Γ-solid Solution Research Articles

XRPD application for laser-treated surface of Fe-based alloys study

Fe−Ni alloys after laser treatment were investigated by X-ray powder diffraction and scanning electron microscopy. As a result it was found out that the microstructure of alloys was reduced to fragments by laser pulse treatment. The lattice parameter value of γ-solid solution showed an abnormally high carbon content at some laser treatment conditions. X-ray investigations of laser-treated thin surface layers showed irregular carbon distribution and other alloying elements throughout the treated layer. The research of thin surface layer showed nonmonotonous dependence of γ-solid solution lattice parameter deep into the treated layer. The carbon concentration in the γ-solid solution of these laser-treated zones was more than its concentration after hardening in water and as a result, the lattice parameter of γ-solid solution increased.

Crystal chemical properties and preparation of single crystals of AgGaSe 2[sbnd]GeSe 2 γ-solid solutions

The phase equilibria in the AgGaSe 2 GeSe 2 quasi-binary system were studied using differential thermal analysis and X-ray diffraction. It was established that the given section is quasi-binary in the Ag 2Se Ga 2Se 2 GeSe 2 ternary system and contains three regions of solid solutions. The crystal chemistry properties of phases of variable composition were studied. The structure of these phases depends directly on the tetrahedral cavity filling by silver ions. A method for obtaining single crystals from the region of γ-solid solutions was worked out. The orientation of the obtained single crystals was determined by X-ray diffraction.

Austenite Stabilization of Fe-Ni Alloy

By X-ray powder diffraction and magnetometric methods we investigated the effect of phase hardening during γ-α-γ transitions. In this case austenite becomes more stable to subsequent γ-α-γ transitions, the dislocation density increases, the grain reduce in fragments and the hardness increases, too. In addition, the γ-solid solution in some steels is unstable during ageing. The phase hardening was found to stabifize the γ-solid solution of Fe-Ni alloy to subsequent thermal treatment. This is consistent with an increase in carbon mobility after γ-α-γ transitions. Tlat is why decarbonizations of austenite iake place during increase in extent of phase hardening. PACS numbers: 61.10.Lx, 61.50.Ks

Lithium ion conducting Li 4−2 xGe 1− xS xO 4 solid electrolytes

A range of stable solid solutions with γ-LISICON type structure forms in the system Li 4−2 x Ge 1− x S x O 4 for 0.08 < x<0.42. This phase has high lithium ion conductivity with a maximum value (bulk) of ∼1.85×10 −5 S cm −1 for x=0.20 at 27° C. The net pellet conductivity for this compositions is ∼1.00×10 −5 S cm −1 at 27°C, rising to ∼0.04 S cm −1 at 300°C. Conductivity Arrhenius plots for different compositions in the γ-solid solution range exhibit markedly non-linear behaviour above ∼ 300°C. The activation energies below ∼ 300°C are in the range 0.50-0.60 eV. The γ-solid solutions are structurally related to orthorhombic γ-Li 3PO 4 and contain interstitial Li + ions; for x=0.20, a=6.253(2) A ̊ , b=10.828(3) A ̊ , c=5.114(2) A ̊ , at room temperature. An approximate phase diagram for the Li 4GeO 4Li 2SO 4 binary system is presented, together with lattice parameter data on the γ-solid solutions.

Microstructural investigation of IN 939 superalloy

The vacuum cast nickel base IN 939 superalloy was investigated in the as-cast condition, as well as in the fully heat treated condition, i.e. after solution treatment followed by ageing. The alloy was characterized by optical microscopy, electron probe microanalysis and X-ray diffraction analysis. Volume fraction of the γ'-strengthening phase was determined by electrolytic phase extraction. The room and high temperature tensile properties and the Vickers hardness were determined for the as-cast and heat treated condition of the alloy. It was determined that the structure of the alloy consists of the γ-solid solution matrix, the γ'-intermetallic precipitate and various carbide phases. The simple heat treatment employed was shown to be effective in raising the γ' volume fraction and the yield and tensile stress.

