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Microstructural response and variations in strength and electrical conductivity of a Cu−20 at. pct Ni–6.7 at. pct Al alloy during isothermal aging at temperatures from 723 K to 1023 K (450 °C to 750 °C) were investigated to discuss the age-induced precipitation behavior and strengthening mechanism. At all aging temperatures, fine spherical γ′-Ni3Al particles were found to nucleate coherently with parent Cu grains by continuous precipitation and then grew gradually by Ostwald ripening. Domains with a high density of twins developed at grain boundaries during aging below 873 K (600 °C) followed by cellular components composed of fiber-shaped γ′-Ni3Al and Cu solid solution phases at the domain boundaries later. Both the domains and cellular components were suppressed at aging above 923 K (650 °C). The age-induced strengthening principally resulted from fine dispersion of γ′-Ni3Al coherent particles in the grains. The precipitation strengthening by the fine γ′-Ni3Al coherent particles exhibited a maximum at an aging temperature of 873 K (600 °C), resulting in excellent mechanical properties such as a high hardness of 340 ± 7 HV and an ultimate tensile strength of 980 ± 14 MPa, which are comparable to those of other commercial age-hardened Cu–Be, Cu–Ni–Si, and Cu–Ti alloys.

Age-hardened Cu-Ti alloys are widely used as conductive materials in small electrical devices, so it is important for them to have suitable mechanical and electrical properties. One of the principal guidelines for improving the mechanical properties of Cu-Ti alloys is to suppress the formation of coarse discontinuous precipitates within them. Herein, we investigated the microstructure and properties of a Cu-4 at. pct Ti alloy aged under hydrogen pressures of 0 to 0.6 MPa, focusing on discontinuous precipitation at the grain boundaries. During the early stages of aging, fine needle-shaped metastable β′-Cu4Ti precipitates formed continuously in the matrix. With further aging, these β′-Cu4Ti precipitates continued to nucleate and grow, and simultaneously cellular components composing of the lamellae of Cu solid solution and the stable β-Cu4Ti discontinuous precipitates were formed at grain boundaries. Nevertheless, the formation of these cellular components was significantly suppressed when aging under hydrogen pressures of above 0.03 MPa. Upon aging under higher hydrogen pressures (> 0.10 MPa), some granular TiH2 precipitates formed, and the preformed β′-Cu4Ti precipitates decomposed. Upon aging under 0.03 MPa hydrogen pressure, fine metastable β′-Cu4Ti precipitates were formed dominantly, because the formation of stable β-Cu4Ti laminates was suppressed and the TiH2 precipitates was still not formed. Hence, the hardness was maintained under over-aging conditions.

Microstructures and mechanical properties of dual two-phase Ni3Al (L12)-Ni3V (D022) intermetallic alloys to which iron (Fe) was added in different substitution manners were investigated by scanning electron microscopy, transmission microscopy, Vickers hardness, and tensile tests. Primary Ni3Al precipitates were extremely fine in the alloys in which Fe was substituted for Al. The changes of the volume fraction in the Ni3Al precipitates by the addition of Fe were explained in association with the partition behavior of Fe into the constituent phases and the relative content of Al to V which was affected by the substitution manner of Fe. The microstructures in the channel region of the alloys in which Fe was substituted for Ni, Al, and V were suggested to be comprised of L12 and D022 phases, L12, D022 , and Ni slid solution (A1) phases, and A1 phase, respectively. From the partition coefficients of Fe estimated using the alloys constituted by L12, D022 , and A1 phases, it was shown that Fe evenly destabilizes the two intermetallic phases. For the alloys in which Fe was substituted for Al and V, the yield strength (or hardness) decreased and the tensile elongation conversely increased with increasing Fe content. For the alloys in which Fe was substituted for Ni, the tensile elongation as well as strength remained unchanged. The changes of the strength (hardness) as well as tensile elongation in the alloys in which Fe was substituted for Al and V were attributed to the imperfect ordering in the two intermetallic phases and/or the presence of the Ni solid solution (A1) phase.

