Papers by Keyword: Cooling Rate

Abstract: The dendritic microstructure formed during solidification plays a critical role in determining the mechanical properties of aluminum castings. In particular, secondary dendrite arm spacing (SDAS) is strongly influenced by the cooling rate and is closely related to yield strength, ultimate tensile strength, and elongation. However, experimental validation of these relationships requires a consistent methodology for defining cooling rate and linking it to microstructural and mechanical measurements. In this study, an experimental framework was established to investigate the relationships among cooling rate, SDAS, and mechanical properties in aluminum castings. Casting blocks with different thicknesses were fabricated to obtain a wide range of cooling rates. Cooling curves were measured during solidification, and cooling rates were determined using the second derivatives of the cooling curves. SDAS measurements and tensile tests were conducted on specimens extracted from symmetric positions within the casting blocks to ensure equivalent thermal histories. The results showed that the cooling rate–SDAS relationship exhibited a linear trend on a logarithmic scale, consistent with previously reported correlations. Smaller SDAS values were associated with increased yield strength, ultimate tensile strength, and elongation. The agreement between the present results and literature data confirms the validity of the proposed experimental framework for correlating solidification conditions, microstructure, and mechanical properties of aluminum castings.

Abstract: To prepare bulk single-crystal REBCO superconductors by the new single-direction growth method (SDMG: Single-Direction Melt-Growth), it is necessary to produce a large-area seed of high quality, for example, based on EuBCO. Since the samples prepared by the SDMG method copy the structure of the seed, for the production of large-area seeds it is necessary to optimize the time-temperature regime in order to grow seeds with a suitable structure and composition and minimize structural defects (limiting the amount of subgrains and others). A higher growth rate was used in comparison with the standard growth rates used to produce EuBCO seeds of larger dimensions. The increased growth rate in the crystal growth window reduces the outflow of the melt from the sample, and thus it is possible to achieve a single-crystal sample in the entire volume of the precursor. The samples were produced at different growth rates: 1; 2; 3 and 5 °C/h. The microstructure of the samples was studied by polarized light microscopy and scanning electron microscopy. The size and distribution of Eu211 particles in the sample volume and the subgrain structure were studied on the fabricated samples.

Abstract: The impact of cooling rates on the microstructural evolution of an Al-Sr eutectic alloy was investigated. Two distinct cooling rates, 0.02 and 57.12 °C/s, were employed during the solidification process. To elucidate the characteristics of phase transformations and microstructural evolution during solidification, thermal analyses were conducted on the recorded cooling curves. Both the first and second derivatives of these curves were examined. At the slower cooling rate, the microstructure predominantly consisted of the eutectic Al phase and the eutectic Al-Sr phase, as identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Conversely, at the higher cooling rate of 57.12 °C/s, primary Al phases were observed, indicating a significant departure from equilibrium solidification conditions. Additionally, a substantial quantity of nanosized eutectic Al-Sr particles was detected, resulting in a markedly refined microstructure.

Abstract: The effects of cooling rates on the microstructure development of an Al-Fe eutectic alloy were studied. Two different cooling rates of 0.03 and 61.00 °C/s were applied to the solidifying alloys. To unfold the characteristics of phase changes and the microstructure evolution taking place during solidification, the recorded cooling curves based on temperature measurements were analyzed by thermal analyses, in which the first and second differences of the cooling curves were derived. The slow cooling resulted in the formation of only the eutectic Al phase and the eutectic Al-Fe phase in the microstructure identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). With the cooling rate increasing to 61.00 °C/s, the primary Al phase appeared, as the solidification became strongly non-equilibrium. A large quantity of the nanosized eutectic Al-Fe particles were detected. Overall, the microstructure refined substantially.

Abstract: Owing to their several attractive features such as high hardness, high elastic modulus, light weight, high strength to weight ratio, high thermal conductivity, and high temperature strength, composites from Al-Mg₂Si family offers promise towards deployment in several industries such as automobile, aerospace, marine, defence and electronic. The present molecular dynamics (employing LAMMPS) based simulation study is one of the first attempt to investigate the nucleation and grain growth mechanisms of Mg₂Si phase at atomic level in case of novel Al-15Mg₂Si-4.5Si composite, during semi-solid processing. Modified embedded atom method (MEAM) potential has been used to study the atomic interactions in the composite. Reaching the melt state at 1000 K, the temperature of the system is first decreased from 1000 K to 853 K and then the system is held at 853 K for 100 ps. The simulations are performed with three different cooling rates. With lowering of temperature, randomly distributed Mg and Si atoms form atomic clusters at arbitrary locations within the system, which is the nucleation stage for Mg₂Si phase formation. Cluster size, radial distribution function has been used to investigate the structural evolution of Mg-Si clusters. Cooling rate significantly influences the grain size as well as the grain growth kinetics. The information about the thermodynamic state of the system has been revealed by extracting the values of internal energy, enthalpy, specific heat. during the slurry preparation and isothermal holding stages. The growth mechanism of Mg₂Si nucleus has been characterized from the temporal variation of (Mg + Si) atoms taking part in the cluster formation. Power-law variation is observed in the cooling stage whereas a linear variation is observed in the isothermal stage.

