Nitridation of Ti/Nb alloys and solid-state properties of d-(Ti,Nb)N (original) (raw)

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,

High-temperature nitridation of Nb–Ti alloys in nitrogen

Journal of Alloys and Compounds, 1999

Microstructure evolution, phase composition, weight gain and layer growth kinetics of Nb-Ti alloys (10, 47, 63 and 90 at.% Ti) annealed in high-purity nitrogen atmosphere (0.3, 3 and 30 bar) were studied in the temperature range 1300-16008C. After nitridation, the formation of an external compact nitride layer as well as extensive internal nitride precipitation was observed. The overall nitridation kinetics (weight gain) is invariably parabolic; a deviation from the initial rate law is observed at 1450 and 16008C for the longer reaction times when the alloy core approaches nitrogen saturation and internal precipitation slows down. The parabolic rate constant is strongly affected by the Nb content in the alloy. The phases detected in the reacted samples are isostructural with those of the Nb-Ti, Nb-N and Ti-N systems. The surface nitride was d-(Ti,Nb)N in any case. The morphology of the internal nitridation zone corresponds to the growth of large, oriented, nitride needles for the three alloys richer in titanium. The needles are composed of a-(Ti,Nb)(N) in the case of Ti Nb alloy and of d-(Ti,Nb)N in the case of Ti Nb and Ti Nb . Such a microstructure is evidence for nucleation difficulty; 90 10 12x 63 37 47 53 coarsening of the existing particles is favoured in comparison to the formation of new precipitates. Homogeneous nucleation is hindered by the small chemical Gibbs free energy available and the elastic strain energy related to volume misfit. After initial reaction, microstructure evolution is mainly determined by the fast inward diffusion of nitrogen and the slow Nb-Ti interdiffusion in the b-(Ti,Nb) alloy. Internal nitridation of Ti Nb at 1450 and 16008C leads to the formation of fine and numerous precipitates of b-(Nb,Ti) N. In this 10 90 2 case heterogeneous nucleation along grain boundaries and dislocation lines is the prevailing mechanism.

Niobium and titanium diffusion in the high niobium-containing Ti–54Al–10Nb alloy

Intermetallics, 2006

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

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.

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.

Morphological study of nitrides of NbTi (50:50, by weight) alloy

Journal of Alloys and Compounds, 1993

Plates of NbTi (50:50, by weight) were nitrided in a nitrogen atmosphere in the temperature range 800-1000 °C for 15, 30, 60, 120 and 180 min. X-Ray diffraction and optical and electronic microscopy were used to characterize the samples. Two nitride layers were identified on the substrate: an external and continuous phase of TiN, named 3, and a deeper and discontinuous phase of Ti2N, named e. The electron rnicrographs reveal the presence of paths rich in Nb which may be responsible for the diffusion of nitrogen into the matrix.

Phase formation in the NB-Ti system

Vacuum, 1995

In this work we report some experimental results on the N-B-Ti system. Boron nitride thin films were prepared by rf sputtering and then ion implanted with 200 keV Ti+ ions at various doses. The films were characterized by scanning electron microscopy (SEM), glancing incidence X-ray diffraction (GXRD), secondary neutral mass spectrometry (SNMS) and nano-indentation, both in the as-deposited and ion implanted condition and also after thermal annealing. SEM pictures show the development of various microstructures as the Ti-dose increases. GXRD shows that TiB2 is formed at low doses while TiN prevails at high doses. At very high doses, elemental Ti is predominantly observed. Hardness and Young's modulus increase as the Ti dose increases up to saturation values. Ti depth profiles of specimens implanted at various doses show a radiation enhanced diffusion of Ti at low doses. However, the Ti diffusivity is reduced with the appearance of TiB2 and TiN phases.

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.