Two-phase Intermetallic Alloys Research Articles

Integrated Laser Additive Manufacturing of α-Al2O3 Nanoparticle-Seeded β/γ' Ni-Al Intermetallic Alloy with Enhanced High-Temperature Oxidation Performance.

The oxidation of β-NiAl at high temperatures leads to the preferential formation of metastable alumina, such as θ-Al2O3, which exhibits a significantly faster growth rate compared to stable α-Al2O3. However, our recent research has shown that through the use of the surface-dispersing nanoparticles (NPs) of metal oxides with a hexagonal closed pack (hcp), such as α-Al2O3, the thermal growth of α-Al2O3 can be facilitated. The present study employed laser additive manufacturing (LAM) to develop an integrated α-Al2O3 NPs surface-seeded two-phase intermetallic alloy comprising brittle β-NiAl and tougher γ'-Ni3Al, which demonstrated better comprehensive mechanical properties. It was found that seeding the α-Al2O3 NPs promoted the early stage growth of α-Al2O3 on both β and γ' phases during oxidation in air at 1000 °C. This led to a decrease in the oxidation rate but an enhancement in adhesion of the formed alumina scale in comparison to the naked β/γ' two-phase alloy. The reasons for this result were interpreted.

Effect of Ta addition on microstructure and mechanical properties of dual two-phase Ni3Al-Ni3V intermetallic alloy

Mechanism for the hardening of two-phase Ni 3 Al-Ni 3 V intermetallic alloy to which 2 at.% Ta was added in different substitution manners for Ni, Al and V was presented, based on the microstructural observation, alloying behavior and lattice properties of the additive in the constituent phases. The hardening behavior was explained in terms of solid solution hardening in which the mixture rule in the volume fraction of the two constituent phases and the atomic size misfit evaluated from the changes of the lattice parameters were incorporated. Consequently, the hardening for the alloys in which the additives were substituted for Ni and V was attributed to solid solution hardening. On the other hand, the hardening for the alloy in which the additive was substituted for Al was attributed to the hardening due to microstructural refining in addition to the solid solution hardening.

Microstructure and mechanical properties of dual two-phase Ni3Al–Ni3V intermetallic alloys charged with carbon

Abstract

Fine Precipitation in the Channel Region of Two-Phase Ni3Al and Ni3V Intermetallic Alloys Containing Mo and W

Fine precipitation was observed in the channel region of the Ni-based, two-phase Ni3Al and Ni3V intermetallic alloys containing Mo and W, which are soluble in the A1 phase at high temperatures but less soluble in the two intermetallic phases at low temperatures. The fine precipitates were identified as Mo- or W-rich phases (Mo solid solution with a body-centered-cubic (bcc) structure or Ni4W with a tetragonal structure) accompanied by a rigid orientation relationship and a habit plane with the constituent phases in the channel region. Fine precipitation was induced when added elements were substituted for Ni, thus, stabilizing the two intermetallic phases; however, it was not induced when the two intermetallic phases were destabilized by the addition of elements to substitute for Al and V. Fine precipitation was induced to a greater extent when Nb was concomitantly added to the alloys with Mo or W and when the two intermetallic phases were stabilized. Annealing at temperatures below the eutectoid temperature was necessary to induce fine precipitation in the alloys containing W. Accordingly, age hardening by annealing did not occur in the alloys containing Mo but did occur in the alloys containing W, whose behavior was correlated with the difference in the diffusivity of the Mo and W elements in the two-phase eutectoid microstructures (phases).

Microstructural stability and age-hardening behavior of Re-added dual two-phase Ni3Al and Ni3V intermetallic alloys

The effect of Re addition on the microstructure and hardening behaviour of the dual two-phase Ni3Al (L12) and Ni3V (D022) intermetallic alloy was investigated by scanning electron microscopy, transmission electron microscopy and Vickers hardness test. The two-phase eutectoid microstructure accompanying the Re-rich precipitates were observed in the channel region of the alloys in which Re substituted for Ni but not in those in which Re substituted for Al and V. The concomitant addition of Nb (or Ta) with Re more stabilized the two-phase eutectoid microstructure and consequently more induced the fine precipitates in the channel region. The annealing at temperatures below the eutectoid temperature was necessary to induce the fine precipitates in the channel region and thereby result in the precipitation hardening. The fine precipitation in the channel region and related hardening was attributed to the alloying feature so that Re is soluble in the A1 (fcc) phase at high temperatures and becomes less soluble in the two intermetallic phases decomposed from the A1 phase at low temperatures.