The effect of off-stoichiometry on the microstructures and tensile properties of Ni3Al–Ni3V pseudo-binary alloys was investigated by a scanning electron microscope, a transmission electron microscope, Vickers hardness test, and high-temperature tensile test. As the alloy deviates from a just-stoichiometric composition toward Ni-rich one, the microstructures constituted by two ordered phases, Ni3Al and Ni3V changed to those constituted by two ordered phases, Ni3Al and Ni3V, and one disordered phase, Ni solid solution. Also, the deviation from the stoichiometric composition resulted in a decrease in flow strength as well as Vickers hardness and conversely increase in tensile elongation. Higher tensile elongation in the off-stoichiometric alloys was induced by the transition from intergranular fracturing to transgranular fracturing. The trade-off relation in the yield strength (or hardness) versus tensile elongation curve, which was drawn plotting the data obtained from the alloys with different off-stoichiometric compositions, was most excellent at 600 °C but rapidly became worse at high temperatures beyond 600 °C. It was demonstrated that the deviation to the off-stoichiometric composition in the two-phase Ni3Al–Ni3V pseudo-binary alloy system was a useful alloying parameter to improve the balance of the flow strength and tensile ductility.

Mechanism for the hardening of two-phase Ni3Al-Ni3V 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.

The strength and electrical conductivity of Cu-Ti alloy wires fabricated by over-aging and intense drawing were investigated as a function of Ti content (2.7 to 4.3 at. pct). The microstructure of all over-aged Cu-Ti alloys before drawing showed mainly coarse cellular components laminating the plates of a terminal Cu solid solution and a β-Cu4Ti intermetallic compound precipitated discontinuously by grain boundary reactions. The volume fraction of β-Cu4Ti plates increased with Ti content, although the compositions of the two phases remained unchanged. When the over-aged alloys were drawn to the same deformation strain, the hardness and tensile strength of the wires increased monotonically with Ti content due to strain-induced strengthening; a high volume fraction of hard β-Cu4Ti fibers formed from laminating plates during drawing promoted a high dislocation density in the matrix. The electrical conductivity of the wires decreased gradually with Ti content due to the higher volume fraction of β-Cu4Ti fibers and due decomposition of the fibers during drawing. The overall performance of the Cu-Ti alloy wires improved as the Ti content increased and was superior to that of conventional Cu-Ti alloy wires fabricated by peak-aging and drawing, and to that of commercial Cu-Be alloy wires.

We designed an optimal procedure to prepare Cu-Ti alloy wires with an excellent combination of strength and electrical conductivity, by drawing conventional peak-aged alloys as well as over-aged ones. When drawing the peak-aged alloy, which exhibited the maximum hardness after aging and a low electrical conductivity, the strength of the wires increased rapidly in the initial stage of drawing but then saturated on further drawing. On the contrary, when drawing the over-aged alloy of inferior hardness but superior electrical conductivity, the strength increased steadily through drawing and eventually exceeded the value of the wires drawn from the peak-aged alloy. Also, the electrical conductivity of the wires drawn from the over-aged alloy was always much greater than that from the peak-aged alloy. Thus, we demonstrated that the procedure of over-aging and then drawing severely is able to enhance both the strength and the electrical conductivity for the Cu-Ti alloys, rather than the conventional peak-aging and drawing process. Noted that the performance of the wires drawn from the over-aged alloy is comparable with that of commercial Cu-Be wires, which are considered to possess the combination of greatest strength and conductivity in Cu-based alloys.

NiTi bulk intermetallic compound with the B19′ structure was irradiated with 1 MeV He, 5 MeV Al, 16 MeV Au and 200 MeV Xe ions, and the change in lattice structure near the surface by the ion bombardment was investigated by using the grazing incidence X-ray diffraction (GIXD) and the extended X-ray absorption fine structure (EXAFS). The lattice structure transformation by the irradiation strongly depends on ion species and/or energies. For the 1 MeV He irradiation, the lattice structure changed from B19′ to the A2 structure, but did not show an amorphization even after the high fluence irradiation. For the 5 MeV Al irradiation, the samples are partially amorphized. For the 16 MeV Au irradiation, the lattice structure of the NiTi samples changed nearly completely from the B19′ structure to the amorphous state via the A2 structure. The value of dpa (displacement per atom) which is needed for the amorphization is, however, much smaller than the case of the Al ion irradiation. For the 200 MeV Xe ion irradiation, the lattice structure completely changed to the A2 structure even by a small ion fluence. The dependence of the lattice structure transformation on elastic collisions (dpa), the spectrum of the primary knock-on (PKA) atoms and the density of energy deposited through electronic excitation was discussed.

