Newtonian Thermal Analysis Research Articles

Calculation of phase transformation latent heat based on cooling curves in end-quench test and its application in nickel-based superalloy

To obtain the phase transformation latent heat corresponding to different cooling rates with low test workload and cost, the Newton thermal analysis method and the improved Newtonian thermal analysis method were discussed based on the cooling curve obtained in the end-quench test. The validity of two methods was given by the latent heat calculation of 45# steel. The results show that the relative error of latent heat is 5.20% through the improved Newtonian thermal analysis method, which is more accurate than the Newtonian thermal analysis method. Furthermore, the latent heat release of phase transformation of the self-designed CSU-A1 powder metallurgy nickel-based superalloy increases from 4.3 to 12.29 J/g when the cooling rate decreases from 50.15 to 33.40 °C/min, because there is more sufficient time for the alloy microstructure to complete the phase transformation process when the cooling rate is smaller.

Variation of solid fraction with cold flow properties of biodiesel produced from waste frying oil

Biodiesel sample utilized in the study was produced from waste frying oil by a base catalyzed one step transesterification reaction. The feedstock oil and the samples produced were tested in accordance with the standards designated by European Committee for Standardization and also by American Society for Testing and Materials. Cold Flow Properties (CFP), namely Cloud Point (CP), Cold Filter Plugging Point (CFPP) and Pour Point (PP) were determined. Since the three CFP should occur at specific solid fractions during freezing, the objective was to examine in details the whole solidification history to estimate the corresponding solid fractions at these temperatures. The so-called computer-aided cooling curve analysis employed in metal casting industry was modified and applied to the current biodiesel sample. Indications of CP, CFPP and PP were noted as slope changes on the cooling curve and also on its first derivative curve. The Newtonian thermal analysis was utilized to estimate the solid fractions in the solid-liquid mixture at CP, CFPP and PP during solidification. The fraction of the solidified biodiesel in the mixture jumped from 0.18 to 0.39 when the CFPP temperature was reached. The visual observations were in agreement with the calculations.

Investigation on the solidification course of Al–Si alloys by using a numerical Newtonian thermal analysis method

A numerical Newtonian thermal analysis (NTA) method was carried out for online monitoring the solidification course of commercial Al–Si alloys. The solidification paths of different molten Al–Si alloys were characterized by the fraction solid curves. The variation of heat capacity of Al and Si were concerned in the determination of baseline evaluation of latent heat. In this experiment, the pure Al, Al–1Si, Al–5Si, Al–9Si, Al–13Si and Al–18Si alloys were molten at 800 °C and cooled at room temperature, respectively. The cooling curves of these alloys were measured by using K-type thermocouples. The liquidus temperatures of these alloys decreased with the increase of Si %. An obvious stage occurred at about 580 °C, which was closely related to Al–Si eutectic reaction. Different phase fractions of these alloys were supported by the microstructure observation.

Thermal analysis of in-situ Al2O3/SiO2(p)/Al composites fabricated by stir casting process

The in-situ fabricated Al2O3/SiO2(p)/Al composites were produced by adding different quantities of SiO2 particles (viz. 0, 3, 6 and 9wt.%) into molten commercial purity Al at 750°C. Newtonian thermal analysis was conducted to investigate the solidification behaviors of these molten composites prepared by the stir casting process. The microstructure and phase identification were achieved via optical microscope, SEM (equipped with EDS) and X-ray diffraction. Results showed the dendrite arm spacing of α-Al grain decreased with the increase of SiO2 addition. The SEM image showed the special duplex phase with Al2O3 layer formed around SiO2 particle in Al matrix. The Si concentration in Al matrix increased with increasing in the SiO2 addition, resulting in the decrease of liquidus temperature of the melts. Compared with the purity Al melt, one more stage related to the exothermic Al-Si phase transformation was revealed in the cooling curves of these molten composites. Cooling rate of the purity Al melt was lower than that of the melts with SiO2 particles addition. The difference in solidification behaviors of these melts was ascribed to the effect of SiO2/Al reaction on the effective heat capacity and different amounts of latent heat released from phase transformation process.

