Crystal plasticity modeling of deformation and creep in polycrystalline Ti-6242

Abstract

This paper develops an experimentally validated computational model based on crystal plasticity for the analysis of two-phase a/b Ti-6242 polycrystalline alloys. A rate-dependent elastic-crystal plasticity model is incorporated in this model to accommodate anisotropy in material behavior and tension-compression asymmetry inherent to this alloy. A combination of microtesting, orientation imaging microscopy, computational simulations, and minimization process, involving genetic algorithms, is implemented in this study for careful characterization and calibration of the material parameters. Size effects are considered in this analysis through a simple scaling process. A homogenized equivalent model of the primary a with transformed b colonies is developed for incorporation in the Ti-6242 FE model. The polycrystalline Ti-6242 computational model incorporates accurate phase volume fractions, as well as statistically equivalent orientation distributions to those observed in the orientation imaging microscopy scans. The effects of orientation, misorientations, and microtexture distributions are investigated through simulations by this computational model. The model is used to simulate constant strain rate and creep tests in compression and tension, and the results are compared with experiments. The effects of microstructure and creep-induced load-shedding on the localization of microstructural stresses and strains are studied for potential crack initiation criteria.

The effect of grain orientation on fracture morphology during high-cycle fatigue of Ti–6Al–4V

“…A model to account for this observation has been suggested in the work of Bache and Evans [8], based on the Stroh pile-up model [9], and later developed by Dunne et al [10]. A similar model to explain load partitioning under creep and dwell fatigue conditions has also been developed by Mills and co-workers [11,12]; both models illustrate the effect of load partitioning from a soft grain onto a neighbouring hard grain and possible critical grain combinations for crack initiation have been suggested.…”

Constitutive Relation for Ambient-Temperature Creep in Hexagonal Close-Packed Metals

“…Several Ti alloys 6) were investigated in the 1960s and 70s such as Ti-5Al-2.5Sn alloy 7,8) and Ti-6Al-4V alloy. 7,[9][10][11] Later, Mills' group [12][13][14][15][16][17] intensively studied this phenomenon using Ti-6Al and Ti-6Al-2Sn-4Zr-2Mo. Among these experimental studies restricted to Ti alloys, the present authors found recently that all hexagonal close-packed (h.c.p.)…”

Estimation of Grain Boundary Sliding During Ambient-Temperature Creep in Hexagonal Close-Packed Metals Using Atomic Force Microscope

“…Several Ti alloys were investigated in the 1960s and 70s such as Ti-5Al-2.5Sn (Kiefer & Schwartzberg, 1967;Thompson & Odegard, 1973) and Ti-6Al-4V (Reiman, 1971;Odegard & Thompson, 1974;Imam & Gilmore, 1979). Later, Mills' group intensively studied this phenomenon using Ti-6Al and Ti-6Al-2Sn-4Zr-2Mo (Suri et al, 1999;Neeraj et al, 2000;Deka et al, 2006). Among these experimental studies restricted to Ti alloys, the present authors found recently that all hexagonal close-packed metals and alloys show creep behavior at ambient temperature below their 0.2% proof stresses, but no cubic metals or alloys show it under the same condition .…”