Nanocrystalline or amorphous matrix Al60Fe15Ti15(Co/Mg/Zr)5–5%B composites produced by consolidation of mechanically alloyed powders – lightweight materials with high hardness

Abstract

Al60Fe15Ti15(Co/Mg/Zr)5B5 powder mixtures were subjected to mechanical alloying. XRD investigations revealed presence of an amorphous structure in the milling products. The calorimetric study showed that the crystallisation onset temperature of amorphous phase is 549 °C, 566 °C and 587 °C for the alloys containing Co, Mg and Zr respectively. The milled powders were consolidated under a pressure of 7.7 GPa in different conditions: at the temperature 40 °C below the crystallisation onset temperature and at 1000 °C. An amorphous structure was retained after consolidation applied at the lower temperature. Compaction at 1000 °C caused crystallisation of an amorphous phase into Al5Fe2 and/or τ2 intermetallic phases, depending on the alloy composition. Structural examinations revealed that all the bulk samples are composites with boron particles embedded in amorphous or nanocrystalline matrix. The hardness of the nanocrystalline matrix composites is in the range of 9.46–9.83 GPa whereas that of amorphous matrix ones is in the range of 8.43–8.65 GPa, depending on the composition. The specific yield strength of the produced samples, estimated using the Tabor relation, is in the range of 689–830 kN m/kg and the highest value is possessed by the nanocrystalline matrix composite containing Mg. We also suppose that application of high pressure affected crystallisation of an amorphous phase, influencing the phase composition of the products of this process.