Phase equilibria of the Al-Cu-Zn system for compositions close to brass alloys

The effect of aluminium on the equilibrium phases of the Cu-Zn alloys has been studied within the range of chemical compositions of interest to brass producers. Ternary alloys were cast by melting two Cu-Zn base alloys (with ∼59.5% and ∼61.2 wt.% Cu) followed by the addition of aluminium up to 3.68 wt.%. Isothermal homogenization, followed by rapid cooling, has been used to determine the equilibrium phases at different temperatures. The alloys have been observed by scanning electron microscopy (SEM) and the respective chemical analysis determined by electron probe microanalysis (EPMA). Statistical analysis of the results enables a correlation of the chemical compositions of the equilibrium phases with temperature within composition range of the study.     

Determination of the Fe-rich portion of the Fe-Ni-S phase diagram

The low-temperature, Fe-rich portion of the Fe-Ni-S phase diagram was determined from Fe-Ni-S alloys (2.5,5,10,20, and 30 wt.% Ni, 10 wt % S, balance Fe) heat treated at 100 °C intervals from 900 to 300 °C. The microstructure and microchemistry of the phases in the heat treated Fe-Ni-S alloys were studied using a high-resolution field-emission gun (FEG) scanning electron microscope (SEM), electron probe microanalyzer (EPMA), and analytical electron microscope (AEM). Tieline compositions were obtained by determining the average phase composition and by measuring compositional profiles across interphase interfaces with the EPMA and AEM. At 600 °C and below, at least one phase was <1 Μm in size requiring the use of the AEM for analysis. The measured α + FeS, γ+ FeS, and α + γ + FeS boundaries in the Fe-rich corner of the Fe-Ni-S isotherms are consistent with previous studies. However, two new phases were observed for the first time coexisting with γ and FeS phases: FeNiγ′′ (∼52 wt.% Ni) at 600 and 500 °C and Ni ₃ Fe, ordered Ll ₂,γ′ (∼64 wt.% Ni) at 400 °C. New ternary isotherms are given at 600,500, and 400 °C that include the newly determined γ+γ′′ + FeS and the γ + γ′ + FeS three-phase fields. The effects of S on the phase boundaries of the α + γ phase field and the application of the Fe-Ni-S phase diagram to explain the microstructure and microchemistry of the metallic phases of stony meteorites are also discussed.     

The Cr-Ni-V system

The Cr-Ni-V system was investigated at 1100 ‡C using XRD, metallography, and energy dispersive chemical analysis of phases using scanning electron microscopy (SEM). The bcc α phase extends from the Cr-Ni binary to the V-Ni binary and has a maximum solubility of Ni in ternary α phase alloys of ∼12 at. %. A wide fcc γ phase field exists at the Ni corner. A ternary Σ phase (Σ₂) exists; it differs from the binary Ni-V Σ phase (Σ₁). The Σ₁ phase has a tetragonal unit cell with parameters almost double those of a normal Σ phase (Σ₂). Results indicate difficulty in achieving equilibrium states in alloys containing more than 30 at. % V and less than 15 at. % Cr even after 480 h annealing. The phase analysis of alloys annealed for 170 to 480 h suggests Σ₂ first forms through a ternary peritectic reaction to subsequently develop the Σ₁, phase by subsidiary reactions in those ternary alloys in the concentration range where Σ₁ is the stable phase. A tentative reaction scheme, consistent with the phase relations established at 1100 ‡C, is proposed.     

The Cr-Ni-V system

The Cr-Ni-V system was investigated at 1100 ‡C using XRD, metallography, and energy dispersive chemical analysis of phases using scanning electron microscopy (SEM). The bcc α phase extends from the Cr-Ni binary to the V-Ni binary and has a maximum solubility of Ni in ternary α phase alloys of ∼12 at. %. A wide fcc γ phase field exists at the Ni corner. A ternary Σ phase (Σ₂) exists; it differs from the binary Ni-V Σ phase (Σ₁). The Σ₁ phase has a tetragonal unit cell with parameters almost double those of a normal Σ phase (Σ₂). Results indicate difficulty in achieving equilibrium states in alloys containing more than 30 at. % V and less than 15 at. % Cr even after 480 h annealing. The phase analysis of alloys annealed for 170 to 480 h suggests Σ₂ first forms through a ternary peritectic reaction to subsequently develop the Σ₁, phase by subsidiary reactions in those ternary alloys in the concentration range where Σ₁ is the stable phase. A tentative reaction scheme, consistent with the phase relations established at 1100 ‡C, is proposed.     

