Structure of the phase equilibrium diagrams of aluminum alloys with scandium

The characteristics of a number of phase equilibrium diagrams of systems containing aluminum and scandium (Al−Sc, Al−(Li, Mg, Zr, Mn, Cu, Zn, Si)−Sc, Al−Mg−(Li, Zr)−Sc) were investigated in the high-aluminum range. A small, but significant, solubility of scandium in solid aluminum was observed, which was little affected by the presence of a third component. Ternary compounds in equilibrium with solid aluminum formed in only two of the systems investigated. Institute of Metallurgy, Russian Academy of Sciences, Moscow. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 12–17, March–April, 1997.     

Equilibrium partition coefficients in iron-based alloys

Accurate relationships between equilibrium partition coefficients and solute concentration are required for the prediction of solute redistribution during solidification. Thermodynamic analyses are presented to relate these coefficients to fundamental thermodynamic quantities. Using the most accurate data available, partition coefficients are calculated for ten Fe−X (X=Al, C, Cr, Mn, Ni, N, P, Si, S, Ti) binary systems and compared with literature values. Equations are presented to allow for prediction of these partition coefficients as a function of temperature, as well as liquidus temperature as a function of composition. In addition, partition coefficient values are examined for the ternary systems Fe−Cr−C, Fe−Mn−Ni, and Fe−Ni−S. THOMAS P. BATTLE, formerly Graduate Research Assistant, The University of Michigan This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

The effects of silicon on the reaction between solid iron and liquid 55 wt pct Al−Zn baths

The effect of various silicon levels on the reaction between iron panels and Al-Zn-Si liquid baths during hot dipping at 610°C was studied. Five different baths were used: 55Al−0.7Si−Zn, 55Al−1.7Si−Zn, 55Al−3.0Si−Zn, 55Al−5.0Si−Zn, and 55Al−6.88Si−Zn (in wt pct). The phases which formed as a result of this reaction were identified as Fe₂Al5 and FeAl3 (binary Fe−Al phases with less than 2 wt pct Si and Zn in solution),T1, T2, T4, T8, andT _5H (ternary Fe−Al−Si phases), andT _5C (a quaternary Fe−Al−Si−Zn phase). Compositional variations through the reaction zone were determined. The phase sequence in the reaction zone of the panel dipped for 3600 seconds in the 1.7 wt pct Si bath was iron panel/(Fe₂Al₅+T ₁)/FeAl₃/(T _5H+T _5C)/overlay. In the panel dipped for 1800 seconds in the 3.0 wt pct Si bath the reaction zone consisted of iron panel/Fe₂Al₅/(Fe₂Al₅+T ₁)/T ₁/FeAl₃/(FeAl₃+T ₂)/T _5H/overlay. In the panel dipped for 3600 seconds in the 6.88 wt pct Si bath the phase sequence was iron panel/Fe₂Al₅/(Fe₂Al₅+T1)/(T1+FeAl3)/(T1+T2)/T2/T8/T4/overlay. The growth kinetics of the reaction zone were also studied. A minimum growth rate for the reaction zone which formed from a reaction between the iron panel and molten Al−Zn−Si bath was found in the 3.0 wt pct Si bath. The growth kinetics of the reaction layers were found to be diffusion controlled in the 0.7, 1.7, and 6.88 wt pct Si baths, and interface controlled in the 3.0 and 5.0 wt pct Si baths. The presence of the interface between theT2/T5H, Fe2Al5/T ₁, orT ₁/FeAl₃ phases is believed responsible for the interface controlled growth kinetics exhibited in the 3.0 and 5.0 wt pct Si baths.     

Effect of Scandium on the Structure and Corrosion Properties of Vapor-Deposited Nanostructured Quasicrystalline Al–Cu–Fe Films

The structure and corrosion properties of quasicrystalline Al–Cu–Fe and Al–Cu–Fe–Sc films 200–260 nm thick produced by three-electrode ion-plasma sputtering of assembled targets were studied. The structural and phase composition of the films was determined by transmission and scanning electron microscopy, electron microprobe analysis, and X-ray diffraction. The corrosion properties were examined in 3, 5, and 16% aqueous NaCl solutions (pH = 6.9) at room temperature. An icosahedral fine quasicrystalline phase was found to form in the films deposited. The sizes of coherent scattering domains indicate that the coatings are nanostructured. The addition of 0.5 at.% Sc to the quasicrystalline Al–Cu–Fe films increases their corrosion resistance as evidenced by measurements of stationary potentials in saline solutions of different concentrations.     

