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This paper presents an investigation on the evolution of microstructure and deformation characteristics of commercial purity Titanium (CP-Ti) during incremental equal channel angular pressing (I-ECAP). CP-Ti grade 2 was subjected to six passes at 300 °C following route BC, using a die with channel angle of 120°. Electron backscatter diffraction (EBSD) technique was used to characterize the microstructure after first, second, fourth and sixth pass, in the flow and transverse plane of the samples. Texture development through subsequent processing was also investigated using pole figures in both planes. Following first pass, the grain boundary maps across both flow and transverse plane showed a high degree of heterogeneity in grain morphology with the presence of elongated and fine grains. Also, misorientation peaks associated with {10-12} tensile twins and a small fraction of {11-22} compressive twins were observed in the microstructure. After second pass, microstructure was further refined and the twinning activity was greatly reduced with no noticeable activity after the fourth pass. Remarkable grain refinement was achieved after sixth pass with majority of grains in the ultrafine grain (UFG) range and with a relatively homogenous microstructure. Continuous dynamic recrystallization (CDRX) has been observed during subsequent I-ECAP processing. It was seen that twinning alongside CDRX acted as a dominant grain refinement mechanism during the initial passes of I-ECAP process beyond which slip was dominant deformation behaviour.

Incremental equal channel angular pressing (I-ECAP) is used in this work to produce ultrafine-grained (UFG) pure iron, aluminum alloy 5083, commercial purity titanium (grade 4), and magnesium alloy AZ31B. Pure iron is processed at room temperature, aluminum alloy at 200 °C, titanium at 320 °C, and magnesium alloy at 150 °C. Strength improvement, attributed to the grain refinement below 1 μm, is reported for all processed materials. The yield strength increase is the most apparent in pure iron, reaching almost 500 MPa after one pass of I-ECAP, comparing to 180 MPa in the as-forged conditions. UFG titanium, aluminum, and magnesium alloys obtained in this study reached yield stress of 800, 350, and 300 MPa, respectively, in each case exhibiting the yield strength increase by at least 30%, comparing to the alloys processed by conventional metal forming operations such as forging and rolling.