Application of metastable transformation of mechanically alloyed Fe-Zn-Si in equilibrium phase studies

A series of six Fe-Zn-Si alloys was investigated with Fe content varying through the range 5.60 to 25.37 wt.% and fixed Si content of 0.12 wt.%. These alloys were formed by mechanical alloying of pure elemental powders—specifically by ball milling. After preparation, uniformity of microstructure was verified by electron microscopy and microprobe analysis. Annealing progress was followed by DSC and XRD. Differential scanning calorimetry measurements through the range 200 to 600 ‡C were used to locate the temperatures of relaxation phenomenon and the structural evolution. X-ray diffraction patterns were used to identify the phases present at various stages of the evolution. An invariant reaction was found near 423 ‡C and was identified as the peritectic melting of Zn. Identification of the formation of FeSi in a broad composition range below 9.1 wt.% Fe and at temperatures through 400 ‡C suggests the existence of phase field change. The formation of this FeSi phase is suggested as a possible cause for the Sandelin effect.     

Solid-liquid phase equilibria in the Al-Fe-Si system at 727 °C

Different experimental techniques were combined to acquire better insight into the solid-liquid phase equilibria that tend to be established in the Al-Fe-Si ternary system at 727 °C under a pressure of 1 atm (101,350 Pa). Isothermal diffusion experiments followed by oil quenching were first carried out. The crystal nature, lattice parameters, morphology, and chemical composition of the different solid phases in equilibrium with the liquid were determined by x-ray diffraction, optical microscopy, scanning electron microscopy, and electron probe microanalysis. Points on the liquidus boundary were then positioned both directly by chemical analysis of liquid samples taken from solid-liquid mixtures equilibrated at 727 °C and indirectly by thermal analysis of Al-Si mixtures with controlled iron additions. On the one hand, it has been confirmed in agreement with currently accepted data that the compounds ϑAl₁₃Fe₄, αAl_7.4Fe₂Si (τ₅), and δAl₃FeSi₂ (τ₄) are in equilibrium at 727 °C with Al-Fe-Si liquids, the compositions of which have been refined. On the other hand, the authors have shown that the ternary compound γAl₃FeSi is in equilibrium at 727 °C with a ternary Al-Fe-Si liquid containing 10.5 to 16.5 at.% Si and 3.2 to 3.5 at. % Fe.     

Investigations of Solidification Structures of High Carbon Alloy Cast Steel Containing RE-V-Ti

The solidification microstructural characteristics of rare earth (RE) and vanadium and titanium-treated high carbon alloy cast steel, whose chemical compositions are 0.90 wt.% C, 3.0 wt.% Si, and 1.0 wt.% Mn, were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), and energy dispersive X-ray spectrometry (EDS). The alloys were prepared in an induction furnace. The results showed that compound additions of RE-V-Ti could obviously refine the solidification structures and decrease the diameter of grains. The average grain diameter of untreated high carbon alloy cast steel was 80 μm. The average grain diameter of high carbon alloy cast steel containing RE-V-Ti decreased to 40 μm. Finally, the reasons that RE-V-Ti refined the solidification structure were analyzed in detail.     

