The Effect of Melt Treatment on Glass Forming Ability and Thermal Stability of Al‐Based Amorphous Alloy

Abstract

Controlling solidification process, such as melt treatment, including melt superheating temperature (T s ) and the time of homogenization (t h ), as well as casting parameters including mold preheating temperature (T m ) and pouring temperature of the melt (T p ), is widely employed to mediate the microstructures, therefore, the anticipated properties are achieved. [1][2][3][4][5] Amorphous phase is thermodynamically metastable, and significantly dependent on the solidification process. Recently, the glass forming ability (GFA) of the Al-based metallic glasses are greatly improved through a melt treatment during the preparation process, such as the critical size of the amorphous sample were improved from micron to millimeter level for Al-La-Ni alloy [6] and from melt-spun ribbon to as-cast-0.75 mm-diameter rod for Al-Ni-Y alloy. [7] Non-classical nucleation theories [8,9] indicate that the GFA of metallic glass formers is related to the existence of localstructural-ordering clusters and high-melting-temperature phases, which usually act as nucleation sites and grow with little resistance when the temperature reduces upon solidification. The local structural ordering and highmelting-temperature phases are largely influenced by the temperature. [10][11][12] Therefore, the melt treatment is designed as that the alloy is firstly heated to a high temperature, which is about 1.4 times of liquidus temperature (T l ), and then cooled down to a low temperature which is about 100 K higher than T l . Heating the melt to a relatively high temperature is designed for the elimination of the local-structural-ordering clusters and high-melting-temperature phases, which enhances the stabilization of a melt and the GFA. [4] A cooling process is followed to realize a high cooling rate in the melt treatment. However, there are still some problems that are expected to be illustrated. The first point is whether the supposed local-structural-ordering clusters and highmelting-temperature phases mentioned above exist. The second point is whether the melt treatment works on the elimination of local-structural-ordering clusters and highmelting-temperature phases, and improvement of stability of the liquid. The influences of cast temperature on the local-structural-ordering clusters have been investigated by different research groups. [13][14][15][16] In this paper, the possible high-melting-temperature phases will be discussed in detail.In order to detect the possible phases in liquid melt, melt-spinning method is employed to prepare the alloy ribbons due to its extremely high cooling rate, which to some extent reflects the characteristics of the liquid. Alloy ingots with the composition of Al 85.5 Ni 9.5 La 5 (in atomic percentage) were prepared by arc-melting a mixture of high purity metals under a Ti-gettered high purity argon atmosphere in a water-cooled copper hearth. Some amount of the ingots were remelted under high vacuum in a quartz tube, and then injected through a nozzle with a diameter of about 1 mm onto the surface of rotating...

Negative expansions of interatomic distances in metallic melts

“…polyhedral, whereas at low temperatures they have high-coordinated polyhedra of icosahedron-like clusters, can explain that reported experimental results, e.g., different temperatures of melts, at which melts are quenched, could affect the glassforming process, thermal stability, and mechanical properties of systems (46)(47)(48)(49)(50)(51)(52). Furthermore, our finding might also shed light on the casting temperature effect on solidification process in crystalline systems, and the glass transition phenomenon in disordered systems because they are atomic packing related as well.…”

Synthesis of high strength aluminum alloys in the Al–Ni–La system

“…For the Al 90.5Àx Ni 9.5 La x (x 5 1-6) alloys, after a careful match with the data in the powder diffraction files (PDF), the phases were indexed as Al, Al 11 La 3 , and Al 3 Ni, which are coincident with the crystallization products of the Al-La-Ni amorphous alloy. 24 Upon increasing the La content, the intensity of the diffraction peaks corresponding to Al 11 La 3 phase becomes stronger, indicating an increase of the volume fraction for Al 11 La 3 phase. In addition, the binary alloy Al 90.5 Ni 9.5 is composed of Al and Al 3 Ni and Al 95 La 5 is composed of Al and Al 11 La 3 phases.…”

Analysis of Melt Temperature Effects on Rapid Solidification of Al Alloy Structure

“…Juan et al investigated the mechanism of melt heat treatment on the amorphous formation and thermal stability of Al-Ni-La alloys. Juan argues that the alloy undergoes a melt heat treatment, and the metastable phase of the rich Ni disappears, and the melt becomes more uniform, which is the main factor for the formation and stability of the amorphous [12].…”