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Volume 72, Issue 12
Displaying 1-22 of 22 articles from this issue
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Special Issue on Strategy for Ubiquitous Titanium Alloys
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Mitsuo Niinomi, Takao Hanawa, Masahiko Ikeda, Akihiko Chiba, Tadashi F ...2008 Volume 72 Issue 12 Pages 915
Published: 2008
Released on J-STAGE: December 01, 2008
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Keiichi Kobayashi, Yuichi Oka, Ryosuke O. Suzuki2008 Volume 72 Issue 12 Pages 916-920
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSTiO2 was successfully reduced at 1223 K by calcium, which was deposited due to the molten salt electrolysis of CaO dissolved in CaCl2. Changing the area of electrodes and the electrodes distances, the current density and the Ca concentration near the cathode were varied, respectively. At the initial stage of reduction, metallic Ti powder with the lower oxygen concentration was obtained at the lower current density, where most of electrochemically deposited Ca was efficiently used for the reduction. Meanwhile, at the final stage of reduction/deoxidation, Ti powder with the much lower oxygen concentration were obtained at the higher current density, where the higher Ca concentration was available near the cathode. On order to obtain the metallic powder with the low oxygen content, the formed Ca can penetrate even into the inner part of the sintered oxide.
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Hiroshi Sakai, Yuichi Oka, Ryosuke O. Suzuki2008 Volume 72 Issue 12 Pages 921-927
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSA new process is developed to synthesize the precious alloy directly from the oxide mixtures. This process consists of calciothermic reduction in molten CaCl2 and electrochemical reaction for the recovery of Ca from CaO in the same bath. The molten CaCl2 can dissolve Ca and CaO for complete reaction. The oxide mixture consisting of TiO2, Al2O3, and V2O5 was prepared. Either a simple mixture of oxides or its calcined sample was reduced in the molten CaCl2+CaO. The obtained metallic powder was identified as α-Ti single phase and it contained only about 3000 mass ppm oxygen. Although its metallic composition was close to Ti-6Al-4V, this reduced powder had a broad compositional distribution. This inhomogeneous distribution was improved by the subsequent sintering in argon.
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Koji Hagihara, Takahiro Tachibana, Keita Sasaki, Yoshiyuki Yoshida, Na ...2008 Volume 72 Issue 12 Pages 928-934
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSIn this study, we focused on the fabrication of titanium single crystal by the floating zone melting process under the Ar gas flow atmosphere where partial pressure of oxygen was kept to be extremely low around PO2=10-23 atm, by using the newly developed oxygen reduction system. In the obtained single crystal, distribution of solute oxygen atoms exhibited a peculiar gradient. In the portion gained in an early stage of the crystal growth, the oxygen content showed a higher value of about 1600 ppm than that in the mother ingot of 980 ppm. As the crystal growth proceeded, however, the oxygen content showed a gradual decrease, and in the final portion of the crystal growth, the oxygen content dropped down to 660 ppm. Such a gradient of oxygen composition was not detected in Ti single crystals fabricated under the standard and usual Ar gas flow condition. Owing to the unique gradient of oxygen content under extremely low oxygen partial pressure, the Vickers hardness in the single crystal showed a gradual decrease along the crystal growth direction.
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Kazuhiro Matsugi, Takuro Endo, Yong-Bum Choi, Gen Sasaki2008 Volume 72 Issue 12 Pages 935-941
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSTi-5.5Al-2Fe alloy has been theoretically designed by modification of Ti-6Al-4V alloy, using ubiquitously alloying elements in order to establish the strategic method for suppressing utilization of rare metals. The utilization of the cold crucible levitation melting (CCLM) is very useful, because titanium is very chemically reactive at high temperature. The experimental alloys with high purity and without contaminations from a crucible were prepared, and the homogeneous melt was also achieved by the diffusion mixing effect of CCLM. The microstructure, phase stability, strength, corrosion-resistance and workable properties of the designed alloy, were comparable to those of Ti-6Al-4V. The alloy design can be successfully carried out even using ubiquitously alloying elements by the d-electrons concept, which leads to the establishment of one method for the strategic utilization of rare metals.
