A novel canning technology to forge gamma-TiAl alloys was developed at the BTU Cottbus. A TiAl specimen was encapsulated with multilayer stainless steel foil and glass. The steel foil layers prevented the heat loss through radiation and the glass layer reduced the temperature decrease through conduction. First, the effect of steel foil on the cooling rate was investigated. Cooling curves were recorded for TiAl specimens without steel foil layer, with 1, 2, 3 and 4 layers of steel foil, as well as with 3 coated steel foil layers, respectively. While the unprotected specimen cooled from 1200 °C to 1100 °C within 12 s, the specimen with 3 coated steel foil layers needed 52 s for the same temperature decrease. The efficiency of the glass layer was examined with forging of steel specimens. The cooling rate during forging of the specimen with a glass layer was only half of that without a glass layer. Based on the results, Ti-45Al-0.5Mo-0.5Cu-0.2Si specimens, canned with steel foil and glass, were successfully forged at strain rates of 0.1 s-1 and 0.04 s-1 with warm dies which were heated to 500 °C. Visual and metallographic examinations revealed no cracks, pores or micropores. The microstructures are fine-equiaxed grains.
Cyclic extrusion is a new bulk deformation method. It consists of two steps. In the first step a part of the work piece will be indirectly extruded. In the second step the extruded part will be backwards pressed into the bulk again so that the original shape of the work piece is retained. Similar to ECAP, cyclic extrusion can be repeated many times without shape change. On the other hand, cyclic extrusion can be applied locally on a work piece so that local grain refining or work hardening is possible. Magnesium alloy AZ31 was cyclically extruded at 400 °C with different tools. The grain size was refined from 800 +m to 15 +m. The local grain refining in the surface zone with cyclic extrusion improved the rollability of cast AZ31. Pure aluminium specimens were cyclically extruded up to 2.5 times, which corresponds to a deformation degree of -7. The microstructure changes were examined with EBSD.
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