Structural transformations of amorphous iron-based alloys upon abrasive and thermal treatments

Abstract

Wear resistance and structural changes have been investigated in amorphous alloys Fe64Co30Si3B3 and Fe73.5Nb3Cu1Si13.5B9 upon wear using a fixed abrasive. The structural studies have been performed by the methods of metallography, electron microscopy, and Mössbauer spectroscopy. It has been shown that the abrasive resistance of amorphous alloys is 1.6–3.1 times lower than that of high-carbon tool steels, which have a close level of hardness. The low abrasive wear resistance of amorphous alloys is caused by the deformation softening of the alloy surface in the process of wear. The major volume of the deformed surface layer of the alloys preserves the amorphous state. Its structural changes upon wear are characterized by the formation of inhomogeneities (fragments with a size of 10–50 nm) and by a decrease in the width of the strongest “halo” in the selected-area electron-diffractions patterns. In the amorphous matrix of the Fe64Co30Si3B3 alloy, a strong magnetic texture is formed and a redistribution of atoms occurs, which leads to an increase in the local shortrange order corresponding to FeB, Fe2B, Fe3B and α-Fe phases. In microvolumes of a thin (several μm) surface layer, the formation of a nanocrystalline structure (on the order of several volume %) was revealed. A tempering of the Fe73.5Cu1Nb3S13.5B9 alloy at temperatures below 500°C does not affect the hardness and wear resistance of the alloy. At 500°C, there occurs an increase in microhardness and wear resistance of the Fe73.5Cu1Nb3S13.5B9 alloy as a result of the formation in it of a nanocrystalline structure with the retention of a certain amount of the amorphous phase. The complete crystallization of the alloy at 540°C increases the brittleness of the alloy, which leads to a sharp reduction in its wear resistance.