United States of America As Represented by the Secretary of the Air Force

James C Malas

Raghavan Srinivasan

Harold L Gegel

Douglas R Barker

Yellapregada V Prasad

Kristine A Lark

James T Morgan, Jr

Sokka M Doraivelu

Seshacharyulu Tamirisakandala

Venkat K Seetharaman

Lawrence E Matson

Anil Chaudhary

Steven C Medeiros

William M Mullins

J S Gunasekera

S Venugopal

Prasad Vrk Yellapregada

William G Frazier

Enrique A Medina

R Dennis Irwin

W Garth Frazier

A high speed titanium alloy microstructural conversion method from lamellar to equiaxed is disclosed. The method includes identification and estimation of process parameters such that the average strain rate is between about 1-100 sand the deformation temperature of the material is in the range of about 975&#xb0;-1010&#xb0; C.

High speed titanium alloy microstructural conversion method

A method for predicting process parameters for optimization and control of microstructure in metal and alloy products of hot working fabrication processes is described. The method uses state-space material behavior models and hot deformation process models for calculating optimal strain, strain rate and temperature trajectories for processing the material. Using the optimal trajectories and appropriate optimality criteria, suitable process parameters such as ram velocity and die profile for processing the material are determined to achieve prescribed strain, strain rate and temperature trajectories.

Optimization and control of microstructure development during hot metal working

A process for manufacturing powder metallurgy (P/M) preforms which are conditioned for optimum intrinsic workability is described which comprises steps of heating a quantity of P/M material in a can to a first preselected temperature under vacuum to degas the material, compacting the canned material at a second preselected temperature under pressure to provide a compact of the material; or cold compacting the powder to about 75% density and degassing it at suitable temperature and then vacuum hot pressing the powder at about 0.75 melting point; generating flow stress data as a function of strain rate and temperature on samples of the compact at predetermined strain within predetermined ranges of temperature and strain rate and determining powder dissipation efficiency of the compact and entropy rate ratio within those ranges of temperature and strain rate; selecting values of strain rate and extrusion temperature at which dynamic recrystallization is the dominant metallurgical mechanism characterizing the compact: and extruding the compact in an extrusion can at the selected extrusion temperature and at an extrusion rate corresponding to the selected strain rate using a streamlined die. An improved processing map for preselecting optimum processing parameters for the material is described.

Billet conditioning technique for manufacturing powder metallurgy

An improved hot forming method for metals, alloys and the like, and in particular, for difficult to process high strength and high temperature metals and alloys of particular use in aerospace applications, is described, which comprises the steps of generating flow stress data as a function of strain rate and temperature on samples of the material at predetermined strain within predetermined ranges of temperature and strain rate; determining from that data the strain rate sensitivity and power dissipation efficiency of the material within the ranges of temperature and strain rate represented by the generated data; selecting values of strain rate and corresponding temperature for a selected value of the dissipation efficiency for the material; and hot forming the material at the selected strain rate and temperature values to a predetermined shape. The improved method may be of particular application to forging, extrusion, rolling or other hot forming process appropriate for titanium, aluminum, nickel, cobalt, copper, iron, zirconium and their alloys. A processing map for hot forming each metal or alloy may be generated according to the methods taught.

Optimizing hot workability and controlling microstructures in difficult

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Dayton, OH, United States of America

James C Malas