Materials Week '97: Tuesday AM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Tuesday morning, September 16.

PROCESS MODELING IN THE HIGH TEMPERATURE MATERIALS INDUSTRY: Session I

Session Chair: Marvin McKimpson, Institute of Materials Processing, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931

OPTIMIZATION OF WORKABILITY FOR HOT EXTRUSION OF CI2200 ALLOY: Steve C. Medeiros, S. Venugopal, W.M. Mullins, and James C. Malas, Materials Process Design, Materials Directorate, WL/MLIM, Bldg. 653, Wright-Patterson Air Force Base, Ohio, 45433-7746

A systematic study to determine the cause of problems such as severe tooling wear, eccentricity, and poor dimensional accuracy associated with hot-tube extrusion of deoxidized high phosphorus copper has been performed by optimizing the intrinsic and extrinsic workabilities. The intrinsic workability was optimized by studying the deformation characteristics in the temperature range from 750 to 950°C and a strain rate range from 0.01/s to 10/s using the constant strain rate, isothermal compression test method. Optimization of the extrinsic workability was performed by analyzing the flow of metal through the system using the upper bound technique. The results of both these analyses are i) current processing conditions are within a stable region and ii) the introduction of a flow control plate into the container will cause a decrease in the lateral loading on the mandrel resulting in decreased wear on the dies.

9:00 am

INDUSTRIAL APPLICATIONS OF PROCESS MODELING: B.A. Mueller, A. Hines, D. Hirvo, T. Simon, Howmet Corporation, 1500 South Warner St., Whitehall, MI 49461

Process modeling is being applied in industry to reduce development cycle times and improve processes. This application is the result of reductions in model construction time and improvements in model accuracy and predictive capability. Process modeling is able to accurately locate macroshrinkage, and provide trends in microporosity location and severity in equiaxed castings. Model size becomes an issue for large structural castings. For single crystal castings where defects such as spurious grains, freckles and boundaries form, process modeling is capable of predicting thermal profiles, the extent and location of the mushy zone, and fundamental parameters such as the thermal gradients and growth rates. However, the technology needs to be developed further to account for the effect of orientation on growth kinetics and to predict yield. In this presentation we highlight the above with examples of applications to production components.

9:30 am

THERMAL-MECHANICAL AND MICROSTRUCTURAL MODELING OF HEAT TREATING PROCESSES FOR SUPERALLOY COMPONENTS: T.C. Tszeng, W.T. Wu, Scientific Forming Technologies Corporation, 700 Ackerman Road, Suite 255, Columbus, OH 43202-1559

The stringent requirements in mechanical properties of superalloy components continue to demand better heat treating processes. In addition, unacceptable distortion or residual stresses are common difficulties in heat treating of superalloy components. A process design engineer is often facing the dilemma of needing to meet all of the mechanical and metallurgical requirements in the heat treated components. To better understand the thermal, mechanical and microstructural changes in the heat treating and subsequent machining processes for superalloy components, a process modeling system was developed based on the existing computer code DEFORM (design Environment for Forging). We will give an overview in the issues of general heat treating conditions, material constitutive models, metallurgical models, implementation and computational results. This study is partially funded by a US Air Force/Navy SBIR Award (Contract # F33615-95-C-5238).

10:00 am

MICROSTRUCTURE DRIVEN DESIGN FOR HOT DEFORMATION PROCESSES: J.C. Malas, S. Venugopal, W.G. Frazier, E.A. Medina, S. Medeiros, W.M. Mullins, N.U. Deshpande, A. Chaudhary, Materials Process Design, Materials Directorate, WL/MLIM, Bldg. 653, Wright-Patterson Air Force Base, OH 45433-7746

A new design approach based on the application of systems engineering principles to optimize microstructure development during hot working processes has been developed. Two stages of analysis and optimization form the basis of this microstructure driven design strategy. In the first stage, the optimal strain, strain rate and temperature trajectories for the `safe' processing of the material have been calculated. The optimum trajectories have been arrived at based on the kinetics of certain dynamic microstructural behaviors, thermo-physical characteristics of the material and the intrinsic hot workability of the material, along with a chosen optimality criterion. In the second stage, a process simulation model is used to calculate process control parameters, (e.g. ram velocity, die shape and billet temperature) needed to insure that the material follows the trajectories calculated in the first stage. This approach has been validated with an example of hot extrusion of steel, nickel and titanium alloys. Extrusion experiments were performed by using the optimized process parameters. The observed microstructural features in the extruded products were in close agreement with the desired ones.

