of the original manuscript: Imayev, V.; Gaisin, R.; Gaisina, E.; Imayev, R.; Fecht, H.-J.; Pyczak, F..: Abstract Microstructure and mechanical behavior of near eutectic Ti-1.5 wt.% B and hypereutectic Ti-2B wt.% B composite materials obtained by casting have been investigated. Commercially pure titanium was used as a matrix material. Homogeneously distributed TiB whiskers were revealed in the as-cast composite materials. Multiple isothermal 2-D forging of the composites was carried out in the temperature range of the beta phase field. The hot forging led to effective alignment of boride whiskers with retaining a high aspect ratio. Tensile mechanical tests in ascast and forged conditions were carried out at room and elevated temperatures. The composites demonstrated much higher strength in comparison with the matrix material without drastic ductility reduction. The effect of boride orientation and morphology on the tensile properties of the composite materials is discussed.
Институт проблем сверхпластичности металлов РАН, ул. Степана Халтурина 39, Уфа, 450001, Россия В работе выполнено сравнительное исследование рекристаллизационного поведения при горячей деформации тех-нически чистого титана ВТ1-0, модифицированного бором, в исходном литом состоянии и технически чистого ти-тана ВТ1-0 в исходном литом и горячекатаном состояниях. Введение 0,2 вес. % бора при выплавке слитка приводит к формированию однородно распределенных коротких волокон моноборида титана (TiB), способствующих суще-ственному измельчению литой структуры. Благодаря этому при комнатной температуре пластичность при сжатии литого модифицированного бором сплава оказалась выше пластичности литого технически чистого титана. При горячей деформации механическое поведение литого модифицированного бором сплава и горячекатаного ВТ1-0 схоже и существенно отличается от механического поведения ВТ1-0 с исходной литой структурой. Рекристаллиза-ционное поведение сплавов изучали после деформации сжатием при Т=900, 800, 700 и 600°С с помощью оптической микроскопии и EBSD-анализа. Установлено, что малые добавки бора, если сравнивать модифицированный бором сплав и ВТ1-0 с исходной литой структурой, способствуют более равномерной деформации и ускоренному разви-тию рекристаллизации при горячей деформации. Обнаружено, что подобная мелкозернистая структура формирует-ся после горячей деформации литого литого модифицированного бором сплава и исходного горячекатаного ВТ1-0. При этом эффективнее всего динамическая рекристаллизация развивается при деформации в двухфазной (α+β) области (900°С). Модифицирование бором в количестве ~0,1 вес. % может быть рекомендовано для деформируемых титановых сплавов с целью измельчения литой структуры, повышения пластичности и облегчения формирования однородной мелкозернистой структуры при горячей деформации. In the present work comparative investigation of recrystallization behavior of cast commercially pure titanium VT1-0 modified by boron and free of boron as well as of CP titanium VT1-0 in wrought condition has been performed after hot compression. Boron additions during the melting process in an amount of 0,2 wt.% lead to formation of uniformly distributed TiB-whiskers, which provided significant refinement of as-cast structure. At room temperature ductility of cast boron-modified alloy was higher than that of cast CP titanium. During hot compression mechanical behaviors of cast boron-modified alloy and wrought CP titanium were similar and considerably differed from the mechanical behavior of cast CP titanium. Recrystallization behavior was studied after hot compression at T=900, 800, 700 and 600°С using optical microscopy and EBSD analysis. It was revealed that the boron addition promoted more uniform strain development and accelerated recrystallization during hot compression in the cast CP titanium modified by boron as compared with the CP titanium free of boron. Similar finegrained structure formed during hot working of cast boron-modified alloy and wrought VT1-0.The most effective dynamic recrystallizati...
A novel two-phase titanium alloy based on VT8 (Ti-6.5Al-3.3Mo-0.3Si) having the composition VT8-20Zr-0.1B (wt. %) has been considered in the present paper. It has been established that modifying with boron leads to refinement of prior β grains and α / β colonies by a factor of about ten and alloying with zirconium results in some additional colony refinement. Alloying with 20 wt. % of zirconium leads to decreasing the α + β → β transformation temperature by about 100°C that along with refinement of the as-cast structure improved the hot workability of the alloy. After multidirectional hot forging in the α + β phase field (T = 800°С) and hardening heat treatment the strength of the ВТ8-20Zr-0.1B alloy at 20-500°C was found to be higher by 30-40 % as compared with that of the VT8 alloy after the same treatment while retaining similar ductility of the alloys. This allows one to characterize the VT8-20Zr-0.1B alloy as an ultrastrong titanium alloy. For the VT8-20Zr-0.1B alloy the following tensile properties have been attained: σ UTS = 1560 MPa and δ = 4 % at room temperature, σ UTS = 1230 MPa and δ = 14 % at T = 500°С. The specific strength reached at T = 500°С (σ UTS / ρ ≈ 248 MPa / g × cm −3) is the highest even obtained at this temperature for currently known titanium alloys. It was revealed that water quenching from the β phase field led to the martensitic β → α" transformation with retained β phase and subsequent ageing resulted in formation of ultrafine lamellar structure with a nanosized lamellae thickness that promoted achieving significant strengthening.
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