Experimental Study On Equal Channel Angular Pressing And Torsion Of Powder Materials

Presently, powder metallurgy materials and ultrafine-grained materials (UFG)are important parts of material family. The former has the unique chemicalcomposition and mechanical properties which could not access by conventionalcasting process. The latter showed extraordinary physical and mechanicalproperties. However, there are problems in the Powder Metallurgy Industry suchas poor working conditions and high energy consumption. And its mechanicalcharacters are often affected due to pores inside. The UFG are usually prepared bythe bulk materials. Removing inner porosity, refining microstructure andimproving its mechanical characters are important aims of powder plasticdeformation technology. Equal Channel Angular Pressing and Torsion (ECAPT) isa new technology which combines the technology for preparing UFG and powdermetallurgy process. In this paper, powder materials were successfully consolidatedinto near fully dense bulk materials with fine grains. The influences of ECAPT onmicrostructure and property of powder materials were studied. And thedistribution mechanism of SiC particle and the fracture mode were explored.To research the influence of ECAPT process on deformation, pure aluminumpowder and8.75vol%-SiC、35vol%-SiC_p/Al particulate composites were used.After comparing microstructure and properties, the distributions of grains, poresand particulates, and the results of relative density, microhardness, compressionproperty and fracture surface of the sample during ECAP and ECAPT processingwere obtained. The results show that, the deformation uniformity of the sampleduring ECAPT is good. Comparing with deformation uniformity, microhardness,and relative density, it was found that the deformation effect of1st pass ECAPT isas good as that of2nd pass ECAP. The consolidation effect of8.75vol%SiC_p/Al isbetter than other materials. Fracture of SiC_p/Al composites after compression testis characteristics of segments of various sizes which are formed by sticky point ofSiC particles and microspores.The most effective way to comparing the deformation uniformity is toresearch the distribution of particulates. The results of quadrat sampling methodshow that, Nq=0is directly related with clusters, however Nq≧3is not directly related with clusters. The ECAPT processing could achieve more uniform ofdistribution than that of ECAP. More deep of the deformation make more uniformof distribution. The strain capacity is directly related with the distribution of SiCparticulates, the higher strain capacity make more uniform of distribution.