Nanostructures and Enhanced Properties in Tungsten and its Alloys Processed by Equal Channel Angular Pressing

摘要

The aim of the present project has been the development of the ECAP technique for processing of UFG structures in tungsten (W) and W-4.3%Ni-2%Fe- alloy, which refer to very low-ductility and hard-to-deform materials. Taking into account the computer simulation results of ECAP there has been conducted a modernization of the die-set, aimed at decreasing the pressing temperature below 1000 deg C at the cost of a decrease in the intensity of deformation for one pass and a use of backpressure. The influence of the number of passes, the rate and the pressing route on the UFG structure formation has been investigated. There has been shown the possibility to obtain the UFG structure with a grain size about 0.5 micrometers in W by optimizing the ECAP regimes. A formation of such small grains leads to a strength enhancement. At the same time manifestations of the viscous character of the UFG W fracture points out at a principal change in its ductile properties. A strong microstructure refinement after several passes of ECAP has been achieved also in the W heavy alloys with a low workability. There have been outlined ways for a further progress in ECAP of W, leading to a formation of a homogeneous UFG structure in bulk billets, which provides extraordinary mechanical properties.