Experimental investigation of crystallization process of nanofluid by DSC

A water-TiO2nanofluid with a weight fraction of 5% and an average particle size of 75 nm is used to investigate the effect of TiO2 nanoparticles on the crystallization and melting behaviors of deionized water by using differential scanning calorimetry（DSC）at four different cooling rates,3,5,7,9 ℃/min.The DSC experimental results show that the water-TiO2 nanofluid has a lower supercooling degree and a faster crystallization rate than the deionized water.With the increase in the cooling rate,the influence of the TiO2 nanoparticles on the supercooling degree of the deionized water becomes greater,but on the crystallization rate it turns lower.During the melting process,compared with the deionized water,the water-TiO2 nanofluid has a lower melting temperature,a less latent heat and a higher melting rate.

Computer Model of Phase Transformation From Hot-Deformed Austenite in Niobium Microalloyed Steels

Based on thermodynamics and kinetics, a new mathematical model was developed to calculate the CCT diagrams and the transformation kinetics in low carbon niobium steels, in which the effect of deformation on the degree of supercooling was taken into account. The undercooling caused by deformation is the major reason for the increase of the starting transition temperature during continuous cooling. The critical cooling rate of bainite formation is within 2--5 ℃s for the studied niobium steels and deformation is suitable for the occurrence of pearlite. The ferrite volume fraction increases with the increase of the austenite boundary area, and decreases with the increase of the cooling rate. The calculated CCT diagrams and the volume fraction of each phase are in good agreement with the measurements.

Investigation on the modification behavior of A356 alloy inoculated with a Sr-Y composite modifier

In the present paper, differential scanning calorimetry （DSC）, scanning electron microscopy （SEM）, and X-ray diffraction （XRD） were used to examine the effects of a Sr-Y composite modifier on the microstructure of A356 alloy. After adding Y to A356, YAl 3 compounds formed, and the size of the α （Al） crystal nucleus increased. The degree of supercooling caused by Sr-Y composite modifier was higher than Sr modification by 2.7 °C, leading to an increased nucleation rate. This increase in supercooling temperature was favorable to the refinement of eutectic structure of the alloy and its eutectic reaction was delayed to the maximum extent. The Si phase in the as-cast Sr-Y composite-modified A356 alloy was either granular or flaky. No large flakes of eutectic Si were found, and the modification effects were completely comparable with those obtained using a lone Sr modifier. After T6 heat treatment, most of the eutectic Si showed a grain-like shape with smaller grains. No eutectic Si with long-strip shapes, significant enhancements in the particle roundness and evenness of the Si crystals, and increased globosity were observed. Both the roundness and evenness of the grained Si crystals were enhanced, and the amount of globular eutectic Si available increased, these findings showed that excellent modification effects were achieved.