Nb–20%Ta alloy powder by the hydriding–dehydriding technique (original) (raw)
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Journal of Alloys and Compounds, 2016
In the present work, Tie40 mass%Nb alloys were successfully fabricated by a powder metallurgy route consisting of mechanical alloying (MA) of TiH 2 eNb powder mixture and spark plasma sintering (SPS). The use of brittle TiH 2 powder, instead of ductile elemental powder, led to significant increment in the yield of mechanically alloyed (MAed) powder. The MAed powder consisted of homogeneously distributed nano-sized Ti/Nb hydride particles together with micron-sized pure Nb particles. The MA also led to the lowering of dehydrogenation temperature of hydride particles. Sintering of MAed powders under low temperature conditions (1223 K, & 1373 K) resulted in the fine-grained heterogeneous microstructure consisting of a, b, and unreacted pure Nb phase. On the other hand, sintering at higher temperatures (1523 K) resulted in a relatively coarse-grained chemically homogeneous microstructure with almost complete b phase. Coarse-grained homogeneous b TieNb alloy exhibited higher average hardness as compared to that of heterogeneous fine grained microstructures. An attempt has been made to illustrate the correlation between the microstructural characteristics and mechanical properties of the sintered Ti e40Nb compacts.
International Journal of Hydrogen Energy, 2012
In this work the results of investigation of mechanism of alloy formation in TieNb system by "Hydride cycle" (HC) method are presented. The temperature regime of dehydrogenation-sintering is defined; the dependences of phase composition of the synthesized alloys on the dispersity and ratio of source reagents (TiH 2 and NbH x powders) are studied. X-ray method is used for determination of structural characteristics of synthesized alloys and their hydrides. The results indicate that the crystal lattice and morphology of TieNb alloys are sensitive to the content of Nb: at increasing of NbH portion in the charge, the b-phase becomes prevailing in the formed BCC alloy. The BCC alloys have been estimated as effective hydrogen storage materials. Therefore, we studied the interaction of synthesized alloys with hydrogen in combustion regime to obtain their hydrides.
Processing and Properties of Nb-Ti-Based Alloys
Superalloys 1992 (Seventh International Symposium), 1992
The processing characteristics, tensile properties, and oxidation response of two Nb-Ti-Al-Cr alloys were investigated. One creep test at 650°C and 172 MPa was conducted on the base alloy which contained 40Nb-40Ti-lOAl-1OCr. A second alloy was modified with 0.11 at. % carbon and 0.07 at. % yttrium. Alloys were arc melted in a chamber backfilled with argon, drop cast into a water-cooled copper mold, and cold rolled to obtain a 0.8~mm sheet. The sheet was annealed at 1100°C for 0.5 h. Longitudinal tensile specimens and oxidation specimens were obtained for both the base alloy and the modified alloy. Tensile properties were obtained for the base alloy at room temperature, 400, 600, 700, 800, 900, and 1000°C, and for the modified alloy at room temperature, 400, 600, 700, and 8OOOC. Oxidation tests on the base alloy and modified alloy, as measured by weight change, were carried out at 600, 700, 800, and 900°C. Both the base alloy and the modified alloy were extremely ductile and were cold rolled to the final sheet thickness of 0.8 mm without an intermediate anneal. The modified alloy exhibited some edge cracking during cold rolling. Both alloys recrystallized at the end of a 0.5-h annealing treatment. The alloys exhibited moderate strength and oxidation resistance below 600°C, similar to the results of alloys reported in the literature. The addition of carbon produced almost no change in either the yield strength or ductility as measured by total elongation. A small increase in the ultimate tensile strength and a corresponding decrease in the reduction of area below 600°C were observed. Carbon addition also served to marginally refine the grain size after annealing. The results of this study and those of similar alloys reported in the literature suggest that 40Nb-40Ti-lOAl-1OCr forms a good base alloy suitable for alloying for improvement in its oxidation and high-temperature strength properties.
Metals, 2018
Toward designing a cost-effective advanced powder metallurgy approach, we present a new insight into the efficient utilization of titanium hydride powder, together with pure Ti powder, to prepare high-strength β-titanium alloys. In the present work, Ti-40 mass% Nb alloy was prepared by mechanical alloying of a mixture of pure Ti, titanium hydride, and Nb elemental powders, followed by a carefully designed two-step spark plasma sintering. The role of relative amounts of titanium hydride and pure Ti powders during mechanical alloying, and their effect on the microstructural and mechanical properties of the Ti-40Nb alloy, have been discussed and elaborated. An increasing amount of titanium hydride results in higher powder yield and smaller resultant powder particle size. Subsequent two-step spark plasma sintering resulted in equiaxed microstructure with primarily β phase, wherein the grain size decreased with increasing amounts of titanium hydride powder. The specimen corresponding to alloys prepared using equal amounts of pure Ti and titanium hydride powders resulted in fine-grained structure, exhibiting the best combination of mechanical properties, that is, a combination of highest hardness, high strength, and high ductility.