Abstract: The temperature of a strip cast using a vertical type high-speed twin-roll caster was measured by inserting a k-type thermocouple into the strip. The effects of the roll speed and roll load on the cooling rate and temperature at the roll gap were investigated using two aluminum alloys: A383 and Al–4.8%Mg. The thickness of the thermocouple was 0.1 mm, and the sampling time was 0.01 s. The cooling rate increased and the temperature at the roll bite decreased with decreasing roll speed and increasing roll load. The positions of the liquidus and solidus lines were measured, and the reduction of the thickness of the strip was inferred from the roll gap at the solidus line.

Abstract: The influence of the cooling rate during sintering of lithium-titanium-zinc-manganese spinel ferrite on its structural, magnetic and electric characteristics was studied. The ferrite was sintered in air at 1283 K for 120 min. Cooling rates were 0.06 K/s and 7.8 K/s. It was established that the observed changes in the characteristics when using slow and quenching cooling are due to the different levels of the near-surface ferrite layers oxidation. For quench ferrite, the Curie temperature of 530 K, the activation energy of electrical conductivity of 0.35 eV in the bulk of the samples, and the magnetic anisotropy constant of 2.6·10^-3 J/m³ (at 300 K) were obtained. Slowly cooled ferrite was characterized by higher values of Curie temperature (560 K), the magnetic anisotropy constant (2.9·10^-3 J/m³), and the activation energy of electrical conductivity (0.80 eV).

Abstract: In continuous casting, the cooling rate, casting speed, and molten metal temperature significantly affect the quality of cast steel billets. Appropriate casting parameters can minimize quality problems such as surface, subsurface and interior crack, rhomboidity, oscillation mark depth, and central porosity. This research determines the relationship between defects and three significant factors temperature, cooling rate, and casting speed. The work has been performed on the two-strand continuous casting machine to investigate the billet (BS-4449 steel grade) cross-section of 150 x 150 cm². The defects analysis through macro examination at different tundish temperatures (1510 °C to 1560 °C), varying cooling rates, and casting speeds (0.9 to 1.6 m/min). The present study provides detailed insight into the three parameters mentioned earlier, which directly affect the quality of cast steel billets.

Abstract: The results of the study of the cooling rate effect on the structure and properties of castings for parts of equipment made of complex alloyed manganese cast iron, which operate under conditions of abrasive and impact-abrasive wear, are presented. The properties and characteristics of microstructures of samples from the investigated cast iron composition for different cooling rates are given: relative and impact-abrasive wear resistance, hardness, volume fraction of the carbide phase, and the average size of carbides. It is shown that the cooling rate (as well as the chemical composition of cast iron) is a determining factor in the primary microstructure formation that affects the properties of castings.

Abstract: Through the Gleeble3500 thermal simulation test machine, the phase transformation law of Nb microalloyed steel was studied and tested. After the compression deformation, it was cooled to room temperature at different speeds. Obtain the dynamic continuous cooling transformation diagram and the scanning structure diagram of the test steel, and then analyze the phase composition under different cooling speeds through JMatPro material performance simulation. The results show that: at a lower cooling speed (0.1°C/s), austenite decomposition is a diffusion-type phase change that takes place in a high-temperature region, and carbon atoms can diffuse sufficiently. At a moderate cooling rate (1°C/s), the bainite phase transition is a semi-diffusion phase transition in which carbon atoms are displaced in a non-cooperative thermally activated transition mode. When the cooling rate is high (15°C/s), the martensitic transformation is a non-diffusion-type transformation carried out in the low temperature region, and the atoms are directly transferred from the austenite lattice to the martensite lattice. With the increase of the cooling rate and the decrease of the transition temperature, from low-speed cooling→medium-speed cooling→high-speed cooling, respectively, the diffusion type phase transition→semi-diffusion type phase transition→the non-diffusion type phase transition. At different cooling rates, the continuous cooling transition diagram simulated by JMatPro is basically the same as the phase transition in the dynamic continuous cooling transition diagram of the test steel, which proves that the simulation prediction of the dynamic continuous cooling transition of the test steel by the JMatPro software has high accuracy and applicability.