Physical metallurgy of Ti–Ni-based shape memory alloys

Despite the intense interest in metallic glasses for a variety of engineering applications, many details of their structure remain a mystery. Here, we present the first compelling atomic structural model for metallic glasses. This structural model is based on a new sphere-packing scheme—the dense packing of atomic clusters. Random positioning of solvent atoms and medium-range atomic order of solute atoms are combined to reproduce diffraction data successfully over radial distances up to ∼1 nm. Although metallic glasses can have any number of chemically distinct solute species, this model shows that they contain no more than three topologically distinct solutes and that these solutes have specific and predictable sizes relative to the solvent atoms. Finally, this model includes defects that provide richness to the structural description of metallic glasses. The model accurately predicts the number of solute atoms in the first coordination shell of a typical solvent atom, and provides a remarkable ability to predict metallic-glass compositions accurately for a wide range of simple and complex alloys.

A structural model for metallic glasses

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 (≥5 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.

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

Recent developments in the research of shape memory alloys

Shape memory alloys (SMAs) with high transformation temperatures can enable simplifications and improvements in operating efficiency of many mechanical components designed to operate at tem...

High temperature shape memory alloys

Alloys of compositions near AuTi, PdTi, and PtTi are B19-type orthorhombic at room temperature and, at higher temperatures, have an ordered CsCl-type structure (B2-type). The martensitic transformations involved were studied by X-ray diffraction. The composition dependence of the martensitic-transformation characteristics, such as Ms, Mf, As and Af-temperatures, were determined. Lattice constants of the high-temperature phases are given.

Martensitic transformations in gold-titanium, palladium-titanium and platinum-titanium alloys near the equiatomic composition

The Atlas of Crystal Structure Types for Intermetallic Phases offers you pictorial detail, clearly illustratedThe Atlas is the perfect reference to keep on your shelf beside the Second Edition of Pearson's Handbook. For each structure type, you can quickly find for all atoms (point sets): A list of all coordination atoms with corresponding coordinates, the distance to its central atom, its coordination number and its polyhedron code. A histogram of the number of surrounding atoms (n) versus interatomic distances between the central atom and surrounding atoms, the interatomic distances are given relative to the shortest distance and nearest in the coordination polyhedron (dn/dnearest). The standard setting of all structure types is analagous to Pearson's Second Edition data. All point sets are numbered consistently throughout a structure type, so you can easily trace each atom in all drawings and tables. For accuracy, all drawings and tables are computer-generated directly from the database. All structure types have been checked for consistency. Published: 1991 Format: 4 Volume Set

Atlas of Crystal Structure Types for Intermetallic Phases

Attempts have been made to investigate the factors governing the relative stability of the various structure types found by mixing different kinds of atoms, A or B, in a large number of AB 3 intermetallic compounds related to Cu 3 Au. A geometric factor, leading to the radius-ratio dependent hexagonality of stacking character, as recognized by Van Vucht and Buschow in rare-earth trialuminides, seems to be predominant in many cases and may be used in predicting ternary phases. This factor has also served as the basis on which trial structures are proposed for three new phases encountered as transition structures between the Cu 3 Au and the Ni 3 Sn types, namely, (Ba 0.95 ,Sr 0.05 )Pb 3 with a rhombohedral unit cell (a = 12.180 A , α = 34°43') ; (Ti 0.97 ,Nb 0.03 )Ni 3 with a hexagonal unit cell (a = 5.10 A , c = 20.80 A , c/a = 4.08) , and Ti(Ni 0.11 ,Pt 0.89 ) 3 with a hexagonal unit cell (a = 5.482 A , c = 15.65 A , c/a = 2.85) . The geometric factor may even be seen as influencing a transition of the layer type to be stacked. A second factor, the electronegativity difference of the atoms A and B, is recognized as the principal reason why the radius-ratio rule cannot be given in a quantitative manner. In many cases a third factor, the valence-electron concentration prevails.

Influence of radius ratio on the structure of intermetallic compounds of the AB3 type

An extensive study has been made of the trialuminides of the rare-earth metals. In addition to showing the existence of several Ni3Sn-type trialuminides hitherto unknown (those of Ce, La, Pr and Nd) the detailed structures are given of a number of rhombohedral trialuminides (those of Y and Tb which are isotypic with BaPb3, and those of HoAl3 and DyAl3 which both have the HoAl3 type of structure). These structures, together with the Ni3Ti type, encountered with the ternary trialuminides (Gdx, Er1−x)Al3 and (Yx, Er1−x)Al3, and also the PuAl3 type form a family of transition structures between the Ni3Sn and the Cu3Au types. As the rare-earth/Al radius ratio decreases the trialuminides adopt structures passing from predominantly hexagonal to predominantly cubic, subject to the two rules that the layer repeat period of the lattice tends to be a minimum and that the alternation of hexagonal and cubic stacking is a maximum.

The structures of the rare-earth trialuminides

The occurrence and crystal structures of ternary compounds of the composition RT 4 Al 8 (T = V, Cr, Mn, Fe, Co, Ni or Cu, R = rare earth, Y or Th) have been investigated. The various effects of the atomic sizes are discussed.

J.H.N. van Vucht

Papers

Martensitic transformations in gold-titanium, palladium-titanium and platinum-titanium alloys near the equiatomic composition

Atlas of Crystal Structure Types for Intermetallic Phases

Influence of radius ratio on the structure of intermetallic compounds of the AB3 type

The structures of the rare-earth trialuminides

Note on the crystal structure of the ternary rare earth-3d transition metal compounds of the type RT4Al8