Thermal conductivities of Ni 3 (Si,Ti) single-phase alloys with an L1 2 structure as functions of composition and temperature were measured to provide information for high-temperature structural applications. It was confirmed that the Ni 3 (Si,Ti) alloy has an extremely large single-phase region for the compositions Ni 78 (Si 22- x ,Ti x ) ( x = 0–12 at.%), Ni 89− y (Si 11 ,Ti y ) ( y = 9.5–12 at.%), and Ni 89− z (Si z ,Ti 11 ) ( z = 9.5–12 at.%). The thermal conductivities at 293 K of all the Ni 3 (Si,Ti) single-phase alloys were estimated to be between 8 W/mK and 12 W/mK, which are lower than those of almost all other stoichiometric compounds. In the Ni 3 (Si,Ti) single-phase region, the thermal conductivity increased more significantly by increasing the Ni content than by varying the Si and Ti contents. The thermal conductivity of all the Ni 3 (Si,Ti) single-phase alloys increased monotonically with an increase in temperature. The temperature coefficient of thermal conductivity increased as the value of the thermal conductivity at 293 K was low, according to Mooij's relationship. Consequently, the thermal conductivity in the Ni 3 (Si,Ti) single-phase region became larger and less sensitive to the composition at higher temperatures above 1073 K, ranging between 22 W/mK and 24 W/mK.

The two-phase Ni3Al and Ni3V intermetallic alloy laser clad on substrate of SUS304 was evaluated by hardness measurement, scanning electron microscopy, electron probe microanalyzer and transmission electron microscopy observations, focusing on the effect of post annealing after laser irradiation. The laser clad coating layer was diluted with approximately 5.4 at.% Fe and 1.6 at.% Cr stemming from the substrate. In the as-clad coating layer, the inhomogeneous eutectoid microstructure due to incomplete phase separation into two intermetallic phases Ni3Al and Ni3V took place. The hardness in the as-clad coating layer was lower than that in post annealed coating layers. In the coating layer annealed at 1553 K for 5 h, a dual two-phase microstructure composed of the primary cuboidal Ni3Al surrounded by the channel regions in which the major constituent is the Ni3V phase was observed, indicating that the complete eutectoid microstructure was developed. In the coating layer annealed at 1248 K for 24 h, the developed microstructure was lamellar-like one composed of the Ni3Al and Ni3V phases. The hardness in the coating layer annealed at 1248 K was the highest in the coatings observed in this study.

OBJECTIVES In this study, we sought to investigate the association between revolution speed of rotational atherectomy (RA) and debulking area assessed by frequency domain-optical coherence tomography (FD-OCT). BACKGROUND The number of patients with severe calcified coronary artery disease requiring treatment with calcium ablation, such as RA, is increasing. However, there is little evidence available regarding the association between debulking area and revolution speed during RA. METHODS We retrospectively investigated 30 consecutive severely calcified coronary lesions in 29 patients who underwent RA under FD-OCT guidance. The association between preset revolution speed of RA and burr size-corrected debulking area of the calcified lesion was evaluated using a multivariable regression model with nonlinear restricted-cubic-spline, which can help assess nonlinear associations between variables. RESULTS The median age of study participants was 73 years (quartile 65-78); 82.8% were male. The median burr size was 1.5 mm (1.5-1.75); median total duration of ablation was 120 s (100-180). FD-OCT revealed that the post-procedural minimum lumen area increased significantly from 1.64 mm2 (1.40-2.09) to 2.45 mm2 (2.11-2.98) (p