Structure and properties of steels after boronizing with the use of laser heating

1. In all the investigated steels saturation with boron leads to the formation of a heterophase structure characterized by dispersity of the structural components, chemical and structural inhomogeneity. In a thin surface layer of the treated zone metallography reveals molten boron particles which did not have time to react with the liquid metal. 2. In dependence on the marque of steel the boronized layers have different phase composition, and in addition to α- and γ-solid solutions they contain iron boride Fe2B and also complex boron carbides with different stoichiometric composition. Metastable crystalline phases were not discovered in the investigated specimens. 3. Laser boronizing increases microhardness because of the more complex phase composition as well as other changes of the structure connected with the high cooling rates of the alloyed layers.

Microstructure and mechanical properties of melt atomized and rapidly solidified ultrahigh boron alloy steels

Abstract Rapidly solidified high alloy steel powders with boron contents up to 4.2wt.% and particle sizes of less than 80 μm have been produced by argon melt atomization. The microstructure consists of metastable and stable borides with dendritic or complex shapes within the α- or γ-solid solution matrix. After consolidation by extrusion the materials exhibit a fine-grained equiaxed microstructure with grain sizes of less than 5 μm. These particle-reinforced ultrahigh boron steels reveal superior elastic and strength properties at room and elevated temperature. In addition, structural superplasticity with large elongation to failure ( > 500%) occurs at higher temperatures of about 1000°C. This is due to grain boundary sliding accommodated by lattice and grain boundary diffusion.

Structure and properties of Fe?Cr?Mn steels after quenching with preheating in the intercritical temperature interval

The quenching of high-alloy chromium-manganese steels, which includes preheating in the intercritical (α+γ) temperature interval and subsequent short-term austenitizing, the latter eliminating homogenization of the γ-solid solution, increases the dispersity of the martensite and stabilizes the austenite.

Features of the phase composition of nickel alloys with high tungsten and molybdenum contents

1. In the high-temperature hardened condition with a total tungsten and molybdenum content in the alloys of not more than 8 at. % α2, σ, and μ type excess phases are not formed and only complex carbides are present. In the alloys without molybdenum but containing 6.5 at. % W hardening α2-phase is precipitated. 2. The high-temperature strength of alloys containing ≥6.5 at. % W is higher than of alloys containing about 8 at. % W+Mo, which is related not only to hardening by these elements of the γ-solid solution but also to formation of excess α2-phase. 3. In the alloys containing more than 5–6% each of W and Mo (or ΣW+Mo≥5 at. %) type M6C binary chromium carbide is present, while with ΣW+Mo≤5 at. % type M23C6 cubic carbide is precipitated, which has a positive influence on the high-temperature strength of the investigated alloys.

Effect of initial-carbide morphology on the structure and properties of high-strength rail steels after quenching from induction heating

1. High strength in combination with sufficient plasticity and ductility are achieved in high-carbon rail steel by the production of a fine-grain highly disperse structure and substructure as a result of rational alloying with Cr, Si, and Mn, and complex modification with V, Ti, and Ce together with combined heat treatment, where spheroidizing annealing to disperse granular pearlite is used as preliminary treatment. 2. Globular carbides, which ensure the slowing of austenite-grain growth and size reduction in the structure, are retained to a certain degree in the γ-solid solution when lowalloy rail Cr−Si−Mn steel, which has been pretreated to disperse granular pearlite, is subjected to final heat treatment using induction heating. In this case, the structure of the martensite is formed with plates having acicular and packet morphology and with an insignificant number of twins.

Microstructure of low-alloy cast iron with spheroidal graphite and high crack resistance

1. The results of investigations of the resistance of cast irons with different structures and shapes of graphite inclusions to brittle failure suggest the absence of correlation between KIc and δ, and the presence of a weak correlation between σu and σo.2. The critical embrittlement temperature can be estimated qualitatively from the results of tests on the resilience of specimens with an acute notch (Charpy-type). 2. Two-stage annealing at 920°C and 720°C with subsequent heating to Ac2, holding for 15...30 min, and cooling in air to 600...500°C, and thereafter in water or oil makes it possible to fix ductile austenite, which is stable to the normal temperature, along the ferrite-grain boundaries; in this case, redistribution of Mn, Ni, Cr, Mo, Cu, Al, and Si occurs between the α- and γ-solid solutions, and the fracture toughness KIc is increased as compared with the KIc of cast iron with an initial ferritic structure. 3. An increase of up to a total of 2.0...3.5% in the extent to which ferritic cast iron with spheroidal graphite is alloyed with Ni, Cu, Cr, Mn, Mo, and Al contributes to an increase in the amount and stability of austenite, even during slow cooling in air. 4. The investigations that we conducted to determine the feasibility of increasing the resistance to brittle failure, which were conducted on compact specimens for eccentric tensioning and which were computed by methods used for steel components, make it possible to expand the range of application of low-alloy cast iron with spheroidal graphite.

