Thermal stability and latent heat of Nb–rich martensitic Ti-Nb alloys (original) (raw)
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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.
In and ex situ investigations of the β-phase in a Nb and Mo containing γ-TiAl based alloy
Intermetallics, 2008
In a -stabilised Ti-43Al-4Nb-1Mo-0.1B alloy (composition in atomic percent) the correlation between the occurrence of -phase and temperature was analyzed experimentally and compared to thermodynamic calculations. Results from in-situ high-energy X-ray diffraction, Manuscript texture measurements, heat-treatments, scanning electron microscopy, and temperaturedependent flow stress measurements were used to study the evolution of the -phase with temperature. Thermodynamic calculations based on the CALPHAD method were applied to correlate the phases developed in the -solidifying TiAl based alloy under investigation. This alloy is characterized by an adjustable -phase volume fraction at temperatures where hotwork processes such as forging and rolling are conducted. Due to a high volume fraction of phase at elevated temperatures the hot-extruded alloy can be forged under near conventional conditions.
GAZI UNIVERSITY JOURNAL OF SCIENCE, 2021
β-titanium shape memory alloys are used as shape memory-based biomedical applications and superelastic materials because they are made up of non-toxic components. Also, their behaviors are more semilar with that of human bone and dental biological tissues, such as biocompatibility, superior corrosion resistance, low density, and low modulus of elasticity. In the current study, the effect of Ta additive on the physical properties of Ti-Nb alloy has been investigated. Ti-Nb-Ta alloy samples were produced such that the Tantalum (Ta) element was substituted instead of Niobium (Nb), and the induction arc melting was used to melting the mixed powders. To investigate the crystal structure, microstructure, and phase transformation temperatures of all samples, the X-Ray Diffraction (XRD), Scanning Electron Microscopic (SEM), and Diffraction Scanning Calorimetry (DSC) measurements have been used. Both βrich and α peaks were observed in the XRD and SEM measurements. Also, the DSC results revea...
Scanning, 2021
A new generation of Ti-xNb-3Fe-9Zr (x = 15, 20, 25, 30, 35 wt %) alloys have been designed using various theoretical approaches including DV-xα cluster, molybdenum equivalency, and electron to atom ratio. Afterward, designed alloys are fabricated using cold crucible levitation melting technique. The microstructure and mechanical performances of newly designed alloys are characterized in this work using scanning electron microscope and universal testing machine, respectively. Each alloy demonstrates monolithic β phase except Ti-35Nb-3Fe-9Zr alloy which display dual α″ + β phases. Typically, niobium acts as an isomorphous beta stabilizer. However, in this work, formation of martensitic α″ phases occurs at 35 wt % of niobium among the series of newly designed alloys. Furthermore, none of the alloys fail till the maximum load capacity of machine, i.e., 100 KN except Ti-35Nb-3Fe-9Zr alloy. Moreover, the Vickers hardness test is carried out on Ti-xNb-3Fe-9Zr alloys which demonstrate slip ...
Materials science & engineering. C, Materials for biological applications, 2015
While the current research focus in the search for biocompatible low-modulus alloys is set on β-type Ti-based materials, the potential of fully martensitic Ti-based alloys remains largely unexplored. In this work, the influence of composition and pre-straining on the elastic properties of martensitic binary Ti-Nb alloys was studied. Additionally, the phase formation was compared in the as-cast versus the quenched state. The elastic moduli and hardness of the studied martensitic alloys are at a minimum of 16wt.% Nb and peak between 23.5 and 28.5wt.% Nb. The uniaxial deformation behavior of the alloys used is characterized by the absence of distinct yield points. Monotonic and cyclic (hysteretic) loading-unloading experiments were used to study the influence of Nb-content and pre-straining on the elastic moduli. Such experiments were also utilized to assess the recoverable elastic and anelastic deformations as well as hysteretic energy losses. Particular attention has been paid to the...
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.
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.
Materials & Design, 2011
Ti-Nb alloys were arc melted in a water-cooled copper hearth in an inert atmosphere. After preparation, the samples were centrifugally cast in copper molds, and rapidly cooled, resulting in a martensitic microstructure. They were then aged at different temperatures. The microstructural characterization of this material suggested that martensite decomposition occurred, leading to precipitation of a, b and x phases. Aging at higher temperatures led to x phase decay. Mechanical characterization indicated that the heat treatment enhanced the strength and ductility of the alloys. Correlations between heat treatment, x precipitation and mechanical behavior are discussed.
Phase fractions, transition and ordering temperatures in TiAl–Nb–Mo alloys: An in- and ex-situ study
Intermetallics, 2010
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The Phase Transformations Induced by High-Pressure Torsion in Ti–Nb-Based Alloys
2021
The study of the fundamentals of the α → ω and β → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Prior to HPT, three alloys with 5, 10, and 20 wt% of Nb were annealed in the temperature range of 700–540°C in order to obtain the (α + β)-phase state with a different amount of the β-phase. The samples were annealed for a long time in order to reach equilibrium Nb content in the α-solid solution. Scanning electron microscope (SEM), transmission electron microscopy, and X-ray diffraction techniques were used for the characterization of the microstructure evolution and phase transformations. HPT results in a strong grain refinement of the microstructure, a partial transformation of the α-phase into the ω-phase, and a complete β → ω phase transformation. Two kinds of the ω-phase with different chemical compositions were observed after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one f...