Precipitation-strengthened austenitic Fe−Mn−Ti alloys

The precipitation of intermetallic compounds in the Fe−20Mn−2Ti and Fe−28Mn−2Ti alloy systems has been investigated over the temperature range 700 to 900°C by hardness measurements, optical and scanning electron microscopy, and X-ray diffraction. In both systems only the equilibrium Laves phase was observed. The precipitate was identified as C14(MgZn₂) type hexagonal Laves phase with a chemical composition close to Fe₂ (Ti, Mn). In an as-annealed sample precipitation occurred in a heterogeneous manner, predominantly along grain boundaries. The effect of a cold deformation between the solution annealing and aging processes was also investigated. In addition to a high density of dislocations, martensitic phases were induced by deformation: a γ→∈ transformation occurred in the Fe−28Mn−2Ti alloy while a γ→α′ transformation was predominant in the Fe−20Mn−2Ti alloy. Subsequent aging was conducted at temperatures above theA _f . A large number of very fine precipitates formed randomly in the matrix after a short aging period. This cold work plus aging treatment resulted in an increase in yield strength. The enhancement of mechanical properties is due to the randomly distributed precipitates combined with the high defect density and fine substructure.     

On the influence of Si−Ge additions on the aging response of Al−Cu

Al−Cu−Si−Ge alloys display a unique combination of ultrarapid aging response, high peak hardness, and extended-aging microstructural stability. The purpose of this work is to explain these properties in terms of the role that the Si−Ge additions have on modifying the conventional Al−Cu aging sequence. In both AlCu and AlCuSiGe, the room-temperature microstructure consists of both Guinier-Preston (GP) zones and ϕ″ precipitates. Upon aging at 190°C, Al−Cu displays the well-known precipitation sequence: the slow dissolution of GP zones and ϕ″ and the gradual formation of ϕ′. In the quaternary alloy, Si−Ge particles quickly nucleate and grow during elevated-temperature aging (they are detected after as little as 30 minutes at 190 °C). The Si−Ge particles then act as nucleation sites for ϕ′ precipitates, resulting in a peak-aged microstructure consisting of a dense distribution of ϕ′ attached to Si−Ge. DAVID MITLIN, Postdoctoral Fellow, formerly with the Materials Science Department, University of California-Berkeley and the Lawrence Berkeley National Laboratory.     

Macrosegregation in ternary alloys

General expressions are given to describe macrosegregation in ternary alloys resulting from mass flow of interdendritic liquid during solidification. Basic parameters determining whether a given alloy element segregates positively or negatively are given, and it is shown that alloy elements which form a second phase,e.g., an inclusion, can often be expected to segregate positively where other alloy elements segregate negatively. Numerical examples are given for alloys from the aluminum rich cornee of the Al−Cu−Ni system and qualitative examples are given for the Fe−Si−O system. Experimental measurements of macrosegregation in the Al−Cu−Ni system are in agreement with theory.     

Finely dispersed composite iron-platinum and iron-gold powders

The physicochemical laws of the formation of Fe−Pt and Fe−Au oxalates have been determined. For the first time finely dispersed Fe−Pt and Fe−Au composite powders have been fabricated by thermal reduction. The physicochemical and biomedical properties of such powders are investigated. We show that the powders are corrosion-resistant, are almost monodisperse, have a hydrophilic surface, are nonpyrophoric, are harmless, are bactericidal, and withstand sterilization temperatures. Their magnetic properties can be controlled during formation. Colloid Chemistry and Water Chemistry Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3-4(400), pp. 1–6, March–April, 1997.     

X-ray-based measurement of composition during electron beam melting of AISI 316 stainless steel: Part I. Experimental setup and processing of spectra

An energy dispersive X-ray (EDX) detector mounted on a laboratory scale electron beam furnace (30 kW) was employed to assess the potential use of X-rays as a means of on-line liquid alloy composition monitoring during electron beam (EB) melting of alloys. The design and construction of the collimation and protection systems used for the EDX are described in Part I. X-ray spectra are obtained from a sample of AISI 316 stainless steel at both beam idle (in the absence of liquid metal) and high power (in the presence of liquid metal). Two different types of molds are employed: (1) a water-cooled copper mold and (2) a ceramic lined water-cooled copper mold. Various strategies for signal processing and filtration are presented and compared. Correction factors for beam voltage were developed and applied in order to develop correlations between the mole fraction and normalized X-ray intensity for Ni−K _α, Cr−K _α, and Fe−K _α based on an analysis of the vapor condensate. Correlations were also developed relating the change in the X-ray intensities to time for (a) Mo−L, (b) Cr−K _α, (c) Fe−K _α, and (d) Ni−K _α. The stability of the electron beam was found to be the principal source of error, and suggestions for further improvements are also discussed. The study confirms the feasibility of the method and is the first reported study of on-line analysis of a high-temperature liquid alloy. In Part II, the technique is applied to the study of the complex evaporation processes occurring during EB melting.     