Effect of W addition on microstructure and mechanical properties of Ni base dual two-phase intermetallic alloys

ABSTRACTThe effect of W addition on microstructure and mechanical properties of Ni3Al (L12) and Ni3V (D022) two-phase intermetallic alloys has been investigated. W was added to the base alloy composition, Ni75Al10V12Nb3 (at. %) in place of either Ni, Al or V. The W-added alloy ingots were heat-treated in vacuum at 1575 K for 5 h. The majority of W-added alloys showed a dual two-phase microstructures while the alloy in which 3 at. % W substituted for Ni exhibited the dual two-phase microstructure containing W solid solution dispersions. Vickers hardness was significantly enhanced by W addition, which is primarily due to solid-solution strengthening.

Effect of Si Addition on Microstructure and Mechanical Properties of Dual Two-Phase Intermetallic Alloys Based on the Ni3Al-Ni3V Pseudo-Binary Alloy System

ABSTRACTThe effect of Si addition on microstructure and mechanical properties of dual two-phase intermetallic alloys was investigated. Si was added to the base alloy composition Ni75Al9V13Nb3+ 50 wt. ppm B by three substitution ways in which Si was substituted either for Ni, for Al and for V, respectively. The alloys added with 1 at.% Si showed a dual two-phase microstructure composed of Ni3Al (L12) and Ni3V (D022) phases, while the alloys added with over 2 at.% Si exhibited the same dual two-phase microstructure but contained third phases. The third phases were G phase (Ni16Si7Nb6) and A2 phase (the bcc solid solution consisting of Nb and V). Yield and tensile strength of the 1 at.% Si-added alloys were high in the alloy in which Si was substituted for Al but low in the alloys in which Si was substituted for Ni or for V, in comparison with those of the base alloy. Tensile elongation was lower than that of the base alloy irrespective of substitution ways. The density of the Si added alloys was close to or slightly lower than that of the base alloy. Oxidation resistance of the Si added alloy was increased. Si addition to the dual two-phase intermetallic alloys is beneficial for reducing the density and enhancing the oxidation resistance without a harmful reduction of strength properties.

V content reduced dual two-phase Ni3Al–Ni3V intermetallic alloys

The objective of this study is to reduce V content of Ni-base dual two-phase intermetallic alloy, with keeping the dual two-phase microstructure and also without sacrificing their mechanical and chemical properties. The dual two-phase microstructure was maintained when Cr and Nb instead of V were added to the alloy and their valence electron concentration (e/a) ranges from 8.59 to 8.43. Consequently, the contents of V in the dual two-phase intermetallic alloy were reduced by 8at%, 8at%, and 3at% by Cr substitutions for V-site, both of Ni- and V-sites, and Ni-site, respectively. The density of the modified alloys slightly increased from that of the base alloy. Hardness was higher in the modified alloys than in the base alloy. The flow strength of the modified alloys is much improved from that of the base alloy in a wide range of temperatures. Also, oxidation resistance of the modified alloys was superior to those of the base alloy.

Friction stir welding in stainless steel sheet of type 430 using Ni-based dual two-phase intermetallic alloy tool

Ferritic stainless steel SUS430 sheets were friction stir welded by using a Ni-base dual two-phase intermetallic alloy tool. After friction stir welding (FSW), the SUS430 work and the tools were evaluated in terms of microstructure and mechanical properties. The tensile specimens cut from the welded joints fractured in the base metal portion and their fracture strength was equal to that of the base metal. The stir zone comprised of recrystallized fine microstructure was observed, and also the thermo-mechanically affected zone was observed in an advanced side. Hardness in the upper one-third layer of the welded cross section was higher than the base metal. The admixture matter from work to tool surface occurred whereas that from tool to work surface did not take place in the scanning electron microscopy-EPMA resolution level. The amount of wear of tool was negligibly small, suggesting that the Ni-base dual two-phase intermetallic alloy is promising as a new type of FSW tool used for high melting materials such as steel.

