Enhanced compressive plasticity in a Cu-Zr-Al – Based metallic glass composite

Abstract

One possible key to improve plasticity in a CuZrAl bulk metallic glass is to introduce soft metallic crystalline particles. Tantalum particles with two different geometries were chosen in the present work: (i) irregularly shaped particles of equivalent average diameter of 45 μm (Ta1) and (ii) spherical particles of average size 25 microns (Ta2). When the volume fraction of tantalum goes from 0% to 50%, the modulus increases (from 95 GPa to 140 GPa), the Poisson's ratio decreases only slightly (from 0.37 to 0.35) and the hardness decreases regularly (from 485 HV30 to about 300 HV30), whatever the particles size. All these results are in agreement with simple laws of mixtures, involving only the volume fraction of the second phase. The results obtained during the compression tests are more complicated. The yield strength decreases when the Ta content exceeds 20% in volume. This evolution is identical for both types of particles. Similarly, an increase in plasticity is always observed when the tantalum content exceeds about 10% in volume. For the highest values of this content, a significant damage of the sample follows this plastic deformation before rupture. But a large dispersion of the values is observed, more particularly for small particles of tantalum. This is due to a problem of heterogeneity of the particles dispersion and the presence of clusters; this difficulty in dispersing the particles is more marked for small spherical particles. An image analysis was performed to characterize this clustering effect. Clusters have a negative effect because they facilitate the propagation of cracks through Ta-Ta weak interface instead of deflecting it. An optimal content to combine a high elastic limit, a good hardness and a high plasticity seems to exist near 30% vol. of crystalline particles.