The effect of the concentration of Ni, Y and La-rich mischmetal on the thermal stability, microstructure and mechanical properties of ribbons tested in the temperature range 25-350°C have been evaluated. The low-alloyed materials were crystalline or partially crystalline while high-alloyed materials were amorphous. The amorphous alloys experienced numerous transformations during heating above 170°C. A transition in the amorphous state was observed in all alloys prior to the crystallization stage. The alloy composition determines the sequence of phase transformations during crystallization. In general, the structure of crystallised amorphous, even at high temperatures, is much finer than that of crystalline materials. A MgxREy intermetallic matrix with other intermetallic phases homogeneously distributed was observed in the crystallised ribbons with high RE contents. However, a magnesium matrix embedding other intermetallic phases was the microstructure observed for low-alloyed materials. The amorphous Mg-10Ni-2.5Y2.5-2.5La(MM) showed the higher tensile strength values up to 200 °C The crystalline Mg-2Ni-1Y-1La(MM) ribbon and the partially crystalline Mg-3Ni-1.5Y-1.5La(MM) alloy also exhibited high mechanical resistance levels which were maintained up to 250 °C. MgNi10Y2.5La(MM)2.5 amorphous and MgNi3Y1.5La(MM)1.5 crystalline broken above 500 and 400 MPa, respectively, at 100°C.
|Materials Science Forum
|Published - 2007