Niobium and titanium diffusion in the high niobium-containing Ti–54Al–10Nb alloy (original) (raw)
Related papers
Tracer diffusion of niobium and titanium in binary and ternary titanium aluminides
Journal of Phase Equilibria and Diffusion, 2005
Titanium and niobium diffusion in the ternary Ti-54Al-10Nb alloy (the composition are in at.%) is investigated in an extended temperature interval by the radiotracer technique. The mechanical sectioning was performed by grinding or sputtering in order to measure the tracer diffusivities at higher and lower temperatures, respectively. Almost linear Arrhenius dependencies are established for Nb (Ti) diffusion with the pre-exponential factor and the activation enthalpy of 1.9!10 K5 (4.0!10 K4 ) m 2 s K1 and 280 (304) kJ mol K1 , respectively. Niobium is a slower diffuser in comparison to Ti in the ternary as well as in the binary (a 2 -Ti 3 Al and g-TiAl) titanium aluminides. The heavy alloying of g-TiAl with 10 at.% niobium, however, enhances significantly both the Ti and the Nb diffusivities. This effect is attributed to an elastic distortion of the L1 0 structure of TiAl induced by the oversized Nb atoms, which may decrease the activation barriers for atomic diffusion. q Intermetallics 14 792-799 www.elsevier.com/locate/intermet 0966-9795/$ -see front matter q
Diffusion of Titanium and Nickel in B2 NiTi
Defect and Diffusion Forum, 2009
a divin @ uni-muenster.de Abstract. Diffusion of both titanium and nickel was measured in the near stoichiometric Ni-49.4at.%Ti alloy with the B2 ordered structure. The radiotracer technique and the 44 Ti and 63 Ni isotopes were applied in the temperature interval from 900 to 1300 K. The penetration profiles were determined by precision parallel grinding or by ion beam sputtering at larger and smaller penetration depths, respectively. Titanium and nickel diffusivities were found to follow linear Arrhenius dependencies with the pre-exponential factors of 2.7×10 -7 and 4.7×10 -9 m 2 /s and the activation enthalpies of 205 and 143 kJ/mol, respectively. A vacancy mediated diffusion mechanism is suggested to provide diffusion of both nickel and titanium in the compound NiTi. 1 here the diffusion mechanism involving two vacancies on the same sublattice is considered [5]. The case of two vacancies on different sublattices is in fact closely related to the triple defect mechanism.
Grain boundary diffusion and precipitates in B2 Ti−50.2 at.% Ni alloy
Intermetallics, 2015
Grain boundary diffusion of 44 Ti and 63 Ni in the B2 TiÀ50.2 at.% Ni polycrystalline alloy was measured in Harrison's B regime (573À923 K) using the radiotracer technique. The triple product P ¼ sdD gb (s is the segregation factor, d the grain boundary width, and D gb the corresponding grain diffusion coefficient) for Ti and Ni was determined. Although the absolute values of the triple products P are typical for the B2ordered alloys, both Ti and Ni GB diffusion in NiTi reveals a unique behavior with significant deviations from a linear Arrhenius-type temperature dependence. Transmission electron microscopy analysis of GB structures at 673 K and 923 K substantiated the occurrence of different interface types which may provide the slower and faster grain boundary diffusion paths in agreement with the experimental data. The influence of different types of precipitates on grain boundary diffusion and possible diffusion mechanisms in the different regimes are discussed.
Intermetallics, 2001
Grain boundary (GB) self-diffusion in a-Ti and titanium aluminides (a 2-Ti 3 Al and g-TiAl) was systematically investigated as a function of temperature and composition of the corresponding alloys. 44 Ti GB diffusion in a-Ti of high purity was studied in the broad temperature interval from 840 to 1120 K. The results can be interpreted in terms of 'normal' vacancy-mediated GB diffusion with a ratio of GB and volume diffusion activation enthalpies Q gb /Q% 0.62. Though Ti bulk self-diffusion is practically independent on composition in the phase Ti 3 Al (Ru¨sing J, Herzig Chr. Intermetallics 1996;4:647), Ti GB self-diffusion reveals a distinct compositional dependence-with increasing Al content on the Al-rich side of a 2-Ti 3 Al the GB diffusivity systematically decreases. On the other hand, the GB diffusion data in g-TiAl reveal practically no compositional dependence. The comparison of the absolute values shows that the Ti GB diffusivity in g-TiAl is by about one order of magnitude larger than in a 2-Ti 3 Al of stoichiometric composition and even by two orders of magnitude larger than in a 2-Ti 68 Al 32 at similar temperatures. Interphase boundary diffusion of 44 Ti was studied in the two-phase Ti 48 Al 52 alloy with samples providing an unidirectional lamellar a 2 /g structure. The absolute values of the a 2 /g interphase diffusivity turned out to be very similar to the GB diffusion data in the Alrichest a 2-Ti 3 Al alloy. This feature is explained by the specific atomistic structure of the a 2 /g interphase boundary.
