Behaviour of Metallic Glasses under Local Loading and after External Action

Abstract

Abstract—To determine the cracking susceptibility for amorphous metal alloys (AMAs) or metallic glasses, a method based on the determining the dependence of the relative crack resistance (χ) on the load applied to intender of PMT-3 microhardness tester is proposed. In the method, the relative crack resistance at a load of 160 g is set equal to unit. At lower loads, crack resistance has been determined as the average of 10 measurements. In this article, we also have proposed a method for determining the heating temperature of AMA ribbons during laser beam machining that is based on a comparison of the dependence of the relative crack resistance of AMAs on load applied to indenter for samples annealed in the furnace and after laser irradiation. It has been found that cracks begin to appear in the samples after a ten-minute annealing at Т = 773 K. Fatigue tests of samples under a load varying from a maximum value of 750 MPa to a minimum of 400 MPa under a condition of repeated stress cycle with a frequency of 2 Hz have been carried out using a specially designed setup. In the domain exposed to laser radiation, four characteristic areas can be distinguished on the sample surface: internal reflow zone; dendritic growth area; area with unfinished growth of dendrites, area not exposed to radiation. In these areas, the relative crack resistance (χ) determined via the critical stress intensity factor of the first kind K1c monotonically decreases from 1 in the center to 0 at the periphery. It has been established that the laser action does not affect fatigue, the fatigue limit of the samples remains the same and is equal to 428 MPa. The characteristic features of the destruction are revealed. Cracks that propagate with branching in the reflow zone and after passing through its boundary develop rectilinearly have been found.