Method for preparing fully dense, near-net-shaped objects by powder metallurgy

A process for manufacturing objects by consolidation of powdered materials of the type capable of being consolidated in powder metallurgy processes, the process comprising the steps of:

• placing a shell in a can so as to leave empty space between the can and the shell, the shell comprising a cavity;
• filling the cavity of the shell with a first powder composition of the type capable of being consolidated in powder metallurgy processes, the first powder composition having a compressibility ratio;
• filling the space between the can and the shell with a second powder composition of the type capable of being consolidated in powder metallurgy processes, the second powder composition having a compressibility ratio which is substantially identical with the compressibility ratio of the first powder composition;
• heating the can having the filled shell and the filled space therein to an elevated temperature sufficiently high to permit, when combined with application of pressure, substantially full consolidation of the first powder composition;
• subjecting the can having the filled shell and the filled space therein at the elevated temperature to a unidirectional pressure for a sufficiently long period of time to accomplish substantially full consolidation of the first powder composition, and
• disassembling the compacted can, the compacted shell, the consolidated first powder composition in the form of a substantially fully densified object, and the consolidated second powder composition in the form of scrap material or reworkable dense stock.

A process of preparing near-net-shape powder metallurgy articles, the process comprising the steps of:

• placing a shell in a can, the shell defining an interior cavity, and the assembled shell and can defining spaces within the can between the shell and the can;
• filling the interior cavity of the shell with a first powder composition selected from a group consisting of powders of metals, powders of metal alloys, ceramic powders, cermet powders, and mixtures of one or more of said powders of metals, powders of metal alloys, ceramic powders, and cermet powders;
• filling the spaces between the shell and can with a second powder composition selected from a group consisting of powders of metals, powders of metal alloys, ceramic powders and mixtures of one or more of said powders of metals, powders of metal alloys, ceramic powders, and cermet powders, the first and second powder compositions having substantially identical compressibility ratios, compressibility ratio being defined as the ratio of the apparent density of the powder to the density of the consolidated article prepared in the process from the respective powder composition;
• heating the assembled can and shell having the first and second powder compositions to a consolidating temperature;
• applying unidirectional pressure to the assembled can and shell having the first and second powder compositions, the pressure being of sufficient magnitude and being applied for sufficient time at said consolidating temperature to obtain substantially full consolidation of the first powder composition to provide the near-net-shape article, dimensions of the consolidated article being substantially identical in the direction perpendicular to the applied pressure to the dimensions of the interior cavity of the shell, whereas dimensions of the consolidated article in the direction of the applied pressure being defined by the dimensions of the interior cavity and by the compressibility ratios of the first and second powder compositions, and
• disassembling the compacted can, the compacted shell, the consolidated first powder composition in the form of the consolidated article, and the consolidated second powder composition in the form of scrap material or reworkable densified stock.

A process for manufacturing objects by consolidation of powdered materials of the type capable of being consolidated in powder metallurgy processes, the process comprising the steps of:

• filling a shell with a first powder composition of the type capable of being consolidated in powder metallurgy processes, the first powder composition having a predetermined compressibility ratio, the shell being placed inside the cavity of a die so that space is located between the shell and interior wall of the die defining the cavity;
• filling the space between the shell and the interior walls of the die with a second powder composition of the type capable of being consolidated in powder metallurgy processes, the second powder composition having substantially the same compressibility ratio as the first powder composition;
• subjecting the first and second powder compositions to elevated temperature and mechanical pressure applied in one longitudinal direction only, the pressure and temperature being of sufficient magnitude to consolidate the first and second powder compositions, the shell being of a material which does not bond to the first powder composition, and
• removing the shell which has been compacted in one direction as a result of the applied pressure, to obtain an object consolidated from the first powder composition.