Formation of simple crystal structures in Cu-Co-Ni-Cr-Al-Fe-Ti-V alloys with multiprincipal metallic elements

Abstract

Crystalline solid solutions are typically formed in conventional alloys based on one or two host elements. Here, in this research, four alloys containing multiprincipal metallic elements (Ն5 elements) were prepared by casting, splat quenching, and sputtering. Their microstructures and crystal structures were investigated. It was interestingly found that solid solutions with simple fcc or bcc crystal structure were also practically formed in these alloys with multiprincipal elements. All different atoms are regarded as solutes and expected to randomly distribute in the crystal lattices without any matrix element defined.An ideal crystal structure is regarded as a superposition of a basis (an atom, or a group of atoms or ions) on a periodical framework, called a Bravais lattice. [1][2][3][4][5][6] Even though real crystals have point defects, such as vacancies and solute atoms, the phases of metallic alloys are known to have crystal structures, consistent with Bravais lattices, excluding quasi-crystals with fivefold symmetry. [3][4][5][6][7][8][9] Table I lists examples of metallic elements. [3,4,5] Their crystal structures normally fall into three main categories-fcc, bcc, and hcp. Most conventional alloys of crystalline solid solutions studied to date are based on one or two host elements, [10,11,12] raising the question of whether other crystalline solid-solution alloys with multiprincipal elements (more than the lattice points per unit cell) exist. Based on the general understanding of physical metallurgy and phase diagrams, abundant formation of intermetallic compounds or ordered phases is anticipated when multiprincipal elements are added into the alloys. [12] The complexity of such microstructures is expected not only to be responsible for their brittleness, but also for difficulties in processing and analysis. This fact has discouraged the design of new alloys with multiprincipal elements.However, solid solutions with multiprincipal elements tend to be thermodynamically stable because of their high mixing entropies. [13,14] Determining whether the alloys with multiprincipal elements could also crystallize into a simple Bravais structure would also be of interest. Some studies have developed a new approach to design alloys with multiprincipal metallic elements (Ͼ5 elements) in equimolar or near-equimolar ratios to exploit fully the high mixing entropy of the solid-solution state. [15][16][17][18] In this investigation, four alloys of multiprincipal metallic elements were prepared by different methods; solid solutions with simple fcc or bcc structures were also formed in alloys without detectable intermetallic compounds or ordered phases. No "matrix or host" element is defined, and all atoms are regarded as solutes, expected to be randomly distributed in the crystal lattices, according to a statistical average probability of occupancy.Four alloys that contain multiprincipal metallic elements were prepared by three methods-conventional casting, rapid solidification, and vacuum sputtering. Bulk CuCoNiCrFe, CuCo...

TCHEA1: A Thermodynamic Database Not Limited for “High Entropy” Alloys

“…Arc-melt octonary Al 1 Co 1 Cr 1 Cu 1 Fe 1 Ni 1 Ti 1 V 1 alloys were investigated and the formation of simple crystal structures was reported by Yeh et al [35] The alloy was either cooled in the cold copper hearth or splat quenched. Both the as-solidified and as-splat-quenched alloys were found to consist of Bcc ?…”

“…As-cast Co 1 Cr 1 Cu 1 Fe 1 Ni 1 HEA alloys were fabricated by Yeh et al [1,35] with splat quenching at a cooling rate around 10 3 -10 4°C /s and by Tong et al [36] using directional solidification in the cold copper hearth with a cooling rate about 1-10°C/s. Only the Fcc structure was detected in the as-cast alloys in these experimental investigations, similar to that in as-cast Co 1 Cr 1 Fe 1 Ni 1 alloys.…”

“…Probably motived by the work of Yeh et al, [35] Zhou et al [38] studied the microstructure and compressive properties of the Al x (TiVCrMnFeCoNiCu) 100-x (x = 0, 11.1, 20 and 40) HEAs prepared by inject casting. The alloy at x = 11.1 actually corresponds to the equiatomic composition.…”

Atomistic simulations of dislocations in a model BCC multicomponent concentrated solid solution alloy

“…An atomistic simulation cell consisting of a BCC lattice with lattice constant 2.86A was created, with periodic boundary conditions along three orthogonal directions x= [1][2][3][4][5][6][7][8][9][10], y= [110] and z= [001], with dimensions of ~300A in each direction (~ 2 million atoms). BCC lattice sites were randomly occupied by Co, Fe, Ni, and Ti atoms to achieve an average composition Co16.67Fe36.67Ni16.67Ti30.…”

“…The number of phases in a HEA system can be significantly smaller than the maximum number of phases present at equilibrium as predicted by the well-known Gibbs phase rule [1]. While many alloys that meet the definition of an HEA [2,3] contain multiple phases, including intermetallics [4,5], there are many single-phase systems [6]. These single-phase systems, both FCC and BCC, generally have unusually high yield strength and/or high ductility.…”