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Tadashi Furuhara, Satoshi Annaka, Tadashi Maki2008 Volume 72 Issue 12 Pages 942-948
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSEffects of carbon addition on microstructure of Ti-V alloys formed at high temperatures were investigated.
By adding carbon to pure Ti and Ti-V binary alloys, precipitation of TiC occurs. With increase of vanadium content, β/(β+TiC) phase boundary shifts to the lower carbon side slightly. On the other hand (α+β)/(α+β+TiC) boundaries shifts largely with decreases in α fraction and peritectoid reaction temperature by addition of vanadium.
Addition of carbon to a Ti-15V-3Cr-3Sn-3Al alloy results in extensive suppression of recovery during hot deformation of β phase by carbon in solution. Also age hardening kinetics of Ti-15V-3Cr-3Sn-3Al after β solutionizing was accelerated by carbon addition.
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Tomohiro Ando, Toshihiro Tsuchiyama, Setsuo Takaki2008 Volume 72 Issue 12 Pages 949-954
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSTi-N alloys with different nitrogen content were tensile-tested, and then the effect of nitrogen on tensile properties and deformation structure were investigated. With increasing nitrogen content, the 0.2% proof stress and tensile stress were markedly increased accompanied with the lattice distortion of enlargement of c/a ratio. Since the work hardening rate was also increased, the uniform elongation was not significantly decreased by the addition of nitrogen. However, the local elongation was reduced drastically through the occurrence of intergranular brittle fracture even by a small amount of nitrogen addition. In the tensile-deformed pure Ti, many deformation twins and dislocations were observed. On the other hand, few deformation twins and a high density of planar dislocation arrays were observed in the high nitrogen alloys. The changes in deformation structure might have caused the reduction of local elongation in nitrogen added alloys because of the intergranular brittle fracture derived from the suppression of twinning deformation and the stress concentration at grain boundary due to piled-up dislocations in the planar array.
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Masaki Tahara, Hee Young Kim, Tomonari Inamura, Hideki Hosoda, Shuichi ...2008 Volume 72 Issue 12 Pages 955-959
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSRecently, the Ti-Zr-Nb alloys have been developed as Ni-free shape memory and superelastic alloys. In this study, the effect of Nb and nitrogen (N) contents on martensitic transformation behavior, shape memory effect and superelasticity in Ti-18Zr-(12~16)Nb-(0~1.0)N (at%) alloys were investigated using tensile tests, optical microscopy and X-ray diffraction. Shape memory effect was observed in Ti-18Zr-(12~13)Nb and Ti-18Zr-12Nb-0.5N alloys at room temperature. The superelastic behavior appeared by the increase of Nb or N content. The Ti-18Zr-(14~15)Nb, Ti-18Zr-(13~14)Nb-0.5N and Ti-18Zr-(12~14)Nb-1.0N alloys exhibited the superelasticity at room temperature. The martensitic transformation start temperature (Ms) decreased by 75 K with 1 at% increase of N content for Ti-18Zr-13Nb alloy. The critical stress for slip deformation and the stress for inducing the martensitic transformation increased with increasing N content. The superelastic recovery strain was also increased by adding N. The maximum recovery strain of 5.0% was obtained in the Ti-18Zr-14Nb-0.5N alloy.
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Masaaki Nakai, Mitsuo Niinomi, Toshikazu Akahori, Hiroshi Ishikawa, Mi ...2008 Volume 72 Issue 12 Pages 960-964
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSThe effect of oxygen content on the microstructure and mechanical properties of Ti-29Nb-13Ta-4.6Zr (TNTZ) solutionized and aged at 723 K was investigated. The microstructure of solutionized TNTZ consists of a single β phase, and addition of oxygen leads to the increase in the hardness and tensile strength because of solid solution hardening, and the increase in Young's modulus, and the decrease in the elongation. On the other hand, the α phase precipitates in the aged TNTZ. The results of transmission electron microscopy and X-ray diffraction imply that the size and volume fraction of the α phase increase with the oxygen content in the aged TNTZ. The mechanical properties of the aged TNTZ change with the oxygen content. Age hardening in aged TNTZ is enhanced by an increase in the oxygen content. Further, with an increase in the oxygen content, both the tensile strength and Young's modulus increase, while elongation decreases due to the precipitation of the α phase. TNTZ with different mechanical properties (Young's modulus: around 60-100 GPa, tensile strength: around 600-1400 MPa, elongation: around 5-25%) can be obtained depending on the oxygen content and the heat treatment technique.
