Multi-phase Intermetallic Alloys Research Articles

Effect of Moist Air and Minor Zr Addition on Oxidation Behavior of Arc-Melted Multiphase Mo–Si–B Alloys in the Temperature Range of 1000 °C–1300 °C

Arc-melted multiphase intermetallic alloys, Mo76Si14B10, Mo74Si14B10Zr2, Mo79.5Si12B8.5 and Mo77.5Si12B8.5Zr2 with microstructures containing Moss, Mo3Si and Mo5SiB2 were isothermally exposed for 1 h or 24 h at 1000 °C, 1150 °C and 1300 °C in dry or moist air. The residual area fraction was found to be the highest on exposure at 1150 °C in dry air, but the least at this temperature in moist air. Examination of dry air formed oxide scales by X-ray diffraction, and scanning electron microscopy with energy-dispersive spectroscopy showed the presence of Mo, and MoO2 with a continuous, protective glassy B2O3–SiO2 top layer. Formation of Zr(MoO4)2 in the Zr-containing alloys had lowered mass loss by arresting MoO3 vaporization, and had enhanced the B2O3–SiO2 scale formation kinetics. Further, Si(OH)4, cristobalite, H3BO3 and MoO3·(H2O)2 appeared to be constituting the oxidation products formed in moist air. Alloying with Zr enhanced the kinetics of protective scale formation by lowering the Moss content, and microstructural refinement. The deterioration of oxidation resistance in moist air was conjectured to be due to longer duration required for protective scale to form, formation of β-cristobalite permitting grain boundary diffusion of oxygen anions, as well as volatile hydrated oxidation products as mentioned above. Formation of ZrSiO4 and dissolved ZrO2 in B2O3–SiO2 scale of the Mo-Si-B-Zr alloys in both dry air and moist air is considered to have contributed to the enhanced protective character of oxide scale by stabilizing the glassy scale.

Microstructure and Tribological Properties of Mo–40Ni–13Si Multiphase Intermetallic Alloy

Intermetallic compounds are increasingly being expected to be utilized in tribological environments, but to date their implementation is hindered by insufficient ductility at low and medium temperatures. This paper presents a novel multiphase intermetallic alloy with the chemical composition of Mo–40Ni–13Si (at %). Microstructure characterization reveals that a certain amount of ductile Mo phases formed during the solidification process of a ternary Mo–Ni–Si molten alloy, which is beneficial to the improvement of ductility of intermetallic alloys. Tribological properties of the designed alloy—including wear resistance, friction coefficient, and metallic tribological compatibility—were evaluated under dry sliding wear test conditions at room temperature. Results suggest that the multiphase alloy possesses an excellent tribological property, which is attributed to unique microstructural features and thereby a good combination in hardness and ductility. The corresponding wear mechanism is explained by observing the worn surface, subsurface, and wear debris of the alloy, which was found to be soft abrasive wear.

Preparation Methods for Examining the ωo-Phase Formation in a β-Solidifying TiAl Alloy via Atom Probe Tomography

Abstract Examinations with the atom probe are an excellent way to analyze all phases of a material on an atomic level, thus enabling a better understanding of their formation. This study aims to provide an appropriate method for the preparation of atom probe specimens made of multiphase intermetallic titanium aluminide alloys. With the help of a focused ion beam system and transmission kikuchi diffraction, tips of defined phases and phase interfaces were prepared, as is shown by the example of the ωo-Ti4Al3Nb phase, which is precipitated from the βo phase. The chemical composition of the two phases was determined by subsequent atom probe measurements which allowed to draw conclusions about the phase formation.

Phase and microstructural characterization of Mo–Si–B multiphase intermetallic alloys produced by pressureless sintering