L12-type Ni3Al alloys containing vanadium are potential candidates for solid-solution and age-hardenable alloy systems, according to the Ni3Al-Ni3V pseudo-binary phase diagram. Therefore, herein, variations in the microstructure and mechanical properties of Ni-13 at.% Al-12 at.% V-50 ppm B alloy during isothermal aging were investigated. Alloy specimens were solution-treated at 1323 K for 48 h, quenched in water, and aged at 1073 K to 1173 K. The quenched specimens exhibited a single phase of Ni3Al (L12 structure derived from Al (fcc) structure), while in the aged specimens, numerous fine disk-shaped precipitates identified as Ni3V (D022 structure from orthorhombic structure) were formed on {001} planes of the Ni3Al matrix. The size of the disk-shaped Ni3V precipitates increased gradually with increasing aging period. The hardness and strength of the specimens increased initially during aging at 1073 K to 1173 K, reached a maximum, followed by a subsequent decrease. The age-hardening behavior observed for the specimens can be explained in terms of precipitation of the fine disk-shaped Ni3V precipitates in the Ni3Al matrix. Furthermore, the peak-aged specimens exhibited an increase in yield strength with increasing testing temperature, similar to other L12-type intermetallic alloys.

Ni base intermetallic alloy coating was fabricated by laser cladding, controlling the laser power and powder feed rate. Atomized powder of the Ni base intermetallic alloy was laser-cladded on the substrate of stainless steel 304. The hardness and microstructure of the clad layers were investigated by Vickers hardness test, SEM, XRD and TEM observations. The hardness of the cladding layer was affected by the dilution with the substrate; it increased with decreasing laser power and increasing powder feed rate. By optimizing the dilution with the substrate, the cladding layer with an almost identical hardness level to that of the Ni base intermetallic alloy fabricated by ingot metallurgy was obtained. The TEM observations revealed that a very fine-sized microstructure composed of Ni3Al and Ni3V was partially formed even in the as-cladded state. After annealing, the two-phase microstructure composed of Ni3Al and Ni3V was developed in the cladding layer, resulting in enhanced hardness in the cladding layers fabricated in the majority of cladding conditions.

The microstructures and mechanical properties of ternary (Ni75Al9V16) and multicomponent (Ni69Al9V9.5Nb3Ti1.5Co4Cr4) dual two-phase intermetallic alloys charged with C were investigated by scanning electron microscope, electron probe microscopic analyzer, x-ray diffraction, Vickers hardness, and tensile tests. Solid solubility limits of C in the dual two-phase microstructures were small, mostly less than 0.1 at.%. When C was charged exceeding the solid solubility limit, large-sized carbides were solidified with no structural coherency with the dual two-phase microstructure. Major transition metals constituting the carbides changed from Nb and Ti to V with increasing charged C content. This transition was correlated with the capability of the carbide formation. C dissolving in the dual two-phase microstructure enhanced hardness and flow strength through solid solution hardening without sacrificing tensile ductility. The formed carbides little contributed to strengthening, rather, contributed to softening through depleting constituent element V as well as alloying metals Nb, Ti, and Cr from the dual two-phase microstructures.

The corrosion behaviour of the intermetallic compound Ni3(Si,Ti) + 4Al has been investigated using electrochemical methods in various chloride concentration up to 1 M at ambient temperature. In addition, open circuitpotential (OCP) and linear polarization resistance (LPR) are portion of electrochemical method. It was foundthat the addition of chloride concentration up to the chloride concentration of 1 M does not shift OCP towardactive region (negative direction) and dissolve passive film on the surface of compounds. The corrosion resistance of the compound was decreased slightly with increasing chloride concentration at ambient temperature.Furthermore, at ambient temperature, the passive film of the compound still tends to sustain a stable condition,even though their corrosion resistances increase slightly. A further experiment must be carried out to clarify thestability of film for Ni3(Si,Ti) + 4Al in more detail Advanced Science Letters, 2017, Vol. 23, 5759–5761

