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Powder metallurgy (P/M) offers a commercial process for producing complex compositions without the severe chemical segregation observed in conventional ingot processing. P/M processing overcomes segregation by confining the solidification of the powder to a fine powder particle rather than a large casting. Also, solidification of the powder is orders of magnitude faster than that of a casting, thus ensuring an ultrafine grain size and superior homogeneity. A further advantage of this technology is the potential to combine the resulting superior properties with the ability to produce near net shape parts.
A variety of monolithic P/M near net shapes have been produced at Crucible. Typically, these parts are for critical service applications where elevated temperature service, severe mechanical stressing, and/or high surface stability is required. Parts are generally made from highly alloyed nickel base or iron base P/M alloys and are used in rotating parts in jet engines, valves and fittings in sour gas wells, and in components for sea water and power generation applications. HIP P/M turbine disks made from P/M superaloys are shown in figures 1 and 2. P/M Alloy 625 valves used in an oil patch application are shown in figure 3. Nickel base pipe fittings (figures 4 and 5) made from nickel base alloys have also been produced. Simpler shapes (figures 6 and 7), such as cylinders and disks can also be made.
figure 1
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figure 2
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figure 3
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figure 4
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figure 5
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figure 6
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figure 7
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The process to produce these near net shape parts is fairly straightforward. The end user supplies Crucible with a drawing of the finish part with nominal dimensions and machining tolerances. To determine the HIP shape, overstock is added onto finish dimensions to yield a near net shape. The container design is established and drawings are generated in order to fabricate cans, which are usually made from steel tubing, pipe, and/or formed sheet metal. Can components are welded together and fill stems are added for loading of powder into the container. After welding, the container is leaked checked to ensure the can is hermetically sealed. Powder is loaded into the container, and the part is consolidated and brought to full densification by HIP. Because of the void space between particles in the as-loaded container, the compact shrinks during HIP to a smaller size than its original pre-HIP shape. Anisotropic shrinkage often occurs due to the part geometry, heating and pressurization rates prior to the HIP hold cycle, material properties of the powder, and container material, thickness, and position of the welds. Design methodology is critical to ensure dimensional control.
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