Compression and Compressive Creep Behaviors in Titanium Aluminides Alloyed with Vanadium comprizing Gamma + Beta Dual Ph
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0980-II05-02
Compression and Compressive Creep Behaviors in Titanium Aluminides Alloyed with Vanadium Comprizing Gamma + Beta Dual Phase Microstructures Tohru Takahashi, Yohji Kojima, and Koshiro Otsuka Department of Mechanical Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo, 1848588, Japan
ABSTRACT Fine grained microstructures containing gamma and beta phases were obtained in ternary aluminum-titanium-vanadium alloys whose chemical compositions were 40 at.% aluminum and 60 at.% (titanium and vanadium). The fraction of the gamma phase was around 50%, and the average grain sizes were about 5, 3, and 2 micrometers in the recrystallized materials containing 20, 30, and 40 at.% vanadium, respectively. Compression tests were performed at temperatures ranging from the room temperature up to 1200K. The materials showed very high strength at room temperature; 0.2% proof stress was around 1200MPa. The compression deformability was not very good and decreased from about 0.2 to 0.05 true strain with increasing vanadium content. 0.2% proof stress showed a considerable weakening at temperatures higher than 900K, and the weakening temperature seemed to decrease with increasing vanadium content. Compressive creep tests were also carried out at 1050-1200K. Creep curves consisted of a small amount of normal primary transient, the minimum creep rate region, and a steady or slightly accelerating creep region. Stress exponent of about 2 was observed in the lower stress region in the 20at.% V material suggesting the sliding on the grain boundaries and interfaces was rate-controlling. INTRODUCTION Titanium aluminide intermetallics are prospective in future application for light-weight and heat-resistant structural materials[1-5]. The gamma TiAl and alpha2 Ti3Al intermetallics will be important as the constituent phases in the alloys that are comprised of two or more phases. One of the present authors studied the composition effects on deformation and strength of binary TiAl[6] and Ti3Al[7] in order to acquire systematic views upon the deformation and strength of titanium aluminide intermetallics. The alloying effect of vanadium upon microstructure and strength of Al-Ti-V ternary alloys was also investigated for many alloy compositions whose aluminum contents were 50at.% or higher[8,9]. The Al-Ti-V ternary alloy system can be characterized by the presence of large gamma single phase field that expands toward aluminumand vanadium-rich compositions[10-12]. Vanadium tends to stabilize the beta phase at vanadium content of 10 or more at.% resulting in gamma + beta dual phase microstructure in Al50(Ti, V)50 alloys[13]. Microstructural investigations revealed that the main constituent phase was the gamma phase that existed as small particles whose total amount was about 80% area fraction in the Al50Ti30V20 alloy. In these Al50(Ti, V)50 ternary alloys, the yield stress became increasingly high as the vanadium content increased, mainly due to the higher hardness of beta phase than that of th
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