Oxidation resistance of SHS Fe–Al–Si alloys at 800 °C in air

Alloys formed by Fe–Al intermediary phases have lower density than common metallic high-temperature alloys and good high-temperature oxidation resistance. Previously it was proved that silicon additions to these alloys enable to produce them efficiently by reactive sintering and improves the wear resistance. In this work, the oxidation resistance of the novel Fe–Al–Si alloys containing 10–30 wt. % of aluminium and 5–30 wt. % of silicon produced by the reactive sintering technology was tested. Cyclic and isothermal oxidation tests were carried out at 800 °C in air. Tested alloys exhibit excellent oxidation resistance, which increases with silicon content up to 20 wt. %. The reasons are discussed in terms of the phase composition of the oxide layer and the changes in chemical composition under the oxide layer during oxidation.     

Tunnel scanning microscopy and spectroscopy in studying Fe-Cr stainless steels

Scanning tunnel microscopy (STM) and scanning tunnel spectroscopy (STS) are used in studying highly pure iron and chromium and Fe-x%Cr (2.4 ≤ x ≤ 60 wt %) alloys at the air boundary, as well as some of the alloys in 0.01 N H₂SO₄. The obtained probability coefficients (α) of the electron tunnel transfer from a specimen to the needle and the slopes (β) of the logarithmic U _t /log (I _t ) dependences as functions of the chromium content in Fe-Cr alloys confirm the critical compositions of the alloys containing ∼6.5 and 10–13% chromium, which is in accord with the results of the steady-state and transient electrochemical measurements. A correlation between these critical compositions of the alloys and sharp changes in the histograms of α and β values is observed. Pronounced extreme properties of the Fe-25.2% Cr alloy surface, which corresponds to the inclusion of Cr atoms in tetrahedral voids of the alloy crystal lattice, are noticed. Original Russian Text ? E.V. Trofimova, E.V. Kasatkin, I.I. Reformatskaya, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 245–255. The work was financially supported by the Russian Foundation for Basic Research, project no. 04-03-32337.     

Ga含量对Al-Mg-Ga-Sn合金组织和降解性的影响

采用电炉熔炼制备了不同Ga含量的Al-Mg-Ga-Sn合金。通过光学显微镜(OM) 、扫描电镜(SEM)和X射线衍射仪(XRD)对其显微组织的形貌和成分进行了表征;在30℃、40℃、70℃、90℃的纯水中进行降解速率的测定;采用电化学工作站测试了室温电化学性能。结果表明：Al-Mg-Ga-Sn合金在Mg+Sn为定值10wt.%的情况下,Ga含量分别为0 wt.%、4 wt.%、8 wt.%、12 wt.%、16 wt.%时,合金组织均有铝基体相和Mg&lt;sub&gt;2&lt;/sub&gt;Sn相,且随着Ga含量的增加合金组织中出现了Ga&lt;sub&gt;5&lt;/sub&gt;Mg&lt;sub&gt;2&lt;/sub&gt;相。Al-Mg-Ga-Sn合金的降解性特点是主要由铝基体相中点蚀开启,由Mg&lt;sub&gt;2&lt;/sub&gt;Sn和Ga&lt;sub&gt;5&lt;/sub&gt;Mg&lt;sub&gt;2&lt;/sub&gt;化合物相的晶间腐蚀加速;不同Ga含量合金的起始降解温度由固溶于铝基体中的低熔点元素(Ga+Sn)的含量决定;相同Ga含量的合金随温度升高降解速率加快,降解反应动力学遵从阿伦尼乌斯公式。室温电化学分析表明：Al-Mg-Ga-Sn合金随Ga含量增加,腐蚀电位不同程度地负移,腐蚀电流逐渐增大。     

Phase state of a Bi-43 wt % Sn superplastic alloy and its changes under the effect of external mechanical stresses and aging

Samples of a Bi-43 wt % Sn superplastic alloy have been studied by X-ray diffraction in the ascast state, after compression of as-cast samples to ∼70% on a hydraulic press, after aging in the as-cast and preliminarily compressed state, and using samples deformed under superplastic conditions. The X-ray diffraction studies have been carried out using a DRON-2.0 diffractometer in Cu Kα radiation. The samples aged and deformed under superplasticity conditions have been studied using electron-microprobe analysis in a JSM-820 scanning electron microscope equipped with a LINK AN/85S EDX system. It has been found that the initial structural-phase state of the alloy was amorphous-crystalline. Causes that lead to a change in this state upon deformation and aging are discussed. A conclusion is made that the superplasticity effect manifests itself against the background of processes that are stipulated by the tendency of the initially metastable alloy to phase equilibrium similarly to what is observed in the Sn-38 wt % Pb eutectic alloy studied earlier.     

