Properties and structural characteristics of Ti–Nb–Al alloys (original) (raw)
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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.
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.
Mechanical Properties and Phase Stability of Ti-Nb-Ta-Zr-O Alloys
MATERIALS TRANSACTIONS, 2007
The effects of niobium and oxygen content on the mechanical properties, phase stability and elastic deformation behavior of Ti-Nb-Ta-Zr-O alloys were investigated by employing tensile tests, microstructure observations and XRD analysis. The basic composition of the tested alloys used was Ti-36%Nb-2%Ta-3%Zr-0.3%O (mass%), with the other alloys having lower niobium content (from 32% to 36%) and higher oxygen content (0.5%). Orthorhombic 00 was observed in the specimens with lower niobium content. Work hardening and elastic deformation behavior in the specimens with lower niobium (33% to 34%) and higher oxygen (0.5%) contents are similar to those of the alloy with basic composition; these specimens showed little work hardening and non-linearity in the elastic range of tensile deformation. The phase configuration analysis of these specimen alloys does not show the presence of any peaks other than the phase before and after cold working. The cold worked Ti-32%Nb-2%Ta-3%Zr-0.5%O has a Young's modulus of 55 GPa, a tensile strength of 1370 MPa and a tensile elongation of 12%. After heat treatment at 623 K for 600 s, the tensile strength of the alloy reaches 1500 MPa, with a Young's modulus of 58 GPa and a tensile elongation of 10%.
A Study of the Kinetics of Phase Transformations in Nb-Ti-Al Alloys
The work reported herein was performed by two Ph.D. students Keith J. Leonard and Joseph C. Mishurda, under the supervision of the PI. The phase equilibria and solid state transformations within fifteen Nb-rich Nb-Ti-Al alloys were investigated. The alloys ranged in composition between 15 and 40 at.% Al with Nb:Ti ratios of 1:1.5 to 4:1. Examination of the as-cast microstructures revealed that all alloys solidified from the ß phase field, with subsequent solid-state transformations occurring within four of the alloys during cooling. The range of primary ß phase solidification was determined to extend beyond the limits of previous liquidus projections. The high temperature ß phase field was verified in each alloy through quenching experiments. The ß phase exhibited B2 ordering at room temperature with the order-disorder transition temperatures evaluated for select alloys. The site occupancy preferences within the ß phase were evaluated through the ALCHEMI technique, which determined that Ti substitution occurred for Nb on Nb sublattice sites with the degree of sublattice partitioning found to depend upon alloy composition.
Nb and B effect on mechanical properties of Ti–Al based intermetallic materials
Vacuum, 2019
Ti-TiAl 3 in-situ composites containing different percentages of Nb and B were effectively produced from Ti, Al, Nb and B powders by electric current assisted sintering (ECAS) technique which is a powder metallurgy processing method. Samples are sintered for 90 s with 2000 A current. The effect of B and Nb on the hardness, fracture toughness and wear resistance of samples were studied. The microstructure properties of the sintered samples were analysed with scanning electron microscopes (SEM), the phases in the samples were determined with XRD and their hardness and fracture toughness values were measured with a Vickers hardness tester with a load of 0.98 N and 98 N respectively. The highest fracture toughness value has been obtained with wt %10 Nb addition as 5.23 MPa m 1/2 , whereas the highest hardness was determined as 965 HV for wt%5 B reinforced in situ-Ti-TiAl 3 composite. Best wear resistance was obtained in the 47.5Ti-47.5Al-5B sample. While Nb additive had a negatory effect on wear resistance, additive B had a positive effect on wear resistance.
Effect of thermomechanical processing on evolution of various phases in Ti-Nb alloys
Bulletin of Materials Science, 2011
This paper deals with the effect of thermomechanical processing on microstructural evolution of three alloys, viz. Ti-8Nb, Ti-12Nb and Ti-16Nb. The alloys were hot rolled at 800°C and then subjected to various heat treatments. Samples from hot-rolled alloys were given solution-treatment in β and α + β phase fields, respectively followed by water quenching and furnace cooling. The solution-treated alloys were subsequently aged at different temperatures for 24 h. Phases evolved after various heat treatments were studied using X-ray diffractometer, optical, scanning and transmission electron microscopes. The alloy Ti-8Nb exhibits α and β phases while the alloys Ti-12Nb and Ti-16Nb show the presence of α ″, β and ω phases in the as-cast and hot-rolled conditions. The β solution treated and water quenched specimen of the alloy Ti-8Nb displays α″ phase while the alloys Ti-12Nb and Ti-16Nb exhibit α″, β and ω phases. The alloy Ti-8Nb shows the presence of α, β and ω phases while those of Ti-12Nb and Ti-16Nb display the presence of α, α ″, β and ω in α + β solution treated and water quenched condition. The observation of ω phase in solution treated condition depends on the cooling rate and the Nb content while in the aged specimens, it is governed by aging temperature as well as the Nb content.
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.
Martensitic transformations in Ti-(16?26 at%) Nb alloys
Journal of Materials Science, 1996
Martensitic phase transformations in the solution-treated and water-quenched binary Ti-Nb alloys in the range of 16-26 at % Nb, were examined. An ordered, base-centred orthorhombic martensite was observed for alloys containing up to 23.4 at % Nb. The substructure of this martensite was generally composed of twins and stacking faults, the presence of antiphase boundaries observed in the plates indicating that the martensite underwent ordering during quenching. Both order-disorder and Ms temperatures were observed to be affected by total interstitial content, higher contents increasing both temperatures. Increasing the niobium content to above 23.4% resulted in retention of the 13 phase, this phase containing either athermal co or "diffuse" c0 depending upon niobium and total interstitial concentration. Finally, the microhardness of the Ti-Nb alloys examined was observed to decrease with increase in niobium and decrease in total interstitial content.
The Physics of Metals and Metallography, 2014
The criteria for the optimization of chemical composition of Ti-Zr-Nb alloys have been selected that allow for obtaining materials with low elastic moduli and which have been used to melt alloys 50Ti-(50-x) Zr-xNb, at 15 < x < 20 at %. Transmission electron microscopy and X ray diffraction analysis have been used to study the phase composition of the as cast alloys and alloys after homogenizing annealing. The minimum elastic modulus (69 GPa) and minimum microhardness (2440 MPa) have been found in the almost single β phase alloy with a maximum niobium content (17.1 at %). An increase in the volume fraction of α'' phase in the alloys with a lower niobium content (to 15 at %) promotes the growth of values of these properties. The phase transformations that occur during the continuous heating of homogenized alloys have been studied. The dependence of the temperature of the polymorphic (α + β)-β transformation on the ratio of the alloying elements in the studied alloys have been shown.