Strain hardening and fracture of VT6 alloy synthesized by the method of powder metallurgy
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STRAIN HARDENING AND FRACTURE OF VT6 ALLOY SYNTHESIZED BY THE METHOD OF POWDER METALLURGY O. I. Dekhtyar, M. V. Matviichuk, I. V. Moiseeva, and D. H. Savvakin
UDC 669.01:669.296
We study the deformation behavior of VT6 alloy produced by the method of powder metallurgy and according to the traditional technology (casting and high-temperature deformation). It is shown that, in both types of materials, the evolution of the dislocation structure and strain hardening in tension obey the same physical laws. The deformation and hardening of both the powder material and VT6 alloy with lamellar structure obtained by using the traditional technology are controlled by the β-phase with bcc lattice according to the mechanism of composition hardening. Independently of the temperature of sintering, powder alloys fail according to the mechanism of ductile shear and tension. The residual pores in the powder material do not play the role of sites of crack initiation.
The deformation behavior of many-phase alloys produced by the method of powder metallurgy is quite complicated because, parallel with the ordinary parameters of compact many-phase polycrystalline materials (including the grain sizes, the strength of interfaces, the characteristics of dislocation structure, and the morphology of the phases), an important role is also played by porosity responsible for the inhomogeneities of stresses and strains. The negative influence of porosity on the mechanical properties of the material can be described by the following general power dependence of strength [1]: σ ( p ) = σ0 ( 1 – P )m ,
(1)
where σ0 is the strength of the poreless material, P is the volume fraction of pores, and m = 3–10 is an empirical parameter. We study the VT6 titanium alloy (Ti – 6.0Al – 4.0V) produced by the method of cold pressing and sintering of mixtures of the powder components based on hydrogenated titanium [2]. The aim of the present work is to investigate specific features of the deformation behavior of the powder alloy and compare it with the behavior of the commercial VT6 alloy produced according to the traditional technology of casting and high-temperature deformation. Procedure of Sintering and Characteristics of the Materials The alloys were synthesized by the method of pressing and sintering of mixtures. The required amounts of the powders of metals and/or hardeners were added to the titanium powder. The powder of hydrogenated titanium used instead of the ordinary powder as basic material of the mixtures activates the processes of sintering and chemical homogenization, whereas hydrogen released from hydrogenated titanium heated above 320°C in a vacuum partially reduces the surface oxides [2]. Kurdyumov Institute of Physics of Metals, Ukrainian Academy of Sciences, Kyiv, Ukraine. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 107–111, May–June, 2008. Original article submitted February 15, 2008. 1068–820X/08/4403–0429
© 2008
Springer Science+Business Media, Inc.
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O. I. DEKHTYAR, M. V. MATVIICHUK, I. V. M
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