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Hirobumi Tobe, Hee Young Kim, Shuichi Miyazaki2008 Volume 72 Issue 12 Pages 965-969
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSRecently, β-type Ti alloys composed of non-toxic elements such as Nb, Ta, Zr, Mo and Sn have been studied for biomedical applications. The present author's research group has also developed these alloys including Ti-Zr-Nb as new biomedical superelastic materials. They reveal strong textures which are formed during thermo-mechanical processing and cause the anisotropy in mechanical properties. In this study, the effect of Nb content on deformation textures of Ti-18Zr-Nb alloys was investigated. The anisotropy in mechanical properties of Ti-18Zr-Nb alloys was also investigated. Ti-18Zr-(15~18) Nb(at%) alloy ingots were fabricated by an Ar arc melting method and then homogenized at 1273 K for 7.2 ks. The ingots were cold rolled with a reduction up to 99% in thickness. For the as-rolled alloys, a very weak γ-fiber texture was observed in Ti-18Zr-(15, 16)Nb alloys, whereas a well developed {001}<110> texture was confirmed in the Ti-18Zr-18Nb alloy. The former alloys revealed weak anisotropy in Young's modulus due to the weak texture, while the latter alloy exhibited strong anisotropy due to the strong texture.
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Effect of Nb Content on Plastic Deformation Behavior and Deformation Textures of Ti-Nb-Zr-Ta-O AlloyYoichi Nii, Hee Young Kim, Shuichi Miyazaki2008 Volume 72 Issue 12 Pages 970-974
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSRecently developed β-Ti alloy Gum Metal is one of attractive materials for biomedical applications due to its excellent combination of low Young's modulus and high strength. Gum Metal also exhibits other unique properties such as non-linear elasticity, plastic deformation without work-hardening. These multifunctional properties in Gum Metal are quite intriguing characteristics not only for practical applications but also for fundamental studies. However the mechanism is not fully understood yet. In this research, in order to obtain new information for special plastic deformation behavior of Gum Metal, the deformation texture and microstructure of Ti-(19-29)Nb-2Zr-0.7Ta-1.2O alloys including typical composition of Gum Metal were investigated by XRD measurement and TEM observation. The major deformation texture of Ti-(21-29)Nb-2Zr-0.7Ta-1.2O alloys was {001}<110> type. However, the maximum orientation density Imax in orientation distribution functions (ODFs) strongly depends on Nb content and the maximum value was obtained at Ti-23Nb-2Zr-0.7Ta-1.2O, indicating that the strongest deformation texture was formed in Gum Metal composition. TEM observation implied that the strong deformation texture formation in Gum Metal is due to its unique deformation mechanism.
