Mechanical properties and deformation mechanisms of a commercially pure titanium

Abstract

AbstractÐThe mechanical behavior of a commercially pure titanium (CP-Ti) is systematically investigated in quasi-static (Instron, servohydraulic) and dynamic (UCSD's recovery Hopkinson) compression. Strains over 40% are achieved in these tests over a temperature range of 77±1000 K and strain rates of 10 À3 ±8000/s. At the macroscopic level, the¯ow stress of CP-Ti, within the plastic deformation regime, is strongly dependent on the temperature and strain rate, and displays complex variations with strain, strain rate, and temperature. In particular, there is a three-stage deformation pattern at a temperature range from 296 to 800 K, the speci®c range depending on the strain rate. In an e ort to understand the underlying mechanisms, a number of interrupted tests involving temperature jumps are performed, and the resulting microstructures are characterized using an optical microscope. Based on the experimental results and simple estimates, it is concluded that the three-stage pattern of deformation at temperatures from 296 to 800 K, is a result of dynamic strain aging, through the directional di usion of dislocation-core point defects with the moving dislocation at high strain rates, although the usual dynamic strain aging by point defects segregating outside the dislocation core through volume di usion is also observed at low strain rates and high temperatures. The microscopic analysis shows that there is substantial deformation twinning which cannot be neglected in modeling the plastic¯ow of CP-Ti. The density of twins increases markedly with increasing strain rate, strain, and decreasing temperature. Twin intersections occur, and become more pronounced at low temperatures or high strain rates. In sum, the true stress±true strain curves of CP-Ti show two stages of deformation pattern at low temperatures, three stages at temperatures above 296 K, and only one stage at temperatures exceeding 800 K, although all three stages may exist even at 1000 K for very high strain rates, e.g. 8000/s. While the dislocation motion is still the main deformation mechanism for plastic¯ow, the experimental results suggest that dynamic strain aging should be taken into account, as well as the e ect of deformation twinning. #

A model for Ti–6Al–4V microstructure evolution for arbitrary temperature changes

“…Anisotropic flow rule for Ti-6Al-4V based on the KhanHuang-Liang model were developed by ; . Dislocation density based models have been used by Nemat-Nasser et al (1999) for commercially pure Titanium and Picu andMajorell (2002) &Gao et al (2011) for Ti-6Al-4V. A model utilizing dislocation density and vacancy concentration as Internal State Variables (ISV) was developed by that included globularization which is assumed to be responsible for flow-softening and stress relaxation.…”

Mechanical behavior of Ti cold spray coatings determined by a multi-scale indentation method

“…Ti has a hexagonal closed packed structure and plastic deformation in the material is limited. It is possible that after the initial plastic deformation, the remainder of the impact stress is converted to heat and no further work hardening takes place [21,[39][40][41][42]. For both spherical and nonspherical coatings, the true hardness was nearly constant over all deposition conditions with the averages being H o = 2.85 ± 0.23 GPa for spherical coatings and H o = 3.25 ± 0.28 GPa for non-spherical coatings.…”

Discovery via Integration of Experimentation and Modeling: Three Examples for Titanium Alloys

“…The initial dislocation configuration consists of random distributed segments that are pinned at their ends, leading to the operation of the multiplication mechanism based on Frank-Read source activation as in real crystals. The single grain is oriented so that a tensile load is applied with a constant strain rate in a specific crystallographic direction ([0001], [11][12][13][14][15][16][17][18][19][20], and ). The time step is dt = 5 9 10 12 , and the strain rate is constant at 10 3 in the simulation setup.…”

“…Indeed, such anisotropic mechanical phenomenon has been observed for some superplastically deformed (SPD) materials with different grain sizes and texture. [13][14][15] However, few studies have been conducted to test and understand the highly anisotropic single crystal a-Ti, whose behavior and microstructure evolutions also have very strong orientation dependence. On the one hand, this is due to the difficulty in obtaining the dislocation distribution.…”