V. G. Khoruzha

Microstructure, Growth Kinetics, and Abrasive Wear Resistance of Boride Layers on Fe–30% Cr Alloy

Two boride layers are found to form at the interface between reacting phases in the course of boriding a Fe–30% Cr alloy in boron powder with KBF4 (activator) in the temperature range of 850–950°C and reaction times 3600–43200 sec (1–12 h). Each of these layers is single-phase structurally (crystallographically) and two-phase compositionally (chemically). The outer boride layer bordering boron consists of the crystals of the (Fe, Cr)B and (Cr, Fe)B compounds, while the inner layer adjacent to the alloy base comprises the crystals of the (Fe, Cr)2B and (Cr, Fe)2B compounds. The characteristic feature of both layers is a profound texture. Diffusional layer-growth kinetics are close to parabolic and can alternatively be described by a system of two non-linear differential equations dx/dt = (kB/x) – (rgkFe/py), dy/dt = (kFe/y) – (qkB/sgx), where x is the outer FeB layer thickness (m), y is the inner Fe2B layer thickness (m), kB is the FeB layer growth-rate constant (m2⋅sec–1), kFe is the Fe2B layer growth-rate constant (m2⋅sec–1), g is the ratio of the FeB and Fe2B molar volumes, p = q = r = 1, and s = 2 (factors from the chemical formulae of FeB and Fe2B). The temperature dependence of the layer growth-rate constants obeys a relation of the Arrhenius type K = Aexp (–E/RT), where K stands for any constant, A is the frequency factor, E is the activation energy, R is the gas constant, and T is the absolute temperature. Application of the least-squares fit method yielded the following equations: kB = 3.42⋅10–8⋅exp(–175.4 kJ × × mol–1/RT) m+⋅sec–1, kFe = 7.45⋅10–9 exp(–144.6 kJ⋅mol–1/RT) m2⋅sec–1. Microhardness values are 18.1 GPa for the outer boride layer, 15.2 GPa for the inner layer, and 1.75 GPa for the alloy base. The dry abrasive wear resistance of the outer boride layer, found from mass loss measurements, is more than 300 times greater than that of the Fe–30% Cr alloy base. Such a huge increase in wear resistance is due to the microstructure of boride layers having a peculiar regular arrangement of enhanced rigidity.

The Constitution of Alloys and Phase Diagram of the Ternary Al–Cr–Pt System at 50–100 at.% Pt. I. Solidus Surface and Isothermal Section in the Al–Cr–Pt System at 1350 C in the Range 50–100 at.% Pt

The results of high-temperature diffraction, metallography, X-ray diffraction, electron microprobe analysis, and differential thermal analysis are used to specify the constitution of the Al–Pt system in the near-equiatomic range. The solidus surface is constructed for the first time on the composition triangle, and the constitution of the isothermal section at 1350°C in the range 50–100 at.% Pt of the Al–Cr–Pt ternary system is specified. The solidus surface consists of six single-phase surfaces corresponding to the ternary τ1 phase (unknown structure), solid solutions based on platinum, and four binary phases existing in the Al–Pt system; nine ruled surfaces bounding two-phase volumes; and four isothermal planes forming invariant four-phase equilibria with participation of a liquid phase. When temperature decreases from subsolidus to 1350°C, stability of the phase based on the <(Al, Cr)Pt2> compound (low-temperature modification) increases substantially. This phase takes part in equilibria with other intermediate phases and with the Pt-based solid solution.