The effect of silicon on the structure of Fe-40 at.% Al type alloys with high contents of carbon (1.9–3.8 at.%)

The phase compositions of alloys based on Fe-40 at.% Al with additions of carbon ranging from 1.9 to 3.8 at.% and with and without the addition of 1.2 at.% Si were studied by light optical and transmission electron microscopies, X-ray diffraction and electron probe microanalysis. The structure of the matrix of all alloys is a B2 lattice, inherent to the intermetallic compound FeAl. Two main precipitating phases are observed: graphite and aluminium carbide Al₄C₃. The quantity of the phases depends in detail on the chemical composition and the heat treatment. The presence of Al₄C₃ in the alloys with the highest carbon content is in agreement with the recent theoretical prediction of a Fe–Al–C ternary phase diagram by Ohtani et al., as well as with older experiments of Vyklický and T?ma. The occurrence of Al₄C₃ is supported by the addition of silicon. Small traces of carbide κ of perovskite-type Fe₃AlC are observed only in the alloys with the lowest aluminium and carbon contents.     

High-temperature phase relations in the ternary Ga-Mn-Ni system

Isothermal sections of the ternary Ga-Mn-Ni phase diagram at 800 and 1000 °C have been investigated for alloys with a manganese content below 70 at.% for 800 °C and a content below 65 at.% at 1000 °C. The high-temperature phase relations among the solid phases have been analyzed with diffusion couples and by energy dispersion x-ray spectroscopy (EDX) on quenched two-phase alloys. For these temperatures, the solidus line was determined from quenched alloys from the solid and liquid two-phase region by EDX analysis and the liquidus line by an overall evaluation of the phases found in the quenched alloys. By powder x-ray diffraction (XRD) measurements, the results for the equilibria among the solid phases were confirmed and the lattice parameters for the martensite formed from the β phase have been determined over a wide range of compositions.     

Positron annihilation spectroscopy in the evaluation of microstructure of cast copper and copper-aluminum alloys during isochronal annealing

Isochronal annealing was carried out for cast Cu, Cu-5wt.% Al, Cu-10wt.% Al, and Cu-20Wt.% Al alloys in the range of 423–1173 K. The annealing behavior was followed by positron annihilation lifetime spectroscopy (PALS). Microhardness (H _v) has been measured and used for comparison. The microstructure variations were observed by optical and scanning electron microscopy. Three stages were distinguished for all samples in the behavior of average lifetime (τ _av) and H _v. In the first stage (room temperature to 573 K), τ _av and H _v reach extremely high values for Cu-20wt.% Al compared with other alloys. The analysis of the first stage indicates anneal softening for cast Cu and Cu-5wt.% Al and anneal hardening for Cu-10wt.% Al and Cu-20wt.% Al. The second stage (573–873 K) is characterized by a maximum of τ _av at 673 K followed by a decrease up to the end of the stage for cast Cu, Cu-5wt.% Al (the highest maximum), and Cu-10wt.% Al; a slight change is observed for Cu-20wt.% Al. The change in H _v is notable only for Cu-10wt.% Al and Cu-20wt.% Al, and indicates that τ _av is sensitive to the change that occurred in the bulk material, while H_v shows the general behavior of the surface of the material. The third stage (873–1173 K) is characterized by near saturation for both τ _av and H _v, indicating complete recrystallization for cast Cu, Cu-5wt.% Al, and Cu-10wt.% Al and complete softening for Cu-20wt.% Al. Recrystallization is shifted to higher temperatures by increasing the amount of Al in Cu. The analysis of positron lifetime presents evidence of the existence of three-dimensional (3D) defects in addition to one-dimensional defects, so a modification to the simple trapping model is needed when considering inhomogeneous trapping.     

