Dependence of microhardness on annealing time of amorphous Al-Mm-Ni-(Fe,Co) alloys

Al-Mm-Ni-(Fe,Co) alloys of two slightly different compositions were melt spun to amorphous ribbons. DSC studies of the ribbons show that the first crystallization stage, responsible for the precipitation of fcc-Al, is well separated from the following. Mixed structures containing nanosized fcc-Al crystals, embedded in amorphous matrix were obtained by isothermal annealing of the initially amorphous ribbons for different times and thus, different crystalline fractions the fcc-Al crystals were obtained. The microhardness of the alloys increases with the increase of annealing time, reaching values of about 550 HV0.02 after 60 min of annealing. Replacing Fe by Co does not significantly influence the microhardness of these alloys. The slight changes of chemical composition do not seem to have a clear effect on microhardness.