatment. Tumor hypoxia (low oxygen concentration) is a major cause for radiotherapy treatment resistance. In this paper, we examine the question of whether hyperthermia reduces hypoxia and, if so, whether reduction in hypoxia is associated with treatment outcome. The review is focused mainly on several clinical trials conducted in humans and companion dogs with cancer treated with hyperthermia and radiotherapy. Detailed measurements of temperature, hypoxia and perfusion were made and compared with treatment outcome. These analyses show that reoxygenation after hyperthermia occurs in patients and is related to treatment outcome. Further, reoxygenation is most likely caused by variable intra-tumoral temperatures that improve perfusion and reduce oxygen consumption rate. Directions for future research on this important issue are indicated.Numerous randomized trials have revealed that hyperthermia (HT) + radiotherapy or chemotherapy improves local tumor control, progression free and overall survival vs. radiotherapy or chemotherapy alone. Despite these successes, however, some individuals fail combination therapy; not every patient will obtain maximal benefit from HT. There are many potential reasons for failure. In this paper, we focus on how HT influences tumor hypoxia, since hypoxia negatively influences radiotherapy and chemotherapy response as well as immune surveillance. Pre-clinically, it is well established that reoxygenation of tumors in response to HT is related to the time and temperature of exposure. In most pre-clinical studies, reoxygenation occurs only during or shortly after a HT treatment. If this were the case clinically, then it would be challenging to take advantage of HT induced reoxygenation. An important question, therefore, is whether HT induced reoxygenation occurs in the clinic that is of radiobiological significance. In this review, we will discuss the influence of thermal history on reoxygenation in both human and canine cancers treated with thermoradiotherapy. Results of several clinical series show that reoxygenation is observed and persists for 24–48 h after HT. Further, reoxygenation is associated with treatment outcome in thermoradiotherapy trials as assessed by: (1) a doubling of pathologic complete response (pCR) in human soft tissue sarcomas, (2) a 14 mmHg increase in pO2 of locally advanced breast cancers achieving a clinical response vs. a 9 mmHg decrease in pO2 of locally advanced breast cancers that did not respond and (3) a significant correlation between extent of reoxygenation (as assessed by pO2 probes and hypoxia marker drug immunohistochemistry) and duration of local tumor control in canine soft tissue sarcomas. The persistence of reoxygenation out to 24–48 h post HT is distinctly different from most reported rodent studies. In these clinical series, comparison of thermal data with physiologic response shows that within the same tumor, temperatures at the higher end of the temperature distribution likely kill cells, resulting in reduced oxygen consumption rate, while lower temperatures in the same tumor improve perfusion. However, reoxygenation does not occur in all subjects, leading to significant uncertainty about the thermal–physiologic relationship. This uncertainty stems from limited knowledge about the spatiotemporal characteristics of temperature and physiologic response. We conclude with recommendations for future research with emphasis on retrieving co-registered thermal and physiologic data before and after HT in order to begin to unravel complex thermophysiologic interactions that appear to occur with thermoradiotherapy.

Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting

Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.

Material Characterisation and Computational Thermal Modelling of Electron Beam Powder Bed Fusion Additive Manufacturing of Ti2448 Titanium Alloy.

Ti-24Nb-4Zr-8Sn (Ti2448) is a metastable β-type titanium alloy developed for biomedical applications. In this work, cylindrical samples of Ti2448 alloy have been successfully manufactured by using the electron beam powder bed fusion (PBF-EB) technique. The thermal history and microstructure of manufactured samples are characterised using computational and experimental methods. To analyse the influence of thermal history on the microstructure of materials, the thermal process of PBF-EB has been computationally predicted using the layer-by-layer modelling method. The microstructure of the Ti2448 alloy mainly includes β phase and a small amount of α″ phase. By comparing the experimental results of material microstructure with the computational modelling results of material thermal history, it can be seen that aging time and aging temperature lead to the variation of α″ phase content in manufactured samples. The computational modelling proves to be an effective tool that can help experimentalists to understand the influence of macroscopic processes on material microstructural evolution and hence potentially optimise the process parameters of PBF-EB to eliminate or otherwise modify such microstructural gradients.

Mechanical and optical properties of as-grown and thermally annealed titanium dioxide from titanium tetrachloride and water by atomic layer deposition

The use of thin-films made by atomic layer deposition (ALD) is increasing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require planar surface and tunability of the refractive index and residual stress. In addition, mechanical properties such as elastic modulus and film hardness influence the performance of the layer, especially, when optics is integrated with microelectromechanical systems. In this work, optical properties, density, elemental analysis, residual stress, elastic modulus and hardness of as-grown ALD TiO2 thin films on silicon were studied at temperature range from 80 to 350 °C and influence of post-ALD thermal annealing was studied on films annealed up to 900 °C. ALD TiO2 films were under tensile stress in the scale of hundreds of MPa. The stress depended both on the ALD temperature and film thickness in a complex way, and onset of crystallization increased the residual stress. Films grown at 110 and 300 °C were able to withstand post-ALD annealing at 420 °C without major change in residual stress, refractive index or extinction coefficient. Elastic modulus and hardness increased upon crystallization with increasing ALD temperature. The results presented here help to improve the design of the optical devices by choosing films with desired optical properties, and further help to design the post-ALD thermal budget so that films maintain their desired features.

