The influence of microstructure on the deformation behavior of beta solution heat treated and aged titanium aluminum tin zirconium molybdenum chromium silicate

Composite alpha/beta stereographic projections and slip system misorientation diagrams were developed and used to establish a new understanding regarding anisotropic deformation behavior of alpha and beta phases aligned according to the Burgers orientation relationship. Application of these tools showed that a 2-fold, maximum common crystal symmetry existed between single variants of Burgers oriented alpha and beta phases, which placed specific requirements on alignment and response of mating slip systems in alpha and beta phases. Of particular import were implications for crystallographic elements of mating slip systems that were found to be oriented within 180° of each other, i.e. anisotropic deformation behavior was predicted according to requirements of 2-fold maximum common crystal symmetry. Inspection of misorientation between mating slip systems established new requirements for determining the breadth of anisotropic slip behavior for a-basal, a-prism, a-pyramidal and c+a pyramidal slip systems. It was shown testing at 3, 6, 6, and 12 maximum Schmid factor loading axes was required to fully measure anisotropic deformation behavior in these slip systems, respectively. This meant each mated slip system would have 1, 2, 2 and 4 unique responses when loaded at orientations of maximum Schmid factor on the alpha slip system. The root cause of these anisotropic responses was shown to result from large changes in Schmid factor on beta slip systems when loading conditions on alpha slip systems were held constant, i.e. at maximum Schmid factor. Changes in Schmid factor on mating beta slip systems were shown to be a natural consequence of differences in crystal symmetry between alpha and beta phases oriented according to the Burgers orientation relationship.;Extension of this information to titanium microstructures consisting of multiple alpha variants in a single beta grain showed that 144 possible combinations of two adjacent alpha variants could be grouped according to six characteristic crystallographic and morphological misorientations. Growth directions between pairs of alpha/beta variants were shown to have interface misorientations of (0°/180°), (24.9°/155.1°), (54.5°/125.5°), (60.76°/119.3°), (77.9°/102.1°) and (80.6°/99.4°). This information, combined with that in slip system misorientation diagrams, was used to make qualitative predictions of relative ease and difficulty of slip transmission between combinations of alpha/beta/alpha variants based on in-plane and out-of-plane misorientations of slip planes and slip directions. For example, slip transmission between variants of near parallel alignment (Delta = 1.38°) between (0001) and {10-11} with a common {011}<111> slip system was predicted, then confirmed through Transmission Electron Microscopy (TEM) imaging techniques.;Six variations of the production "Triplex" Ti-62222S heat treatment process were developed and applied to effect large changes in room temperature tensile deformation behavior. Large changes in morphology of primary alpha features and the presence of alpha2-Ti3Al in the alpha promoted large reductions in fracture stress and fracture strain capability of beta solution heat-treated and aged Ti-62222S. These effects were shown to be additive, so that the combination of high amounts of aligned colony alpha + high presence of alpha2-Ti3Al in the alpha produced the lowest fracture stress and fracture strain. Work hardening in all six microstructures was relatively low, e.g. n ranging between ∼0.05 and 0.1. As with fracture behavior, increasing the amount of aligned or colony microstructure and/or increasing the presence of alpha2-Ti 3Al in the alpha were shown to lower work hardening. Examination of fracture surfaces and polished cross sections perpendicular to fracture surfaces revealed an associated transition from transgranular to intergranular fracture with increasing amount of aligned or colony alpha and if the final aging treatment increased the presence of alpha2-Ti3Al in the alpha. An important factor distinguishing the two fracture modes was the presence of fine voids at alpha/beta interfaces in sub-fracture surface regions just below the main crack.;More detailed inspection of deformed materials using OIM and TEM imaging techniques showed several interesting and previously unreported behaviors for Ti-62222S. These included the presence of deformation twins in the alpha, emission of dislocations from alpha/beta interfaces, very strong fringe contrast between pairs of dislocations gliding on all slip systems and dislocations in the beta with b = [010] in pile-ups associated with dislocations gliding on an unaligned a2-basal slip system. Information gleaned from composite alpha/beta stereographic projections and slip system misorientation diagrams proved critical in developing proper interpretations of these observations. (Abstract shortened by UMI.)...