A thermomechanical treatment for producing useful microstructures in the nickel base superalloys is described. The process is applied to material which has been placed in a condition of super-plasticity, and utilizes isothermal hot deformation under conditions which produce a uniform dislocation density and a resultant propensity for abnormal grain growth. The material is then recrystallized in a thermal gradient to produce a final structure consisting of elongated grains.

Thermomechanical treatment for nickel base superalloys

A formed article comprising a nanostructured ferritic alloy is provided. Advantageously, the article is not formed via extrusion, and thus, cost savings are provided. Methods are also provided for forming the article, and the articles so produced, exhibit sufficient continuous cycle fatigue crack growth resistance and hold time fatigue crack growth resistance to be utilized as turbomachinery components, and in particular, large, hot section components of a gas or steam turbine engines. In other embodiments, a turbomachinery component comprising an NFA is provided, and in some such embodiments, the turbomachinery component may be extruded.

Methods for processing nanostructured ferritic alloys, and articles produced thereby

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 preforms

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 to process high strength and high temperature materials

Directional recrystallisation processing is a solid-state process in which a specimen traverses a sharp hot zone and one or a few grains grow as they pass through the hot zone. The mechanism can be...

Directional recrystallisation processing: a review

A columnar grain structure and improved high temperature, high mechanical strength properties are provided in a metal article by solid state method. First the article is formed in a manner which places the metal microstructure in a condition of dislocation density which results in the metal microstructure undergoing relatively rapid transformation to relatively large grains when heated in the range of about 50 to less than 100 percent of the metal incipient melting temperature in degrees Rankine. Then the article so preconditioned is progressively and selectively heated in that temperature range but below the incipient melting temperature of the metal. This is accomplished by heating the article in a narrow zone. Such zone traverses the article, as a result of relative movement between the article and the source of heat energy, from the cooler portion and in the direction desired for growth of the principle axis of the columnar grains, with the zone having a thermal gradient of at least about 500 DEG F/in. A preferred form of a processed wrought article is characterized by grains of at least about 2000 microns in diameter and a length to diameter ratio of at least about 10.

Clyde David Calhoun

Papers

Alloy microstructure control