Regional Control and Optimization of Heat Input during CMT by Wire Arc Additive Manufacturing: Modeling and Microstructure Effects.

Wire arc additive manufacturing (WAAM) of aluminum-magnesium (Al–Mg) ER5356 alloy deposits is accomplished by cold metal transfer (CMT). During the process, the temperature change of the alloy deposits has a great influence on molding quality, and the microstructure and properties of alloy deposits are also affected by the complex thermal history of the additive manufacturing process. Here, we used an inter-layer cooling process and controlled the heat input process to attempt to reduce the influence of thermal history on alloy deposits during the additive process. The results showed that inter-layer cooling can optimize the molding quality of alloy deposits, but with the disadvantages of a long test time and slow deposition rate. A simple and uniform reduction of heat input makes the molding quality worse, but controlling the heat input by regions can optimize the molding quality of the alloy deposits. The thermophysical properties of Al-Mg alloy deposits were measured, and we found that the specific heat capacity and thermal diffusivity of alloy deposits were not obviously affected by the temperature. The microstructure and morphology of the deposited specimens were observed and analyzed by microscope and electron back-scatter diffraction (EBSD). The process of controlled heat input results in a higher deposition rate, less side-wall roughness, minimum average grain size, and less coarse recrystallization. In addition, different thermal histories lead to different texture types in the inter-layer cooling process. Finally, a controlled heat input process yields the highest average microhardness of the deposited specimen, and the fluctuation range is small. We expect that the process of controlling heat input by model height region will be widely used in the WAAM field.

Importance of experienced thermal history: Effect of acclimation temperatures on the high-temperature tolerance and growth performance of juvenile marbled flounder.

Experienced thermal history often affects the temperature tolerance of fish; however, the effect of thermal history on growth performance is unclear. To contribute to effective stocking (release of hatchery-reared juveniles in the field), we conducted four laboratory experiments using juvenile marbled flounder (Pseudopleuronectes yokohamae, around 30mm standard length and 0.3g body wet weight) acclimated at 12°C and 24°C for approximately 2 weeks to investigate the effects of acclimation temperature on high-temperature tolerance, food consumption, and growth performance. The acclimation to 24°C increased tolerance to high temperatures, as shown in a 24-h exposure experiment and in a temperature elevation experiment. The 50% lethal temperature (upper incipient lethal temperature) was estimated to be 25.9°C and 29.0°C for the 12°C and 24°C acclimation groups, respectively. In subsequent experiments, we tested the effects of high and low temperature acclimation on the food consumption and growth performance of two size groups of juveniles (28.7±2.0 and 34.5±2.9mm, mean±SD), that were reared at temperatures ranging from 14°C to 23°C. The optimal temperature for growth was 20°C and did not differ between the acclimation temperatures or between the size groups. However, food consumption and growth performance were suppressed by acute temperature changes. Specifically, feeding and growth were lower in the 24°C-acclimated group than in the 12°C-acclimated group when exposed to 14°C, which is close to the natural water temperature at release in the field. These results suggest that experienced thermal history does not affect the optimal temperature but can affect the growth performance of juveniles. To maximize the post-release growth of hatchery-reared juveniles, the influence of thermal history should be taken into consideration and acute thermal changes before release should be avoided.

The influence of thermal history on the microstructure and mechanical properties of AlSi8Cu2Fe alloy

In this work the influence of cyclic thermal tistory on the microstructure and mechanical properties of AlSi8Cu2Fe alloy was studied. The commercial aluminum alloy was subjected to a special heat treatment dur-ing which the alloy repeatedly changed from a liquid to a semi-solid state. During this process, samples were taken, and the castings were subjected to another study. Gradual changes in the microstructure, chemical com-position of the alloy, hardness and mechanical properties under pressure at normal temperatures have been documented. With the increasing number of cycles, the content of alloying elements, especially magnesium, decreased significantly, the proportion of casting defects increased, especially hydrogen bubbles, microshrinkage and oxide inclusions in the alloy. These changes also led to a decrease in the mechanical properties of the alloy. A series of samples without cyclic heat loading was also prepared for comparison.

Real-time monitoring the order-disorder conformational transition of xanthan gum

The viscoelastic behavior of xanthan gum was carefully investigated in aqueous solutions (between 0.1% and 3% wt.) and in presence of extra-salt (NaCl) by following different thermal procedures. Thus, by a gradual rise of temperature, a sharp increase of the viscoelastic moduli was highlighted between 55 °C and 70 °C, depending on the polymer and salt concentration. This behavior is due to a conformational transition between an ordered state (helix) to a disordered conformation (random coil) which allows xanthan chains to interact each other forming a network structure.In order to investigate the thermal history influence on the macromolecular conformation, homogeneous xanthan solutions of different concentrations were kept at 4 °C and used for rheological measurements at different constant temperatures. The conformational transition observed in oscillatory shear measurements occurs after a characteristic storage time at a given temperature. It was noted that the transition time decreases as the temperature is higher. The results obtained in frequency sweep experiments before and after the conformational changes show a strong influence of the thermal history on the viscoelastic parameters. A fast cooling at 4 °C determines a rearrangement of xanthan chains that tend to adopt again the ordered state which is the stable conformation at low temperatures. This process evolves in time and is influenced by salt content. The reported experimental observations should be considered in all thermal treatments applied to xanthan solutions because the properties are strongly influenced by the ordered or disordered state adopted as a function of temperature and also influenced by salt addition.

