Thermophysical properties of steels under microgravity conditions

Thermophysical properties of liquid metals play a significant role in casting and solidification processes. Particularly, viscosity of metal melts exhibits a crucial effect on continuous casting of metals. The scope of this study is to measure the viscosity of metals in the liquid state under terrestrial and microgravity conditions. The investigation of viscosity is an important necessity for the prediction of liquid metal flow in casting and solidification and hence for the efficient control of metallurgical processes conditions. The comparison between the terrestrial and microgravity viscosity data leads to significant conclusions on how containerless measurements generate reliable viscosity data, eliminating the effect of crucible contamination. Therefore, the aim of this study is to investigate the effect of containerless conditions on viscosity and generate reliable and accurate data for modelling casting and solidification processes from microgravity measurements. In this study, Al-Si and Fe-Si alloys were used for viscosity measurements, the first systems under terrestrial conditions using a rotational rheometer, and the second under terrestrial conditions and micro-gravity. The Al-Si system measurements generate high viscosity values between 0.4 Pas and 1.3 Pas depending on Si addition, in agreement with literature using the same method. Fe-Si alloys exhibit viscosities between 5.64 mPas to 74.8 mPas with microgravity viscosity values at the melting point from 7.67 to 11.77 mPas. The discrepancies in viscosity values measured under terrestrial conditions are caused due to container contamination and non-vacuumed conditions. The microstructure analysis of the samples before and after the viscosity measurements were conducted using Confocal Laser Scanning Microscopy (CLSM), Automated Scanning Electron Microscopy (SEM) and SEM with Energy Dispersive Spectroscopy (EDS). The results show an increase of inclusions density after viscosity measurement of ten-fold. The SEM with EDS elemental maps illustrates alumina particles and aluminium nitrides. CLSM analysis shows an increase in alumina particles agglomeration with time. For verification of the viscosity measurements and microscopy analysis results, COMSOL modelling software is used to study the effect of inclusion particles and shear rate on viscosity, along with Roscoe and Einstein models