Essentials in diffusion behavior of nickel- and titanium-aluminides
Intermetallics, 2004
Recently we have extensively investigated bulk and grain boundary diffusion in technologically important Ni-and Ti-aluminides. These compounds exhibit different lattice structures and different types and concentrations of lattice defects on their sublattices (vacancies, antistructure atoms of constitutional and/or thermal origin). The study therefore provides fundamental insight into the interdependence of diffusion behavior and diffusion mechanisms on structure and ordering. An overview is presented, including the direct tracer diffusion measurements of the transition metal component and the determination of the Al diffusivity through interdiffusion data and by using Alsubstituting solutes, like Ga. The interpretation of the experiments is strongly supported by EAM-potential calculations of defect properties and Monte-Carlo simulations of possible diffusion mechanisms. Among other features, the experimentally established curvature in the Arrhenius plot of Ti self-diffusion in TiAl, the surprising effect of the missing diffusion enhancement from structural Ni-vacancies in Al-rich NiAl, the paradoxically appearing deep minimum of the chemical diffusion coefficient in stoichiometric NiAl, and interphase diffusion along oriented Ti 3 Al/TiAl interfacesare successfully explained. q
Nitridation of Ti/Nb alloys and solid-state properties of δ-(Ti,Nb)N
Journal of Alloys and Compounds, 1997
The Ibrmation of microstructures and diffusion layers in the Ti-Nb-N system was investigated by annealing compact Ti/Nb alloys ((l= IIlll air/-~ Ti) in a high-purity nitrogen atmosphere (3 and 311 bar N 2) in the temperature range 1300~1600°C. The alloy starting material was in the form of wedge-type samples as well as in the form of phmc sheets. After nitridation ~11 samples showed a yellow colonr which is characteristic for lhe fcc MTi,NbIN phase, the layer growth rate of which was a minimum at 75 at% Ti. Tile nitride layer as well as the plecipiiates were rich in Ti whereas in the ~ alloy an Nb incre~ w~t~ observed. During nitridation needles with different length and width grew from the inner layet ~ boundilry into the original alloy, ~lectron probe microanalysis (EPMA) wits performed to gain insight into the time evolution of the diffusion protil¢~ of Ti, Nh and N. I to,~logeneous phmeosheel samples were used fi~r ineasuremcnls of the microhardncs~, the ~upcrc~mducting transition lenlperatlitc and tile hlll{ce parameter of 6oITi,NhIN0 to) 1,107 Elsevier Sci¢llCC S,A,
Nitridation of Ti/Nb alloys and solid-state properties of d-(Ti,Nb)N
J Alloys Compounds, 1997
The Ibrmation of microstructures and diffusion layers in the Ti-Nb-N system was investigated by annealing compact Ti/Nb alloys ((l= IIlll air/-~ Ti) in a high-purity nitrogen atmosphere (3 and 311 bar N 2) in the temperature range 1300~1600°C. The alloy starting material was in the form of wedge-type samples as well as in the form of phmc sheets. After nitridation ~11 samples showed a yellow colonr which is characteristic for lhe fcc MTi,NbIN phase, the layer growth rate of which was a minimum at 75 at% Ti. Tile nitride layer as well as the plecipiiates were rich in Ti whereas in the ~ alloy an Nb incre~ w~t~ observed. During nitridation needles with different length and width grew from the inner layet ~ boundilry into the original alloy, ~lectron probe microanalysis (EPMA) wits performed to gain insight into the time evolution of the diffusion protil¢~ of Ti, Nh and N. I to,~logeneous phmeosheel samples were used fi~r ineasuremcnls of the microhardncs~, the ~upcrc~mducting transition lenlperatlitc and tile hlll{ce parameter of 6oITi,NhIN0 to) 1,107 Elsevier Sci¢llCC S,A,
