Mechanical properties and structure of rapidly solidified bulk Fe89 − xHf4Ta1Cu1Gd1SixB4 (x = 0–15) and Fe74Hf4Ta1Cu1Gd1LaySi15 − yB4 (y = 7) alloys

Abstract

Authors investigated mechanical properties of microcrystalline Fe89−xHf4Ta1Cu1Gd1SixB4 (x=0–15) and Fe74Hf4Ta1Cu1Gd1LaySi15−yB4 (y=7) alloys obtained by copper mold injection casting to a form of rods, 3mm in diameter. Structure of the samples was analyzed by Cu K-α powder X-ray diffractometry and the unit cell parameters of identified h-Fe2Hf0.8Ta0.2 (C14 Laves), fcc-Fe16Hf6Si7 (D8a) and bcc-Fe phases were calculated. The study revealed that ascending Si content leads to reduction in values of both unit cell parameters of C14 phase in the alloys studied while causes the expansion of D8a lattice; decrease in secondary dendrite arm spacing in the middle of the rods; stepwise improvement of yield and compressive strength at the expense of plastic deformation region, what was attributed to the precipitation of C14 Laves/D8a in the interdendritic regions of bcc-Fe; decrease in flexural strength with no effect on deflection-at-yield and exponential increase in hardness of the studied alloys. There is also clear correlation between unit cell volume of fcc-Fe16Hf6Si7 phase, yield and compressive strength on Si content. For the alloys with x=0–13, relation between yield strength and Vickers hardness was described with logarithmic function. It was found, that the lattice expansion of bcc-Fe and, in lesser extent, C14 Laves phase is correlated with the value of bending modulus in the whole composition range.