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Masahiko Ikeda, Michiharu Ogawa, Masato Ueda2008 Volume 72 Issue 12 Pages 975-982
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSTitanium and its alloys first found applications in the fields of aerospace and chemical engineering. Recently, titanium alloys have been used in consumer products due to their high specific strengths and corrosion resistances. They have also been employed in medical applications because of their excellent biocompatibility. Unfortunately, the principal alloying elements of titanium alloys are very expensive due to their low crustal abundances; this is especially true of the beta-stabilizing elements (e.g., V, Mo, Nb, and Ta). Although titanium is considered to be a ubiquitous element since it has the tenth highest Clarke number of all the elements, it is actually classified as a rare metal because its current refinement process is more environmentally damaging than the processes used to refine iron or aluminum. By contrast, iron and chromium are very attractive as beta stabilizers for titanium alloys since iron is highly ubiquitous and chromium is relatively inexpensive and abundant, while aluminum is very attractive as an alpha stabilizer. It is thus very important to investigate the properties of Ti-Fe-Cr-Al system alloys. In this study, the effects of iron content and the cooling rate after solution treatment on the tensile properties of Ti-3.2 to 5.1 mass%Fe-7.1 mass%Cr-3.0 mass%Al alloys were investigated. This investigation was done by measuring their electrical resistivities and Vickers hardnesses, by performing X-ray diffraction and optical microstructure investigations, and by conducting tensile testing. It was found that the beta phase could only be identified in solution-treated and quenched (STQed) alloys. For alloys in the STQed state, the resistivity ratio decreased with an increase in iron content, whereas the Vickers hardness exhibited the opposite trend. From the results of isochronal heat treatment, the beta transus was estimated to be 1093 K in 3.2 and 3.5Fe alloys and 1073 K in 3.9Fe to 5.1Fe alloys. Alloys in the STQed state have almost the same tensile strength, elongation, and area reduction. The tensile strength, elongation, and area reduction in all the alloys cooled in air were almost the same as those of the STQed alloys. Employing furnace cooling increased the tensile strength of the alloys, but reduced their elongation and area reduction. For the air-cooled alloys, the tensile properties of the Ti-3.2 to 5.1 mass%Fe-7.1Cr-3.0Al alloys were almost the same as those of the STQed alloys.
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Michiharu Ogawa, Toshiharu Noda, Masato Ueda, Masahiko Ikeda2008 Volume 72 Issue 12 Pages 983-988
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSBy their high specific strength and good cold workability, β titanium alloys have been used for various applications, e.g. parts of airplanes and eyeglass frames. Generally, β titanium alloys contain vanadium and molybdenum as alloying elements. However, the official quotations of vanadium and molybdenum are unstable. Therefore, use of those alloying elements is limited. Chromium and iron are attractive element as β stabilizer due to more stable official quotations than vanadium and molybdenum. Ti-13Cr-1Fe-3Al alloy was developed and some properties of that alloy were reported by present authors. It is very important to investigate the influence of cooling rate on mechanical properties of that alloy because of higher diffusion coefficient of chromium and iron.
In this study, effect of cooling rate on tensile properties of Ti-13Cr-1Fe-3Al alloy was investigated by measurement of Vickers hardness, X-ray diffraction, optical and scanning electron microscope observations and tensile tests. The results obtained are as follows.
Tensile strength and reduction in area of Ti-13Cr-1Fe-3Al alloy cooled at 0.02 K/s (show furnace cooling) showed about 860 MPa and about 45%, respectively. Reduction in area at 0.02 K/s is slightly lower than that at other cooling rate. It is considered that α precipitation on cooling at 0.02 K/s causes that decrease. Therefore, cooling rate above 0.02 K/s is recommended in Ti-13Cr-1Fe-3Al alloys, though tensile properties at 0.02 K/s is not bad.
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Hiroaki Matsumoto, Kazuki Kodaira, Akihiko Chiba2008 Volume 72 Issue 12 Pages 989-996
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSMicrostructure and mechanical properties of cold grooved rolled α′ Ti-V-Al and Ti-V-Sn alloys were investigated. Microstructure after solution treatment at 950°C and quenching into ice water showed the acicular martensitic structure of α′ phase for (Ti-12 mass%V)-2 mass%Al and (Ti-8 mass%V)-4 mass%Sn alloys and (α′+α″) phases for (Ti-12 mass%V)-6 mass%Sn alloy. After cold groove rolling at reduction of 75%, microstructure evolved into the equiaxed refined dislocation cell structure having the preferred rolling texture of <1010> parallel to rolling direction. After cold groove rolling, Young's modulus decreases to 47 GPa, in contrast, tensile strength increases to more than 1000 MPa accompanying with work hardening and grain refinement.