Ni and Fe tracer diffusion in the B2-ordered Ni40Fe10Al50 ternary alloy
Intermetallics, 2004
Ni and Fe bulk diffusion in the B2-ordered Ni 40 Fe 10 Al 50 ternary alloy is investigated by means of radiotracer measurements ( 63 Ni and 59 Fe tracers) and SIMS analysis ( 64 Ni tracer) in an extended temperature interval from 1150 to 1550 K. Almost linear Arrhenius behavior was observed for both, Ni (pre-exponential factor D Ã Ni 0 =1.3 . 10 À5 m 2 /s and activation enthalpy Q Ni =270 kJ/ mol) and Fe (D Ã Fe 0 =1.2 . 10 À4 m 2 /s and Q Fe =279 kJ/mol) diffusion. The Fe diffusivity was found to be by a factor of three to five larger than that of Ni. Furthermore, Ni diffuses in Ni 40 Fe 10 Al 50 faster than in stoichiometric NiAl and the activation enthalpy of Ni diffusion in Ni 40 Fe 10 Al 50 is significantly smaller as compared to the stoichiometric binary NiAl alloy (by about 35 kJ/mol). The activation enthalpy of Ni diffusion in the Ni 50Àx Fe x Al 50 ternary alloys was found to reveal a minimum for ternary compositions with about 10% of Fe addition. The apparent controversial behavior of creep resistance and self-diffusivity in the NiFeAl ternary alloys is discussed. The analysis of experimental data favors nearest-neighbor jumps (most likely the triple defect mechanism) as a dominant diffusion mechanism in the alloy. #
Niobium diffusion in niobium-doped titanium dioxide
Journal of Solid State Electrochemistry, 2009
The present work studied the self-diffusion coefficient of 93Nb in Nb-doped TiO2 single crystal (4.3 at.% Nb) at high oxygen activity [p(O2) = 21 kPa] over the temperature range 1,073 to 1,573 K. The diffusion-induced 93Nb concentration profile was determined by using secondary ion mass spectrometry (SIMS). The subsequently determined self-diffusion coefficient of 93Nb exhibits the following temperature dependence: D93textNb=1.77times10−9,textm2,texts−1,expleft(frac−197pm9,textkJ,textmol−1textRTright)D_{{}^{93}{\text{Nb}}} = 1.77 \times 10^{ - 9} \,{\text{m}}^2 \,{\text{s}}^{ - 1} \,\exp \left( {\frac{{ - 197 \pm 9\,{\text{kJ}}\,{\text{mol}}^{ - 1} }}{{{\text{RT}}}}} \right)D93textNb=1.77times10−9,textm2,texts−1,expleft(frac−197pm9,textkJ,textmol−1textRTright) . This study builds upon a similar study performed previously for 93Nb tracer diffusion in undoped TiO2, and identifies the effect of compositional change on self-diffusion behaviour. The obtained activation energy has been considered in terms of migration and formation enthalpies of titanium vacancies.
Bulk Diffusion of Niobium in Single-Crystal Titanium Dioxide
Journal of Physical Chemistry B, 2007
The present work reports the tracer diffusion coefficient for 93 Nb in rutile TiO 2 single crystals using secondary ion mass spectrometry (SIMS). The determined tracer diffusion coefficient exhibited the following temperature dependence in air ( p(O 2 ) ) 21 kPa) over the range 1073-1573 K: D 93 Nb ) (4.7 m 2 s -1 )×10 -7(0.4 exp ((-244 ( 9 kJ mol -1 )/RT) Through comparison to the self-diffusion of 44 Ti in rutile TiO 2 , 93 Nb is interpreted to diffuse via the interstitialcy mechanism. The obtained tracer diffusion data are useful for ensuring compositional control during the processing of Nb-doped TiO 2 -based semiconductors using solid-state reactions between Nb 2 O 5 and TiO 2 .