Plastic Flow During Hot Working of Ti-7Al
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of advanced structural components typically relies on mechanical and thermal properties summarized in handbooks and databases for specific alloys, product forms (e.g., plate, sheet, bar), and heat treatments (e.g., solution-treated, solution-treated-and-aged).[1] Often, ranges of properties are quoted. However, the microstructure and crystallographic texture of the material that was evaluated to obtain the data are rarely reported. Such lack of information makes it difficult to ascertain the source of property variability, thus resulting in the use of property minima and concomitant conservative part design, excessive part weight, and less-than-optimal system performance. To remedy this challenge, the
S.L. SEMIATIN and A.L. PILCHAK are with the Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXCM, Wright-Patterson Air Force Base, OH 45433-7817. Contact e-mail: [email protected] N.C. LEVKULICH is with UES, Inc., Dayton, OH 45432. A.A. SALEM is with Materials Resources, LLC, Dayton, OH 45440. Manuscript submitted March 11, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
integrated computational materials engineering (ICME) methodology[2] has emerged as a useful framework for the development and linkage of advanced processing, mechanical behavior, and lifing simulation techniques and material databases; the simulation techniques and related material input data may incorporate models that are empirical or physics-based. Ultimately, ICME may enable the prediction and control of location-specific microstructure, texture, and properties in finished components. Two-phase titanium alloys comprising a majority of the hcp (a) phase and a small amount of the bcc (b) phase are engineering materials for which ICME tools could be especially useful. In particular, wrought a/b Ti products are usually fabricated via a series of thermomechanical processing (TMP) steps including open and closed-die forging and intermediate and final heat treatments. The non-uniformity of deformation and heating/cooling cycles inherent in production-scale manufacture of billets, slabs, forgings, etc. invariably leads to spatial variations in both microstructure and texture. The texture of the a phase is of especial importance because of the low symmetry of hcp crystals and the resulting mechanical-property anisotropy.
The simulation of deformation texture evolution during TMP is performed by a variety of techniques. These include the coupling of local strain-increment predictions from a continuum finite-element-method (FEM) code and a crystal-plasticity (CP) routine such as those based on the Taylor[3–5] or viscoplastic-self-consistent (VPSC) [6,7] linking hypotheses. Alternatively, local deformation, rigid-body rotation, and crystallographic rotation are treated concurrently in more complex and computationally-intensive CPFEM codes.[8] Irrespective of the approach, a key input to computer simulations is the constitutive behavior of the workpiece material. Typically, plastic-flow response is quantified using one of thr
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