Dual-phase Ni3Al-based alloys feature extensive applicability even under high-temperature conditions. We selectively modified the microstructure of a representative dual-phase Ni3Al-based alloy from equi-axed grains to unidirectional grains, using a kW-class high-power laser irradiation technique. On employing the laser probe to linearly scan the Ni-9 at.% Al-16 at.% V alloy specimen, the laser-irradiated region was partially molten and then immediately solidified from the two edges of the molten pool toward the center. Laser irradiation under low-speed scanning increased the molten pool width. The grains in the laser-irradiated region extended preferentially from the two edges toward the center, their crystal orientation was similar to adjacent substrate grains, suggesting epitaxial growth. Therefore, the unidirectional orientation of grains could be extended via wide-range scanning using laser irradiation. This suggests that the microstructure of the alloy can be selectively modified to unidirectional orientated grains by optimizing laser irradiation conditions, such as the power density, scanning speed, and scanning paths. The hardness of the laser-irradiated region decreased due to the phase transformation from the ordered Ni3Al and Ni3V phases to the disordered fcc phase. However, the hardness improved to a value comparable to that of the alloy subjected to heat treatment at 980 &deg, C for 1 h.

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).

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 i...

The environment-induced cracking (EIC) of as cold-rolled Ni 3 (Si,Ti) and Ni 3 (Si,Ti) with 2Mo has been investigated as functions of applied stress, chloride ion concentration, test temperature, and pH by using a constant load method in NaCl solutions. The EIC susceptibility of both intermetallic compounds increased with increasing Cl − ion concentration and test temperature; and increased with decreasing pH. Both intermetallic compounds had the same transgranular fracture appearance and the relationship between log t f (time to failure) and log l ss (steady state elongation rate) became the identical straight line irrespective of applied stress, Cl − ion concentration, test temperature, and pH, which means that l ss becomes a relevant parameter for predicting t f . The EIC susceptibility of Ni 3 (Si,Ti) with 2Mo was lower than that of Ni 3 (Si,Ti), which showed the beneficial effect of Mo. From the results obtained, EIC of both intermetallic compounds was presumed to take place by hydrogen embrittlement (HE).

The Ni 3 Al bulk intermetallic compound was irradiated with 5.4-MeV Al, 10-MeV I and 16-MeV Au ions at room temperature. The effect of irradiation on the lattice structure was observed by X-ray diffraction (XRD). The change in Vickers hardness by irradiation was estimated. A crystal structure analysis showed that, the Ni 3 Al lattice structure transforms from an ordered L1 2 lattice structure to a disordered A1 (fcc) lattice structure by energetic ion irradiation. The relative degree of order correlates well with the density of energy that was elastically deposited by irradiation. The Vickers hardness tends to decrease with an increase in ion fluence. The hardness is not correlated with the elastically deposited energy. The effect of annealing at elevated temperatures on the irradiation induced crystal phase transformation and the Vickers hardness is also discussed.

The effect of changes in the composition and microstructure of the Ni3V–Ni3Al pseudo-binary alloys on their thermal conductivity has been investigated. For Ni3V and Ni3Al-based single-phase alloys, the thermal conductivity shows a maximum value at the stoichiometric compositions, and it decreases as the V (or Al) content of the Ni3Al (or Ni3V) alloy increases, following the Nordheim rule. For Ni3V–Ni3Al two-phase alloys, the thermal conductivity of the constituent Ni3Al phase exhibits a smaller value than that of the Ni3V phase. Eventually, the thermal conductivity of the two-phase alloys decreases as the Al content increases because of the increase in the volume fraction of the Ni3Al phase with low conductivity. As the temperature increases from 293 K to 1073 K, the conductivity increases for all of the alloys but not for stoichiometric Ni3V. However, the dependence of the thermal conductivity on the alloy composition between 293 K and 1073 K is similar. Hence, it is confirmed that the thermal conductivity of the Ni3V–Ni3Al pseudo-binary alloys is controlled by the composition and volume fraction of the constituent phase.

Dual two-phase Ni3Al–Ni3V intermetallic compound with the ordered structure was irradiated with 16 MeV Au5+ ions at room temperature. The observation by a transmission electron microscope has revealed that the lattice structure of this intermetallic compound changes from the ordered structure to the disordered A1 (fcc) structure by the ion irradiation, which accompanies a remarkable decrease in the surface hardness. The annealing treatment at elevated temperatures for the irradiated specimen induces the recovery of surface hardness. The present experimental result shows that the combination of energetic ion irradiation and the thermal treatment could be a means of modification for the workability of dual two-phase Ni3Al–Ni3V intermetallic compound.

