Materials with fine microstructures by advanced powder metallurgy

A new powder metallurgy method

A gas operated part forming die apparatus has compact high tonnage presses which are operated by high pressure gas generated within chambers and controlled to operate high pressure pistons and dies for compressing particulate material into dense formed parts. Combustion chambers are filled with pressurized mixtures of combustible gases and diluents. Elongated chambers have insulating walls and spaced electrodes. Some contain liquid or particulate ablatable materials or ablatable liners. Others extend fuzes between the electrodes and are filled with pressurized gases. Gas is removed from the particulate material. Die cavities may be precompressed during filing of chambers with pressurized gas. Igniting the combustible gases or creating arcs between the electrodes produces rapidly expanding high pressure resultant gases for driving pistons and movable dies and rapidly compressing die cavities. Pressures in the chambers are contained, or pistons are restrained until releasing and driving the pistons. Large area pistons drive smaller movable dies.

Dynamic consolidation of powders using a pulsed energy source

A method for producing very dense bodies of material from particulate materials. A particulate material is placed within an electrically conductive container (108'). A solenoid or coil (36') encompasses the electrically conductive container, and large magnitude of electrical current is caused to flow through the solenoid or coil. As the electrical current flows through the solenoid or coil, large magnitudes of magnetic pressures are created upon the electrically conductive container, and the electrically conductive container is compressed, and the transverse dimension thereof is reduced. Thus, the particulate material within the electrically conductive container is very firmly compacted, and a rigid body of material is provided.

Structure and method for compaction of powder-like materials

The feasibility of consolidating rapidly solidified MAR M-200 powders by explosive means is demonstrated. MAR M-200 powders produced by the rapid solidification rate (RSR) technique and exhibiting a microdendritic structure were consolidated in an axisymmetric set-up, consisting of a steel pipe (in which the powder was placed) surrounded by explosives. The converging shock waves produced full densification, after optimization of the process parameters. The microindentation hardness showed a dramatic increase: 357 HV in the as-received condition, to 700 HV in the shock-consolidated condition. The substructure was analyzed by TEM, and two distinct regions were identified. The center of the particles exhibited planar arrays of dislocations, stacking-faults, and twin faults characteristic of shock-loaded superalloys, while the melted and re-solidified interfacial layers consisted of a microcrystalline structure with homogeneous composition.

Shock-Wave Consolidation of Rapidly Solidified Superalloy Powders

transmit a shock pulse into the powder so as to effect its compaction. The controlling parameter of the process is assumed to be the ratio of the powder mass to the explosive mass, Mp/ME, and values of this ratio necessary to fully compact various powders have been quoted· for specified explosives. Apart from an attempt by Leonard4 to relate the Mp/ME ratio for full compaction to the compressive yield strength of five powder materials, no definite relationship has been established between this ratio and any measurable. property of a metal powder. Although details of the powder container are not normally included in the literature, initial work by Ludlow,S subsequently verified by Bhalla,6 showed that compacted density was dependent on the container tube wall thickness and material, even when Mp/ME was maintained constant. Bhalla subsequently found that a rel(~tionship existed between the compacted density Dc and the kinetic energy per unit area of the tube E immediately after detonation of the explosive charge. This relationship took the form:

A. K. Bhalla

Papers

Explosive Compaction of Metal Powders