Fine-tuning the ductile-brittle transition temperature of Mg_2Si intermetallic compound via Al doping

Brittleness is a dominant issue that restricts potential applications of Mg_2Si intermetallic compounds(IMC). In this paper, guided by first-principles calculations, we found that Al doping will enhance the ductility of Mg_2Si. The underlying mechanism is that Al doping could reduce the electronic exchange effect between Mg and Si atoms, and increase the volume module/shear modulus ratio, both of which are beneficial to the deformation capability of Mg_2Si. Experimental investigations were then carried out to verify the calculation results with Al doping contents ranging from Al-free to 10 wt%. Results showed that the obtained ductile-brittle transition temperature of the Mg_2Si–Al alloy decreased and the corresponding ductility increased. Specifically, the ductile-brittle transition temperature could be reduced by about 100℃. When the content of Al reached 6 wt%, α-Al phase started to precipitate, and the ductile-brittle transition temperature of the alloy no longer decreased.

A review on heat transfer in nanoporous silica aerogel insulation materials and its modeling

Silica aerogels are widely used in many fields for thermal insulation,such as building insulation,electric power energy,energy storage systems,and high-temperature thermal protection due to their excellent insulation per-formance.Therefore,the heat transfer in silica aerogels and its modeling in recent years have attracted much attention and many valuable achievements have been acquired.The heat transfer in nano-porous silica aerogels and its modeling methods are reviewed in this work.This review starts with a brief introduction of heat transfer characteristics in silica aerogels,including the multi-component and multi-mode coupling effect,size effect,and multiscale effect.Then the heat transfer mechanism of each mode,including heat transfer via gas phase,solid phase,and thermal radiation,is reviewed,and the models for predicting the gaseous thermal conductivity in nanoscale pores,gas-contributed thermal conductivity,the apparent thermal conductivity of solid skeleton,and finally the effective thermal conductivity are collected and discussed in details.Besides,modeling of transient heat transfer in silica aerogels is also briefly introduced.Finally,the conclusions and some problems which need to be further investigated in the future are provided.