The Al-rich region of the Al-Mn-Ni alloy system. Part II. Phase equilibria at 620-1000 °C

Phase equilibria in the Al-rich region of the Al-Mn-Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620 °C. Three ternary thermodynamically stable intermetallics, the φ-phase (Al₅Co₂-type, hP26, P6₃/mmc; a = 0.76632(16), c = 0.78296(15) nm), the κ-phase (κ-Al_14.4Cr_3.4Ni_l.1-type, hP227, P6₃/m; a = 1.7625(10), c = 1.2516(10) nm), and the O-phase (O-Al₇₇Cr₁₄Pd₉-type, Pmmn, oP650,: a = 2.3316(16), b = 1.2424(15), c = 3.2648(14) nm), as well as three ternary metastable phases, the decagonal D₃-phase with periodicity about 1.25 nm, the Al₉(Mn,Ni)₂-phase (Al₉Co₂-type, P112₁/a, mP22; a = 0.8585(16), b = 0.6269(9), c = 0.6205(11) nm, β = 95.34(10)°) and the O₁-phase (base-centered orthorhombic, a ≈ 23.8, b ≈ 12.4, c ≈ 32.2 nm) were revealed. Their physicochemical behaviour in the Al-Mn-Ni alloy system was studied.     

The isothermal section of Dy-Co-Cr ternary system at 500 °C

The isothermal section of the Dy-Co-Cr ternary system at 500 °C was investigated by X-ray powder diffraction (XRD), metallography and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The isothermal section consists of 11 single-phase regions, 20 two-phase regions and 10 three-phase regions. The only ternary compound DyCo_12−xCr_x (space group I4/mmm) with ThMn₁₂-type structure was confirmed in this system. The homogeneity range in DyCO_12−xCr_x was found to be about x = 3.6-4.4. The lattice parameters for DyCO_12−xCr_x with 3.6 ≤ x ≤ 4.4 are a = 0.8312-0.8334 nm and c = 0.4706-0.4722 nm. The maximum solid solubilities of Cr in Dy₂Co₁₇, DyCo₃ and DyCo₂ are about 16.0, 5.0 and 17.0 at.%, respectively.     

Experimental study of the isothermal section of the Ho-Fe-Cr system at 873 K

The isothermal section of the Ho-Fe-Cr ternary system was investigated by means of X-ray powder diffraction (XRD), metallography and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The ternary compound HoFe_12−xCr_x (x = 2) was characterized and the homogeneity range of the various ternary solutions was studied. It crystallizes with ThMn₁₂-type structure, space group I4/mmm and unit parameters a = 0.8406 nm and c = 0.4756 nm. The homogeneity range in HoFe_12−xCr_x was determined as x = 1.9-3.6, i.e. 14.6-27.7 at.% Cr. The maximum solid solubilities of Cr in Fe, Ho₂Fe₁₇, Ho₆Fe₂₃, HoFe₃ and HoFe₂ are about 28.0 at.%, 4.0 at.%, 13.0 at. %, 3.0 at.% and 11.0 at.%, respectively.     

