Abstract
X-Ray diffraction (XRD) analysis was used to study the influence of alloying with 5 at.% Nb, 5 at.% Zr and 5 at.% (Zr+Hf) on the lattice parameters of the γ(TiAl) and α2(Ti3Al) phase in the intermetallic alloys based on Ti-44Al-0.2B (at.%). Before XRD analysis duplex structures with near the same microstructural parameters were obtained in samples of the alloys. The XRD data were used to calculate the tetragonal distortion (cγ / aγ ratio) of the γ phase, the cα2 / aα2 ratio of the α2 phase and the γ / α2 lattice misfits of the alloys. The highest tetragonal distortion (cγ / aγ) of the γ unit cell (cγ / aγ =1.0124) is observed for the base Ti-44Al-0.2B alloy, followed by the Nb-, (Zr+Hf)- and Zr-containing alloy (cγ / aγ =1.0116, 1.0075 and 1.0069, respectively). The cα2 / γα2 ratio is insignificantly changed depending on alloying. Doping with Zr and Zr+Hf leads to a noticeable decrease in the γ / α2 lattice misfits as compared with the alloy doped with Nb and the base alloy. For instance the γ / α2 lattice misfits determined in both crystallographic directions of the γ phase in the Ti-44Al-5Zr-0.2B and Ti-44Al-5Nb-0.2B alloys were found to be ε110 / ε101= 0.93 / 0.59 and ε110 / ε101=1.38 / 0.79, respectively. It has been recently revealed that γ-TiAl alloys with near the same duplex structures based on Ti-44Al-0.2B and doped with Zr and Zr+Hf demonstrated appreciably higher creep resistance than the alloy doped with Nb and the base alloy. It is assumed that the lower cγ / aγ ratios obtained for the Zr- and (Zr+Hf)-containing alloys contribute to the reduction of creep resistance. The fact that the Zr- and (Zr+Hf)-containing alloys showed higher creep resistance than the Nb-containing alloy should be mostly attributed to the lower γ / α2 lattice misfits in the Zr- and (Zr+Hf)-containing alloys and the higher solution hardening caused by doping with Zr and Hf. Therefore, the impact of alloying on the creep and heat resistance in β-solidifying γ-TiAl alloys should be considered taking into account the changes of the lattice parameters of the γ(TiAl) and α2(Ti3Al) phase, which influence the physical processes determining the creep behavior.
Highlights
Влияние Nb, Zr и Zr+Hf на параметры решеток интерметаллидных фаз и сопротивление ползучести γ-TiAl сплавов на основе Ti-44Al-0.2B
X-Ray diffraction (XRD) analysis was used to study the influence of alloying with 5 at.% Nb, 5 at.% Zr and 5 at.% (Zr+Hf) on the lattice parameters of the γ(TiAl) and α2(Ti3Al) phase in the intermetallic alloys based on Ti-44Al-0.2B
Doping with Zr and Zr+Hf leads to a noticeable decrease in the γ / α2 lattice misfits as compared with the alloy doped with Nb and the base alloy
Summary
По-видимому, некоторые из них, такие как несоответствие параметров решеток фаз γ и α2, твердорастворное упрочнение и диффузия, оказывают большее влияние на сопротивление ползучести, чем другие. Как имеющие примерно равное влияние, то можно заключить, что число факторов, положительно влияющих на сопротивление ползучести, выше в случае сплавов, легированных Zr и Zr+Hf, чем легированного Nb. Этим объясняется более высокое сопротивление ползучести сплавов, легированных Zr и Zr+Hf Полученные результаты показывают, что влияние легирования на сопротивление ползучести следует рассматривать с учетом его влияния на параметры решеток фаз γ и α2, которые, в свою очередь, влияют на различные физические процессы, определяющие сопротивление ползучести сплава. - н есоответствие параметров решеток фаз γ и α2 является фактором, оказывающим сильное влияние на сопротивление ползучести β-затвердевающих γ-сплавов даже в случае дуплексной структуры, содержащей около 50 об.% пластинчатой составляющей. Качественная оценка влияния легирования Nb, Zr и Zr+Hf сплава Ti-44Al-0.2B на сопротивление ползучести через различные физические факторы (обозначена знаками «+», «±» и «−»)
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