Crystallography of in-situ transformations of the <Emphasis Type="Italic">M</Emphasis><Subscript>7</Subscript>C<Subscript>3</Subscript> carbide in the cast Fe–Cr–Ni alloy

In the process of holding of the cast heat-resistant Fe–Cr–Ni (0.45C–25Cr–35Ni) alloy at 1150°C, the eutectic chromium carbide present in its structure undergoes a gradual transition M ₇C₃ → M ₂₃C₆. The gradual formation of domains of the M ₂₃C₆ carbide inside the particles of the M ₇C₃ carbide makes it possible to assume that the observed phase transition is the well-known carbide transformation of the in situ type. The mechanism of the in situ transformation of the crystal structure of the carbide from M ₇C₃ into M ₂₃C₆ with a change in the number of nearest metal neighbors of carbon atoms is explained within the previously developed combinatory model of polymorphic transitions in the metals.     

Geometrical Model of Polymorphous Transformations in Titanium and Zirconium

A geometrical model of transformation of a body-centered cubic lattice of α-phase into a hexagonal close-packed lattice of α-phase is developed with the aim of explaining the special features of the crystal geometry of formation of martensite phases in titanium and zirconium and in alloys based on them. The transformation is described as mutual reconstruction of coordination polyhedra of the cubic and hexagonal lattices through an intermediate configuration of the crystal structure of ω-phase. In the language of algebraic geometry the transition is implemented as reconstruction of an 11-atom cluster that represents a union of three octahedra around a common edge into an 11-atom cluster composed of 11 tetrahedra united over faces. Experimentally observed orientation relations and habit planes at α → ω and β → α transformations are describable by elements of the structure of the mentioned clusters.     

Polytope topological approach to describing martensite transformation

Conclusions  

Structure of quenched metallic alloys and phase equilibrium diagrams

Experiments on the quenching of cast iron from the liquid state were carried out by A. Ulitovskii as early as the 1930's. Intensive studies of the structure of quenched melts which were carried out in the early 1960's revealed several new structural states in metallic systems: supersaturated solid solutions, new metastable intermediate phases (not typical of the given system at equilibrium), metallic glasses (amorphous phases), and quasicrystalline phases. In order to explain these effects (not including new phases) special theoretical models are usually proposed, which are at times yen elaborate. Based on the published data it is possible to describe these structural states from a unified point of view excluding the concept of diffitsionless solidification.Penne, September 19–23, 1994.Institute for Problems of the Technology of Microelectronics and Very Pure Materials, Russian Academy of Sciences, Chernogolovka. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 2–12, October, 1994.     

Mechanism of Nucleation of Precipitates of Carbides of Refractory Metals Under Hot Rolling of Automotive Sheet Steel

Metal Science and Heat Treatment - The problem of formation of properties in microalloyed sheet steels is considered. The cause and the possible mechanism of precipitation of carbides of refractory...