Elastic constants of martensite

The elastic constants of Fe−Ni−C martensite are increased by retained austenite. Also, nickel markedly decreases the elastic constants of such martensite. Therefore, to properly evaluate the effect of carbon on the elastic constants of Fe−Ni−C martensite, it is necessary to first correct for both retained austenite and nickel content. When these corrections are made, both the Young's modulus and the shear modulus of Fe−Ni−C martensites. decrease with increasing carbon content, in agreement with earlier work on Fe−C martensites. thus, an increased lattice stiffness cannot be used to explain the high strength of martensite.     

Obtaining Fe—Ni—Co—Ti alloys having a thermoelastic martensite transformation

Using powder metallurgy methods, we have produced Fe—Ni—Co—Ti alloys that have a thermoelastic martensive transformation, which is the basis of the shape-memory effect manifested by such materials. Since pores are believed to improve the shape memory, specifically the reversible nature of the strain, attention was focused on development of the technology and investigation of the characteristics of porous Fe—Ni—Co—Ti alloys. The problems that arise during sintering of such alloys from sputtered powders are due to the chemical inhomogeneity of the initial structure and of the structure formed when the liquid phase appears. Various forms of activation, such as cyclic sintering and a stepped increase in temperature, were used to prevent the liquid phase from appearing. The properties of Fe—Ni—Co—Ti alloys with a shape memory effect can be improved if the porosity is increased by obtaining larger powder grains with a more complicated shape. Materials Science Institute, Ukrainian Academy of Sciences Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 79–85, January–February. 1997.     

Effect of antimony and bismuth on the electrochemical corrosion of cast aluminum–silicon alloys in 3% NaCl solution

Powder Metallurgy and Metal Ceramics - The corrosion behavior of Al–Si–Bi (to 0.5 wt.% Bi) and Al–Si–Sb (to 0.5 wt.% Sb) ternary alloys is studied with polarization curves...     

Development of a new method to produce melts suitable for the production of amorphous Fe−Si−B materials

Research work was performed on the development of a new reduction process for the melting and refining of boron containing alloys used in the production of amorphous material for transformer cores. Based on fundamental thermodynamics principles, a reduction refining process was developed which employs conventional steelmaking vessels for using steel scrap, ferro alloys, and boron ores to produce an Fe−Si−B alloy. The process can eliminate the need for ferro boron alloy, high purity iron, and remelt stock to produce the Fe−Si−B alloy. Process variables were established which show the effects of mixing time, reductant alloy additions, slag chemistry, and temperature on the reduction kinetics. Final melt chemistries have lower levels of sulfur, nitrogen, and other tramp elements than conventional methods for producing the Fe−Si−B melt.     

Phase relations associated with the aluminum blast furnace: Aluminum oxycarbide melts and Al-C-X (X=Fe,Si) liquid alloys

The thermodynamic properties and the phase relations were evaluated and estimated for the Al-O-C, Al-Si-C, and Al-Fe-C systems which are important to understand the chemical behavior in an aluminum blast furnace. The mixing properties of binary liquid alloys, including metal-carbon systems, were represented by the Redlich-Kister equation. The properties of liquid Al−C and Si−C alloys were estimated so as to be consistent with their phase diagrams. The coefficients of Al−Fe and Fe−C liquids were evaluated from reported values for activity and enthalpy. The extrapolation to the higher order systems was made by Maggianu's method. The aluminum oxycarbide melt was represented by a subregular solution model. In the Al-O-C system, liquid alloy/oxycarbide melt equilibria were calculated and compared with earlier experimental results and estimates. Attempts were made to clarify the volatilization of aluminum oxycarbide melts, and also the carbidation of liquid aluminum alloys. An empirical correlation between the first terms of the Redlich-Kister equation for the enthalpies and the excess entropies was discussed.     

The effect of chromium on the activity coefficient of sulfur in liquid Fe−Cr−S alloys

The effect of chromium on the activity coefficient of sulfur in the ternary system Fe−Cr−S has been determined in the temperature range 1525° to 1755°C for chromium concentrations of up to 40 wt pct, using a levitation melting technique in H₂−H₂S atmospheres. The first order free energy interaction coefficient,e _S ^Cr , which is derived on the assumption that the thermal diffusion error is constant for both binary Fe−S and ternary Fe−Cr−S melts under controlled levitation conditions, is given by the relationship:e _S ^Cr =−94.2/T+0.040 The first order enthalpy and entropy interaction coefficients are found to beh _S ^Cr =−430±70 ands _S ^Cr =−0.183±0.007 respectively. These results are in good agreement with recently published data.     

Thermodynamic simulation of the Ni—Ru binary-system phase diagram

Calculations have given a consistent set of interaction constants for all the phases of variable composition in the Ni−Ru binary system, and also a set of stability constants for the ruthenium phases in its stable and virtual modifications. These data have been used to calculated a phase diagram for the Ni−Ru system. It is found that there is satisfactory agreement between the calculated phase diagram and the experimental one when one uses the subregular solution approximation for the solid and liquid phases of variable composition. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 48–55, May–June, 1999.     