High resolution electron microscopic studies of Ni-9.3 and 14.7 at.%Ti alloys

The early stages of decomposition in Ni-9.3 and 14.7 at.% Ti alloys are studied by means of high resolution electron microscopy. The microstructure of the as-quenched Ni-9.3 at.% Ti alloy shows contrast of broad circular regions, and local lattice images show some difference in lattice spacing suggesting compositional modulations. Electron and optical diffraction patterns indicate faintly ordered regions. After ageing for 15 min at 570°C, the ordered regions, approx. 50 Å in diameter, appear as clear lattice images surrounded by dark areas of the f.c.c. γ-solid solution. The Ni-14.7at.% Ti alloy aged for 15 min at 570°C shows ordered lattice images in wide areas of the matrix, apart from some large needle-like precipitates of the equilibrium η-phase formed during the homogenization at 1200°C. As the atomic arrangement in the ordered regions corresponds to the (110) projection of the L1 2 structure, the image is interpreted as the structure image of ordered L1 2, Ni 3(Ti x Ni 1− x ). The lattice spacings locally change in the ordered regions, suggesting some modulation in composition and degree of order.

Solid-phase reactions and diffusional homogenization in Fe-Cr3C2-Mo2C powder composites

In the Fe-Cr3C2-Mo2C system the carbides rapidly dissolve, with the formation of a γ-solid solution characterized by a very uniform distribution of the alloying elements and carbon. The powder metallurgy method has made it possible to obtain a single-phase alloy containing 8.5% Mo, 8% Cr, and 1.5–1.7% C.

Characteristic features of the formation of metastable structures in alloys of the Mn?Cu system

1. When Mn−Cu alloys contain more than 55% of Mn, pronounced heterogenizing of the solid solution, which results in the formation of metastable segregations of almost pure copper for a short homogenizing time, occurs during cooling from the homogeneous γ-region. 2. Heterogenizing of the solid solution during cooling is governed by the presence of a high-temperature β-region not only in alloys with an Mn content higher than 55%, but also in an alloy with 55% of Mn and low copper solubility in the β-modification of the manganese. 3. The difference in the decomposition kinetics of the solid solution in alloys with a different manganese content is governed not by a change in the decomposition mechanism on conversion from an alloy with 45% Mn to alloys with a high Mn content, but by the occurrence of two concurrent processes in alloys containing more than 45% of Mn: manganese enrichment of manganese-impoverished regions during cooling from the temperature of the heat in quenching to values below the solubility limit in the γ-solid solution, and the lamination process of the matrix solid solution with the formation manganese-enriched and-impoverished regions.

Crystallization and the primary structure of Fe-C-Al alloys

1. The primary structure of Fe-C-Al alloys based on α- and γ-solid solutions forms by dendrite crystallization. 2. Formation of peritectic γ- and ɛ-phases occurs on the basis of primary dendrites by rim growth. 3. Intracrystalline liquation of aluminum depending on alloy composition may be direct or inverse.

Nickel-free iron-manganese alloys

1. Melt purity has a marked effect on the level of mechanical properties for Fe−Mn alloys and the nature of their change with an increase in manganese concentration. 2. For high-purity alloys strength properties increase markedly in the two-phase (e+γ)-region. Alloy with 21–24% Mn has the maximum strength (σf = MPa; σ0.2 = 4.50 MPa). 3. At the boundary of the (e+γ)-and γ-regions for high-purity alloys "boundary" or concentration superplasticity is observed; a reduction in test temperature to −196°C is accompanied by an increase in relative elongation. 4. For industrial purity alloys strength properties decrease gradually with a changeover from α- to e- and γ-solid solutions. Strength and ductility properties of these alloys are insensitive to the position of the (e+γ)- and γ-region boundary. 5. With an increase in melt purity reserve ductility for Fe−Mn alloys increases, and this has been established by fractographic study of the nature of their failure.