Evaluation of the wear properties of dual two-phase Ni3Al/Ni3V intermetallic alloys

Two-phase Ni3Al3V intermetallic alloys with and without carbon addition, composed of geometrically closed-packed (GCP) structures of Ni3Al (L12) and Ni3V (D022), were investigated for dry sliding wear against a G5 disc (WC carbides with a hardness of 1350 HV) at 298K and 573K by using a pin-on-disc type configuration. The dry sliding wear of a commercial Inconel 718 was also studied under the same experimental conditions for comparison. The wear mass loss measured for the Ni3Al3V intermetallic alloys increased with increasing sliding distance. In the dry wear test at 298K, the 0.1 C intermetallic alloy showed the lowest wear mass loss, followed by the 0 C alloy and then the 0.5 C alloy. At 573K, the 0.5 C alloy showed the smallest wear mass loss, followed by the 0.1 C alloy and then the 0 C alloy. All three intermetallic alloys showed better wear resistance compared to Inconel 718 at both test temperatures. The good wear resistance of the Ni3Al/Ni3V two-phase intermetallic alloys was attributed to the combination of the positive temperature dependence of the flow strength and the strong friction-induced work hardening during the dry sliding wear process.

Effect of Re addition on microstructure and mechanical properties of Ni base dual-two phase intermetallic alloys

ABSTRACTThe effect of Re addition on microstructure and hardness of the Ni3Al (L12) and Ni3V (D022) dual two-phase intermetallic alloys was investigated as functions of alloying (substituting) method of Re and aging condition (temperature and time). Re was added to the base alloy composition by three methods: Re was substituted for Ni, Al and V, respectively. The Re-added alloys were solution-treated at 1553 K and then aged at lower temperatures of 1123 K-1248 K. Apparent age hardening occurred in the alloy where Re was substituted for Ni while no age hardening was observed in the alloys where Re was substituted for Al or V. In the case of the latter two alloys, the hardness was unchanged or reduced with a progression of aging time. These results were discussed in terms of phase separation and ordering in the channel region, and hardening due to Re-rich phase precipitation.

Aging effect on microstructure and hardness of two-phase Ni3Al–Ni3V intermetallic alloys containing Ta and Re

Abstract Two-phase intermetallic alloys composed of geometrically closed packed (GCP) Ni3Al (L12 phase) and Ni3V (D022 phase) have very attractive mechanical properties at high temperatures and are therefore being considered for use as high temperature structural materials. In this study, it was found that the addition of Ta remarkably enhanced the alloys’ hardness due to solid solution hardening in the constituent phases but did not result in an age hardening effect. On the other hand, the addition of Re inhibited the formation of the two-phase microstructure in the solution treated condition, resulting in the lowest hardness. After aging at 1223 K, the Ni solid solution phase in the channel region of the Re-added alloy was decomposed into Ni3Al and Ni3V, accompanied by the precipitation of a Re-rich phase. Consequently, the hardness rapidly increased with increasing aging time. Simultaneous addition of Ta and Re induced fine, dense precipitation of Re-rich phase after aging and consequently resulted in higher hardness than the addition of Ta or Re individually.

Deformation Microstructures of Two-Phase Intermetallic Alloy Composed of Ni<sub>3</sub>Al and Ni<sub>3</sub>V in Single Crystalline Form

Two-phase single-crystal intermetallic alloys composed of Ni3Al (L12) and Ni3V (D022) with some orientations were compressed at various temperatures, and their deformation microstructures were observed by transmission electron microscopy (TEM). The deformation at room temperature was governed by the glide motion of dislocations in the primary Ni3Al precipitates and the activation of the microtwins in the Ni3V variant structures in the channel regions. The interfaces between the primary Ni3Al precipitates and the Ni3V variant structures are suggested to work as the barriers to the dislocation motion. While, at temperature above the peak temperature (873 K), the deformation microstructures of the two-phase intermetallic alloy exhibited the ribbon-like deformation microstructures penetrating the constituent phases i.e. through the interfaces between primary Ni3Al precipitates and the Ni3V variant structures in the channel regions. It was also suggested that the superior strength in the two-phase intermetallic alloys is due to the high flow strength of the Ni3V phases and to the interfacial hardening receiving when the dislocations activated in the primary Ni3Al precipitates propagate to the channel regions.