Fabrication and characterization of monolithic nanoporous copper through chemical dealloying of Mg–Cu alloys

A new Mg–Cu system has been developed to fabricate monolithic nanoporous copper (NPC) ribbons and bulk NPC through chemical dealloying in a 5 wt.% HCl solution. The microstructures of the NPC ribbons were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The results show that the compositions of the melt-spun Mg–Cu alloys have an important effect on the dealloying process and microstructures of the NPC ribbons. Moreover, the synergetic dealloying of Mg₂Cu and MgCu₂ in two-phase Mg–Cu alloys results in the formation of NPC with a uniform porous structure.     

Microstructure and phase equilibria in Ni–Al–Cr–Co alloys

Several alloys of Ni–Al–Cr–Co system with Ni content close to 60 at.% were prepared and annealed at 1273 and 1373 K with the aim to reach the state of thermodynamic equilibrium. The microstructure of quenched samples was studied by means of scanning and transmission electron microscopy. Phases equilibrated at high temperature were identified using selected area diffraction in transmission electron microscope. Energy dispersive X-ray analysis was used for evaluation of nominal alloy compositions as well as the chemical composition of individual phases. The results obtained experimentally are compared with the results of thermodynamic calculation using software ThermoCalc and a commercial database of thermodynamic data for Ni-based alloys. In most cases the results of calculation show good agreement with experiment. A few differences of the results obtained by the two approaches are pointed out and briefly discussed.     

High-temperature phase relations in the ternary Ga-Mn-Ni system

Isothermal sections of the ternary Ga-Mn-Ni phase diagram at 800 and 1000 °C have been investigated for alloys with a manganese content below 70 at.% for 800 °C and a content below 65 at.% at 1000 °C. The high-temperature phase relations among the solid phases have been analyzed with diffusion couples and by energy dispersion x-ray spectroscopy (EDX) on quenched two-phase alloys. For these temperatures, the solidus line was determined from quenched alloys from the solid and liquid two-phase region by EDX analysis and the liquidus line by an overall evaluation of the phases found in the quenched alloys. By powder x-ray diffraction (XRD) measurements, the results for the equilibria among the solid phases were confirmed and the lattice parameters for the martensite formed from the β phase have been determined over a wide range of compositions.     

Experimental investigation of the Tb-Mg phase diagram

The Tb-Mg alloys were studied in the range 0 to 100 at.% Mg, by using X-ray powder diffraction, optical and scanning electron microscopy, electron probe microanalysis (EPMA), and differential thermal analysis (DTA). The following intermediate phases were identified and their crystal structures confirmed: TbMg (cubic,cP2 CsCl type), TbMg₂ (hexagonal,hP12-MgZn₂ type), and TbMg₃ (cubic,cF16-BiF₃ type). Two phases, moreover, were confirmed or identified in a composition range very close to 83 at.% Mg: χ₁ phase (cubic,cF440-GdMg₅ type) and χ₂ phase (cubic,cI58-αMn type). All the phases show peritectic formation with the possible exception of the χ₂ phase. The following phase equilibria were also determined: a eutectic reaction at 530 °C and 90.5 at.% Mg and a eutectoidal decomposition of the (βTb) phase at 670 °C and ∼28 at.% Mg.     

Reaction sintering of Fe-Al-Si alloys

The present study concerns the production of multiphase alloys of the Fe-Al-Si system using a powder metallurgical approach. Several compositions have been considered based on α-Fe, α′-FeAl; and α″-Fe₃Al intermetallic phases. Elemental powder mixtures were compacted and sintered in a dilatometer. In this way, the dimensional changes involved with thermally induced transformations could be followed during continuous heating runs up to the sintering temperature. The effect of heating rate has been considered. The characterization of the final products was based mainly on x-ray diffraction (XRD) analyses, particularly as concerns the quantification of the crystalline phases present in the final products. Grain and porosity morphologies were characterized by scanning electron microscopy (SEM). In this way, clear indications of the reaction and densification processes occurring during the sintering treatments were obtained.