ANNEALING OF SHEAR BANDS IN METALLIC GLASSES

Shear bands introduced into the as-quenched metallic glass alloy, Metglas 2826 (Fe//4//0Ni//4//0P//1//4B//6), were etched by immersion in a solution of CuSO//4 and HCl. Elimination of the etchability property through isothermal annealing had an apparent activation enthalpy of 250 kJ mol** minus **1, similar to that of stress relaxation. Direct microscopic observations indicated that the etching of shear bands may be a result of stress corrosion cracking. The electrochemical etchability of shear bands in the nickel-based alloy, BNi//2 (Ni//6//8//. //8Cr//6//. //6Fe//2//. //6B//1//4//. //1Si//7//. //9), polarized in a solution of perchloric acid and acetic acid at 12 degree C, could also be eliminated by thermal annealing. The loss of etchability had an apparent activation enthalpy of 580 kJ mol** minus **1, a value indicative of more complex atomic rearrangements taking place within the deformed material. Finally, shear bands introduced into the as-received BNi//2 material retained the ability to reverse shear after heat treatment at temperatures in the range of 192 to 375 degree C even if the electrolytic etchability was apparently diminished.