• Active and ultra-fine Mo–Si–B powders were produced by mechanical alloying. • The phases of MoSi 2 and MoB were obtained by sintering Mo–57Si–10B at 1400 °C for 2 h. • Composite based on MoB/MoSi 2 was obtained by sintering Mo–47Si–23B at 1300 °C for 3 h. • High content of MoB in the composite based on MoB/MoSi 2 increased density. • High hardness of the composite based on MoB/MoSi 2 is related to MoB matrix. In this study Mo–47Si–23B and Mo–57Si–10B powders (at.%) was milled for 20 h in attritor ball mill with a rotational speed of 365 rpm and the ball/powder mass ratio 20/1. After degassing of As-mechanically alloyed powders at 450 °C, the powders were pressed into cylindrical samples with 25 mm diameter under 600 MPa pressure. The samples were sintered by using of a tube resistance furnace under Ar atmosphere. Phase and microstructure characteristic of mechanically alloyed powders and sintered samples, were investigated by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. Also hardness test was performed. Homogeneous distribution of active and ultra-fine powders were obtained after milling for 20 h. Mo–57Si–10B alloy with MoB and MoSi 2 dominant phases was produced by sintering at 1400 °C for 2 h. Dominant phases similar to Mo–57Si–10B alloy sintered at 1400 °C for 2 h could be synthesized in Mo–47Si–23B alloy after sintering at 1300 °C for 3 h, but volume fraction of MoB phase was different. The Mo–47Si–23B alloy contained a higher phase fraction of MoB compound as compared to Mo–57Si–10B alloy. Very high density in Mo–47Si–23B alloys was obtained, due to the presence of high volume fraction of MoB phase. Formation heat of MoB acted as a positive potential to increase driving force of sintering and consequently bulk density. Finally, a uniform and fine distribution of MoSi 2 particles in MoB continuous matrix in the microstructure of Mo-47Si-23B alloys led to the high hardness up to 660 Vickers.

Effect of Microstructure on Cold Workability of Ni3Si base Multi-Phase Intermetallic Alloys

ABSTRACTThe effect of microstructure on cold-rolling workability and tensile properties of Ni3Si (L12)−Ni3Ti (D024)−Ni3Nb (D0a) multi-phase intermetallic alloys was investigated. The cast alloys with different microstructures containing the D024 phase and/or the D0a phase particles in the L12 matrix were homogenized and then cold rolled. For the alloys with the microstructure consisting of coarse plate-like D024 particles in the L12 matrix, serious cracks initiated at the coarse D024 particles in the early stage of the cold rolling process and then propagated, resulting in failure of the rolled plate. On the contrary, for the alloys with the microstructure consisting of fine needle-like D024 precipitates and/or granular-shaped D0a particles, these second phase particles did not spoil the cold workability, leading to successful cold rolling to 90 % reduction. After 90 % cold rolling, the rolled sheets were fully recrystallized at 1173 K for 1 h, resulting in the formation of a fine-grained microstructure. The room-temperature tensile strength and the yield stress of the recrystallized sheet were remarkably enhanced compared with that of the unrolled alloys, possibly due to the fine-grained microstructure as well as the particle hardening. Also, the high-temperature tensile strength and the elongation were improved in the recrystallized sheets compared to an L12 single-phase Ni3(Si,Ti) alloy sheet. Consequently, it was found that the cold rolling and annealing process was beneficial to improve the tensile properties for the present multi-phase intermetallic alloys.

Structure and mechanical properties of Al 65Cu 20Ti 15-based amorphous/nanocrystalline alloys prepared by high-pressure sintering

High strength, amorphous or partly nanocrystalline, multiphase intermetallic alloys with average composition of Al 65Cu 20Ti 15 have been processed by mechanical alloying of the elemental powders followed by consolidation using high-pressure (8 GPa) sintering either at room temperature or at 300–450 °C for 1 min. Examination of the microstructural constituents using X-ray diffraction and transmission electron microscopy shows that the alloy pressed at 400 °C is primarily amorphous, while nanocrystalline intermetallic phases, Al 2Cu, Al 4Cu 9 and Al 5CuTi 2 evolve from the amorphous matrix on pressing at 450 °C. The pressing temperature of 400 °C appears most promising, leading to products with negligible porosity, increment in the Young's modulus by about 85% with respect to that of Al alloys, as well as impressive hardness (7.9 GPa) and compressive strengths (1490 MPa). However, absence of ductility and poor fracture toughness (3.8 ± 0.8 MPa√m) appear as the major challenges to be met for widespread application of these alloys.

Microstructure and wear resistance of laser deposited Ti 3Co 2Si–Ti 5Si 3–TiCo multiphase intermetallic alloy

A wear resistant Ti 3Co 2Si–Ti 5Si 3–TiCo multiphase intermetallic alloy was fabricated by the laser melt deposition process. Microstructure of the intermetallic alloy was characterized by OM, SEM, XRD and EDS. The alloy has excellent wear resistance and extremely low load-sensitivity of wear under dry sliding wear test conditions. Wear resistance of the alloy is up to 6–24 times higher than the hardened high-carbon low-alloys tool steel 1.0%C–1.5%Cr. The excellent wear resistance of the alloy is attributed to the combination of high hardness of the Ti 3Co 2Si and Ti 5Si 3, good toughness of TiCo and the formation of a smearing-layer on the worn surface of the alloy under room-temperature dry sliding wear test conditions.