Analytically Solved Solid Fraction Model for the Newtonian Thermal Analysis of Casting

This study reports on the development of an alternative model which overcomes the drawbacks of the Newtonian thermal analysis of casting summarized from the literature. The alternative Analytically Solved Solid Fraction Model (AS-SFM) aims to improve the reliability of the measurement of latent heat and solid fraction. The latent heat of pure tin is computed by AS-SFM and the other models in the literature, and the results are compared with the literal value of the latent heat. The new method is shown to be a more reliable latent heat predictor than the other methods given in the literature.

Methodology of Comparative Validation of Selected Foundry Simulation Codes

Abstract The validation of each simulation code used in foundry domain requires individual approach due to its specificity. This validation can by elaborated on the basis of experimental results or in particular cases by comparison the simulation results from different codes. The article concerns the influence of grey cast iron density curve and different forms of solid fraction curve Fs=f(T) on the formation of shrinkage discontinuities. Solid fraction curves applying Newtonian Thermal Analysis (NTA) were estimated. The experimental and numerical simulation tests were performed on the castings, which were made with Derivative Thermal Analysis (DerTA) standard cups. The numerical tests were realized using NovaFlow&Solid (NF&S), ProCast and Vulcan codes. In this work, the coupled influence of both curves on the dynamics of the shrinkage-expansion phenomena and on shrinkage defects prognosis in grey cast iron castings has been revealed. The final evaluation of the simulation systems usefulness should be based on validation experiment, preceded by comparing the simulation results of available systems which are proposed in given technology.

A new baseline for the Newtonian thermal analysis of casting: two-capacitive system baseline

Computer-aided cooling curve thermal analysis for the casting process is usually applied to predict the latent heat of transformation and the solid fraction. In this study, one of the important limitations of the Newtonian thermal analysis for the prediction of the latent heat was determined as the disregard of the thermal capacity of mold. Therefore, a new baseline technique, two-capacitive system baseline (TCSBL), was developed by taking the thermal capacity of the mold into account. This new method was modeled by considering the analogy between RC circuits and the metal–mold thermal capacitance system. It was improved by a Taylor series expansion approach to express the cooling rates in terms of the metal and mold temperatures. Ten experiments with four types of pure metals were undertaken to compare the latent heat results of TCSBL with the Newtonian and Dynamic Baselines (NBL and DBL). The mean percentage error for the latent heat prediction of TCSBL, NBL, and DBL were calculated as 4.3, 29, and 24 %, respectively, in comparison with the literal value of the latent heats.

Effects of liquid structure transition on solidification by the Newton thermal analysis method

This paper is to explore the effects of the liquid structure transition (LST) on the solidification kinetics of Sn-30 wt% Sb alloy by the Newton thermal analysis (NTA) method and the solidified microstructure analysis. Influence of the cooling rate on solidification behavior and microstruc- ture was also concerned. With a self-designed sand mold, the cooling curves of five points were collected automatically in the process of solidification by a HYDRA. In the case of the liquid structure transition and a faster cooling rate, the mod- ification melt treatment will lead to a higher undercooling of nucleation and an increased solidification latent heat in cen- tral part of solidifying castings, then the eventual grain size was evidently refined.

Change in solidification behavior of Bi–Sb10 alloy after liquid structural transition

Prior investigation suggested that a new cluster forms at hundreds of degrees above the liquidus in Bi–Sb10 alloy and this new cluster is irreversible after subsequent cooling. The aim of this work was to explore the effect of the unknown cluster on the solidification kinetics of Bi–Sb10 alloy by using the Newton thermal analysis (NTA) method, complemented with information provided by microstructural characterization. The hypothesis about the formation of plentiful clusters with similar structure, owing to liquid structural transition (LST), was proposed to rationalize the great change of solidification process and microstructure.

Quantification of the microconstituents formed during solidification by the Newton thermal analysis method

This work was intended to explore the reliability of the Newtonian thermal analysis method as a tool for the quantification of the amount of alloy microconstituents formed during solidification as observed at room temperature in alloy systems without phase transformations in the solid state. This technique was applied to three hyper eutectic Pb–Sn alloys with different primary phase content using different approaches to determine the time of start of solidification and for the zero curve calculation. Quantitative metallography was used to determine the primary phase content in the experimental probes. The outcome of this work shows that the use of Newton method for prediction of the amount of microconstituents formed during solidification obtain good results in two of the three cases under study suggesting that this method is not reliable.

