Dual Two-phase Intermetallic Alloys Research Articles

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

Abstract

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 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.

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 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.

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 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.

The Effect of Alloying Elements on Microstructure and Strength Property of Dual Two-Phase Intermetallic Alloys Based on Ni3Al-Ni3V Pseudo-Binary Alloy System

The microstructures and hardness property of dual two-phase intermetallic alloys that arecomposed of various kind of volume fractions of geometrically closed packed (GCP) Ni3Al(L12) and Ni3V(D022) phases were studied. The hardness of dual two-phase intermetallic alloys basically was explained by mixture rule in hardness between primary Ni3Al precipitates and eutectoid region.Nb and Ti addition raised the hardness of dual two-phase intermetallic alloys by solid solute hardening in the constituent phases.The additional hardening arising from interfacial area between primary Ni3Al precipitates and eutectoid region was also found. As temperature increases, theadditional hardening decreased for the base and Nb added alloys but decreased little for the Ti added alloys.

Effect of Nb and Ti Addition on Microstructure and Hardness of Dual Two-Phase Intermetallic Alloys Based on Ni<SUB>3</SUB>Al-Ni<SUB>3</SUB>V Pseudo-Binary Alloy System

The microstructures and hardness property of dual two-phase intermetallic alloys that are composed of various kind of volume fractions of geometrically closed packed (GCP) Ni 3 Al(Ll 2 ) and Ni 3 V(DO 22 ) phases was studied. Higher volume fraction of primary Ni 3 Al precipitates was observed in the Ti and Nb added alloys when keeping Al content the same. Also, the microstructures in the eutectoid (channel) region consisting of N i 3Al+Ni 3 V were sensitive to alloying addition. The hardness of dual two-phase intermetallic alloys was basically explained by mixture rule in hardness between primary Ni 3 Al precipitates and eutectoid region. Nb and Ti addition raised hardness of dual two-phase intermetallic alloys by solid solution hardening in the constituent phases. This hardening was more significant in Nb addition than in Ti addition. In addition to hardness owing to the mixture rule, additional hardening arising from interfacial area between primary Ni 3 Al precipitates and eutectoid region was found. With increasing Ni 3 Al/channel (eutectoid) interfacial area, the additional hardening increased. As temperature increases, the additional hardening monotonously decreased for the base and Nb added alloys but little decreased for the Ti added alloys.

Microstructural factors affecting hardness property of dual two-phase intermetallic alloys based on Ni 3Al–Ni 3V pseudo-binary alloy system

Dual two-phase intermetallic alloys that have alloy compositions of Ni 75Al x Nb 2.5V 22.5− x and are composed of geometrically close packed (GCP) Ni 3Al (L1 2) and Ni 3V (D0 22) phases containing Nb were studied, focusing on the relationship between microstructural parameter and high-temperature hardness property. The two-phase microstructures defined by primary Ni 3Al precipitates and eutectoid (i.e., channel) region (consisting of Ni 3Al and Ni 3V phases) were characterized in terms of size, volume fraction and number density of primary Ni 3Al precipitates. The high-temperature hardness was evaluated as a function of temperature. The volume fraction of primary Ni 3Al phase precipitates, and interfacial area between primary Ni 3Al precipitates and channel region were found to be important factors affecting the hardness of the dual two-phase intermetallic alloys. Possible mechanisms responsible for the observed extra hardening were discussed, taking the role of interfaces among the constituent phases into consideration.

Microstructural evolution and mechanical property in dual two-phase intermetallic alloys composed of geometrically close-packed Ni3 X (X: Al and V) containing Nb

Dual two-phase intermetallic alloys composed of geometrically close-packed (GCP) structures of Ni3Al (L12) and Ni3V (D022) containing Nb were investigated in terms of microstructural evolution during low-temperature annealing (aging) and the related mechanical properties. The eutectoid region, i.e. the prior Al phase (Ni solid solution) is composed of the lamellar-like structure consisting of Ni3Al (L12) and Ni3V (D022) even at an early aging stage, and then coarsen with increasing aging time. The lamellar-like structure tend to align along $$ \langle {\text{001}}\rangle $$ direction and on {001} plane in the prior A1 phase (or the L12 phase). In a wide range of temperature, the dual two-phase intermetallic alloys showed high yield and tensile strength, and also reasonable tensile ductility, accompanied with ductile fracture mode. The observed mechanical properties were less sensitive to the microstructural evolution during low-temperature annealing (aging), meaning that the present dual two-phase intermetallic alloy is promising for a new type of high-temperature structural material.

Microstructure and mechanical property in dual two-phase intermetallic alloys composed of geometrically close-packed Ni 3X (X: Al and V) containing Nb

Dual two-phase intermetallic alloy, which is composed of Ni 3Al (L1 2) and Ni solid solution (A1) phases at high temperature and is refined by a eutectoid reaction during low temperature aging, was prepared on the basis of the Ni 3Al–Ni 3Nb–Ni 3V pseudo-ternary alloy system. The eutectoid reaction decomposes the A1 phase to a mixture of geometrically close packed (GCP) structures of Ni 3Al (L1 2) and Ni 3V (D0 22). Dual two-phase intermetallic alloys were characterized by scanning electron and transmission electron microscopy. High-temperature compression and tensile tests, and compression creep test were conducted. It was found that the dual two-phase intermetallic alloys showed high yield and tensile strength with good temperature retention, accompanied with reasonable tensile ductility. The dual two-phase intermetallic alloys showed lower creep rate than conventional Ni-base superalloys. Also, the present two-phase intermetallic alloys are superior to the counterparts containing Ti, and they are promising for the development of a new-type of high-temperature structural material.

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.