Nanoglass and Nanocrystallization Reactions in Metallic Glasses

Abstract

Strategies to change the properties of metallic glass by controlling the crystallization and the glass transition behavior are essential in promoting the application of these materials. Aside from changing the composition approaches to stabilize the glass and frustrate the nucleation and growth of crystals, new strategies at a fixed glass composition are of special interest. In this review, some recent work is summarized on new strategies to tune the properties of metallic glasses without changing composition. First, the nanocrystallization strategy is introduced that is based on the nanocrystallized microstructures such as those that develop in marginal Al-based metallic glasses. The heterogeneous and transient nucleation effects in the nanocrystallization reactions in Al-based metallic glasses are systematically investigated and can be assessed by the determination of delay time based on Flash DSC measurements. These results provide a basis to understand the strong effect of minor alloying additions on the onset of primary Al nanocrystallization and to design the novel Al-based composites with improved properties. Secondly, by an optimal annealing treatment, a liquid-cooled Au-based metallic glass can achieve very high kinetic stability to yield a large increase in glass transition temperature of 28 K and this is 3-5 times larger than the increase usually reported. The measured enthalpy decrease is about 50% of the difference between the as-cooled glass and the equilibrium crystalline state and reaches the extrapolated enthalpy of the supercooled liquid. Finally, the nano-glass strategy makes an Au-based nanoglass show ultrastable kinetic characters at low heating rate (e.g., 300 K/s) compared to a melt-spun ribbon, which is attributed to the kinetic constraint effect of nanoglobular interfaces. These results indicate that the nanoglass microstructure can act to increase metallic glass stability and provide another mechanism for the synthesis of ultrastable glass. These developments open new opportunities to improve the stability and properties and largely increase the application potentials of metallic glasses.

Influence of annealing conditions on changes of the structure and selected properties of Al88Y7Fe5 and Al88Y6Fe6 alloys

“…The properties of metallic glasses, including those based on Al, are closely connected with their structure, which is amorphous and metastable. During thermal activation, an amorphous structure decomposes, affecting changes in mechanical, magnetic, and electrochemical properties of metallic glasses [3][4][5]. Heat treatment of amorphous alloys may consist of annealing leading to relaxation of the amorphous structure and annealing resulting in full crystallization of metallic glasses, which in this case is disadvantageous due to the degradation of the properties of such materials, including, for example, loss of high corrosion resistance, as well as a significant increase in brittleness, preventing their practical use.…”

“…Much more advantageous for metallic glasses is annealing, as a result of which the amorphous structure relaxes, as this phenomenon usually leads to preservation and sometimes even improvement of the desired physical and mechanical properties of metallic alloys [6][7][8]. The reasons for the properties of improvement of amorphous alloys after heat treatment are constantly discussed; therefore, more research is needed in this area [1,4,9]. Considering that physical and chemical properties are extremely important for practical applications of aluminumbased metallic glasses as engineering materials, the aim of the present work is to investigate the influence of annealing conditions on changes in the structure and selected properties of Al88Y7Fe5 and Al88Y6Fe6 alloys casted by melt spinning.…”