Alloy design for reducing V content of dual two-phase Ni3Al-Ni3V intermetallic alloys

ABSTRACTThe objective of this study is to establish alloy designing which can reduce the amount of V for a Ni-base dual two-phase intermetallic alloy, without degenerating the dual two-phase microstructure. It was demonstrated that the favorable dual two-phase microstructure will be maintained as far as the valence electron concentration (e/a) of the alloys added by Cr is not so much different from that of the base alloy (i.e. the alloy without additive elements). Consequently, it was found that the dual two-phase microstructure was maintained even though the amounts of V were reduced by 7 at.%, 7 at.%, and 10at.% by substituting of Cr for V, Cr for both of Ni and V, and Cr for Ni, respectively. The hardness of the alloys with reduced V content was higher than that of the base alloy.

TEM observation of the channel regions in a two-phase intermetallic alloy based on Ni 3Al–Ni 3V pseudo-binary alloy system

A new type of intermetallic alloy with a two-phase microstructure composed of Ni 3Al (L1 2) and Ni 3V (D0 22) phases was investigated by using a transmission electron microscope (TEM), focusing on the microstructures in the channel regions. TEM bright-field images indicated that the two-phase microstructure consisted of well-defined primary Ni 3Al precipitates and channel regions with peculiar contrast. In the narrower channel regions, single Ni 3V variant structures, whose c-axis is normal to {1 0 0} plane of the primary Ni 3Al precipitates, were observed. In the wider channel regions, the lamellar-like microstructures that are composed of alternately arranged two-types of Ni 3V variant structures whose c-axes are perpendicular to each other were observed. The lattice misfit between the a-axis of Ni 3Al and the c-axis of Ni 3V was determined to be larger than that between the a-axis of Ni 3Al and the a-axis of Ni 3V. It was suggested that the crystallographic orientation of the Ni 3V phase in the channel regions was aligned in the manner of lowering an internal stress due to the lattice misfit between the primary Ni 3Al precipitates and the Ni 3V domains.

Microstructure Analysis of The Channel Regions in Dual Two-phase Intermetallic Alloy Based on The Ni3Al-Ni3V Pseudo-binary Alloy System

ABSTRACTDual two-phase intermetallic alloys based on the Ni3Al-Ni3V pseudo-binary alloy system have been reported to display high phase and microstructure stabilities and good mechanical properties at high temperature and are therefore considered to be used as a next generation type of high temperature structural materials. The microstructure of the dual two-phase intermetallic alloys is composed of primary Ni3Al and the channel (eutectoid) regions consisting of Ni3Al+Ni3V. In this study, the microstructure of the channel regions was investigated by a transmission electron microscope (TEM). The contrasts of the channel regions showed a complicated microstructure in bright-field images. However, the electron beam diffraction consisted of a single set of patterns and the spots did not accompany streaks, indicating that crystallographic coherency among the constituent phases or the domains is very high. It was also shown that the lattice misfit between the a-axis of Ni3Al and the c-axis of Ni3V is larger than that between the a-axis of Ni3Al and the a-axis of Ni3V. From the dark-field observation, it was found that the c-axis of Ni3V domains in the channel regions is oriented perpendicular to the interface between primary Ni3Al and Ni3V. Therefore, it is suggested that the crystallographic orientation of Ni3V in the channel regions is aligned in the manner of lowering an internal stress caused by the lattice misfit between primary Ni3Al precipitates and Ni3V domains.

Effect of The Refractory Element Additions on Microstructure and Mechanical Property of Two-phase Intermetallic Alloys Based on The Ni3Al-Ni3V Pseudo-binary Alloy System

ABSTRACTTwo-phase intermetallic alloys composed of geometrically close packed (GCP) Ni3Al (L12 phase) and Ni3V (D022 phase) have attractive mechanical properties at high temperature, and are therefore considered to be used as high temperature structural materials. In this study, the effect of Ta and Re addition on the microstructure and hardness of two-phase intermetallic alloys was investigated. The addition of Ta remarkably enhanced the hardness due to solid solution hardening of the constituent phases. On the other hand, the addition of Re retarded the formation of the two-phase microstructure, resulting in the lowest hardness in the solution treated condition. By aging at 1223 K, the Ni solid solution in the Re added alloy decomposed to Ni3Al and Ni3V, accompanied by precipitates of a Re-rich phase. Consequently, the hardness rapidly increased with increasing aging time. Simultaneous addition of Ta and Re induced very fine precipitates of a Re-rich phase after aging, and consequently resulted in a higher hardness than by the addition of Ta or Re alone.

