Spontaneous vitrification in Cr-Ti bulk alloys

Abstract

We describe a new process that enables the formation of amorphous Cr40Ti60 cubelets with dimensions in the millimeter range by a sequence of standard metallurgical procedures. Vitrification occurs spontaneously during low-temperature furnace annealing. The resulting amorphous material contains small-grained crystalline inclusions. Mechanically, the process results in a marked increase of the microhardness and a decrease of the elastic modulus of the material.

<i>In Situ</i> TEM Observation of Structural Changes in Rapidly Solidified bcc Solid-Solution Phase in Ti&ndash;Cr Alloy Focusing on Spontaneous Vitrification (SV)

“…7(b), 7(c) and 7(d)). The diffuse scattering observed in the present study is similar to those reported in the previously reports, 2,4,1922) and can be attributed to the mechanical instability and/or the ½ transition of the bcc phase. 4,20,26,27) The evolution of diffuse scattering during annealing indicates the decrease in the stability of the irradiated bcc solidsolution phase by annealing, however, the occurrence of SV cannot be seen.…”

“…The annealing temperature was fixed at 873 K on the basis of the results of the above thermal analysis and of previous reports. The formation of an amorphous phase through SV was previously reported for Ti 60 Cr 40 thin film annealed at 873 K, 1) for water-quenched Ti 60 Cr 40 alloy annealed at 873 K for 1.8 © 10 4 s, 2) for mechanically alloyed Ti 60 Cr 40 (obtained from an elemental powder blend of Ti 60 Cr 40 ) annealed at 823 K for 1.2 © 10 3 s, 17) and for mechanically alloyed Ti 50 Cr 50 annealed at 850 K for 1.8 © 10 3 s, 18) indicating that ex situ annealing at 873 K for a period on the order of 10 4 s was a suitable condition for the current experiment to determine whether SV actually occurs. The changes in the microstructure of the alloy were investigated using XRD and TEM, where the alloy was ex situ annealed at 873 K for various periods, and the results are shown in Fig.…”

“…(2) In the in situ annealing experiment, specimens were, prior to annealing, irradiated with 2 MeV electrons aiming to introduce a high density of defects and to enhance the diffusion, but it was in vain. (3) The SV previously reported for TiCr alloys may actually correspond to the formation of a finely grained polycrystalline structure through the decomposition of the bcc solid-solution phase.…”

“…60 Cr 40 (at%) alloy were prepared by arc-melting Cr and Ti in a water-cooled Cu hearth under a purified Ar atmosphere. The composition of the alloy was the same as that of alloys used by Blatter et al 1,2) and by Kim et al 17) A single-roller melt-spinning method was used to produce rapidly quenched ribbons from the master ingots. A quenching apparatus consisting of a 200-mm-diameter copper roller was operated at 4000 rpm in an Ar atmosphere; therefore, the roller-surface velocity was about 42 ms ¹1 .…”

Scattering study of vitrifying Cr-Ti solutions

“…In this system, the high temperature bcc solid solution (fl-phase) is metastably frozen by temperature quenching. Only a moderate cooling rate is required, which allows the preparation of bulk fl-phase material [5]. A series of polymorphous transformations has been found to precede and accompany amorphization [6]: At a temperature TH between 370 and 450 ° C (depending on composition), alloys with 30M0 at.% Cr undergo an exothermic transition.…”