Martensitic transformation in titanium alloys with a high damping capacity

Abstract

Results of an x-ray diffraction analysis of the lattice parameters of martensite in titanium alloys are used to refine the crystallography of the martensitic transformation, which has made it possible to explain the extremal dependence of the internal friction on the temperature of heating for quenching.In studying the effect of the quenching regime of titanium alloys of the martensitic class we established that the dependence of their damping capacity on the temperature of heating for quenching had an extremum (Fig. 1). The damping capacity was determined from the value of the relative damping ~g by the method of damped torsional vibrations at an initial vibration amplitude 7 = 1.0 x 10-3.To determine the mechanism of damping in quenched titanium alloys we found the parameters of the martensite lattice formed in quenching from various temperatures. The study was conducted on specimens of titanium alloys VT14 and VTI6 (Table 1) quenched from temperatures ranging from 740 to 880~ with an interval of 20~Crystallographic diagrams of phase transformations in the alloys that occurred in accordance with the sequence 13 ct" ~ ct are presented in Figs. 2 and 3. It follows from these diagrams that the bcc lattice of the 13-modification of titanium can be represented as a tetragonal face-centered lattice with the parameters a t = a13 , b t = c t = ap q2-and a monoclinic lattice with the parameters a m = ap x 0.5"~/3-, b m = ap x 0.5 lqTI, c m = ap ~-, 7 = 800. For the tetragonal interpretation the face planes will be (100) and (010), and for the monoclinic one the face planes will be (130) and (110).To make the transformations more visualizable we will treat the crystal symmetry somewhat freely. In the classical interpretation the tetragonal lattice should have a = b ~ c; we will assume that a ;~ b = c. In the description of the monoclinic lattice we will assume that the condition c < a < b is violated.In our scheme the martensitic transformation will occur in two stages, namely, (1) an incomplete twinning shear characterized by the twinning plane (100) and the direction [110] (Fig. 3) and leading to formation of a monoclinic lattice and I Samara State Engineering University, Samara, Russia.(2) removal of the monoclinic distortion, which completes the formation ofa rhombic martensite lattice a".Restructuring of the martensite lattice into the stable tetragonal lattice of the o~-phase occurs by a trivial shuffling mechanism, i.e., shifting of the even planes of the (002) During the twinning shear the parameters b m and a t decrease and the parameters b t and a m increase (Fig. 3). As a resuit, they become equal at a certain shear angle q) ~ 10 ~ i.e. 207

A Study on Thermal Properties and α(hcp) → β(bcc) Phase Transformation Energetics in Ti–5 mass% Ta–1.8 mass% Nb Alloy Using Inverse Drop Calorimetry

“…In Table 2, the X-ray diffraction results are summarized and the calculated lattice parameter values for the α-phase are also listed. Since, to the best of our knowledge, no prior structural characterization of this alloy has been reported in the literature, a comparison of the lattice parameter of this alloy with reported values for other related Ti-based alloys has also been made in Table 3 [12][13][14][15][16][17]. It is readily observed that there is a close agreement between the lattice parameter values of the present alloy with reported ones at related compositions.…”

“…Lattice parameters of Ti-5 mass% Ta-1.8 mass% Nb alloy and a few other titanium alloys having α (hcp), α (hcp-martensite), and α (orthorhombic-martensite) phases Data for the latter alloys are taken from Refs [12][13][14][15][16][17]. 3.2 Enthalpy Increment Variation with Temperature…”