Flash Joule heating for ductilization of metallic glasses

Abstract

Metallic glasses (MGs) inherit their amorphous structure from the liquid state, which predetermines their ability to withstand high loads approaching the theoretical limit. However, the absence of slip systems makes them very sensitive to the type of loading and extremely brittle in tension. The latter can be improved by precipitation of ductile crystals, which suppress a catastrophic propagation of shear bands in a glassy matrix. Here we report a novel approach to obtain MG-matrix composites with tensile ductility by flash Joule heating applied to Cu47.5Zr47.5Al5 (at.%) metallic glass. This homogeneous, volumetric and controllable rapid heat treatment allows achieving uniformly distributed metastable B2 CuZr crystals in the glassy matrix. It results in a significant tensile strain of 6.8±0.5%. Moreover, optimized adjustment of the heat-treatment conditions enables tuning of microstructure to achieve desired mechanical properties.

Fabrication of Metastable Crystalline Nanocomposites by Flash Annealing of Cu47.5Zr47.5Al5 Metallic Glass Using Joule Heating

“…Heating along line 2 and cooling along lines a and b results in devitrification of the metallic glass into B2 CuZr with subsequent decomposition of B2 CuZr into the LT-EPs. As it has been shown in earlier works [20,33], the mechanical properties of the composites obtained depend strongly on the constituent phases. [20].…”

“…As it has been shown in earlier works [20,33], the mechanical properties of the composites obtained depend strongly on the constituent phases. [20].…”

“…Fast cooling is required to avoid decomposition of B2 CuZr into the thermodynamically favourable low temperature eutectic phases (LT-EPs) Cu 10 Zr 7 and CuZr 2 , and thus to stabilize B2 CuZr at room temperature. The ductile B2 CuZr crystals hinder localization of deformation in the glassy phase leading to tensile ductility of the glass-matrix composites [20]. Moving the cooling curve closer to the nose of the stability regime of the LT-EPs leads to a higher solid fraction of B2 CuZr, ultimately leading to complete suppression of the glassy phase.…”

“…In many cases, the properties of composite materials even exceed the properties of their constituent materials. Some examples include anomalously low elastic modulus in Fe-Mg microcomposites [10], outstanding strength in metal-polymer nanocomposites [5,[11][12][13] fabricated from nanoporous metals [14][15][16][17][18][19], and significantly enhanced plastic deformability in metallic glass composites [20,21]. The design of non-equilibrium composite microstructures in as-cast nanostructured titanium alloys [22][23][24][25][26] leads to the high strength and good plastic deformability required for structural and biomedical applications [27,28].…”

“…Both techniques were applied to CuZr-based metallic glasses, which were partially devitrified into the metastable B2 CuZr structure to form glass-matrix composites. The thus obtained homogeneously distributed B2 CuZr crystals in the glassy matrix result in a significant improvement of the mechanical properties of the CuZr-based metallic glasses and even allow for tailoring the tensile ductility [20]. Furthermore, it has been shown that the strength of fully crystalline composites containing ultrafine-grained crystalline phases even exceeds that of the parent glass [20].In this study, we focus on the effect of heating rate and time on the formation of stable and metastable crystalline phases in the Cu 47.5 Zr 47.5 Al 5 metallic glass upon flash annealing and the mechanical properties of the crystalline nano-and microcomposites obtained.…”