Advanced Powder Technology, 2019
The mechanical alloying process was employed to produce C103 alloy with Nb-10% Hf-1% Ti (wt.%) com-28 position using Nb, Hf and Ti powders. The mechanical alloying process was performed in an argon atmo-29 sphere in the chamber and bullets of tungsten carbide with a ball-to-powder weight ratio (BPR) of 20:1 at 30 rotation speed of 200, 300 and 400 rpm for 2, 5 and 8 h. At rotation speeds of 200 and 300 rpm particle 31 size decreased and became more spherical during MA. While increasing milling time at 400 rpm caused 32 agglomeration of particles. XRD results showed that increasing milling time at a constant rotation speed 33 has no considerable effect on reduction of crystallite size, but the lattice strain is strongly affected by it 34 and increased obviously with further rotation speed. The results showed that the optimum milling time 35 and rotation speed to attain Nb-10Hf-1Ti alloy powders with the least amount of contamination and 36 appropriate morphology are 5 h and 300 rpm, respectively.
Effect of the addition of Ta on microstructure and properties of Ti–Nb alloys
Journal of Alloys and Compounds, 2010
This work is a study of the microstructures and properties of a series of Ti-xNb-yTa alloys (x = 25, 30, 35; y = 0, 2.5, 5, 7.5) (wt. %), solution treated and cooled under the following conditions: furnace cooling (FC), air cooling (AC), oil quenching (OQ) and water quenching (WQ). The results showed the existence of a high density of precipitates in FC and AC samples. The microstructures of OQ and WQ alloys containing 25 and 30 wt.% Nb were basically formed by ␣ martensite and Ti-35Nb-7.5Ta was the only composition where the  phase was entirely retained. In FC and AC samples, phase was most responsible for the high values of elastic modulus and hardness, whereas the OQ and WQ samples showed a continuous decrease in elastic modulus due to the high  retention as the content of alloying elements increased; the WQ sample of composition Ti-35Nb-7.5Ta presented the lowest value of elastic modulus (64 GPa). Hardness tends to decrease with Ta additions. Reduction in area seemed to be independent on Nb and Ta contents but mechanical strength decreased as Nb and Ta percentages increased. Some alloys showed low reduction in area as a consequence of a combination of irregular phase distribution and oxygen contamination; these alloys presented the  phase preferably retained at the periphery of specimens, which is attributed to the fall of M s due to the influence of the cooling rate in Ti-alloys containing Nb and Ta elements, since the higher cooling rate are obtained superficially, and the effect of the oxygen contamination.
International Journal of Hydrogen Energy, 2018
The body-centered cubic (BCC or b) titanium alloys are attractive materials for hydrogen storage applications, due to their relatively high absorption capacities that can be attained in some cases, even at room or moderate temperatures. It is known that the ball milling techniques improve the H-absorption/desorption kinetics. Thus, different compositions with Ti/Nb atomic ratios of 1.0, 1.5 and 2.3 were prepared by mechanical alloying (MA) and reactive milling (RM), and the composition effects on the microstructure and the hydrogenation properties were characterized. Both procedures, MA and RM, were able to produce Ti x Nb 1-x BCC alloys. It was observed a significant influence of Ti/Nb atomic ratios on lattice parameters, crystallite and particle sizes, effective kinetic parameter, Avrami exponent, hydrogen storage capacities, reversibility, and desorption temperature ranges. The RM synthesized hydrides acquired better H-absorption/desorption properties than the TieNb hydrides produced by mechanical alloying hydrogenated at 250e300 C. The results demonstrated changes in the hydride nucleation manner and improvement of the hydrogenation rates when the Nb addition is increased.
Structure of mechanically alloyed Ti-Al-Nb powders
Metallurgical and Materials Transactions A, 1995
Ti-A1-Nb ternary powder mixtures containing 24Al-llNb, 25A1-25Nb, 37.5Al-12.5Nb, and 28.5AI-23.9Nb (at. pct) were mechanically alloyed in a SPEX 8000 mixer mill using a ballto-powder weight ratio of 10: 1. The structural evolution in these alloys was investigated by X-ray diffraction and transmission electron microscopy techniques. A solid solution of A1 and Nb in Ti was formed at an early stage of milling, followed by the B2/body-centered cubic (bcc) and amorphous phases at longer milling times. The stability of these phases and their transformation to other phases have been investigated by heat treating these powders at different temperatures. The B2/bcc phase transformed into an orthorhombic (O-Ti2A1Nb) or a mixture of the orthorhombic (O) and hexagonal close-packed (a2-Ti3Al) phases, the proportion of phases being dependent on the powder composition. Milling beyond the amorphous phase formation resulted in the formation of an fcc phase in all the powders, which appears to be TiN, formed as a result of contamination of the powder.
Properties and structural characteristics of Ti–Nb–Al alloys
Materials Science and Engineering: A, 2005
The use of Al as an ␣ stabilizer in different Ti-Nb alloys has been investigated for its effect on some properties and changes in structural characteristics. Quenched alloys with 10-40% Nb and 2-15% Al were analyzed in terms of their phase transformations, as well as elastic modulus, density and internal friction. It was found that the rhombic distortion introduced in the ␣ -HCP phase transforms into another martensitic ␣ structure. Above 5% Al, metastable -BCC is formed and eventually predominates. The appearance of another metastable phase, , was verified in alloys between 2 and 5% Al with less than 35% Nb. These structure transformations are a consequence of the obstructing effect of Al on the redistribution of Ti and Nb. The elastic modulus increases with Al and decreases with Nb percentage due to different developed structures, especially at lower Al content. Small fluctuations in the generally increasing variation of the density with Nb, for Al percentages, were attributed to the phase transformations. The internal friction was relatively large for the martensitic, ␣ or ␣ , structure but decreases significantly with the appearance of  phase.