Quench Sensitivity and Continuous Cooling Precipitation Diagrams

2019 ◽  
Author(s):  
Olaf Kessler ◽  
Benjamin Milkereit ◽  
Christoph Schick
Keyword(s):  
Phase Transformations ◽  
Solid Phase ◽  
Secondary Phase ◽  
Scanning Calorimetry ◽  
Technical Application ◽  
Continuous Cooling ◽  
Quench Sensitivity ◽  
Heating And Cooling ◽  
Physically Based ◽  
Mass Fractions

The application properties of metallic materials are frequently adjusted by heat treatments utilizing controlled microstructural changes—i.e., solid–solid phase transformations like nondiffusional martensitic transformation or diffusional secondary phase precipitation and/or dissolution. For technical application, knowledge about the characteristic temperatures and times but moreover about their time dependence (kinetics) is required. As the relevant solid–solid phase transformations all show a heat effect (e.g., precipitation → exothermic; dissolution → endothermic), one outstanding measurement technique to follow these phase transformations is calorimetry, particularly differential scanning calorimetry (DSC). Appropriate combinations of DSC methods and devices to cover nine orders of magnitude in heating and cooling rates (10−4–105 K/s) will be introduced, using dissolution and precipitation reactions in aluminum alloys as examples. Basically, these techniques allow one to record time–temperature transformation (or precipitation/dissolution) diagrams for various materials during heating, isothermal annealing, and even during continuous cooling, making DSC a very powerful tool for the investigation of solid–solid phase transformations. Nowadays, physically based models verified with DSC results moreover allow one to predict precipitation volume fractions and solute mass fractions.

NUMERICAL MODELING OF PHASE TRANSFORMATION DURING GRINDING PROCESS

2017 ◽  
Vol 79 (5) ◽  
Author(s):  
Syed Mushtaq Ahmed Shah ◽  
M. A. Khattak ◽  
Muhammad Asad ◽  
Javed Iqbal ◽  
Saeed Badshah ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Thermal Stresses ◽  
Heating Temperature ◽  
Temperature History ◽  
Grinding Process ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Heating And Cooling

The rapid heating and cooling in a grinding process may cause phase transformations. This will introduce thermal strains and plastic strains simultaneously in a workpiece with substantial residual stresses. The properties of the workpiece material will change when phase transformation occurs. The extent of such change depends on the temperature history experienced and the instantaneous thermal stresses developed. To carry out a reliable residual stress analysis, a comprehensive modelling technique and a sophisticated computational procedure that can accommodate the property change with the metallurgical change of material need to be developed. The objective of this work is to propose a simplified model to predict phase evolution during given temperature history for heating and cooling as encountered during grinding process. The numerical implementation of the proposed model is carried out through the developed FORTRAN subroutine called PHASE using the FEM commercial software Abaqus®/standard. Micro-structural constituents are defined as state variables. They are computed and updated inside the subroutine PHASE. The heating temperature is assumed to be uniform while the cooling characteristics in relation to phase transformations are obtained from the continuous cooling transformation (CCT) diagram of the given material (here AISI 52100 steel). Four metallurgical phases are assumed for the simulations: austenite, pearlite, bainite, and martensite. It was shown that at low cooling rates high percentage of pearlite phase is obtained when the material is heated and cooled to ambient temperature. Bainite is formed usually at medium cooling rates. Similarly at high cooling rates maximum content of martensite may be observed. It is also shown that the continuous cooling transformation kinetics may be described by plotting the transformation temperature, directly against the cooling rate as an alternative to the continuous cooling transformation diagram. The simulated results are also compared with experimental results of Wever [20] and Hunkle [21] and are found to be in a very good agreement. The model may be used for further thermo-mechanical analysis coupled with phase transformation during grinding process.

