Microstructure evolution and mechanical properties of Ti-15-3 alloy during cold-rolling

The microstructure evolution and mechanical properties of Ti-15-3 alloy during cold rolling were investigated by optical microscopy, transmission electron microscopy and X-ray diffractometer. The results show that fibrous microstructure in which grains are refined to about 200 nm was formed in the sheet of Ti-15-3 alloy with total thickness reduction of 80% after five passes cross cold rolling. The structure formation may be divided into three steps: firstly, the partial shear bands form in some grains; secondly, the shear bands of different direction within the banded structure cross and refine; thirdly, the fibrous microstructure with sub-micron grains forms. During cold rolling, the ultimate strength of alloy increases sharply to 949 MPa after 1 pass and slightly to 1021 MPa in the following passes. After 5 passes cross cold rolling with cold rolling rate of 30% per pass and aging at 450°C for 4 h, the ultimate strength of alloy can be increased to 1646 MPa.