Prealloyed Powder

The reaction of carbon with prealloyed powders or powdered alloys proceeds at a faster rate and overcomes the obstacle of the slow diffusion rate of metal atom interdiffusion. Homogeneous multicomponent carbides can be formed at much lower temperatures as compared with method (i). 

Figure 3. Microstructures ofTi-6Al-4 V-1,6B (wt %) produced by (a) hot compaction of prealloyed powder, illustrating the typical micron-sized TiB needles with a random orientation ...

Blended elemental P/M parts of Ti-6A1-4V are currently in production for aerospace and nonaerospace apphcations where fill wrought properties are not required and where there is economic advantage to this approach. (See the section Apphcations for examples). The PA approach, however, has been less successfiil in estabhshing a commercial market. Prealloyed powders are not cold compactable, and their cost is high ( 60 to 100/lb). 

Powder Metallvirgy. Although a great deal of experimentation has taken place with both elemental and prealloyed powders, nothing has reached near-production levels. Reference 5 provides a review of methods. 

The above analysis assumes unit activity for pure Pd. In a Ag-Pd alloy, the activity of Pd will be reduced and the temperature for Pd oxidation wUl depend on Pd content. Rapid cooling of the composition during firing can reduce the amount of PdO formation by reducing the oxidation kinetics. As discussed earlier, Ag-Pd formulations can utilize either prealloyed powders or individual constituents that can alloy in situ. Palladium oxidation can inhibit the solid solution process as illustrated by Vest, where 80% Ag-20% Pd (by weight) did not completely form a solid solution even after 24 h at 850°C. In this study, an... 

ODS materials are produced by powder metallurgy and the first step of the process consists in cogrinding a metal powder with a yttrium oxide powder. The metal powder is composed either of a prealloyed powder with the same chemical composition as the material wanted except for yttrium and oxygen, or of several metal powders with various chemical compositions which, during grinding, will form a powder with a homogeneous distribution of all elements. This step, known as mechanical alloying, produces a powder that can be described in a first approximation as a solid solution. 

Once the powder is obtained, the consolidation of ODS materials can be achieved either by hot extmsion, or by hot isostatic compression (HIC). It could be possible to replace those processes by consolidation by spark plasma sintering (SPS). CEA ODS materials were mainly obtained from prealloyed powder atomized by Aubert et Duval... 

A PM preform could be made using recently developed prealloyed steel powders, and full densification could be achieved by hot precision forging to final configurations after the sintering operation... 

A Military Specification (MIL-F-45961), the first of its kind,for prealloyed steel powder forgings was then drafted and has been accepted as a standard by Department of Defense and commercial organizations. The significance of this work is that the improved PM manufacturing technology is applicable to all weapon systems which require complex-shaped steel forgings... 

Figure 4. Tensile properties of wrought Ti-6A1-4V and extruded Ti-B alloys produced via prealloyed and blended elemental powder approaches. The loading axis is parallel to the extrusion direction. BE signifies material produced by the blended elemental approach. All compositions are in weight percent.

Sve] Partial prealloying of powder, SEM, laboratory-scale tensile tests Dimensional change, tensile strength... 

Sve] Svensson, L.E., Engstroem, U., Improved Precision of Sintered Steel Components Made from Partially Prealloyed Copper-Iron Powders , Powder Metall, 22(4), 165-174 (1979) (Morphology, Experimental, Phys. Prop., 11)... 

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