Structural and phase transformations in electrical spark modification in a ceramic-ceramic system

The composition and structure of the surface layer and kinetics of electric-stimulated mass transfer in electrical spark alloying in ceramic-ceramic systems are studied. It is established that the mechanism underlying the kinetics of mass transfer typical for metallic electrical spark surfaces is three-stage in nature. Electrical spark modification of the surface of composite materials is shown to be possible.     

Structural and phase transformations in α + β brasses

The effects of the chemical composition of α + β brasses and heat treatment conditions on the amount, morphology, and chemical composition of the phases forming these brasses have been studied. Apart from the main phases (an α solid solution of alloying elements in copper and a β phase based on the electronic compound CuZn), all brasses under study are shown to contain M ₅Si₃ (M = Fe, Mn, Ni) silicides and particles of free lead (1–2 vol %). The amount and morphology of α and β grains can be controlled by heat treatment, whereas the quantitative characteristics of the silicides are mainly determined by the chemical composition of the alloy. Cu-Zn-Mn-Al-Fe-Si brasses can be additionally hardened due to the formation of ultradispersed Mn₅Si₃ silicides and martensite upon quenching and due to the partial dissolution of these particles and the formation of a bainite structure upon subsequent tempering at 260–270°C.     

Structural and phase transformations in the cooling of rail steel

Thermokinetic diagrams of supercooled-austenite decomposition are plotted for K76Ф rail steel with the addition of 0.026% and 0.092% Cr. The hardenability of the steel is determined. The temperature of Jominy samples is analyzed. The microstructure of the steel is established. The influence of the cooling rate, temperature, and chromium content on the microstructure and hardness of the steel is investigated. The cooling rate such that uniform pearlite microstructure is obtained is established. The limiting hardness of the pearlite microstructure is determined.     

Solutionizing effects on deformation-induced phase transformations in 2014 aluminum composite

A solutionizing heat treatment of 2014 aluminum alloy reinforced with 0.15 volume fraction of alumina particles (VFAP) results in deformation-induced precipitation during rolling and tensile deformation, with 0.10 VFAP, at room temperature. The extent of precipitation increases with increase in time and/or temperature of solutionizing. An attempt has been made to identify the various types of precipitates in the samples deformed to a given strain and in fractured conditions. The work-hardening curves and tensile properties of the composites have been shown to be dependent on the time and temperature combination of the solutionizing process.     

Structural and phase transformations in the continuous cooling of steel for one-piece railroad wheels

The influence of the cooling rate on the phase transformations and the position of the critical points during the continuous transformation of the supercooled austenite in steel for one-piece railroad wheels is established by means of the Gleeble 3500 system. The microstructure is established, and the influence of the cooling rate on the structure and hardness is analyzed. Thermokinetic diagrams of supercooled-austenite decomposition in 2, T, and C wheel steel are presented. Recommendations are made for correction of the cooling in the heat treatment of railroad wheels.     

Radiation as a tool in understanding phase transformations

Radiation may affect the course of a phase transformation in many ways, ranging from such a simple effect as enhanced diffusion or solute segregation to more complex effects such as dissolving thermally stable precipitates, inducing compositional instabilities, or altering phase boundaries. In the case of Invar-type Fe-35Ni-XCr alloys, irradiation-enhanced diffusion of all elements and segregation of nickel at sinks accelerate and make observable a spinodal reaction otherwise observable only after extended thermal annealing. Moreover, irradiation apparently also expands the boundaries of the miscibility gap. Irradiation may also be used to obtain structures unattainable thermally, even through such techniques as rapid quenching from the vapor or liquid. This paper is based on a presentation made in the symposium “Irradiation-Enhanced Materials Science and Engineering” presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25–29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD.     

Radiation as a tool in understanding phase transformations

Radiation may affect the course of a phase transformation in many ways, ranging from such a simple effect as enhanced diffusion or solute segregation to more complex effects such as dissolving thermally stable precipitates, inducing compositional instabilities, or altering phase boundaries. In the case of Invar-type Fe-35Ni-XCr alloys, irradiation-enhanced diffusion of all elements and segregation of nickel at sinks accelerate and make observable a spinodal reaction otherwise observable only after extended thermal annealing. Moreover, irradiation apparently also expands the boundaries of the miscibility gap. Irradiation may also be used to obtain structures unattainable thermally, even through such techniques as rapid quenching from the vapor or liquid. This paper is based on a presentation made in the symposium “Irradiation-Enhanced Materials Science and Engineering” presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25–29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD.     

