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

Kristine A Lark

Harold L Gegel

James C Malas

Douglas R Barker

James T Morgan, Jr

Sokka M Doraivelu

Yellapregada V Prasad

Raghavan Srinivasan

Lawrence E Matson

J S Gunasekera

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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Enon, OH, United States of America

Kristine A Lark