Development of Multi-Phase Intermetallic Alloy Composed of Ni<sub>3</sub>X-Type Structures

Dual multi-phase intermetallic alloy, which is composed of Ni3Al(L12) and Ni solid solution (A1) phases at high temperature annealing and is additionally refined by a eutectoid reaction at low temperature annealing, according to which the Al phase is transformed into the Ni3Al(L12)+Ni3V(D022) phases, was prepared. High-temperature tension and creep test were conducted using single crystalline materials. The alloy with such a novel microstructure showed extremely high yield and tensile stresses with good temperature retention. The creep test conducted at high temperature showed extremely low creep rate and creep rupture time when compared with advanced Ni-based superalloys. The results obtained are promising for the development of a new-type of high-temperature structural materials.

The effect of second-phase dispersions on mechanical property of Ni 3Si based multi-phase intermetallic alloys

Using alloys whose initial microstructures are composed of Ni 3Si(L1 2), Ni 3Si(L1 2) + Ni 3Ti(D0 24) and Ni 3Si(L1 2) + Ni 3Nb(D0 a), aging phenomenon and the associated high-temperature tensile property were investigated. The plate-like Ni 3Ti (D0 24) phase was precipitated from the Ni 3Si (L1 2) matrix at high temperature. It was shown by micro-hardness measurement that age hardening behavior due to the precipitation of the Ni 3Ti (D0 24) phase occurs in all alloys in the temperature range from 923 K to 1323 K. It was however shown by tensile test that the precipitated Ni 3Ti (D0 24) phase is not so much effective in improving the mechanical properties of alloys whose initial microstructures are composed of Ni 3Si(L1 2) + Ni 3Nb(D0 a) or Ni 3Si(L1 2) + Ni 3Ti(D0 24). In alloys whose initial microstructures are composed of Ni 3Si(L1 2) + Ni 3Nb(D0 a), a good combination of tensile strength and tensile elongation was found over a wide of test temperature regardless of presence or absence of the precipitated Ni 3Ti (D0 24) phase. It is suggested that the primary coarse Ni 3Nb (D0 a) phase precipitates are beneficial to improving the mechanical properties.

Mechanical properties of dual multi-phase single-crystal intermetallic alloy composed of geometrically close packed Ni 3X (X: Al and V) type structures

Dual multi-phase intermetallic alloy, which is composed of Ni 3Al(L1 2) and Ni solid solution (A1) phases at high-temperature annealing and is additionally refined by a eutectoid reaction at low temperature aging, according to which the Al phase is transformed into the Ni 3Al(L1 2) + Ni 3V(DO 22) phases, was prepared based on the pseudo-ternary system Ni 3Al–Ni 3Ti–Ni 3V. The high-temperature tensile deformation, fracture behavior and tensile creep were investigated using single crystalline material. The alloy with such a novel microstructure shows extremely high yield and tensile strength with good temperature retention, when compared not only with conventional Ni-based superalloys but also with polycrystalline materials reported previously. Over a broad temperature range fracture occurred along octahedral plane in the major component L1 2 phase, accompanied with high tensile elongation and ductile fracture mode. The tensile creep test conducted at 1173 K and 1223 K showed the presence of threshold stress, and also extremely low creep rate and long creep rupture time when compared with conventional Ni-based superalloys. The obtained results are promising for the development of a new-type of high-temperature structural material.

Microstructural evolution of dual multi-phase intermetallic alloys composed of geometrically close packed Ni 3X (X: Al and V) type structures

The microstructural evolution of intermetallic alloys, which have dual two-phase microstructure composed of Ni 3Al (L1 2) and Ni 3V (D0 22) phases, was investigated as a function of aging time at 1273 K, using transmission electron microscopy and X-ray diffraction. Even from early aging time, the lower (i.e. eutectoid) microstructure showed structurally decomposed clusters composed of L1 2 phase and three D0 22 variant structures. With proceeding aging time, the decomposed L1 2 and D0 22 phases coarsened and transformed to lamellar-like microstructures where two types of interfaces between the L1 2 and D0 22 phases, and between two different D0 22 variant structures were developed. At longer aging time, the L1 2 phase disappeared from the lamellar-like microstructure and alternatively the D0 22 phase composed of two different variant structures prevailed over the lamellar-like microstructures. Corresponding to this microstructural change, the direction of the lamellar and its interfacial plane rotate (i.e. change) from 〈001〉 to 〈011〉 and from {001} to {011}, respectively. At a final aging stage, a specific set of two different D0 22 variant structures tend to expend other set of two different D0 22 variant structures.