Ledges and dislocations in phase transformations

The coupling of dislocations and ledges in phase transformations is considered in terms of the symmetry of phases meeting at an interface. Growth and structural ledges and a variety of dislocation arrays are treated. Symmetry and the absence of long-range strain fields alone are shown to produce few restrictions on possible interface structures. This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Cavitation-erosion-lnduced phase transformations in alloys

Previously reported surface phase transformations occurring during cavitation erosion in cobalt- and iron-base alloys have been confirmed. However, an examination of the effect of aging treatments on Stellite 6B failed to demonstrate any simple relationship between transformation characteristics and erosion resistance. For several iron-base transformable alloys, the erosion resistance was shown to be related to strength and again no direct correlation could be established between transformation and erosion. It is concluded that the phase transformation is incidental to the erosion process. However, since many erosion resistant alloys do undergo a deformation-induced phase transformation, a more general explanation for the erosion resistance of alloys with close-packed structures is offered in terms of stacking fault energy.     

Interfacial dynamics in diffusion-driven phase transformations

The migration of ledges in a semicoherent α/β interface is considered to participate in solid-state transformations driven by diffusion. The advance of the ledge and/or the progress of the transformation can require the climb of misfit dislocations both in the ledge and in its path. The creation or annihilation of vacancies required for the transformation and the legde advance is provided by a combination of three vacancy sources or sinks: (a) the net vacancy flux to/from the interface resulting from the difference in lattice plane shift (Kirkendall effect) within the two contacting phases, (b) the climb of misfit dislocations from the interface into the bulk of the α and β phases, and (c) the climb of misorientation dislocations within the interface. Thus, the dynamic action of the interface during the phase transformation would include: (i) climb of misfit dislocations out of the interface, with ensuing dissociation into glissile dislocations which resupply the interface by return glide, and (ii) climb of misorientation dislocations in the interface necessitating a continuing arrival of such dislocations from sources in the bulk or in the interface.     

Mass transport and phase transformations in a system of small Mo-W-C particles

Translated from Poroshkovaya Metallurgiya, No. 7(319), pp. 17–22, July, 1989.     

Secondary structures of friction at the surface of bronze alloyed with tungsten disulfide

Methods of x-ray microprobe analysis, metallography, and continuous impression of an indentor are used to study secondary structures covering the friction surface of a bronze-tungsten disulfide (VAFC) composite-steel pair. Differences in the structure, composition, and properties of the friction track on a VAFC composite for four stages of testing in air, in a vacuum, in a vacuum with screen cooled by liquid nitrogen, and action of a current are found. It is established that the friction track is narrowest and most homogeneous using action of a current with the use of optimum friction conditions. It differs essentially not only from the initial VAFC phase but also from the initial friction tracks in the first three cases. The friction track material is a chemical compound corresponding in composition to the formula Me₂S. It is assumed that the anomalously low friction in this case is due to presence of readily sliding planes in this substance.Translated from Poroshkovaya Metallurgiya, No. 5, pp. 33–39, May, 1993.     

Hydrogen-induced phase and structural transformations in titanium alloys with β-eutectoid stabilizers

The mechanism of hydrogen-induced structure formation in titanium alloys with β-eutectoid stabilizers is analyzed. Additional hydrogen alloying of Ti-Cr alloys is shown to increase the stability of the β phase with respect to the α phase and to decrease its stability with respect to the intermetallic compound TiCr₂. Hydrogen dissolved in a commercial multicomponent TS6 alloy containing 11.3% Cr is found to favor the precipitation of an intermetallic compound Ti_xCr_y, which also contains other alloying elements present in the alloy. The mechanism and kinetics of the formation of this intermetallic compound during hydrogenation annealing and isothermal heat treatment are considered. Structures with the intermetallic compound Ti_xCr_y can be produced upon low-temperature vacuum annealing of a hydrogen-charged TS6 alloy.