Thermal stability and consolidation behavior of mechanically alloyed Zr-Al-Cu-Ni powders with varying oxygen, iron and tungsten content

Amorphous Zr65Al7.5Cu17.5Ni10 and Zr55Al10Cu30Ni5 alloys with varying oxygen, iron and tungsten content are prepared by mechanical alloying of elemental crystalline powders of high purity. Milling is performed in a planetary ball mill using different milling tools, e.g. hardened steel and tungsten carbide. The resulting powders are characterized by x-ray diffraction, differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA). The influence of iron, tungsten and oxygen on the thermal stability is investigated by constant-rate DSC. With increasing oxygen content the crystallization temperature T-x shifts to lower values and the glass transition temperature T-g increases. Therefore, the supercooled liquid region Delta T-x = T-x-T-g is smaller than for pure alloys. Similar results are found for iron additions. Nevertheless, the results show that it is possible to produce mechanically alloyed metallic glasses with wide supercooled liquid region even for rather high impurity levels, e.g. 3.5 at.% oxygen and 0.6 at.% iron. Therefore, the impurity content can be much higher than it is tolerable for glass formation by slow cooling from the melt. Finally, the influence of oxygen, iron and tungsten additions on the preparation and consolidation of mechanically alloyed powders is critically assessed.