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Kyo Takahashi, Eiichi Sato2008 Volume 72 Issue 12 Pages 997-1001
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSTypically, titanium does not have good seizure toughness. In general, a surface treatment must be applied if the component is subjected to sliding contact. Various surface treatments, including ion plating, plasma spray, metal plating, etc., are used to increase seizure resistance. This report details a surface modification process using a low cost interstitial element (oxygen) in a standard atmosphere furnace as the surface diffusion element. We investigated changes in the microstructure and mechanical properties in the vicinity of the surface and sliding properties. As a result, we were able to improve seizure resistance by effectively using oxygen for surface modification.
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Y. Z. Kim, Takashi Konno, Taichi Murakami, Takayuki Narushima, Chiaki ...2008 Volume 72 Issue 12 Pages 1002-1009
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSSurface hardening using solute oxygen formed by dissociation of oxidation film on C.P. (commercially pure) titanium, α+β type Ti-4.5Al-3V-2Fe-2Mo (SP-700) alloy and β type Ti-15Mo-5Zr-3Al (Ti-15-53) alloy was investigated. This method consists of two processes at 1073 K; surface hardening in use of Ar-5%CO gas with a short period of time and subsequent heat treatment under vacuum. The maximum surface hardness and hardening layer depth of C.P. titanium obtained by surface hardening for 1.8 ks were 420 Hv and 30 μm, respectively and these values increased to 820 Hv and 70 μm, respectively, by post heat treatment for 14.4 ks. The extra-surface hardening obtained by post heat treatment was yielded by solid solution hardening of oxygen with the following steps; the solute oxygen is continuously formed at oxide/titanium interface by the dissociation of oxidation film formed by the surface hardening treatment, and then it diffuses into titanium matrix. The maximum surface hardness was the highest in C.P. titanium and the lowest in Ti-15-53. On the other hand, the hardening layer depth was the deepest in Ti-15-53 and the shallowest in C.P. titanium. These results could be explained by the difference of solubility and diffusivity of solute oxygen between titanium α and β phases. This two-step process seems to be a beneficial industrial surface hardening method for titanium materials because it enables to remove the oxide film, achieving the very high maximum surface hardness comparable to that obtained by one-step surface hardening under the same total processing time.
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Regular Articles
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Shota Nishio, Ryota Goto, Masashi Matsuura, Nobuki Tezuka, Satoshi Sug ...2008 Volume 72 Issue 12 Pages 1010-1014
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSThe wettability between Nd2Fe14B and Nd-rich phases has been investigated through the sessile drop method. The compositions of prepared Nd-rich ingots were Nd72.0Fe26.1B1.9 (ternary) and Nd72Fe22.4Cu3.7B1.9(Cu-added). Nd-rich ingots were cut and put on a polished Nd2Fe14B plate and heated in a furnace. Contact angles between Nd2Fe14B plate and Nd-rich ingots were measured as a parameter of wettability under controlled temperature. For the Cu added sample, both contact angles in all temperature range and temperatures when contact angle starts to change were lower than those for ternary sample. These results indicate Cu substitution yields improvement of wettability. DTA measurements for two Nd-rich ingots reveal that their contact angles starts to change at lower temperature than their melting points It is considered that those phenomena are derived from the existence of Nd2Fe14B/Nd-rich interface.
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Yusuke Shimada, Mitsuhiro Matsuda, Yuji Kawakami, Masaaki Otsu, Kazuki ...2008 Volume 72 Issue 12 Pages 1015-1020
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSThe micromechanical tests have been performed for melt-spun Nb-TiNi ribbons, and the relation between the mechanical properties and microstructural change with heat treatment has been investigated. Micro-cantilever specimens with dimensions of 10(B)×20(W)×50(L)μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out at room temperature in air using a mechanical testing machine developed for micro-sized specimens. The fracture toughness value (KQ) of as-melt spun ribbon which consists of an amorphous phase was 5.3 MPam1/2. In contrast, the KQ of the melt-spun ribbon annealed at 773 K for 3.6 ks decreases to 2.8 MPam1/2. With annealing above 973 K fracture toughness increases again. This is due to the nanocrystallization of the amorphous phase and the formation of aggregates which are composed of B2-TiNi and bcc-Nb(Ti) phase with the cube-on-cube orientation relationship. These results suggest that the high temperature annealing is required for the application to the hydrogen permeation membrane.