10:30 am

APPLICATION OF PROCESS MODELING FOR HEAT TREAT OPTIMIZATION OF A HIGH STRENGTH CAST PLUS WROUGHT SUPERALLOY FOR ADVANCED SHAFT APPLICATIONS: Paul D. Genereux, Sue Goetschius, Jack Shirra, Pratt & Whitney Aircraft, MS 114-43, 400 Main Street, East Hartford, CT 06108

The current generation of high thrust turbofans require high strength shaft materials to withstand the torque loads applied due to high fan bypass ratios. In this paper, the development of a model to optimize the processing of a high strength superalloy for shaft applications will be discussed. The critical property requirement for shaft applications is elevated temperature yield strength. The modeling approach consisted of first developing a relationship between yield strength and microstructure / processing for the alloy. This was followed by the development of a process model predicting the microstructure (g' size) resulting from the heat treatment of the shaft. The model was then utilized to identify the effect of key process parameters such as solution temperature, transfer time and quench media on yield strength. It was determined that the greatest strength benefit resulted from reducing the transfer time and a heat treat facility was identified to minimize transfer time delays. Additional areas for process model development will be highlighted, particularly simulating the effect of billet conversion processes on billet/product grain size.

11:00 am

A UNIFIED APPROACH TO THE MODELING OF PLASMA ARC COLD HEARTH MELTING: Y. Pang, K.O. Yu, Concurrent Technologies Corporation, 1450 Scalp Ave., Johnstown, PA 15904

Titanium alloys are primarily melted, refined and cast into ingots via plasma arc melting (PAM), electron beam melting (EBM), and vacuum arc remelting (VAR) for jet engine applications. The PAM process offers superior ability to remove harmful hard alpha and high density inclusions and to potentially improve chemical segregation and product yield. To date, computer models are unavailable to establish the relationships between refining efficiency, ingot structure, and process conditions for the process. The NCEMT is developing a state-of-the-art PAM process simulation system, which includes three process models: plasma torch, refining hearth, and ingot solidification, to enhance the level of understanding and to optimize the process windows for consistent elimination of inclusions and imperfections in cast ingots. The objective of this presentation is to illustrate what capabilities these individual models entail and how they are integrated to yield a useful tool for process optimization. This work was conducted by the National Center for Excellence in Metalworking Technology, operated by Concurrent Technologies Corporation under contract No. N00140-92-C-BC49 to the U.S. Navy as part of the U.S. Navy Manufacturing Technology Program.

11:30 am

KNOWLEDGE-INTEGRATED SOLUTION HEAT TREATMENT PROCESS FOR TURBINE AIRFOILS: J.S. Chou, K.O. Yu, Concurrent Technologies Corporation, 1450 Scalp Ave., Johnstown, PA 15904

An optimization methodology for the solution heat treatment of directionally solidified (DS) and single crystal (SX) superalloy turbine airfoils has been developed. This methodology includes modeling the dissolution kinetics, predicting the alloy incipient melting temperatures, and preventing the formation of recrystallized grain defects. It provides a way to solution heat treatment processes for alloys René N4 and René N5 have been developed and implemented in production at PCC Airfoils and Howmet. These two new processes halved the total solution heat treatment time for René N4 and René N5 turbine airfoils used in F404 and F414 engines. This work was conducted by the National Center for Excellence in Metalworking Technology, operated by Concurrent Technologies Corporation under contract No. N00140-92-C-BC49 to the U.S. Navy as part of the U.S. Navy Manufacturing Technology Program.