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doi: 10.1007/BF02474881pmid: N/A
The results of research in the field of martensite transformations reflect the complexity and inexhaustible nature of this many-sided process, which shows the importance and expediency of continuation of the work in this field with the aim of finding new, still unknown possibilities for varying this process and discovering new aspects of its practical use.
Kraposhin, V.; Talis, A.; Pankova, M.
doi: 10.1007/BF02474882pmid: N/A
1. A topological concept of four-dimensional polyhedrons is used to suggest a geometric scheme of mutual transformation of coordination polyhedrons of crystal lattices in polymorphic transformations of metals. 2. A known scheme of transformation of a cube octahedron into an icosahedron is used to describe the transformations between b.c.c. and h.d.p. lattices; a special scheme of transformation of the rhombododecahedron of a b.c.c. lattice into a Frank-Casper polyhedron with coordination number 14 is suggested for transformations of a densely packed structure into a b.c.c. structure. 3. The polymorphic transformation between f.c.c. and h.d. modifications occurs in the following way: cube octahedron of f.c.c. lattice→icosahedron→anti-cube-octahedron of h.d. lattice. 4. The polymorphic transformation between densely packed (f.c.c. and h.d.) and b.c.c. modifications occurs through an intermediate atomic configuration that coincides with crystal structure A15, i.e., f.c.c. (h.d.) → A15 → b.c.c. The choice of structure A15 is explainable by the three-dimensional packing of interpenetrating linear chains of cosahedrons and 14-vertex Frank-Casper polyhedrons. 5. The suggested scheme of transformation of coordination polyhedrons agrees with the observed orientation relations and habitus planes in martensite transformations occurring in iron-base alloys. The indices of martensite habitus planes {15.10.3}, {522}, {755} are indices of a Frank-Casper coordination polyhedron that is an intermediate configuration in the martensite transformation.
doi: 10.1007/BF02474883pmid: N/A
1. The suggested new variant of grouping of martensite plates is represented by a closed rhombic bipyramid faced by eight habitus planes of the same type united around one common direction (110). The direction (110) constitutes the minimum of all possible angles with the poles of the normals to the habitus planes of the grouping. 2. This pyramidal grouping of plates has been observed in a metallographic study of cooling martensite in alloy 50N29. 3. The space of an austenite grain is filled by the formed martensite phase by translation of pyramidal groups with formation of a kind of macrolattice. The pyramidal groups combine like coordination octahedrons of densely packed crystal structures along the common edges and vertices. 4. Different variants of growth of faces in pyramidal groups in combination with different variants of cutting of the macrolattice by the plane of the metallographic specimen make it possible to explain the origin of the morphological variants of martensite.
Lelatko, J.; Morawiec, N.; Koval', Yu.; Kolomyttsev, V.
doi: 10.1007/BF02474884pmid: N/A
Martensite transformation in alloys of the system Cu−Al−Nb occurs at temperatures much above 200°C. The hysteresis of the reversible martensite transformation is 108–128°C, which is less than for alloys of the system Cu−Al−Ag [3]. Alloys of the system Cu−Al−Nb possess a high effect of shape memory and an elevated ductility and strength. The degree of recovery of shape for an alloy with 2.56% Nb exceeds 90% at σГ MPa and δ20=12.7%
Golovin, S.; Golovin, I.; Nilsson, J.; Serzhantova, G.
doi: 10.1007/BF02474885pmid: N/A
1. We have developed a method for plotting C-curves of isothermal martensite transformation by analyzing the temperature and amplitude dependences of IF with thermostatic control in the range of temperatures of martensite transformation. We have obtained data on the inelasticity and microplasticity of the studied alloys in the course of isothermal martensite transformation and have determined the inelastic effects (internal-friction peaks) in warming the alloys up after the martensite transformation. 2. We have determined the activation energy of isothermal martensite transformation in an Fe−Cr−Ni−Mo steel within the framework of the theory of absolute reaction rates, namely,H≅20 kJ/mole. In alloys of the system Fe−Ni−Mo with a double kinetics of martensite transformation the activation energy changes fromH≅6–8 kJ/mole at the nose of the C-curve toH≅2–3 kJ/mole at a temperature approaching the point of adiathermal martensite transformation. 3. We have established the effect of the content of interstitial atoms on the kinetics of the change in the properties of the alloys in subsequent cooling in the temperature range of martensite transformation and the role of trapping of dislocations by interstitial atoms. The formation of saturated impurity atmospheres on dislocations diminishes the role of the dislocations as sites of martensite nucleation due to compensation of the energy of elastic distortions around the dislocations and growth of the energy of formation of martensite nuclei, diminishes the mobility of the dislocations, increases the relaxation stability of austenite, and hampers the development of the isothermal kinetics of initiation and progress of MT.
doi: 10.1007/BF02474886pmid: N/A
1. We have computed the energies of paired elastic (strain) interaction of carbon atoms in austenite and have shown that this interaction is strong and long-range and can effect considerably the structure formed in the transformation of austenite. 2. The model of strain interaction of introduced atoms supplemented with repulsion in the first coordination sphere is applicable for describing the thermodynamic properties of austenite.
doi: 10.1007/BF02474887pmid: N/A
Sudies begun in the 1960s under the guidance of R. I. Éntin at the Institute of Metal Physics of the Bardin Central Research Institute of Ferrous Metals have shown that high stability of low-carbon austenite in both the “normal”2 and bainite regions can be provided at a specific proportion of carbon and the alloying elements. The starting temperature of martensite transformationM 5 remains at 300–400°C. This makes it possible to obtain in steels the structure of lath martensite in large cross sections by air cooling. These low-carbon martensite steels (LCMS) possess a favorable combination of mechanical properties and a number of technological advantages even in the quenched state, which widens their range of application in industry. In recent years several new groups of LCMS have been created.
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