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Being a key feature of a glassy state, low temperature relaxation has important implications on the mechanical behavior of glasses; however, the mechanism of low temperature relaxation is still an open issue, which has been debated for decades. By systematically investigating the influences of cooling rate and pressure on low temperature relaxation in the ZrCu metallic glasses, it is found that even though pressure does induce pronounced local structural change, the low temperature-relaxation behavior of the metallic glass is affected mainly by cooling rate, not by pressure. According to the atomic displacement and connection mode analysis, we further demonstrate that the low temperature relaxation is dominated by the dispersion degree of fast dynamic atoms rather than the most probable atomic nonaffine displacement. Our finding provides the direct atomic-level evidence that the intrinsic heterogeneity is the key factor that determines the low temperature-relaxation behavior of the metallic glasses.

A ZrSi 2 -ZrC-SiC/SiC double layer coating was prepared on the surface of carbon/carbon (C/C) composites by pack cementation. The microstructure, oxidation and thermal shock resistance of the coating were studied. These results show that the outer coating is mainly composed of ZrSi 2 , ZrC, SiC and Si respectively. Oxidation tests were conducted in air at 1173 K for 100 min and 1773 K for 67 h and a weight decrease of 0?37 and 0?12% were recorded. After 20 times thermal shocks between 1773 K and room temperature, the weight of the coated specimens increased by only 0?12%. The excellent thermal shock resistance is attributed to the aptness to oxidation of the minor phases distributing in the gaps among the SiC particles and the coarseness of the coating.