Plasticity enhancement of Mg₅₈Cu_28.5Gd₁₁Ag_2.5 based bulk metallic glass composites dispersion strengthened by Ti particles

Abstract

We have successfully synthesized the Ti particles reinforced Mg₅₈Cu_28.5Gd₁₁Ag_2.5 metallic glass composites (BMGCs) rods with a diameter of 2–4 mm by injection casting method in an Ar atmosphere. The glass forming ability (GFA) and the mechanical properties of these Mg-based BMGCs have been systematically investigated as a function of volume fraction (V_f) of Ti particles. The results show that the compressive plasticity increases with the volume fraction of Ti particles. A drastic improvement of compressive plastic strain (reach up to 24%) occurs at the Mg-based BMGC with 40 vol.% Ti particles. In parallel, multiple shear bands were revealed on the sample surface after compression test. This suggests that these dispersed Ti particles can highly absorb the energy of shear banding and branch the primary shear band into multiple shear bands, thus decrease the stress concentration for further propagation of shear band and so as to significantly enhance plasticity. Additionally, the yield strength can be kept at 800 MPa as increasing the addition of Ti particles to 40 vol.%. This was found presumably due to the good bonding of interface between the Ti particle and amorphous matrix.

Introduction

Mg-based bulk metallic glasses (BMGs) have attracted great attention recently because of its low density and high damping capacity as compared to most other bulk metallic glasses (BMGs), such as the Pd, Zr, and Fe-based amorphous alloys [1], [2], [3]. However, the Mg-based BMGs do not exhibit appreciable plastic deformation in a uniaxial mode, they tend to break into pieces before yielding [4], [5], [6], [7]. Therefore, the improvement on plasticity has been strongly requested for the progress in the application of Mg-based BMGs. To solve the brittleness of Mg-based BMGs, the development of bulk metallic glass composites (BMGCs) with micro- or nano-scaled second phase dispersed homogeneously in a BMG matrix have been proven to be an effective way for improving plasticity. Two main approaches of forming BMGCs have been explored so far, one is to in situ precipitate crystalline phases in the BMG matrix, the other is to ex situ introduce foreign particles (i.e., metallic or refractory ceramic particles) into the BMG matrix [2], [8], [9], [10], [11], [12], [13], [14]. In Mg-based alloys, the first development of Mg-based BMGC, a Mg₆₅Cu_7.5Ni_7.5Zn₅Ag₅Y₁₀ with Fe dispersoid, was reported by Ma et al. in 2003 [2]. Since then, many other types of Mg-based BMGCs have been developed with ceramic and metallic particles (e.g., TiB₂ [15], ZrO₂ [16], WC [17], SiC [18], and Nb [19], porous Mo [20], Ti [21], and Fe [22]) and all exhibits remarkable plasticity improvement. Among these developed Mg-based BMGCs, the Mg₆₅Cu₂₅Gd₁₀/40 vol.% Ti BMGC displays the highest plastic strain of 41% [21]. However, this BMGC presents much low value of yield strength (470 MPa) than the base BMG (850 MPa). This differs from the phenomena of the Mg₅₈Cu_28.5Gd₁₁Ag_2.5/25 vol.% porous Mo BMGC, possessing much higher yield strength than the base BMG [20]. Therefore, we believe that there exist some factors which may significantly affect the mechanical performance of these Mg-based BMGC, including particle size, vol. fraction, and interface between the particle and the glassy matrix. Accordingly, the composition of Mg₅₈Cu_28.5Gd₁₁Ag_2.5 which posses high GFA [20] is selected as the raw alloy for preparing the BMGC by reinforcing with ductile Ti particles (which has spherical shape) in this study. The effect of particle size, vol. fraction, and the interface between the particle and the glassy matrix on the mechanical performance of these BMGCs were investigated.