Constitution of alloys and phase diagram of the Al–Ti–Rh system. III. Solidus surface of the Ti–TiRh–AlRh–Al partial system

The data obtained by metallography, x-ray diffraction, electron microprobe and differential thermal analyses as well as by Pirani–Alterthum incipient melting technique are used to construct the solidus surface projection of the Ti–TiRh–AlRh–Al partial system onto the composition triangle for the first time. The participation of two ternary compounds (τ1, Al67Ti27Rh6, with AuCu3-type structure, and τ2, Al49.6Ti27.1Rh23.3, with Th6Mn23+1-type structure) in phase equilibria is confirmed. Thirteen single-phase surfaces corresponding to solid solutions based on components and to the phases based on binary and ternary compounds are found on the solidus surface. This surface also contains 25 ruled surfaces bounding two-phase volumes as well as 13 isothermal planes that are constituents of invariant four-phase equilibria.

CONSTITUTION OF ALLOYS AND PHASE DIAGRAM OF THE Al-Ti-Rh SYSTEM. IV. MELTING DIAGRAM OF THE Ti-TiRh-AlRh-Al PARTIAL SYSTEM

Based on constitution of the solidus surface of the Ti–TiRh–AlRh–Al partial system and on metallography, X-ray diffraction, electronic microprobe, and differential thermal analyses of its ascast alloys, the liquidus surface projection of the system is constructed onto the concentration triangle for the first time and the processes occurring in the crystallization of its alloys are studied. This has given an opportunity to construct the melting diagram of the Ti–TiRh–AlRh–Al partial system for the first time. Its liquidus surface is completed with 13 surfaces of primary crystallization of solid solutions based on components and phases based on binary and ternary compounds. In the Ti–TiRh–AlRh–Al partial system, there are 13 invariant four-phase equilibria involving liquid as well as nine invariant three-phase equilibria, eight of them being eutectic and one peritectic.

Alloy behavior and the Sc-Ru-Rh phase diagram. Part 1. Solidus surface in the Ru-ScRu-ScRh-Rh partial system

Data obtained by microstructural, x-ray phase, and microprobe analysis have been used together with measurements of the temperature for the start of melting by the Pirani - Alterthum method to obtain a projection of the solidus surface in the partial Ru-ScRu-ScRh-Rh system on the concentration triangle. It is found that ternary compounds are not formed. The solidus surface is made up of five surfaces for the primary crystallization of solid solutions based on ruthenium and rhodium together with phases based on the compounds ScRu2, ScRh3, and the 6 phase (a continuous series of solid solutions between isostructural phases of CsCl type based on ScRu and ScRh), together with seven lineated surfaces, which enclose two phase volumes, and three isothermal areas, which relate to nonvariant four-phase equilibria involving the liquid: L — + + 6 (1650°C), L + ⇌ + (1640°C) and L ⇌ + ⇌ + (1520°C).

Phase Equilibria in the Aluminum Corner of the Al–Ti–Pt System

A series of physicochemical analysis techniques are employed to study the phase equilibria in the aluminum corner of the Al–Ti–Pt system at subsolidus temperatures and in the alloy crystallization process. It has been established for the first time that a ternary τ1 phase (AuCu3 structural type) forms by peritectic reaction L + + ⇄ τ1 at 1405°C. On the solidus surface in the studied composition range at 1405, 1310, 1275, 1060, 925, 820, and 660°C, there are seven isothermal planes that participate in invariant four-phase equilibria involving the liquid phase, three of them being peritectic and the others transitional.

Liquidus surface and melting diagram of the Al–Ti–Pd system in the Al–AlPd–TiPd–Ti region

The solidification of Al–Ti–Pd alloys is studied by light optical and scanning electron microcopy, electron microprobe analysis, X-ray diffraction, and differential thermal analysis in the composition range 0–50 at.% Pd in the Al–AlPd–TiPd–Ti partial system. The liquidus surface projection, melting diagram, and Scheil diagram are constructed for the first time. Eleven regions of primary solidification of ternary compounds, solid solutions based on binary phases, and Ti and Al components are found to exist. The τ3 phase melts congruently while τ1 is formed incongruently.Eleven four-phase invariant equilibria involving a liquid phase exist in the system: two of them are congruent and nine incongruent. The invariant four-phase reactions occur in the temperature range between 630 and 1425–1456°C.