Electron-beam cold-hearth melting (EBCHM) is finding increasing application for the production of titanium alloys due to its ability to dissolve or eliminate inclusions with high melting temperatures. However, the melting of titanium alloys under vacuum results in the marked vaporization of volatile alloying elements, such as aluminum, having vapor pressures exceeding that of titanium. In this article, the evaporation rates of Al, Ti, and V from Ti-rich Ti-Al-V melts, in particular, Ti-6Al-4V, are evaluated on the basis of the thermodynamics of liquid solutions of the melt components. First, the ideal evaporation rate is estimated based on Langmuir's equation and thermodynamic calculations of the activity of the alloying elements. Second, the rate-limiting influence of diffusion of aluminum to the surface of the melt on the evaporation kinetics is considered.The rate of ideal evaporation of component i into vacuum (W i ) varies with temperature according to Langmuir's equation:[1] [2] in which X i , ␥ i , and M i are the molar fraction, activity coefficient, and molar mass of the evaporating species, respectively; P i is the partial pressure of vapor of component i over the multicomponent melt; R is the gas constant; T is the absolute temperature; and is the vapor pressure above the melt of pure element i. The vapor pressures of pure Al, Ti, and V can be estimated using the Clausius-Clapeyron equation:The constants A, B, and C in Eq.[3] are listed in Table I for Al, Ti, and V.The activity coefficients of the components, ␥ i , may be expressed through the partial excess Gibbs energy ; i.e.,In turn, the values of ⌬G -i ex are related to the integral thermodynamic functions ⌬G ex , which are as follows for a ternary system (with components 1, 2, and 3):If the Redlich-Kister equation is used to express the excess Gibbs energy of the Al-Ti, Al-V, and Ti-V binary systems, ⌬G ex of the Al-Ti-V ternary solution can be expressed for the general case as [6] in which X Al , X V , and X Ti denote the mole fractions of components in the melt; ␣ 1 , ␣ 2 , and ␣ 3 are interaction parameters for the ternary solution; and the terms for binary A-B systems are temperature-dependent model parameters; viz.[7]In practice, the maximum number n in the series expansions for ⌬G rarely exceeds 3, and the number of terms in Eq. [7] is taken less than that indicated. The thermodynamic properties of the Ti-Al, Al-V, and Ti-V binary liquid solutions are known and presented in Reference 2. The corresponding model parameters for Ti-Al, Al-V, and Ti-V systems are given in Table II.In view of the typical absence of experimental information on the thermodynamic properties of ternary solutions, the corresponding interaction parameters are usually put to zero, and the extra terms are omitted in Eq. [6]. Such thermodynamic evaluations were performed in Reference 2 for the Al-Nb-Ti, Al-Ta-Ti, and Al-Ti-W ternary systems. In the case of the Al-Ti-V ternary system, the same approximation was used in the present work, taking into account the fact that the...

Processing, Microstructure, Texture, and Tensile Properties of the Ti-6Al-4V-1.55B Eutectic Alloy OREST M. IVASISHIN, ROMAN V. TELIOVYCH, VOLODYMYR G. IVANCHENKO, SESHACHARYULU TAMIRISAKANDALA, and DANIEL B. MIRACLE Boron (B) addition to conventional titanium (Ti) alloys instigates precipitation of intermetallic TiB whiskers that provide significant increases in strength and stiffness. The eutectic composition is the maximum boron concentration that provides these benefits via melt processing while maintaining reasonable ductility and damage tolerance. The eutectic point for the most widely used Ti alloy, Ti-6Al-4V (wt pct), modified with B, was determined to occur at 1.55 ± 0.05B and 1545 ± 5°C. The microstructure, texture, and tensile properties of the eutectic alloy are sensitive to ingot solidification conditions and melt pool morphology. Several microstructural forms in the as-cast condition as well as their transformation during thermomechanical processing (TMP) were identified. Two types of eutectic structures, aligned and random, were obtained. Cast microstructures with random eutectic colony orientation had no marked crystallographic texture, while cast aligned microstructure had a strong [020] texture for the TiB phase and a 110 h i circular texture for the a-Ti phase. As-cast microstructure could be significantly modified via TMP. Fragmentation of TiB occurred during three-dimensional (3-D) forging and aligned microstructures were produced after rolling or extrusion. An attractive balance of strength and ductility was obtained after solution treatment in the full b condition followed by aging. The microstructure of the Ti-6Al-4V-1.55B eutectic alloy can be controlled to tailor the property combinations.

An analysis of the evaporation of aluminum during electron-beam melting (EBM) of alpha/beta-titanium alloys was performed. The analysis was based on the solution of the one-dimensional diffusion equation for the solute-concentration gradient in the melt pool subject to the flux boundary condition for the evaporation rate at the melt surface quantified using the Langmuir equation. The effect of process parameters and material coefficients (e.g., the diffusivity and solute activity in the melt) on predicted concentration gradients and melt losses under steady-state melting conditions was established for both the finite-domain and the semi-infinite-domain diffusion problems. The accuracy of the modeling approach was validated by comparison to previous measurements for the EBM of alloys with a nominal Ti-6Al-4V composition.

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Sorption properties and kinetic parameters of hydrogenating and dehydrogenating processes of Ti 0.475 Zr 0.3 Mn 0.225 eutectic alloy, in which partial substitution of each of its component with 2% and 5% of vanadium is performed, are investigated by Sieverts' method. As determined, the introduction of vanadium within the specified limits results in decrease of the temperature of the start of intensive hydrogen absorption, decrease of the duration of hydrogenating process, and also in substantial increase of sorption capacity (up to 2.85% wt.). As shown, the alloys, which are subjected to the sorptiondesorption cycling, possess as much activated surface that behave themselves with regard to hydrogen similar to intermetallic compounds and can absorb hydrogen at the room temperature and the pressure of 0.23 MPa from the first seconds of the contact of the specimen with the hydrogen-containing medium with the average rate of (2-4)10 3 wt.%/s. Сівертсовою методою досліджено сорбційні властивості і кінетичні параметри процесів гідрування і дегідрування виливаного евтектичного стопу Ti 0,475 Zr 0,3 Mn 0,225 , в якому було виконано часткову заміну кожного з його компонентів на 2% і 5% Ванадію. Встановлено, що введення Ванадію в зазначених межах приводить до зниження температури початку інтенсивного вбирання Гідроґену, зменшення тривалости процесу гідрування, а також до істотного збільшення сорбційної місткости (до 2,85% мас.). Показано, що стопи, які пройшли циклування сорбція-десорбція, мають настільки активовану поверхню, що ведуть себе щодо водню неначе інтерметаліди і здатні вбирати Гідроґен за кімнатної температури і тиску у 0,23 МПа з перших секунд контакту зразка з водневим середовищем із середньою швидкістю у (2-4)10 3 мас.%/с. Методом Сивертса исследованы сорбционные свойства и кинетические параметры процессов гидрирования и дегидрирования литого эвтектического сплава Ti 45,5 Zr 30 Mn 22,5 , в котором была произведена частичная замена каждого из его компонентов на 2% и 5% ванадия. Установлено, что