Effect of growth rate on microstructure and mechanical properties of directionally solidified multiphase intermetallic Ni–Al–Cr–Ta–Mo–Zr alloy

The effect of growth rate on microstructure and mechanical properties of directionally solidified (DS) multiphase intermetallic alloy with the chemical composition Ni–21.9Al–8.1Cr–4.2Ta–0.9Mo–0.3Zr (at.%) was studied. The DS ingots were prepared at constant growth rates V ranging from 5.56 × 10 −6 to 1.18 × 10 −4 ms −1 and at a constant temperature gradient at the solid–liquid interface of G L = 12 × 10 3 K m −1. Increasing growth rate increases volume fraction of dendrites and decreases primary dendritic arm spacing, mean diameter of α-Cr (Cr-based solid solution) and γ′(Ni 3Al) precipitates within the dendrites. Room-temperature compressive yield strength, ultimate compressive strength, hardness and microhardness of dendrites increase with increasing growth rate. All room-temperature tensile specimens show brittle fracture without yielding. The brittle-to-ductile transition temperature for tensile specimens is determined to be about 1148 K. Minimum creep rate is found to depend strongly on the applied stress and temperature according to the power law with a stress exponent of n = 7 and apparent activation energy for creep of Q a = 401 kJ/mol.

Microstructure and Mechanical Properties of Dual Two-Phase Intermetallic Alloys Composed of GCP Ni3Al and Ni3V Phases containing Nb

AbstractDual multi-phase intermetallic alloys composed of Ni3X (X: Al and V) containing Nb were developed, on the basis of the Ni3Al-Ni3Nb-Ni3V pseudo-ternary alloy system. The dual multi-phase intermetallic alloys were characterized by scanning electron and transmission electron microscopies. High-temperature compression and tension tests, and compression creep test were conducted. It was found that the dual multi-phase intermetallic alloys show high yield and tensile strength with good temperature retention, accompanied with reasonable tensile ductility. The compression creep test conducted at high temperature showed lower creep rate in the dual multi-phase intermetallic alloys than in conventional Ni-base superalloys. The obtained results are superior to the dual multi-phase intermetallic alloys containing Ti.

Development of Dual Multi-Phase Intermetallic Alloys Composed of Geometrically Close Packed Ni3X(X:Al and V) Structures

AbstractDual multi-phase intermetallic alloys composed of Ni3Al (L12)+Ni3V (D022) phases were developed, based on the Ni3Al-Ni3Ti-Ni3V pseudo-ternary alloy system. High-temperature tensile deformation, fracture behavior, and compression and tension creep were investigated using polycrystalline and single crystalline materials. The alloys with such a novel microstructure show extremely high yield and tensile strength with good temperature retention, and also reasonable tensile ductility. Also, creep test conducted at high temperature showed extremely low creep rate and long creep rupture time. The obtained results are promising for the development of a new-type of high-temperature structural material exceeding conventional superalloys.

Dual multi-phase intermetallic alloys composed of geometrically close packed Ni 3X (X: Al, Ti and V) type structures – II. Mechanical properties

The mechanical data of novel alloys based on the pseudo-ternary system Ni 3Al–Ni 3Ti–Ni 3V was assessed. This alloy system exhibits dual multi-phase microstructures and was described in part I of this paper [Acta Mater 2005:53]. The mechanical characterization was performed on as-cast and hot-worked material. The new alloys show extremely high yield stresses with good temperature retention, when compared with conventional nickel-based alloys. Over a broad temperature range fracture preferentially occurred along grain boundaries. The compressive creep test conducted at temperatures between 1150 and 1250 K showed the presence of threshold stress and also extremely low creep rates when compared with the conventional Ni-based superalloys with dispersed oxide particles. The obtained results are promising for the development of a new type of high-temperature structural material.

Dual multi-phase intermetallic alloys composed of geometrically close-packed Ni 3X (X: Al, Ti and V) type structures – I. Microstructures and their stability

The constitution and microstructure of intermetallic alloys based on the Ni 3Al–Ni 3Ti–Ni 3V pseudo-ternary system and composed of the phases L1 2, DO 22 and DO 24 were investigated. Particular emphasis is paid to alloys with a relatively low Ti content. High-temperature annealing of these alloys leads to the formation of a two-phase microstructure at the micron-scale, which consists of the phases L1 2 + A1. This microstructure can additionally be refined by a decomposition reaction occurring upon annealing below the eutectoid temperature, according to which the Al phase is transformed into the L1 2 + DO 22 phases. In this way, a novel microstructure is formed at the sub-micron scale. The dual multi-phase intermetallic alloys exhibit highly coherent interface structures between the constituent phases of L1 2 and D0 22 not only at a micron scale but also at a sub-micron scale and also display high microstructural stability at high temperature.