Structure of Vacuum Brazed BNi-5 Joint of Inconel 718

Structural investigations of the brazed joint of Inconel 718 with BNi-5 filler metal were carried out on specimens with geometries simulating a real joint. Three identification methods applied in parallel were used. Fused and solidified filler metal showed the presence of at least four microstructural components: the dominant γ-solid solution, two binary eutectics (G phase + γ) and (θ-phase + γ@#@), and prismatic objects identified as cr-phase. The influence of brazing time and temperature was studied with specimens heated in accordance with three different thermal regimes. The Ni-base γ-phase solidifies in dendritic form and contains Cr, Fe, Nb, and Mo, the concentrations of which are dependent on the thermal regime and on the distance from the former liquid-solid interface. The intermetallics (G, 0) and the matrix form binary and ternary eutectics. In overheated brazed joints the filler metal penetrates into the grain boundaries of the base metal, resulting in the formation of new phases. The dominant phase was identified as a hexagonal Laves phase (λ,). The diffusion zone in the base metal can be divided into two subregions. In subregion I the precipitating phase is a Nb-rich G-phase, while in subregion II, the depth of which can be directly related to the width of the gap, preferentially oriented carbides of Nb and Ti are formed. The phase formation in the BNi-5 brazing of Inconel 718 may be described by a quasi-quarternary diagram on the Ni-Cr-Nb-Si system.

Structure of high-speed steel with high solidification rates

1. The interaction of the particles in spraying to a significant degree determines the conditions of solidification and the final structure of high-speed steel powder. After colliding with larger drops the highly dispersed, rapidly solidifying particles play the role of foreign internal centers of solidification on the surface of which heterogeneous formation of nuclei of the crystallizing phase starts. 2. After cooling of the molten metal at rates of 104–4·105 deg/sec the primary phases in the structure of the high-speed steel are martensite, austenite, and types MC, M2C, and M6C carbides. An increase in the cooling rate within these limits leads to an increase in the share of austenite and a corresponding decrease in the share of martensite in the structure of the steel with a simultaneous reduction in the carbon and alloy element content in the martensite. 3. To a certain degree the structural inhomogeneity characteristic of cast high-speed steels is maintained after cooling at high rates. The branches of the dendrites consists of lamellar martensite and high-alloy austenite and the carbides are concentrated in the interdendritic space, forming a continuous network in the volume of the particles. 4. An increase in the cooling rate in solidification to 106 deg/sec and more causes sharp changes in the structure of the high-speed steel. The sharply expressed dendritic structure at low cooling speeds disappears, the processes of precipitation of primary carbides are partially or completely suppressed, and the primary phases in the structure become α- and γ-solid solutions.

The intermediate transformation in steels ShKh15 and ShKh15SG

1. For each of the steels investigated a relationship was found between the variation of the austenite lattice constant during the intermediate transformation and the carbon content of the original austenite before transformation of the γ-solid solution similar to that for a number of steels with approximately the same alloying. 2. Heats containing larger amounts of carbon in the original austenite have an elevated hardness in the intermediate transformation zone due to the more intensive formation of carbide.

蒸着法で製造したAg-Cu合金の組織と機械的性質

When alloys are vacuum-deposited on cooled substrates, super-rapidly cooled alloy films in the unequilibrium state can be obtained. As an application of this method, alloy films of Ag-Cu solid solution were prepared in the thickness of about 5 μ, and the changes in their microstructure and mechanical properties with tempering temperature were investigated. The results obtained are summarized as follows: (1) When alloys of about 50%Ag-50%Cu were deposited on metallic substrates placed on a copper plaque cooled with liquid nitrogen, solid solutions containing a small amount of amorphous phase were formed. (2) The solid solution was hardened by tempering at 150°C. The hardening is considered to occur when the solid solution begins to decompose into α and β phases. (3) The Knoop hardness number of a 40 at%Ag-Cu alloy film deposited on a cooled glass substrate was 390 kg/mm2. The as-deposited films were generally very hard but fractured under stresses below their elastic limits. (4) Liquid-quenched 50 at%Ag-Cu alloys consisted of a lamellar structure of α and β, and contained a small amount of γ-solid solution. They showed ductility.