Correlations between aging heat treatment, ω phase precipitation and mechanical properties of a cast Ti–Nb alloy (original) (raw)
Related papers
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.
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.
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.
Effect of Strain Rate on the Hot Ductility Behavior of a Continuously Cast Ti–Nb Microalloyed Steel
steel research international
ductility curve presents a trough. This range is usually between 700 and 1000 C, depending on the chemical composition of the alloy. [4-7] This loss in ductility can mainly be attributed to the austenite-ferrite transformation and the nucleation of precipitates. [1,8,9] The ferrite forms films at the austenite grain boundaries, and as it has a lower strength than austenite, strain is accumulated making the material more prone to failure. [6,9,10] Precipitates, when formed, provoke a local hardening, leading to stress concentration, that also worsens the ductility. [1,11] The evaluation of the hot ductility in steels is made with the reduction of area (RA), calculated from the relation between the initial cross-sectional area and the final, after the rupture of the sample. [1-3] To evaluate the results, a reference value of 40% proposed by Mintz is used: when below this point, the ductility can be considered low and favorable to the formation of cracks. [1,12] The ductility of a steel grade can be influenced by diverse factors, such as the alloying elements, cooling rate, surface quality, strain rate, and others. This work evaluates the hot ductility behavior of a Ti-Nb microalloyed steel under variation of strain rate by performing hot tensile tests in in situ melted samples. The investigation focused not only on the ductility behavior, but also on the changes on the fractured surface, the microstructure, and precipitates. For the completeness of the evaluation, computer simulations were also performed for the transformation temperatures, Scheil-Gulliver solidification simulation, and precipitation kinetics. [13]
Journal of Materials Engineering and Performance
In this study, Ti-(0-30 wt.%)Nb alloys developed from elemental powders were fabricated by the Selective Laser Melting (SLM) process. Compositional homogeneity, microstructure and mechanical performance were investigated as a function of energy density. The proportion of un-melted Nb particles and isolated pore count reduced with increasing energy density, while Ti allotropic content (i.e. α’, α” and β) varied with energy density due to in-situ alloying. Increasing the Nb content led to the stabilisation of the α” and β phases. The mechanical properties were similar to those compositions manufactured using casting methods, without further post processing. The addition of 20Nb (wt.%) and using an energy density of 230 J/mm3 resulted in a Young’s Modulus of 65.2 ± 1.8 GPa, a yield strength of 769 ± 36 MPa and a microstructure of predominantly α” martensite. This strength to stiffness ratio (33% higher than Ti-10Nb and 22% higher than Ti-30Nb), is attributed to in-situ alloying that pr...
Thermal stability and latent heat of Nb–rich martensitic Ti-Nb alloys
Journal of Alloys and Compounds, 2017
Ti-Nb-based alloys are candidate materials for load-bearing and for functional biomedical implant components. For these applications alloy compositions with relatively low martensitic transformation (MT) temperatures are of highest interest. In this work we examine the thermal stability and the temperature-induced β ↔ α'' MT of Nb-rich martensitic and partially martensitic Ti-Nb alloys exhibiting martensite start temperatures C 300°< s M. The first part of this article investigates the phase transformations and precipitation reactions occurring during isochronal cycling in dependence of the Nb content using differential scanning calorimetry and dilatometry in combination with X-ray
Advanced Materials Research, 2014
In this study, Ti-30at.%Nb was subjected to solution annealing at 900°C followed by ageing at 300o, 400°C, 500°C and 600°C for one hour in order to investigate the effect of ageing temperature on the microstructures and mechanical properties behaviour. It was found that the microstructures of the sample in solution anneal consists of β austenite phase. This indicates that the transformation temperature, Ms, of the material is below room temperatures. The presence of other phases such as α phase and ω precipitates has been detected on the samples after ageing at 500°C and 600°C. Maximum hardness value and tensile strength obtained on the sample aged at 500°C was associated with the presence of ω phase, however the existence of α phase in the sample aged at 600°C provides the lowest hardness and tensile strength. The solution treated sample shows the best shape memory behaviour compared to other heat treated alloys. However, the best superelastic behaviour was observed on the sample a...
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.