The anomalous hardening and microstructural evolution accompanied by the reordering and restoring of cold-rolled Co 3 Ti alloy annealed at 573–773 K were investigated by hardness testing, SEM and TEM observations, XRD analysis and DSC measurements. The hardening observed in the heavily cold-rolled samples was similar to that observed in precipitation reactions, with the hardness increasing with increasing annealing time to a point and then decreasing. The hardness peak occurred more rapidly at higher annealing temperatures, and the annealing time leading to this peak was insensitive to the degree of cold-rolling reduction. The stored lattice strain evaluated from the half-width of the X-ray reflection peak steadily decreased with increasing annealing time but remained relatively high regardless of the degree of cold-rolling reduction or annealing temperature. The TEM deformation microstructures showed that a high density of dislocations was attained, even in an over-aged state. DSC measurements showed two exothermic peaks at low and high temperatures, which were attributed to the annihilation of point defects and/or reordering and to the rearrangement of dislocations, respectively. The observed anomalous hardening was discussed in association with the reordering of the mechanically disordered structure and the restoring of the plastically deformed microstructure.

Ni 3 V bulk intermetallic compounds with ordered D0 22 structure were irradiated with 16 MeV Au ions at room temperature. The irradiation induced phase transformation was examined by means of the transmission electron microscope (TEM), the extended X-ray absorption fine structure measurement (EXAFS) and the X-ray diffraction (XRD). We also measured the Vickers hardness for unirradiated and irradiated specimens. The TEM observation shows that by the Au irradiation, the lamellar microstructures and the super lattice spot in diffraction pattern for the unirradiated specimen disappeared. This TEM result as well as the result of XRD and EXAFS measurements means that the intrinsic D0 22 structure of Ni 3 V changes into the A1 (fcc) structure which is the lattice structure just below the melting point in the thermal equilibrium phase diagram. The lattice structure change from D0 22 to A1 (fcc) accompanies a remarkable decrease in Vickers microhardness. The change in crystal structure was discussed in terms of the thermal spike and the sequential atomic displacements induced by the energetic heavy ion irradiation.

Anomalous hardening behavior accompanied by reordering of cold-rolled Ni 3 (Si,Ti) alloy annealed at 723–823 K was investigated by means of hardness test, microstructural observation and X-ray analysis. Hardening similar to that in precipitation reaction in which hardness increases with increasing annealing time and made a peak, followed by a decrease was observed in heavily cold-rolled samples but not in lightly cold-rolled sample. Hardness increment increased with increasing cold-rolled reduction and took place more rapidly as annealing temperature increased. Reordering proceeded more rapidly as annealing temperature increased and also as cold-rolled reduction increased. Lattice strain evaluated from X-ray half width of reflection peak steadily decreased with increasing annealing time in the same manner not only for the heavily cold-rolled samples but also for the lightly cold-rolled sample. TEM deformation microstructures showed that high density of dislocations was rearranged and polygonized by annealing. The hardening owing to ordered gradient from dislocations to the region distant from it was proposed as a most likely mechanism.

High temperature compression properties of Al-, Cr-or Nb-added Ni3(Si,Ti) based intermetallic compounds were investigated by uni-axial compression test and microstructural observation. The Al-or Cr-added Ni3(Si,Ti) alloys after homogenization heat treatment exhibited a two-phase microstructure consisting of L12 and Ni-solid solution phases. The Nb-added Ni3(Si,Ti) alloy after homogenization heat treatment exhibited a triple-phase microstructure consisting of G-phase with D8a structure and Ni-solid solution phase in the L12 matrix. The volume fraction of Ni-solid solution phase increased in order of Cr-, Nb-and Al-added Ni3(Si,Ti) alloys. The Cr-added Ni3(Si,Ti) alloy was deformable at high strain rate, while the Nb-added one was deformable at low strain rate. It can be considered that the deformability of Ni3(Si,Ti) at high temperature is closely correlated with volume fraction of Ni-solid solution phase and recrystallization behavior.

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 8 at%, 8 at%, and 3 at% 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.