Redetermination of the Fe-rich portion of the Fe−Ni−Co phase diagram

The iron rich portion of the Fe−Ni−Co ternary diagram (<10 pct Co, <15 pct Ni) was redetermined at four temperatures (800, 750, 700 and 650°C). The phase boundaries and tie-lines of the (α+γ) phase field were measured by analyzing the α and γ phases with an electron microprobe. Samples, whose compositions were located in the (α+γ) region of the phase diagram, were subjected to two different, long term heat treatments at the temperatures of interest. Grain boundary allotrimorphs of the α phase were observed in the polished and etched sections of samples which were step cooled from the γ phase into the (α+γ) region. Widmanstatten-type microstructures composed of γ-precipitates were observed in samples which were directly heated from room temperature into the (α+γ) region. The addition of cobalt to Fe−Ni alloys helps nucleate the alpha phase on cooling and also shifts the α/(α+γ) and the (α+γ)/γ phase boundaries to higher nickel contents. Diffusion controlled phase growth in the ternary Fe−Ni−Co system has also been investigated.     

On crack closure of precipitation hardened steels in aqueous solution

Fatigue crack propagation tests were carried out in air and in a 3.5 pct NaCl aqueous solution under cathodic potential of −0.85 V (Ag/AgCl) for aged-hardened high strength steel (Ni−Al−Cr−Mo−C steel). the emphasis in the study was placed on the crack closure behavior of age-hardened materials in air and in the NaCl aqueous solution. The degree of crack closure in air was dependent on the behavior of plastic deformation such as inhomogeneous or homogeneous slip under mixed modes I and II. The underaged material containing coherent precipitates with the matrix had a higher crack opening load in air, compared with the overaged steel containing incoherent precipitates with the matrix. The degrec of crack closure of the underaged material in the NaCl aqueous solution was lower than that in air and was similar to that of overaged materials in the NaCl aqueous solution. It was shown that the decreased crack closure level for the underaged material resulted from accelerated fatigue crack growth under mode I due to hydrogen embrittlement in the aqueous solution.     

Autogenous gas tungsten arc weldability of cast alloy Ti−48Al−2Cr−2Nb (Atomic percent) versus extruded alloy Ti−46Al−2Cr−2Nb−0.9Mo (Atomic percent)

This study examines procedures for consistently producing sound (crack and void free) welds using the autogenous (without filler metal) gas tungsten arc (GTA) welding process. Cast alloy Ti−48Al−2Cr−2Nb (at. pct) and extruded alloy Ti−46Al−2Cr−2Nb−0.9Mo (at. pct) have been examined to determine if sound welds can be produced using autogenous GTA welding without any preheat. Experimentation consisted of GTA spot welding samples of gamma titanium aluminide at weld current levels of 45, 55, 65, and 75 A for a duration of 3 seconds. For the cast alloy, current levels of 45, 55, and 65 A for 3 seconds produced similar fusion zone microstructures, which consisted of a dendritic solidification structure. The fusion zone microstructure of the 75A for 3 seconds current level differed significantly from the lower current levels. It also consisted of a dendritic solidification structure; however, the morphology was quite different. For the extruded alloy, current levels of 45 and 55 A for 3 seconds produced fusion zone microstructures similar to the lower current level samples of the cast γ-TiAl, which consisted of a dendritic solidification structure. The fusion zone microstructures of the 65 and 75 A samples were similar to each other, but they had a dendritic solidification structure of a different morphology than that of the 45 and 55 A samples. For both alloys at all current levels, microhardness profiles showed an increase in hardness from the base metal to the fusion zone. There were no significant differences in the average fusion zone hardness as a function of increasing current level. However, nanoindentation testing did show that certain phases and microconstituents in the fusion zone did have significant variations in hardness in relation to the enrichment and depletion of chromium. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Phase equilibria in the Cr-Ni-C system and their use for developing physicochemical principles for design of hard alloys based on chromium carbide

The Cr—Ni—C phase diagram at the melting point was plotted by a combination of procedures (metallography, x-ray, microprobe, differential thermal analysis, Pirani—Alterthum method, etc.). A general feature of this system is the existence of equilibria between the nickel-based phase and all the other phases. The temperature of the quasibinary (Ni)+(Cr₇C₃) eutectic was determined to be 1324±6°C. Based on both the phase diagram of the Cr—Ni—C system and the bending strength and Rockwell hardness of the alloys, the optimal composition of the initial carbide ingredient for production of hard alloys based on Cr₃C₂ with nickel—phosphorus binder was estimated as 13.0–13.3 at.%, substoichiometric with respect to Cr₃C₂. Institute of Problems in Materials Science, National Academy of Sciences of Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya. No. 5/6(395), pp. 13–24, May–June, 1997.