Investigation of the Al-Ti-Pt alloy system at 1100 °C

The 1100 °C isothermal section of the Al-Ti-Pt system was experimentally studied in the compositional region below 50 at.% Pt. Most of the binary Al-Ti and Al-Pt intermetallics dissolve about 1.5-3.5 at.% of the third element. Only TiAl and Ti₃Al contain up to ∼5.5 at.% Pt and Al₂Pt ∼13 at.% Ti. The Ti₃Pt, Ti₃Pt₄ and TiPt phases extend up to 7.5, 9 and 30 at.% Al, respectively. The homogeneity range of the ternary phase τ₁ extends from Al_63.3Ti_30.6Pt_6.1 to Al_69.0Ti_24.2Pt_6.6 and that of τ₂ from Al_44.1Ti_34.0Pt_21.9 to Al_55.1Ti_20.9Pt_24.0. The τ₃-phase is formed in the compositional region from Al₃₇Ti_37.5Pt_25.5 to Al₄₂Ti₃₂Pt₂₆. Only the Nb(Ir,Al)₂-type structure of the latter was revealed. The τ₄-phase exists between Al_31.3Ti_33.7Pt₃₅ and Al_36.6Ti_29.4Pt₃₄ while the τ₅-phase exists between Al_12.9Ti_58.9Pt_28.2 and Al_27.3Ti_57.3Pt_15.4. Apart from these previously reported phases, five new ternary compounds designated τ₆ to τ₁₀ were revealed. The τ₆-phase exists between the Al_25.5Ti_54.2Pt_20.3 and the Al₃₀Ti₅₄Pt₁₆ compositions, and probably has a primitive cubic structure with a = 0.68477(6) nm. The τ₇-phase was found to be formed around the Al₁₂Ti₅₁Pt₃₇ composition, τ₈, τ₉ and τ₁₀-phases exist in the compositional ranges of Al_28.5Ti₅₅Pt_27.5 to Al_33.7Ti₄₀Pt_26.3, Al_34.5Ti₄₈Pt_17.5 to Al₃₈Ti₄₄Pt₁₈ and Al_32.6Ti_44.3Pt_23.1 to Al_37.4Ti₄₁Pt_21.6, respectively.     

Al-rich region of Al–Pd–Ru at 1000 to 1100 °C

Partial isothermal sections of the Al–Pd–Ru phase diagram at 1000, 1050 and 1100 °C are presented here. The Al–Pd orthorhombic -phases dissolve up to 15.5 at.% Ru, Al₁₃Ru₄ <2.5 at.% Pd and Al₂Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (, a = 0.7757 nm), C₁ (, a = 1.5532 nm) and C₂ (, a = 1.5566 nm) were revealed. An additional complex cubic structure with a ≈ 3.96 nm was found to be formed at compositions close to those of the icosahedral phase.     

Phase equilibria of the Cu-Ni-Si system at 700 °C

The phase equilibria at the isothermal section of the Cu-Ni-Si system at 700 °C were experimentally investigated. Thirty Cu-Ni-Si alloys were prepared by arc melting and annealed at 700 °C for 30 or 80 days, and examined with optical microscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and electron probe microanalysis. Twelve three-phase regions were determined. The existence of the ternary compound τ₁-Cu_56.8-63Ni_10.4-16.1Si_26.6-27.3 reported in literature was confirmed and a new compound τ₂-Cu_45.8Ni₂₅Si_29.2 with nearly no homogeneity range was observed. The θ-Ni₂Si compound, which exists above 820 °C in the binary Ni-Si system, was found to be stable at 700 °C and the composition range of Cu is 12.7-20.6 at.% Cu. The ternary solubilities of binary compounds were measured and noticeably the Cu₅₆Si₁₁ compound can dissolve Ni up to 21.9 at.%.     

Isothermal section of the Co-Er-Y ternary system at 500 °C

The isothermal section of the phase diagram of the Co-Er-Y ternary system at 500 °C was investigated by X-ray powder diffraction technique, differential thermal analysis, scanning electron microscopy with energy dispersive analysis and optical microscopy. The 500 °C isothermal section consists of 14 single-phase regions, 19 two-phase regions, and 6 three-phase regions. Six pairs of corresponding compounds Er₂Co₁₇ and Y₂Co₁₇, Er₂Co₇ and Y₂Co₇, ErCo₃ and YCo₃, ErCo₂ and YCo₂, Er₄Co₃ and Y₄Co₃, Er₃Co and Y₃Co and metals Y and Er form a continuous series of solid solutions. The maximum solid solubility of Y in the compounds Er₁₂Co₇ is about 19 at.% Y.     

