Growth of (αTi) grain-boundary layers in Ti–Co alloys

Abstract

Izvestiya vuzov. Tsvetnaya metallurgiya • 5 • 2016 69 Введение Образование прослоек второй фазы на границах зерен (ГЗ) сильно влияет на механические свойства многофазных материалов, в частности сплавов на основе титана, которые нередко подвер-УДК: 538.9 Институт физики твердого тела (ИФТТ) РАН, г. Черноголовка Национальный исследовательский технологический университет «МИСиС», г. Москва Статья поступила в редакцию 29.01.15 г., доработана 18.10.15 г., подписана в печать 22.10.15 г. Исследовалось влияние температуры на образование зернограничной прослойки (αTi) в сплавах Ti-2мас.%Co и Ti-4мас.%Co в двухфазной области (αTi) + (βTi) фазовой диаграммы Ti-Co в интервале температур 690-810 °С. Изучена кинетика роста толщины (∆) зернограничной прослойки фазы (αTi) в сплаве Ti-2мас.%Co при температуре 750 °С. Показана ее зависимость от времени отжига как ∆ ~ t 1/3 . Анализ результатов экспериментальных наблюдений позволяет предположить, что увеличение ∆ является проявлением процесса коалесценции (αTi), который контролируется объемной диффузией. Ключевые слова: титановые сплавы, кобальт, распад пересыщенного твердого раствора, выделение второй фазы, границы зерен, кинетика, диффузия, коалесценция. Горнакова А.С. -канд. физ.-мат. наук, ст. науч. сотр. лаборатории поверхностей раздела в металлах ИФТТ РАН (142432, Московская обл., г. Черноголовка, ул. Акад. Осипьяна, 2).The paper studies the effect of temperature on the formation of (αTi) grain boundary layer in Ti-2wt.%Co and Ti-4wt.%Co alloys in the (αTi) + (βTi) two-phase region of the Ti-Co phase diagram within the temperature range of 690-810 °C. The paper studies kinetics of thickness growth (∆) of the (αTi) phase grain boundary layer in Ti-2wt.%Co alloy at a temperature of 750 °C. It demonstrates dependence of the thickness of grain boundary layer on the annealing time as ∆ ~ t 1/3 . Analysis of experimental results suggests that increase in ∆ is a manifestation of the (αTi) coalescence process controlled by volume diffusion. Citation: Gornakova A.S., Prokofjev S.I., Straumal B.B., Kolesnikova K.I. Rost zernogranichnoi prosloiki (αTi) v splavakh Ti-Co. Izv. vuzov. Tsvet. metallurgiya.

Bulk and Surface Low Temperature Phase Transitions in the Mg-Alloy EZ33A

“…As the microstructure after such long annealing times is close to equilibrium, the difference to the fraction of covered GBs in the first sample confirms the existence of the solid phase GB wetting transition in EZ33A. Similar phenomenon of GBs completely and/or incompletely covered with layers of a second solid phase have been observed also in Al- [11,12], Cu- [13,14], Co- [15], Fe- [16], Zr- [17], and Ti-based alloys [18,19]. Thermodynamically, this phenomenon is very similar to the GB wetting by the melt [20,21].…”

Formation and Thermal Stability of ω-Ti(Fe) in α-Phase-Based Ti(Fe) Alloys

“…Some TiFe particles were ordered in chains along the boundaries of the α-Ti grains (see, for example, Figure 1a). This phenomenon is called incomplete or complete grain boundary wetting by a second solid phase and it has been previously observed in various Ti-based alloys [23,[33][34][35][36][37]. In the corresponding SEM/BSE micrographs, the TiFe grains appear to be bright due to a higher Fe content and, thus, a higher mean atomic number of TiFe as compared to α-Ti.…”

Effect of Heat Treatment Temperature on Martensitic Transformation and Superelasticity of the Ti49Ni51 Shape Memory Alloy

“…The microstructures in Figure 2 show that the grains of TiNi phase are surrounded by the continuous or discontinuous layers of Ti 3 Ni 4 phase. This phenomenon is connected with the so-called complete and incomplete wetting of grain boundaries by the second solid phase both in the Ti–Fe(Co) and Ti–Fe–Sn alloys [36,37,38]. A large and/or long grain of Ti 3 Ni 4 phase between two β-Ti phases form continuous layers, and this phenomenon is called complete grain boundary wetting (labeled in Figure 2a by the letter C); while multiple adjacent Ti 3 Ni 4 phases precipitated on grain boundaries form the discontinuous layers, corresponding to the incomplete or partial wetting of grain boundary (labeled in Figure 2a by the letter P).…”