Tailoring Thermally Induced Nano-Quasicrystallization and Deformation-Assisted Nanocrystallization for Mechanical Property Improvement in Zr-Al-Ni-Cu-Pd Bulk Metallic Glasses

Abstract

The material design tailoring of a synergistic effect of an in-situ nano secondary phase formation and deformation-induced nanocrystallization for improving the mechanical strength and ductility, has been investigated in Zr 65 Al 7:5 Ni 10 Cu 17:5Àx Pd x bulk metallic glasses (BMGs). As-cast Zr 65 Al 7:5 Ni 10 Cu 17:5Àx Pd x (x ¼ 5{17:5) BMGs have significant ductility in compressive deformation, which is attributed to deformation-induced dynamic nanocrystallization. The 10 at% Pd-containing BMG with a low volume fraction of the quasicrystalline (QC) phase of less than 6% exhibits increases in strength and Young's modulus, in addition to a remaining plasticity of $5%, compared with the monolithic glassy alloy. Such improvements in the mechanical properties originate from the combination of two effects of in-situ homogeneous nano-QC formation and deformation-induced inhomogeneous nanocrystallization. The present method should be regarded as a new technique for the production of BMGs with high strength and good ductility.

Plastic deformation by glassy structure control in Zr–Al–Ni–Cu-based BMGs

“…Repeating the process of such deformation-induced nanocrystallization, a significant plasticity is exhibited by shear band branching compared to that in deformation without any structural change. We have already reported that similar nanocrystallization induced by deformation is also observed in the BMGs with the Pd concentration over 10 at.% [10,19]. Table 1 summarizes mechanical properties of several Pdcontaining BMGs cast in ambient Ar pressure.…”

“…We have already clarified that plasticity is significantly improved in the Zr 65 Al 7.5 Ni 10 Cu 12.5 Pd 5 BMG cast in ambient Ar or He (∼6%), comparing to that cast in vacuum (∼2%) [18]. Here, the multiple shear bands are observed in the BMGs cast in Ar and He [19]. The measured enthalpy of relaxation is 4.4 J/g (vacuum), 8.2 J/g (ambient Ar) and 9.8 J/g (ambient He), indicating a correlation with plastic strain.…”

Effect of Nb on Transformation Kinetics and Mechanical Properties in Zr-Al-Ni-Cu Metallic Glasses

“…We have previously reported that plasticity is not lost so significantly even by the QC precipitation below its volume fraction of approximately 6% in the Zr 65 Al 7:5 Ni 10 Cu 7:5 Pd 10 BMG. 27) However, in the present alloy, it is noted that the plasticity vanishes suddenly even in the structural relaxation prior to the QC precipitation. Although the reason for it is not cleared completely, we should consider the higher nucleation rate at elevated temperature as well as a disappearance of free volume.…”

Cooling Process and Cast Structure of Zr-Al-Ni-Cu–Based Bulk Metallic Glasses Produced in Various Atmospheres

“…The excellent plasticity in the Pd-containing BMG is caused by the synergy effect of the deformation-induced nanocrystallization and less relaxed glassy structure. [23,24] The minor additive, i.e., Pd, with a different size from others also may contribute to it by inducing the excess free volume in the glassy state. [25] Even in such case, the improvement of plastic strain with the increase of DH relax clearly indicates that the relaxation state of glassy structure is a fundamentally effective factor for deformability.…”