A low alloy sintered steel contains at least 0.15 percent by weight and less than 0.8 percent by weight of carbon. Its matrix is formed by a tempered martensite containing prior austenite crystal grains of not more than 15 μm in mean grain size. Pores and nonmetallic inclusions contained in the matrix are not more than 50 μm in maximum diameter, and the density of the low alloy sintered steel is at least 96 percent of theoretical density. A raw material powder for forming the low alloy sintered steel includes iron alloy powder which is prepared by an atomizing process, and is treated with a dry mill in an inert gas atmosphere or in the atmospheric air. Thus, dislocations are introduced into the raw material powder, and nonmetallic inclusions contained in the raw material powder are pulverized to be not more than 50 μm in maximum diameter. Not only static characteristics but also dynamic characteristics, such as fatigue strength, of the low alloy sintered steel are improved.

Low alloy sintered steel and method of preparing the same

A process for producing composite materials which comprises subjecting particles of a malleable matrix material, i.e., a metal or alloy or the components of a matrix alloy and particles of a reinforcing material such as a carbide or an oxide or an intermetallic to energetic mechanical milling under circumstances to insure the pulverulent nature of the mill charge so as to enfold matrix material around each of said reinforcing particles to provide a bond between the matrix material and the surface of the reinforcing particle. The process is exemplified by the use of aluminum alloy as the matrix material and silicon carbide as the reinforcing particles. Reinforcing particles are present in an amount of about 0.2 to about 30 volume percent of total matrix and reinforcing particles. The invention is also directed to the product of the process.

Process for producing composite material by milling the metal to 50% saturation hardness then co-milling with the hard phase

A sintered rhenium crucible, highly suitable for growing single crystals from refractory metal oxides, for example by the Czochralski technique, is formed of fine rhenium powder, by sintering. A compact is formed by cold isostatic pressing and thereafter the compact is sintered at 500-2800° C. to obtain a sintered crucible. Product density is limited to 88-95% of theroretical in order to maximize creep resistance.

Crucible for growing single crystals, process for making the same and use of the same

A metal matrix composite is produced by plastically deforming a metal powder, either or after blending the powder with ceramic fibers, and compacting the mixture at elevated temperatures to achieve substantially full density. Imparting strain energy to the metal allows reduction of the compaction temperature to eliminate reaction between the fibers and the metal or degradation of the fibers. Silicon nitride fibers are thermodynamically superior for use in aluminum or titanium metal matrix composites, since silicon nitride fibers are more stable at the temperatures required for full compaction. Secondary phase reactions are avoided.

Method for making metal matrix composites

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

A method of producing a densified compact from a loose metal powder, the method comprising introducing strain into each particle of the loose metal powder to impart a residual stress to increase the potential energy level of the particles above the potential energy which the particles may have acquired during production thereof, the strain being introduced at a temperature below the recrystallization temperature thereof, and thereafter hot consolidating the loose metal powder.

Havel Charles J

Papers

Method for processing and densifying metal powder

Metallpulver, verfahren zur behandlung losen metallpulvers und verfahren zur herstellung eines verdichteten presslings