Newton Thermal Analysis of Gray and Nodular Eutectic Cast Iron

The purpose of this work is to analyze the capability of Newton Thermal Analysis (NTA) to detect differences of the solidification kinetics between eutectic gray and ductile irons obtained from the same base alloy. The NTA experimental output has been analyzed with a simple micromacro modeling approach. The outcome of this work suggests that NTA has a good potential as a qualitative tool to characterize the solidification kinetics of alloys.

Use of Newton Thermal Analysis for the Prediction of the Amount of Microconstituents Formed during Solidification

This work explores the feasibility of using the Newton Thermal Analysis method (NTA) as an alternative technique for quantitative determination of the relative volume fractions of the microconstituents formed during solidification of three hypereutectic Pb-Sn alloys. The results suggest that NTA has a good potential as a quantitative microstructure analysis tool. However, it is required to further improve the method in order to match the microstructure predictions with the experimental measurements obtained by quantitative metallography.

Macro-Micro Modeling and Simulation of Solidification Kinetics of Pb-Sn Alloys

The purpose of this work is to explore the effect of the presence of two different primary phases on the microstructure and solidification kinetics of Pb-Sn alloys. The experimental results have been compared with predictions obtained from the Newton Thermal Analysis of cooling curves generated by a conventional heat transfer-solidification kinetics model. Three Pb-Sn alloys have been considered in this work in order to explore the solidification characteristics of the eutectic in hypoeutectic, hypereutectic and eutectic compositions. Experimental results indicate that the Pb-Sn eutectic morphology and the solidification rate depend on the nature of the pre-existent primary phase during eutectic solidification. From the observed discrepancies between experimental and simulated results it is concluded that further improvements are needed to simulate the solidification kinetics of eutectic microconstituents in the presence of pre-existing primary phases.

On the problems of thermal analysis of solidification

Thermal analysis is a widely used method for metallurgical process control and investigation of cast alloy solidification. Thermal analysis involving thermocouples immersed in the molten metal is convenient to quickly obtain information on the solidification behaviour. The paper intends to elucidate the difficulties of thermal analysis induced by using one or several thermocouples, the shape of the analysed thermal field and the boundary conditions of the experimental set-up. Classical thermal analysis methods such the Newtonian thermal analysis and the Fourier thermal analysis differ because of the number of used thermocouples. The paper discusses the migration of the hot spot of a thermal field during solidification as well the migration of the thermocouples in complex shaped castings due to thermally induced stresses. Simulation and thermal analysis are made on both idealized 1-D cylindrical test geometry and common industrially used 3-D thermal analysis cup to compare different interpretation methods.

Quantification of the SiC p content in molten Al–Si/SiC p composites by computer aided thermal analysis

The aim of this work is to explore the feasibility of the computer aided thermal analysis as a tool for SiC p content quantification in molten Al–Si/SiC p composites. This technique was applied to three cases of interest: (1) the metal matrix alloy A356, without SiC p particle reinforcement, (2) A356/8% SiC p MMC and (3) A356/18% SiC p MMC. Tests were performed in order to identify, within the commonly used thermal analysis parameters, the parameters that could be used for SiC p content quantification. In this regard, the parameters: eutectic temperature, T EG, and local solidification time, t S, show clear trends and low dispersion in their changes as functions of SiC p content. It is found that an increase in SiC p content produces a statistically significant increase of T EG and a decrease of t S. The behavior of t S may be explained as a result of the decrease of the latent heat released during solidification as the SiC p content is increased, such as was indicated by the latent heat data obtained from Newton thermal analysis (NTA) applied to the experimental cooling curves. A simplified analysis of the experimental results indicates that, for the experimental conditions used in this work, the best resolution that could be expected from this method is ±1.3 vol.% of SiC p content, if the local solidification time is the parameter used to quantify the particle content.