Isothermal section of the Y-Co-V ternary system at 500 °C

The isothermal section of the Y-Co-V system at 500 °C has been investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Only one ternary compound YV_xCo_12−x with a homogeneity range of 1.30 ≤ x ≤3.64 was found in this system. The maximum solid solubilities of V in Y₂Co₁₇, Y₂Co₇, YCo₃, YCo₂ and Y₃Co are about 10.0, 1.0, 3.0, 4.0 and 4.0 at.% V, respectively. The compounds VCo and VCo₃ have a homogeneity range of 46-66 at.% V and 22-30 at.% V, respectively. The maximum solid solubility of Y in VCo is about 2.0 at.% Y.     

The Yb–Zn–In system at 400 °C: Partial isothermal section with 0–33.3 at.% Yb

The phase relations in the ternary system Yb–Zn–In have been established for the partial isothermal section in the 0–33.3 at.% ytterbium concentration range at 400 °C, by researching of more than forty alloys. X-ray powder diffraction (XRPD), optical microscopy (OM) and scanning electron microscopy (SEM), complemented with energy dispersive X-ray spectroscopy (EDS), were used to study the microstructures, identify the phases and characterize their crystal structures and compositions. The phase equilibria of this Yb–Zn–In partial section at 400 °C are characterized by the presence of three extended homogeneity ranges, indium solubility in Yb₁₃Zn₅₈ and YbZn₂ and of zinc solubility in YbIn₂, and the existence of one ternary intermetallic compound, YbZn_1−xIn_1+x, x = 0.3. This new compound crystallizes in the UHg₂ structure type (space group P6/mmm), with a = 4.7933(5) Å, c = 3.6954(5) Å. The studied partial isothermal section has eight ternary phase fields at 400 °C.     

The oxidation of two ternary Fe-Cu-10 at.% Al alloys in 1 atm of pure O2 at 800-900 °C

The oxidation of two ternary Fe-Cu-Al alloys containing 10 at.% Al (Fe-65Cu-10Al and Fe-30Cu-10Al) has been studied at 800-900 °C under 1 atm O₂. Under all conditions both alloys show an initial faster stage during which Fe-65Cu-10Al corrodes more rapidly at 800 °C than at 900 °C, while Fe-30Cu-10Al follows nearly identical kinetics at both temperatures. As oxidation proceeds, a continuous alumina layer is eventually established on the surface of the two alloys, thus decreasing significantly their oxidation rates. Altogether, the Fe-rich alloy Fe-30Cu-10Al oxidizes slightly faster than the Cu-rich alloy Fe-65Cu-10Al at both temperatures. The possible reasons for the decrease in the critical Al content needed to form external alumina scales for the Cu-rich alloy in comparison with binary Cu-Al alloys are examined.     

Phase equilibria in the Fe–Al–Mo system – Part I: Stability of the Laves phase Fe2Mo and isothermal section at 800 °C

Phase equilibria in the Fe–Al–Mo system were experimentally determined at 800 °C. From metallography, X-ray diffraction and electron probe microanalysis on equilibrated alloys and diffusion couples a complete isothermal section has been established. It is shown that the Laves phase Fe₂Mo is a stable phase. The phase Al₄Mo, which only becomes stable above 942 °C in the binary system, is the only ternary compound found at 800 °C. For all binary phases the solid solubility ranges for the third component have been established. The D0₃/B2 and B2/A2 transition temperatures have been determined for a selected alloy by differential thermal analysis and transmission electron microscopy. The results confirm that the D0₃/B2 transition temperature substantially increases by the addition of Mo, while the B2/A2 transition temperature is about that for a binary alloy with the same Al content.     

Oxidation of single crystal PWA 1483 at 950 °C in flowing air

The oxidation behaviour of single crystal PWA 1483 at 950 °C was investigated by means of XRD, SEM and EDS. The parabolic oxidation behaviour, as defined by mass gain and the respective oxide layer thicknesses, is characterized by a parabolic rate constant of about 4 × 10⁻⁶ mg²/(cm⁴ × s) and the formation of a multi-layered oxide scale. An outer scale contains a Ti-bearing thin film composed of TiO₂ and NiTiO₃ but mostly Cr in Cr₂O₃ and (Ni/Co)Cr₂O₄ besides NiTaO₄. This outer scale is connected to a discontinuous layer of Al₂O₃ and an area of γ′-depletion within the base material.     