The comprehensive mechanisms for the hardening of two-phase Ni3Al-Ni3V intermetallic alloys by transition metal addition were presented, based on the microstructural observation, alloying behavior and lattice properties of the additives in the constituent phases. The alloys to which 2 at.% Ti, Nb and Ta were added in different substitution manners for Ni, Al and V, respectively were studied by scanning electron microscopy, electron probe microscopic analyzer, X-ray diffraction and hardness test. The alloys in which the additives were substituted for Al exhibited microstructures with finer and cuboidal Ni3Al precipitates. Nb and Ta addition resulted in larger lattice expansion in the two constituent phases than Ti addition. The hardness increase by the Nb and Ta addition was larger than that by the Ti addition. Also, the hardness increase was larger in the substitution manner of the additives for Al than in those for Ni and V. The hardening behavior was explained in terms of solid solution hardening mechanism 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 wholly attributed to solid solution hardening. On the other hand, the hardening for the alloys in which the additives were substituted for Al was attributed to the hardening due to microstructural refining in addition to the solid solution hardening.

In this study, Ta was added to an L1 2 -type Ni 3 (Si,Ti) alloy at different levels and into different substitution sites, substituting for either Ni, Ti or Si. The solubility limits of Ta in the L1 2 phase were 1.9 at%, 5.7 at% and 1.0 at% when Ta substituted for Ni, Ti and Si, respectively. The lattice parameters in the L1 2 phase region increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys, in which Ta substituted for Ni, Si and Ti, respectively. The room-temperature hardness in the L1 2 phase region increased linearly with increasing Ta content, and the increment rate increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys. Similarly, the room-temperature 0.2% proof stress as well as the tensile strength in the L1 2 phase region increased linearly with increasing Ta content, and the increment rate increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys. High tensile elongation was observed at room temperature when the microstructures remain in the L1 2 single phase. At high temperatures, a positive temperature dependence of the hardness as well as the flow strength was observed in the quaternary alloys. It was also shown that the wear resistance of the quaternary Ta(Ti) alloys was improved and attributed to plastically induced hardening of the worn surfaces combined with the positive temperature dependence of the flow strength. The strengthening and hardening resulting from Ta addition was suggested to be due to the hardening of the solid solution arising from the misfits in the atomic radius between Ta and the constituent atoms Ni, Ti or Si.

The effects of stoichiometry on microstructural evolution during ordering of Ni 3 V compound that transforms from cubic disorder phase (A1(fcc)) to tetragonal order phase (D0 22 ) were investigated by scanning electron microscopy, X-ray diffraction and Vickers hardness measurement. In as-homogenized state, either Ni 75 V 25 , Ni 74 V 26 or Ni 76 V 24 alloys exhibited lamellar-like microstructure composed of three sets of D0 22 variant structures with an orthogonal orientation relation to each other, and therefore the disorder phase stable at high temperature was not retained at low temperature. Recrystallized new grains nucleated preferentially at grain boundaries and then eliminated the lamellar-like microstructure as annealing time or annealing temperature increases, like ordinary recrystallization process. The microstructural evolution from the lamellar-like microstructure to the recrystallized grains was the fastest in the Ni 74 V 26 alloy, followed by the Ni 75 V 25 alloy and was the slowest in the Ni 76 V 24 alloy. Hardness of the lamellar-like microstructure was higher than that of the recrystallized grains. Boron doping retarded the microstructural evolution in the Ni 75 V 25 alloy. The microstructural evolution was correlated with anisotropic parameter between two lattice constants, a and c , and was shown to be more significant as this parameter is larger. The results were discussed in terms of the effects of stoichiometry and boron doping on driving force and atomic diffusion by which the microstructural evolution is affected.

Al–Mg–Si alloys were irradiated with 5.4 MeV Al ions, 7.3 MeV Fe ions, 10 MeV I ions, and 16 MeV Au ions at room temperature and the Vickers microhardness was measured. The hardness of Al–Mg–Si alloys increases with increasing the ion fluence. In a viewpoint of ion fluence, hardness change of the Al alloys is different by the kind of irradiating ions. But, in a viewpoint of the density of elastically deposited energy, the effect of the four kinds of them on hardness is almost the same. This result means that the effect of irradiation on hardness of Al–Mg–Si alloys is dominated by the elastically deposited energy. The microstructure of the ion-irradiated specimens were investigated by means of three-dimensional atom probe (3DAP). The experimental result was compared with the microstructure and the hardness for thermally aged specimens. We also discuss the difference in ion-irradiation induced change in hardness between Al–Mg–Si alloys and Al–Cu–Mg alloys (duralumin).

