Effect of temperature and strain rate on the compression properties and crystallization of a Fe based metallic glass

The present study investigates the effect of temperature (room temperature or 635°C) and strain rate (10 -1 or 10 -3 s -1 ) on the compression behavior of a Fe 64 B 24 Nb 6 Y 4 bulk metallic glass (BMG). Compression tests were performed using a Gleeble TM electro-thermal-mechanical testing system. The multiscale analysis of the microstructure after compression provides insight into the effect of both strain rate and temperature on the BMG phase transformations and deformation mode. A low strain rate is required at room temperature to enable the rearrangement of Y atoms necessary for the Fe 62 B 14 Y 3 phase formation. The deformability and mechanism of flow of the BMG strongly depend on both the glass volume fraction and the atomic structure which are governed by the testing conditions. The brittleness of the samples tested at room temperature or at 635°C and 10 -1 s -1 is explained by the inefficiency of a too sparse crystal dispersion to hinder the shear bands propagation. At 635°C, by contrast with the 10 -3 s -1 case, the 10 -1 s -1 strain rate is too high to keep the overcooled structure of the glass. At 635°C under 10 -3 s -1 , overcooling ensures a significant deformation achieved by viscous flow. In this case, the high density of crystals plays only a secondary role.