Synthesis of Dual Two-Phase Ni<SUB>3</SUB>Al-Ni<SUB>3</SUB>V Intermetallic Alloys Containing Nb by Pulse Current Sintering

A dual two-phase Ni3Al-Ni3V intermetallic alloy with a nominal composition of Ni75.0Al7.5V15.0Nb2.5 (at%) doped with 50 mass ppm boron was synthesized by the powder metallurgy process using elemental powders. Raw powder mixture was sintered at temperatures from 1073 K to 1373 K by the pulse current sintering method and then annealed in a vacuum at 1553 K for 3 h. The dual two-phase intermetallic alloy whose microstructure exhibits the cuboidal primary Ni3Al phase and the surrounding channel region composed of Ni3Al and Ni3V phases, and contains neither voids nor intermediate products were obtained by sintering at a high temperature of 1373 K and by subsequent annealing at 1553 K. Also, the well synthesized and annealed samples showed finer grain sizes, i.e., about 30 μm than the cast alloys fabricated by the ingot metallurgy process. The hardness of the synthesized samples increased with increasing sintering temperature and also by the subsequent annealing at 1553 K.

Effect of NbC addition on mechanical properties of dual two-phase Ni 3Al–Ni 3V intermetallic alloy

Dual two-phase intermetallic alloy that has an alloy composition of Ni 75Al 9V 13Nb 3 and is composed of geometrically close packed (GCP) Ni 3Al (L1 2) and Ni 3V (D0 22) phases was studied, focusing on the effect of NbC addition on high-temperature tensile properties. The two-phase microstructures defined by primary Ni 3Al precipitates and eutectoid region consisting of Ni 3Al and Ni 3V phases were kept and were dispersed by Nb 2C particles regardless of NbC content. EPMA analysis showed that alloy compositions in matrix of the NbC added alloy were different from those in the base alloy. The positive temperature dependence of flow strength was observed for all NbC added alloys. In low temperature range the maximum strengthening took place at 1 at.% NbC content. On the other hand, tensile elongation increased with increasing NbC content up to 1 at.% NbC content and gradually decreased at NbC content over 1 at.% content in whole temperature ranges. Also, the NbC addition resulted in change of the fracture mode from brittle transgranular fracture to ductile transgranular fracture in low temperature range, and from brittle intergranular fracture to ductile transgranular in high temperature range. Possible mechanisms responsible for the strengthening and ductilization by NbC addition were discussed, based on the behavior of C solutes in the matrix, which were released from the charged NbC carbides.

Effect of C addition on mechanical properties of dual two-phase Ni3Al–Ni3V intermetallic alloys

Two kinds of dual two-phase intermetallic alloys containing Nb and Ti that are composed of geometrically close packed (GCP) Ni3Al (L12) and Ni3V (D022) structures were studied, focusing on the effect of C addition on microstructures and high-temperature tensile properties. The dual two-phase microstructures defined by primary Ni3Al precipitates and eutectoid region consisting of Ni3Al and Ni3V phases were dispersed by carbides at a majority of C contents. The positive temperature dependence of the flow strength was observed for all C-added alloys. The maximum strengthening took place at a C content below 0.5 at.%, irrespective of test temperatures. On the other hand, the tensile elongation rapidly increased with increasing C content, irrespective of test temperatures. Also, the C addition resulted in the change of the fracture mode from brittle transgranular fracture to ductile transgranular fracture in the low temperature range, and from brittle intergranular fracture to ductile transgranular fracture in the high temperature range. Possible mechanisms responsible for the strengthening and ductilization by the C addition were discussed, based on the behavior of solutes (such as C, V, Nb and Ti) and the carbides in the matrices, and also on the dual two-phase microstructure modified by the C addition.