The pitting corrosion of Ni 3 (Si,Ti) with 4 at% Al consisting of two regions of a Ni 3 (Si,Ti) single-phase of L1 2 structure and two phases of L1 2 and fcc Ni ss was investigated as function of chloride concentrations by using electrochemical method, scanning electron microscope and energy dispersive X-Ray spectroscopy in neutral sodium chloride solutions at 293 K. In addition, the pitting corrosion of Ni 3 (Si,Ti) and type C276 alloy were also studied under the same experimental condition for comparison. The pitting potential obtained for the Ni 3 (Si,Ti) with 4 at%Al decreased with increasing chloride concentration. The specific pitting potential and pitting potential of Ni 3 (Si,Ti) with 4at%, Ni 3 (Si,Ti) and C276 were the lowest, the moderate and the highest, respectively, which means that the pitting corrosion resistance of Ni 3 (Si,Ti) was higher than Ni 3 (Si,Ti) with 4at% Al, but lower than that of C276. A critical chloride concentration of Ni 3 (Si,Ti) with 4at% Al was found to be lower than that of Ni 3 (Si,Ti). The Pitting corrosion of Ni 3 (Si,Ti) with 4at% Al occurred in the two phase mixture (L1 2 + Ni ss ).

Two-phase Ni3Al3V intermetallic alloys with and without carbon addition, composed of geometrically closed-packed (GCP) structures of Ni 3 Al ( L 1 2 ) and Ni 3 V ( D 0 22 ), were investigated for dry sliding wear against a G5 disc (WC carbides with a hardness of 1350 HV) at 298 K and 573 K 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 298 K, 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 573 K, 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 Ni 3 Al/Ni 3 V 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.

A Ni3(Si,Ti) intermetalic alloy was synthesized by the powder metallurgy method using elemental powders. The raw powder mixtures with various compositions were sintered by a spark plasma sintering apparatus and then homogenized at high temperatures. Microstructure, hardness, tensile properties and density of the sintered alloys were investigated as functions of the chemical composition and sintering temperature. It was found that a highly-densified Ni3(Si,Ti) sintered alloy was obtained by choosing proper chemical composition and sintering temperature. Also, the Ni3(Si,Ti) sintered alloy with an L12 single-phase microstructure exhibited high hardness and tensile strength.

The corrosion behavior of specimens consisting of two regions of a Ni 3 (Si,Ti) single-phase of L1 2 structure and two phases of L1 2 and fcc Ni was examined in 0.5 kmol/m 3 HCl, H 2 SO 4 and HNO 3 . Ni 3 (Si,Ti) with Cr showed the highest corrosion resistance. The single L1 2 phase region was preferentially dissolved for all specimens in all solutions. This fact was interpreted in terms of lower corrosion resistance of the region due to the presence of active Al or due to the absence of protective Cr and Mo. Ni 3 (Si,Ti) with Al and Ni 3 (Si,Ti) with Cr showed intergranular corrosion in less corrosive HNO 3 .

The effects of alloying elements (Ti, Nb, Ta, Cr, W, Re, Co and Si) on the phase equilibria among Ni (A1), Ni 3 Al (L1 2 ) and Ni 3 V (D0 22 ) phases were studied by means of microstructure observation and energy dispersive spectroscopy analysis on thin foils. It was found that the alloying elements can be classified into four categories: (a) Ti stabilizing the phases in the order: L1 2 > D0 22 > A1, (b) Nb and Ta stabilizing the phases: D0 22 > L1 2 > A1, (c) Cr, W, Re and Co stabilizing the phases: A1 > D0 22 > L1 2 , (d) Si stabilizing the phases: Al > L1 2 > D0 22 . The elements in the categories (a) and (b) raise the temperature of a eutectoid-type reaction (A1 → L1 2 + D0 22 ) while the elements in the category (c) reduce the temperature. The alloying effects were examined in terms of mixing enthalpy and electron concentration.

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.