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The relationship between the tendencies towards rigidity (measured by shear modulus, G) and hardness (measured by Vickers hardness, HV) of early transition metal (ETM)-based refractory high-entropy alloys (RHEA) and bond parameters (i.e., valence electron concentration (VEC), enthalpy of mixing (ΔHmix)) was investigated. These bond parameters, VEC and ΔHmix, are available from composition and tabulated data, respectively. Based on our own data (9 samples) and those available from the literatures (47 + 27 samples), it seems that for ETM-based RHEAs the G and HV characteristics have a close correlation with the bonding parameters. The room temperature value of G and HV increases with the VEC and with the negative value of ΔHmix. Corresponding equations were deduced for the first time through multiple linear regression analysis, in order to help design the mechanical properties of ETM refractory high-entropy alloys.

The eventual aim of this research work was to develop a new low-cost synthesis route to produce ultralight aluminum oxide ceramic fibers for high temperature insulation. This paper mainly focuses on the application of Al2O3 fibers as insulation materials in space vehicles. The study extended to check the fibers during the launch and in the conditions of space by a satellite test. The materials were monitored by thermo-vacuum and vibration tests before the launch. The long-term stability, the daily maximum and minimum temperature, and the temperature fluctuation were investigated in the satellite test. The data derived from satellite was collected in about 9 months. The other focus of this study was the characterization of fibers at high temperature. Al2O3 fibers were prepared by a new solution method and electrospinning technique. The developed Al2O3 fibers can be characterized by 0.035–0.037 W⋅mK−1 thermal conductivity, excellent heat resistance (up to 1600 °C), and good flexibility.