Consolidation of metallic glass ribbons and powder using a pulsed high current discharge

Since the first preparation of amorphous metal, there has been a major driving force to produce a three dimensional amorphous product for engineering applications. The consolidated amorphous metal alloys, however, have one important drawback. They undergo transformation by crystallization at low temperature which complicates bulk processing. Recently, several metallic glasses were formulated with transition metals and metalloids which allowed the crystallized materials to attain superior properties upon heat treatment at high temperature. The conventional consolidation techniques usually involve prolonged high temperature exposure and therefore thermal degradation occurs. For this reason, high-energy high-rate (HEHR) consolidation methods are preferable. The homopolar generator (HPG) and a capacitor bank arrangement were used for the consolidation of metallic glass ribbon and powder. The basic mechanisms of consolidation are Joule heating between powders and microwelding between ribbon layers. It has been found that the amorphous state was retained after the capacitor bank consolidation of metallic glass ribbons. Powder consolidations by HPG were fully crystallized. The initial phases in the as-consolidated state went through several phase transformations with post-consolidation annealing. As a preliminary study, crystallization behavior of metallic glass has been investigated. The resulting material properties of HEHR processed materials are sensitive to the HPG processing parameters. In-situ variations of current and voltage with processing time can be monitored. It has been found that the mechanical properties and microstructure of the consolidates varied significantly with the initial degree of crystallinity, the input energy and the post-consolidation annealing.