Papers by Keyword: Grain Refinement Mechanism

Abstract: Equal Channel Angular Pressing (ECAP) and Surface Mechanical Attrition (SMAT) are the two Severe Plastic Deformation (SPD) processes that have been used to process ultrafine grained (UFG) materials. These two kinds of processes have been used to refine the grain size of coarse-grained commercial pure titanium (CP-Ti). The development of microstructure during equal channel angular pressing (ECAP) and surface mechanical attrition (SMAT) of commercial pure titanium (CP-Ti) is investigated to establish the mechanisms of grain refinement. Based on the various experimental results and analysis, it has been found that the high-strain-rate and many direction loading is conducive to the formation of nanograins and also the grains with less than 100 nm cannot be obtained by the single equal channel angular pressing (ECAP).

Abstract: The grain refining effects of Al-Ti, Al-TiC and Al-Ti-C master alloys on commercially pure aluminum were compared, and the grain refinement mechanism of TiAl₃ and TiC among master alloys was discussed. The results show that: the grain refinement of the master alloys Al-TiC and Al-Ti toward pure aluminum mainly stems from the heterogeneous nucleation role of TiC and TiAl₃ particles, but with the extension of heat preservation time of fused mass, its role of heterogeneous nucleation will decline due to dissolution of TiAl₃ and aggregation and precipitation of TiC. The preferable grain refinement effects of Al-Ti-C master alloys toward pure aluminum are mainly due to the fact that when TiAl₃ and TiC particles are acted commonly as heterogeneous nucleation particles, the heterogeneous nucleation effect of TiC particles will be enhanced because of the presence of TiAl₃.

Abstract: The present work is an attempt to contribute the current understanding of the operating mechanisms responsible for the development of ultrafine grains during severe plastic deformation (SPD) in aluminium. Equal channel angular pressing (ECAP) at room temperature has been applied to a commercial Al-Mg-Si alloy. Route A was used in all pressings and the first two passes were studied in most detail. Advanced characterization methods such as FEG-SEM with a state-of-the-art microdiffraction unit has been applied when characterizing samples carefully prepared from different positions along certain flow paths in the process shear zone. Intrinsic strain measurements are done in parallel in order to describe the actual strain tensor in each position studied. Detailed information on phenomena involved in the grain break-up mechanisms has been obtained by high resolution EBSD data collected through the deformation zone. The microstructural development seems to be dominated by deformation banding and may be explained in terms of the LEDS theory.