Ceramics particulate reinforced Mg65Cu20Zn5Y10 bulk metallic glass composites
Introduction
The extensive research worldwide on bulk metallic glasses (BMG) is motivated by their potential applications as new high-strength structural materials. However, all BMGs face a challenging problem that they fail by the formation of highly localized shear bands, which lead to catastrophic failure without much macroscopic plasticity [1], [2]. To solve this problem, BMG matrix composites with ductile metal, or refractory ceramic particles, as reinforcements were developed to hinder the propagation of run-away shear bands and encourage the formation of multiple shear bands [3], [4], [5], [6], [7], [8]. Such composites exhibit enhanced compressive strains and occasionally even tensile plastic strains and a significantly improved impact toughness compared to monolithic BMGs. However, such composites are achieved mostly in the Zr-based BMGs. To our knowledge, composites containing ceramic particles have not been prepared in any Mg-based BMGs.
Mg65(Cu,TM)25Y10 (TM=Ag, Zn and/or Pd) alloys have been found to be good glass formers, for which fully glassy rods 4–7 mm in diameter can be fabricated by using copper mold casting [9], [10], [11], [12]. Among them, the Mg65Cu15Ag5Pd5Y10 BMG exhibits a high compressive fracture strength of 770 MPa [12]. These low-density Mg-based BMGs are highly attractive for applications. Unfortunately, they have been found to be the most brittle in comparison with other BMGs and always fail in the elastic regime with no observable plasticity.
In the present work, the Mg65Cu20Zn5Y10 (in atomic percentage) BMG former was chosen as a matrix alloy for the composite and reinforced with the SiC or TiB2 particles. A process to prepare the particle-containing composites was developed. The effect of the added particles on the thermal stability of the amorphous matrix as well as on the mechanical properties in uniaxial compression was investigated.
Section snippets
Experimental
Elemental pieces (>99.9% purity) were used as starting materials. Cu–Y ingots as an intermediate alloy were prepared by arc melting under a Ti-gettered argon atmosphere in a water-cooled copper crucible. This alloy was then melted together with Mg and Zn pieces by induction melting under inert atmosphere to obtain master alloys with the desired compositions. Subsequently, a mixture of the master alloy and the SiC or TiB2 particles was induction melted under a purified inert atmosphere. The
Results and discussion
Fig. 1 shows XRD patterns taken from the cross-sectional surface of the as-cast rods of the Mg65Cu20Zn5Y10 monolithic glass and the composites containing 10%SiC or 15%TiB2 particles. The Mg65Cu20Zn5Y10 alloy without particles is a single-phase BMG. The XRD patterns of the two composites show diffraction peaks from SiC or TiB2, respectively, superimposed on the broad diffuse scattering maxima from the amorphous phase. In both cases, the matrix alloy in the as-cast composite is amorphous. The
Summary
As the reinforcements in the Mg65Cu20Zn5Y10 bulk metallic glass, SiC or TiB2 particles have no obvious adverse effect on the glass forming ability of the matrix alloy. The composites have been successfully prepared, with the particles uniformly dispersed in the Mg-based glass matrix, through copper mold casting. Compressive fracture strength of the ceramics particulate reinforced composites reached about 1 GPa, a factor of 1.2 higher than the Mg65Cu20Zn5Y10 monolithic glass. In contrast to the
Acknowledgments
The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China under contracts No. 50171069 and No. 50021101.
References (15)
- et al.
Scripta Metall. Mater.
(1994) - et al.
Acta Mater.
(1999) - et al.
Scripta Mater.
(2002) - et al.
J. Mater. Res.
(1996) - et al.
Appl. Phys. Lett.
(1997) - et al.
J. Mater. Res.
(1999) - et al.
Mater. Trans. JIM
(1997)