Modeling for the Robust Design of Materials for Superplastic Forming Processes for Titanium Structural Components

Modeling for the Robust Design of Materials for Superplastic Forming Processes for Titanium Structural Components
Navy STTR FY2012.A

Sol No.:	Navy STTR FY2012.A
Topic No.:	N12A-T018
Topic Title:	Modeling for the Robust Design of Materials for Superplastic Forming Processes for Titanium Structural Components
Proposal No.:	N12A-018-0120
Firm:	Scientific Forming Technologies Corporation 2545 Farmers Drive Suite 200 Columbus, Ohio 43235
Contact:	Wei-Tsu Wu
Phone:	(614) 451-8322
Web Site:	www.deform.com
Abstract:	Superplastic forming process (SPF) takes advantage of unique ability of certain materials such as titanium alloys that exhibit exceptionally high tensile ductility beyond its normal limits of plastic deformation at elevated temperatures and low strain rates. Within a narrow window of a combination of elevated temperatures and low strain rates, titanium alloys can withstand elongation as high as 300%. One of the critical factors that determine the effectiveness and the optimum design of a SPF part is the quality of incoming sheet material used for the manufacture of the part. The key microstructural features of alpha-beta titanium sheet material that needs to be optimized include alpha grain size, grain aspect ratio, grain size distribution, relative volume fraction of alpha and beta phase and texture of the alpha phase. While there are established models to simulate cogging, rolling and SPF processes, there is still no single integrated material modeling tool that would predict the microstructural evolution during the primary processing of alpha-beta titanium alloys. Understanding how the key process variables and material behavior impact the microstructural evolution of sheet products during the rolling process will be paramount task in this project. Scientific Forming Technologies Corporation (SFTC) is teaming with the University of Texas at Austin, Timet and Boeing for the Phase I of this project. The objective of this project is to develop a modeling framework that enables the prediction of microstructure evolution leading to optimum design of sheet material for the SPF of titanium structural components. The various rolling, cross rolling and pack rolling schedules that a titanium plate material undergoes in its conversion process to sheet material need to be modeled and optimized for ideal microstructural features in the finished titanium sheet product. With the sensitivity analysis framework in DEFORM system, the user will be able to systematically analyze the variabilities and uncertainties associated with the processing conditions, boundary conditions, material properties and incoming starting grain size distribution of the plate material, thus providing a robust design of material for the SPF processes. At the end of phase I, our team would complete characterization of Ti 6-4 and Ti 54M plate, intermediate plate-sheet and final sheet product. Our team will complete modeling of lab scale rolling, cross rolling and pack rolling processes and track material history of selected locations across the various thermo-mechanical processing operations. Our team will investigate appropriate alpha lath spheroidization models as well as recrystallization and grain growth models for Ti 6-4 material that are available in the literature. Our team will work closely with Navy to develop an implementation and a validation plan for subsequent Phase 2 activities. It is envisioned that the implementation and validation of microstructure evolution models will be undertaken in the phase II of this project.
Benefits:	It is anticipated that the proposed efforts in this project will enable implementation of microstructure evolution models in DEFORM to analyze the complex sequence of rolling processes in the manufacture of titanium alloy sheets from plates. It is expected that at the end of this project, DEFORM users will be able to analyze the effect of variations and uncertainties in processing conditions and material properties on microstructure evolution during the thermo-mechanical processing of titanium sheets that may involve a complex sequence of rolling, cross rolling and pack rolling processes. By working with titanium sheet material partner Timet, SFTC intends to use the models implemented in this program to optimize the microstructural features of the sheet product as deemed appropriate for the subsequent SPF process. This project will also provide an improved understanding of the evolution of microstructure and will aid in a better design and control of primary processing, especially rolling of titanium plates. Our team will work with our industrial partner Boeing to demonstrate and validate the applicability of microstructural evolution models and a better quality sheet product in the manufacture of a SPF part. Coupling material models with SPF process modeling will help Boeing and other material fabricators to achieve a better optimized SPF process at reduced cost due to potential quality cost avoidance and longer tooling life due to reduced operating temperature. It is anticipated that at the end of this project, our team will be able to compare and contrast the rolling processing capabilities and performance of Ti-54M sheets in SPF process against that of the benchmark material, Ti 6-4 sheets. It is expected that our team will work on the implementation of alpha lath spheroidization models in Phase II which will benefit the material suppliers, forging industry and the OEMs. In the long run, this project will provide a building block to facilitate Integrated Computational Materials Engineering (ICME) methodology, thus helping the industry in the accelerated insertion of new materials into service.

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