THE INFLUENCE OF THE COMPOSITION ON AMORPHIC ALLOYS THERMAL STABILITY BASED ON LIGHT LANTANOIDS

Abstract

A comparative analysis of the thermal stability of rapidly quenched amorphous alloys based on light rare-earth elements (LRE - La, Ce, Pr) with normal metals (M - Al, Ga, Cu, Ag, Mg, Ge, In, Sn, Pb) depending on the nature and concentration of alloying components. The studied samples were obtained by colliding a portion of the melt with the inner surface of a rotating bronze cylinder in the form of foils with a thickness of 30 to 100 μm, which correspond to cooling rates of ~ (106-5·104) K/s. The temperature of the onset of amorphous samples crystallization was determined from the start points of irreversible changes in electrical resistivity under conditions of continuous heating in vacuum at a rate of 1,7·10-2 K/s.The minimum values of the parameter Tk characterize the alloys of LRE -Cu systems, the crystallization of which begins at temperatures of 333-363 K, while the thermally most stable are REM alloys with Al and Ga, which amorphize in wide concentration ranges, was shown. In particular, in La-Al and La-Ga alloys, as the content of the M-component increases, the stability of the amorphous structure noticeably increases: from 428 to 558 K for the La-Al system and from 373 to 458 К for the La-Ga system.Both the relative stability of binary amorphous alloys of different systems and the dependence of Tk on the concentration of Al and Ga correlate with the temperature of the equilibrium liquidus T was established. For all studied amorphous alloys, the Tk/TL ratio is practically independent of composition and varies in the range 0.40-0.53. This result indicates the possibility of using the values of Tk≈0.46·TL obtained by averaging the array of experimental values of Tk/TL, as an estimated characteristic of the thermal stability of the structure of amorphous REM-M alloys.The possible relationship between the thermal stability of amorphous alloys and the electron concentration factor e/a was analyzed. It is concluded that all experimentally observed variations of the parameter Tk cannot be explained by changes in a single parameter e/a.