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Tsuyoshi Sasaki, Tomohiro Ueno, Toshiki Kabutomori, Kazuhiro Ishikawa, ...2008 Volume 72 Issue 12 Pages 1021-1027
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSMicrostructures, crystal structures and hydrogen permeation properties of the Nb52Ti25Co23 alloy after cold rolling and subsequent annealing were investigated. This alloy could be cold rolled up to 60% reduction without annealing. The thin alloy membrane (25 μm) was easily prepared by cold rolling and subsequent annealing above 1000°C. The mixed microstructure of the primary (Nb, Ti) phase and eutectic {(Nb, Ti)+TiCo} phase in as-cast alloy changed to the lamellar structure of the (Nb, Ti) and TiCo phases by several cycles of rolling and annealing. The alloys having the primary (Nb, Ti) phase or the lamellar microstructure which the (Nb, Ti) phases are connecting each other along the hydrogen permeation direction showed higher hydrogen permeability than 2.0×10-8(molH2/m/s/Pa0.5) at 400°C. Grain growth of the (Nb, Ti) phase and the suppression of coarsening of the Ti2Co phase which is brittle and easy to crack are achieved under the final annealing of 1000°C×100 h. The Nb52Ti25Co23 alloy membrane with 25 μm thickness prepared by the above annealing conditions showed higher hydrogen flux J than 1.5 times of Pd77Ag23 alloy membrane with the same thickness.
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Kazuyuki Ogawa, Takahiro Sawaguchi, Setsuo Kajiwara2008 Volume 72 Issue 12 Pages 1028-1035
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSAtomic arrangement of bainite/austenite interface was examined by high resolution electron microscopy in a Fe-2Si-1.4C alloy. Lattice transition region with an intermediate lattice structure between two phases, which is a characteristic feature of shear-type deformation, was not observed either between upper bainite and austenite or between lower bainite and austenite. However, high density dislocations existed inside upper and lower bainites, which may be introduced as a result of lattice invariant shear deformation. Based on these experimental facts, the shear deformation assisted-diffusional transformation model was proposed for the bainitic transformation.
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Kazuyuki Ogawa, Takahiro Sawaguchi, Setuo Kajiwara2008 Volume 72 Issue 12 Pages 1036-1043
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSHigh resolution transmission electron microscopic observations have revealed that isothermal fcc (γ) to hcp (ε) transformation accompanies the bainitic transformation from γ austenite to bcc (α) bainite in an Fe-2Si-1.4C(mass%) alloy heated at lower bainitic transformation temperature of 570 K. The ε plates are formed at the ledges of α bainite/γ austenite interfaces. The unit volume of the ε phase with respect to that of the γ austenite increases by as much as 16% when the ε plate has grown from 4 nm to 100 nm in thickness, probably due to enhancement of interstitial carbon. There is no visible stacking fault in the ε phases. These experimental results are interpreted by the concept of bainitic transformation both with shear-type and diffusion-type nature.
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Tomoshi Takahashi, Yoritoshi Minamino, Masao Komatsu2008 Volume 72 Issue 12 Pages 1044-1051
Published: 2008
Released on J-STAGE: December 01, 2008
JOURNAL FREE ACCESSThe interdiffusion in Ti-rich β Ti-Al-V alloys has been investigated in the temperature range from 1323 to 1473 K. The direct interdiffusion coefficients, DAlAlTi and DVVTi, and indirect interdiffusion coefficients, DAlVTi and DVAlTi, are positive in the ternary alloys, and these four interdiffusion coefficients have slight concentration dependence. The values of DAlAlTi are larger than those of DVVTi, and the values of DAlVTi are also larger than those of DVAlTi. The repulsive interactions exist between Al and V atoms in the Ti-Al-V alloys, because the ratio values of indirect coefficient to direct one are positive. On the other hand, the interactions between Ti (solvent) and Al (or V) atoms are attractive in the present alloy, since the ratio of converted interdiffusion coefficients in the ternary alloys shows negative values.
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