Structure and physicomechanical properties of eutectic Ti-Si-X alloys
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STRUCTURE AND PHYSICOMECHANICAL PROPERTIES OF EUTECTIC Ti – Si – X ALLOYS S. O. Firstov, I. D. Horna, K. O. Horpenko, M. D. Beha, O. Yu. Koval’, and A. V. Kotko
UDC 669.295.539.22: 541.12.03
We study the structure and physicomechanical properties of various eutectic alloys of Ti – Si – Zr, Ti – Si – B, and Ti– Si – Ga systems. It is shown that Ti – Si – Zr alloys with elevated concentrations of Zr reveal, due to the presence of (Ti, Zr)2 Si dispersed silicides with sizes of about several hundred nanometers, improved mechanical properties as compared with the properties of alloys based on Ti5 Si3 silicides. The cast eutectic alloy of the Ti – Si – Zr – Sn system with a plasticity of ∼ 1.7% is obtained for the first time. The formation of superfine eutectics based on the Ti6 Si2 B ternary compound in alloys of the Ti – Si – B system enables one to obtain titanium composites with improved refractory properties and elevated moduli of elasticity (of about 150 GPa or, after additional alloying, as high as 165 GPa). This can be promising for the development of new refractory titanium composite materials with elevated stiffness. The analysis of the combined effect of gallium and silicon in Ti – Si – Ga alloys reveals the possibility of getting titanium materials with high heat resistance, i.e., materials based on the (α-Ti ( α2-Ti3 Ga) + Ti5 (Si, Ga)3 binary eutectics.
On the basis of the binary equilibrium diagram, the process of eutectic crystallization in the Ti – Si system can be used for the creation of composites [1] whose mechanical properties can be noticeably changed by the additional alloying with combined solid-solution, dispersion, microstructural, and composite (eutectic) hardening. Therefore, the development of new eutectic compositions according to the equilibrium phase diagrams of the Ti – Si – X systems, where X is Zr, B, Ga, Al, or any other alloying element, and the analysis of the influence of thermal and/or thermomechanical treatment on the phase composition, morphology, the volume fraction of hardening phases, and the structure of the titanium matrix are the principal directions of creation and investigation of new titanium alloys with a given complex of properties (high-strength alloys, superalloys, refractory alloys, high-modulus alloys, etc.) [2 – 4]. Specifically, the alloys of the Ti – Si – Zr, Ti– Si – B, and Ti– Si – Ga ternary systems prove to be quite promising [5–7]. As the zirconium content of alloys of the Ti – Si – Zr system increases (Fig. 1a), we observe the formation not only of the well-known Ti5 Si3 titanium silicides but also of the (Ti, Zr) 2 Si compound [5, 8–11]. This compound is also detected in Ti – Si – Zr – Al and Ti – Si – Zr – Sn alloys with ≥ 5 wt.% of Zr and the optimal ratio of the amounts of silicon and zirconium. The Ti – 6Si – 18Zr composition (here and in what follows, in wt.%) corresponds to the eutectic alloy in the Ti – Si – Zr system based on the (Ti, Zr)2 Si compound [10, 11]. The characteristics of these eutectic alloys are investigated quite poorly. In rece
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