Phase relation and microstructure in multi-phase intermetallic alloys based on Ni 3Al–Ni 3Nb–Ni 3V pseudo-ternary alloy system

The phase relation and microstructure of alloys based on the Ni 3Al–Ni 3Nb–Ni 3V pseudo-ternary alloy system at 1273 and 1373 K were investigated by optical microscopy, X-ray diffraction, and scanning electron microscopy (attached with a wavelength dispersive spectroscope). There was no other intermediate phase besides L1 2 (Ni 3Al), D0 a (Ni 3Nb) and D0 22 (Ni 3V). The phase fields of L1 2 (Ni 3Al), D0 a (Ni 3Nb) and D0 22 (Ni 3V) have been shown to primarily depend upon the free electron concentration ( e/ a) of the constituent atoms. Among the three constituent intermetallic phases, one kind of three-phase relation (i.e. L1 2–D0 a –D0 22) and three kinds of two-phase relations (i.e. L1 2–D0 a , D0 a –D0 22 and L1 2–D0 22) were found to exist at 1273 K. The prepared alloys exhibited widely different microstructures, depending on alloy composition and temperature. In the low Nb concentration region, dual multi-phase microstructures composed of L1 2+D0 a +A1(→L1 2+D0 22) were formed by a eutectic reaction.

Microstructure, mechanical property and oxidation property in Ni 3Si–Ni 3Ti–Ni 3Nb multi-phase intermetallic alloys

Microstructure, high-temperature compressive and tensile deformation, and oxidation property of multi-phase intermetallic alloys, which were based on the Ni 3Si–Ni 3Ti–Ni 3Nb pseudo-ternary alloy system and composed of L1 2, D0 24 and D0 a phases, were investigated. The microstructures of these multi-phase intermetallic alloys were largely dependent on alloy composition. The Widmansttaten-like Ni 3Ti(D0 24) phase was precipitated from L1 2 matrix by a solid-state reaction, accompanied with a certain orientation relationship and habit plane. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L1 2 phase in the wide range of test temperatures. Fifty parts per million boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. It was found that the multi-phase intermetallic alloy with a high Si content had good oxidation resistance, accompanied with a continuous silicate layer. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy that had a high Si content and was composed of L1 2 matrix dispersed by D0 24 and D0 a phases had the most favorable properties as high-temperature mechanical and chemical materials.

Phase relation and microstructure in multi-phase intermetallic alloys based on Ni3Al–Ni3Ti–Ni3V pseudo-ternary alloy system

The phase relation and microstructure of alloys based on the Ni3Al–Ni3Ti–Ni3V pseudo-ternary alloy system at 1273 and 1373 K were investigated by optical microscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy (attached with a wavelength dispersive spectroscope). As the constituent intermetallic phases at 1273 K, L12(Ni3Al), D024(Ni3Ti), D022(Ni3V) and rhombohedral (Ni3Ti0.7V0.3) were identified and then their phase fields were shown to depend upon the electron concentration (e/a) and the atomic size factor (Rx/RNi) of the constituent atoms. Among four intermetallic phases identified at 1273 K, five kinds of two-phase relations (i.e. L12–D024, D024–rhombohedral, rhombohedral–D022 D022–D024 and D022–L12) and two kinds of three-phase relations (i.e. L12–D024–D022 and D024–rhombohedral–D022) were found to exist. Also, D024 (Ni3Ti) phase extended up to concentration field in which a majority of constituent Ti elements were replaced by Al and V elements, keeping their concentrations identical. The prepared alloys exhibited widely different microstructures, depending on alloy composition and temperature. In the low Ti concentration region, dual multi-phase microstructures composed of L12+D024+A1(→L12+D022) were formed by a eutectic reaction.

Microstructures and Mechanical Properties in Ni3Si-Ni3Ti-Ni3Nb-Based Multi-Intermetallic Alloys

ABSTRACTMicrostructure, high-temperature tensile deformation and oxidation property of Ni3Si-Ni3Ti-Ni3Nb multi-phase intermetallic alloys with a microstructure consisting of L12, D024 and D0a phases were investigated. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L12 phase in the wide range of test temperatures. 50-ppm boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. The multi-phase intermetallic alloy with a high Si content had good oxidation resistance, and also the boron addition to this alloy resulted in enhanced oxidation resistance. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy, which has a high Si content and is composed of L12 matrix dispersed by D024 and D0a phases, had the most favorable properties as high-temperature mechanical and chemical materials.