Experimental investigations on the influence of temperature for Laser Metal Deposition with lateral Inconel 718 wire feeding

In the present work, the thermal history influence on Inconel 718 thin-wall structures fabricated by wire-based Laser Metal Deposition (LMD-w) was analyzed. To perform the depositions, a novel processing head with wire force and gas nozzle temperature monitoring was employed. Based on the thermal radiation a temperature threshold for a stable process could be defined. General process trends and typical defects as cracks, pores and lack of fusion are also discussed. Additionally, Scanning Electron Microscope (SEM) images and Energy Dispersive Spectroscopy (EDS) were employed to verify the influences of different cooling rates and the deposition strategy on the microstructure. Finally, to verify the resulting mechanical properties, hardness measurements were performed on each sample. It was found that, for thin-wall fabrication by LMD-w, heat accumulation can adversely affect the build-up. Therefore, cooling of interlayers is suggested as a strategy to mitigate such a problem.

Influence of thermal history on the intermediate and low-temperature reversible aging properties of asphalt binders

This paper aims to investigate the influence of thermal history on the intermediate and low-temperature characterisation of asphalt binders. First, various asphalt binder intermediate and low-temperature characterisation methods and the significance of thermal history on asphalt characterisation were reviewed. Second, regular Superpave performance grading (PG) test, extended bending beam rheometer (Ex-BBR) test, double edge-notched tension (DENT) test and torsion bar low-temperature frequency sweep test were performed on selected asphalt samples with different treated thermal history. In addition, black space diagrams were also drawn to show the phase separation properties of varying asphalt binder formulations. The results showed that grade loss of wax-based warm mix asphalt almost kept constant when a small amount of microcrystalline wax (1% by mass of binder) was added. However, grade loss increased obviously with adding more microcrystalline wax (higher than 2%). Prolonged isothermal conditioning had a different degree of influence on the small-strain rheological and large-strain damage properties of asphalt binder. Applying slower loading frequency in dynamic shear rheometer (DSR) caused more obvious decrease in phase angle due to prolonged conditioning time.

Influence of thermal history on swell pressures of compacted bentonite

The deep geological disposal system is an internationally adopted option for the disposal of high-level nuclear waste (HLW). It consists of a highly expansive bentonite, which is used as a buffer material and as a part of an engineered barrier system. Bentonite provides sufficient swelling pressure and low hydraulic conductivity to the barrier system giving long-term stability. The high-temperature waste canister in DGR and the variation in temperature due to thermal gradient impose a thermal loading on the compacted bentonite buffer and may alter the swelling pressures of the compacted bentonite. Hence it is necessary to investigate the influence of thermal loading on the swelling pressure of compacted bentonite. The paper discusses an assessments of swell pressures of two compacted bentonites (Barmer 1 (B1) and Barmer 2 (B2)) from Barmer district of Rajasthan, India with initial dry densities of 1.5 Mg/m3, 1.75 Mg/m3, and 2 Mg/m3 and subjected to 110 °C and 200 °C, hydrated with distilled water. The swelling load is recorded and compared with non-heated samples of same densities. Experimental and theoretical evidences indicated that the swelling pressure of heated compacted bentonite decreased with an increase in the temperature. Statistical analysis is also presented with the help of analysis of variance (ANOVA).

Supercooling and Nucleation of Fatty Acids: Influence of Thermal History on the Behavior of the Liquid Phase.

Saturated fatty acids are an exceptionally important class of liquids, used in many consumer products and suggested as phase change materials (PCMs) for thermal energy storage, in part because they crystallize with minimal supercooling. Here we investigate fatty acid nucleation to understand why crystallization is so facile, as a step toward identifying potential mechanisms for the suppression of supercooling in other PCMs. We find that fatty acid supercooling can be induced only if the liquid is first heated above a material-dependent threshold temperature. NMR spin-lattice relaxation time studies show that the average mobility of the alkyl chains in the fatty acids increases more rapidly with temperature above the supercooling threshold temperature, and NMR T1 hysteresis also sets in at that temperature. Measurements of the real portion of the dielectric constant as a function of temperature show that a liquid fatty acid heated far above its melting point behaves with an apparent temperature upon cooling that is higher than the actual temperature, when compared to its behavior at the same temperature upon heating. Our results suggest that molecular clusters in the liquid fatty acids break apart when the liquids are heated above their threshold temperature and do not immediately re-form on cooling. The breakup of clusters leads to an increase in the mobility of the fatty acid molecules. Because the clusters do not re-form quickly on subsequent cooling, nucleation does not occur, and substantial supercooling results.