scholarly journals Thermomechanical analysis of nitinol memory alloy behavior

2021 ◽  
Vol 102 (2) ◽  
pp. 161-167
Author(s):  
Nazarii Bykiv ◽  
Volodymyr Iasnii ◽  
Petro Yasniy ◽  
Robert Junga
Keyword(s):  
Strain Rate ◽  
Shape Memory ◽  
Phase Transformations ◽  
Functional Materials ◽  
Thermomechanical Analysis ◽  
Mechanical Tests ◽  
Scanning Calorimetry ◽  
External Temperature ◽  
Austenitic Transformation ◽  
Heating And Cooling

Shape memory alloys are functional materials characterized by the effect of shape memory and superelasticity. Due to these properties, they are widely used, particularly, in bioengineering, aeronautics, robotics and civil engineering. The temperatures of phase transformations and the influence of external temperature and strain rate on the functional and mechanical characteristics of Ni55.75Ti44.15 shape memory alloy are investigated in this paper. The temperature of alloy phase transformations is obtained by differential scanning calorimetry (DSC) in the temperature range from -70°C to 70°C. Diagrams of differential scanning calorimeters at different heating and cooling rates of Ni55.75Ti44.15 alloy is constructed and analyzed. Samples for mechanical tests are made of round rod 8 mm in diameter. The samples working area is 12.5 mm in length and 4 mm in diameter. Mechanical tests are carried out at temperatures close to the maximum value of the completion temperature of martensitic-austenitic transformation Af = 14.7°C. Diagrams of deformation under uniaxial tension are constructed and stresses of phase transformations, Young's modulus and relative elongations of transformation areas at different loading speeds and exterior temperatures are determined. Using Clausius-Clapeyron formula, it is shown that with simultaneous changes in temperature and strain rate, the stresses of phase transformations are largely due to changes in temperature rather than load rates. The coefficients of Clausius-Clapeyron equation for superelastic Ni55.75Ti44.15 alloy with shape memory, which are consistent with those known in the literature, are determined.

Comparative Study of Heat Treatment Effects Performed with Solar Energy and Electric Furnace on EN 1.4848 Stainless Steel Alloyed with Co, W, Cu and Mo

2018 ◽  
Vol 69 (5) ◽  
pp. 1050-1054
Author(s):  
Ioan Milosan ◽  
Gilles Flamant ◽  
Ionelia Voiculescu ◽  
Victor Geanta ◽  
Daniel Munteanu ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Differential Scanning Calorimetry ◽  
Stainless Steel ◽  
Solar Energy ◽  
Comparative Study ◽  
Phase Transformations ◽  
Solid Phase ◽  
Phase Transformation Temperature ◽  
Scanning Calorimetry ◽  
Delta Ferrite

This paper presents a comparative study of the microstructure characteristics resulted from heat treatments performed with solar energy and with electric resistance furnace of EN 1.4848 steel alloyed with Co-W-Cu-Mo. In order to increase the hardness characteristics, mechanical strength and fatigue, this steel was previously alloyed with 6.15 wt% Co, 1.8 wt% W, 0.3 wt% Cu and 0.2 wt% Mo. The alloying with Co and W aimed at increasing the hardness, while Cu was added to improve the tensile strength and Mo to increase the fatigue strength. The thermal treatment of EN 1.4848 austenitic stainless steel alloyed with Co-W-Cu-Mo consisted in solid solution quenching in liquid, after heating the samples at 1050�C, maintaining the plateau temperature for about 10 min and subsequently cooling in water or oil. The purpose of this treatment was to dissolve the compounds possibly formed during the production of steel, if any, and to form supersaturated solid solutions, stable at low temperatures and in corrosive environments. The microstructural aspects, microhardness, and Differential Scanning Calorimetry (DSC) results were highlighted, in order to emphasize the solid phase transformations, on both heat treatment variants. The microstructure consists of high-alloy austenite, supersaturated with carbon, with small proportions of delta ferrite with interdendritic precipitations and various intermetallic compounds, very stable and without showing phase transformations up to negative temperatures (- 75 C). Comparing the solar quenched samples to the electric-quenched one, regarding to the differential scanning calorimetry (DSC) analysis, showed that independently of the applied cooling process (in water or oil) the phase transformation temperature is lower for the solar-quenched samples compared to the electric-quenched ones.

Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

1988 ◽  
Vol 53 (12) ◽  
pp. 3072-3079
Author(s):  
Mojmír Skokánek ◽  
Ivo Sláma
Keyword(s):  
Heat Capacity ◽  
Phase Transformation ◽  
Phase Transformations ◽  
Dimethyl Sulfoxide ◽  
Liquidus Temperature ◽  
Molar Heat Capacity ◽  
Solid Phase ◽  
Zinc Nitrate ◽  
Heat Capacities ◽  
Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

scholarly journals pH-controlled synthesis of sustainable lauric acid/SiO2 phase change material for scalable thermal energy storage

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shafiq Ishak ◽  
Soumen Mandal ◽  
Han-Seung Lee ◽  
Jitendra Kumar Singh
Keyword(s):  
Electron Microscopy ◽  
Phase Change ◽  
Lauric Acid ◽  
Photoelectron Spectroscopy ◽  
Phase Change Materials ◽  
Precursor Solution ◽  
Thermal Reliability ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Heating And Cooling

AbstractLauric acid (LA) has been recommended as economic, eco-friendly, and commercially viable materials to be used as phase change materials (PCMs). Nevertheless, there is lack of optimized parameters to produce microencapsulated PCMs with good performance. In this study, different amounts of LA have been chosen as core materials while tetraethyl orthosilicate (TEOS) as the precursor solution to form silicon dioxide (SiO2) shell. The pH of precursor solution was kept at 2.5 for all composition of microencapsulated LA. The synthesized microencapsulated LA/SiO2 has been characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The SEM and TEM confirm the microencapsulation of LA with SiO2. Thermogravimetric analysis (TGA) revealed better thermal stability of microencapsulated LA/SiO2 compared to pure LA. PCM with 50% LA i.e. LAPC-6 exhibited the highest encapsulation efficiency (96.50%) and encapsulation ratio (96.15%) through Differential scanning calorimetry (DSC) as well as good thermal reliability even after 30th cycle of heating and cooling process.

scholarly journals Li-Nafion Membrane Plasticised with Ethylene Carbonate/Sulfolane: Influence of Mixing Temperature on the Physicochemical Properties

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1150
Author(s):  
Aigul S. Istomina ◽  
Tatyana V. Yaroslavtseva ◽  
Olga G. Reznitskikh ◽  
Ruslan R. Kayumov ◽  
Lyubov V. Shmygleva ◽  
...  
Keyword(s):  
Physicochemical Properties ◽  
Ethylene Carbonate ◽  
Membrane Integrity ◽  
Amorphous Structure ◽  
Nafion Membrane ◽  
Polymer Gel ◽  
Scanning Calorimetry ◽  
Practical Applications ◽  
Heating And Cooling ◽  
Solvent Uptake

The use of dipolar aprotic solvents to swell lithiated Nafion ionomer membranes simultaneously serving as electrolyte and separator is of great interest for lithium battery applications. This work attempts to gain an insight into the physicochemical nature of a Li-Nafion ionomer material whose phase-separated nanostructure has been enhanced with a binary plasticiser comprising non-volatile high-boiling ethylene carbonate (EC) and sulfolane (SL). Gravimetric studies evaluating the influence both of mixing temperature (25 to 80 °C) and plasticiser composition (EC/SL ratio) on the solvent uptake of Li-Nafion revealed a hysteresis between heating and cooling modes. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the saturation of a Nafion membrane with such a plasticiser led to a re-organisation of its amorphous structure, with crystalline regions remaining practically unchanged. Regardless of mixing temperature, the preservation of crystallites upon swelling is critical due to ionomer crosslinking provided by crystalline regions, which ensures membrane integrity even at very high solvent uptake (≈200% at a mixing temperature of 80 °C). The physicochemical properties of a swollen membrane have much in common with those of a chemically crosslinked polymer gel. The conductivity of ≈10−4 S cm−1 demonstrated by Li-Nafion membranes saturated with EC/SL at room temperature is promising for various practical applications.

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