The oxidation of three Ni-6Si-xAl alloys in 1 atm O2 at 1000 °C

The oxidation of three ternary Ni-6Si-xAl alloys containing 6, 10 and 15 at.% Al and of the corresponding binary Ni-Al alloys has been studied at 1000 °C under 1 atm O₂ to examine the effect of different Al additions on the behavior of ternary Ni-Al-Si alloys containing 6 at.% Si. Of the three binary Ni-Al alloys only Ni-15Al was able to form external alumina scales. Conversely, all the three ternary alloys formed an innermost layer of alumina directly in contact with the alloy following very similar and approximately parabolic kinetics after a short faster initial stage due to transient formation of NiO. Thus, the presence of silicon is very effective to reduce the critical Al content needed to form exclusive alumina scales with respect to binary Ni-Al alloys. The third-element effect due to silicon is interpreted on the basis of an extension of Wagner’s criterion for the transition from the internal to the external oxidation of the most reactive component in binary alloys.     

Oxidation properties of Zr-Nb alloys at 500-600 °C under low oxygen potentials

Zr-Nb alloys with 1-10 wt.% Nb content were oxidized at 500-600 °C in the CO-CO₂ gas mixtures. The oxidation weight gain increased with Nb content and the kinetics except for Zr-1Nb alloy changed from cubic rate to linear one at 600 °C for a long period of time, 7 d. The cubic rate constant was almost insensitive to oxygen potential of oxidizing atmosphere. As the oxidation resistance deteriorated, the volume ratio of tetragonal to monoclinic zirconia phase and the relevant compressive stress in oxide film decreased with increase of Nb content. Before and after oxidation, Nb re-distribution could not be observed under the present experimental condition.     

The isothermal section of the phase diagram of Ce-Mg-Zn ternary system at 470 K

The isothermal section of the phase diagram of Ce-Mg-Zn ternary system at 470 K in a full concentration range was built, and a formation of seven ternary compounds was observed. For five ternary compounds: τ₁ - Ce₃(Zn_0.863Mg_0.137)₁₁ (Immm space group, La₃Al₁₁ structure type), τ₃ - CeMg_1+xZn_2−x (Fm-3m, MnCu₂Al), τ₄ - CeMg_2.5Zn_4.5 (P6/mmm, TbCu₇), τ₅ - Ce₃Mg₁₃Zn₃₀ (P6₃/mmc, Sm₃Mg₁₃Zn₃₀) and τ₇ - Ce₂₀Mg₁₉Zn₈₁ (F-43m, own structure type) the crystal structures were investigated. The crystal structures of CeMg_1−xZn_x continuous solid solution and of CeMg_12-xZn_x and CeMg_3-xZn_x limited solid solutions were studied more precisely by the X-ray single crystal and powder diffraction, and also using the WDS and EPMA techniques. The Ce-Mg-Zn ternary phases are structurally related to the binary phases of RE-Mg and RE-Zn (RE - rare-earth metals) systems.     

Isothermal section of the Ho-Co-Fe system at 773 K

The 773 K isothermal section of the phase diagram of the Ho-Co-Fe ternary system was investigated by using X-ray diffraction technique, metallographic analysis and scanning electron microscopy with energy dispersive analysis. The isothermal section of the ternary system consists of 6 three-phase regions, 16 two-phase regions and 11 single-phase regions. Three pairs of corresponding compounds of Ho-Co and Ho-Fe systems, i.e., Ho₂Co₁₇ and Ho₂Fe₁₇, HoCo₃ and HoFe₃, HoCo₂ and HoFe₂, form a continuous series of solid solution. At 773 K the compound Ho₆Fe_23−xCo_x was found to have a wide homogeneity range from 0 to 29 at.% Co. The maximum solid solubilities of Fe in Co, Ho₂Co₇, Ho₁₂Co₇ and Ho₃Co were determined to be about 10, 9, 2 and 5 at.% Fe, respectively. The maximum solid solubility of Co in Fe is found to be 78 at.% Co.     

The effect of growth rate on microstructure and microindentation hardness in the In–Bi–Sn ternary alloy at low melting point

In–21.5 at.% Bi–17.8 at.% Sn ternary alloy which has 333 K melting point was directionally solidified upward with a constant temperature gradient (G = 0.91 K/mm) in a wide range of growth rates (3.2–157.1 μm/s) with a Bridgman type directional solidification furnace. The lamellar spacings (λ) and microhardness values (H_V) were measured from both transverse and longitudinal sections of the samples. The dependence of lamellar spacings (λ) and microhardness (H_V) on the growth rate (V) was determined by using linear regression analysis. According to these results, it has been found that the value of λ decreases with the increasing value of V and whereas, the value of H_V increases for a constant G. The values of λ²V were determined by using the measured values of λ and V. The results obtained in this work have been compared with the previous similar experimental results obtained for binary or ternary alloys.     

Influence of grain size on the oxidation behavior of NbCr2 alloys at 950-1200 °C

The oxidation behavior of mechanically alloyed microcrystalline NbCr₂ intermetallics was investigated at 950-1200 °C in air by SEM in comparison with coarse-grain cast alloys. Results indicate that the mechanically alloyed alloys possess a better oxidation resistance and are less permeable to nitrogen than the cast alloys. At 1200 °C, the mechanically alloyed NbCr₂ alloys show a better resistance to scale spallation than the cast materials. The differences observed above are attributed to the finer grains increasing the relaxation of the oxide scale stress and improving the adhesion of the oxide layer on the matrix.     

Oxidation of a quaternary three-phase Cu-20Ni-20Cr-5Fe alloy at 700-900 °C in 1 atm of pure O2

The oxidation of a quaternary Cu-Ni-Cr-Fe alloy containing approximately 20 at.% Ni, 20 at.% Cr and 5 at.% Fe, balance Cu (Cu-20Ni-20Cr-5Fe), was studied at 700-900 °C in 1 atm of pure oxygen. The alloy is composed of a mixture of three phases, where the lightest α phase with the largest Cu content forms the matrix, while the other two, much richer in Cr, form a dispersion of isolated particles. At variance with the ternary three-phase Cu-20Ni-20Cr alloy examined previously, which was unable to form protective chromia scales over the alloy surface even after an extended period of oxidation, the present alloy formed complex external scales containing mixtures of the oxides of the various components plus a deep internal region containing a mixture of alloy and oxide phases. With time, a very irregular and thin but essentially continuous chromia layer formed at the bottom of the mixed internal oxidation region, producing a gradual decrease of the oxidation rate. Thus, the addition of 5 at.% Fe to Cu-20Ni-20Cr alloy is able to decrease the critical Cr content required to form the most stable oxide and promotes the formation of a continuous chromia scale under a lower Cr content in spite of the simultaneous presence of three different phases.     

Effect of water vapor on the phase transformation of alumina grown on NiAl at 950 °C

This particular study includes the analysis of the effect of H₂O on promoting the phase transformation in thermally grown aluminum oxides formed on NiAl at 950 °C. Oxidation of NiAl is carried out at 950 °C in O₂ and O₂ + 15 vol.% H₂O. It is observed that transient alumina initially formed on NiAl transforms to stable α-alumina in the presence of water vapor which promotes the subject transformation and eventually results in a compact scale, offering superior oxidation resistance. Present study includes the analysis of θ to α-alumina transformation under the effect of temperature and environment.