A Novel Lubricating Method for Improving the Mechanical Properties of Ultrafine-grained Titanium Fabricated via Equal Channel Angular Hot Pressing

In this research, the hot pressing of a pure titanium grade 2 was carried out by an equal channel angular tooling. The novel design of die with 90° channel angle eliminated the undesired material flow into the die parting line, increasing forming load and the workpiece sticking. After trials, it was indicated that the combination of the copper foil and molybdenum disulfide lubricant led to the desired product. In this situation, ECAP was successfully carried out up to four passes at 260 ℃. The tensile testing was performed on the sound samples. The results showed after fourth ECAP pass with only 14% decreasing in reduction of area, the ultimate tensile strength increased by 57%. As well, due to decreasing the forming temperature and employing the suitable lubricant the ultimate tensile strength reached 799 MPa which is greater than related articles. In order to examine the microstructure and damage property of ECAPed pure titanium, the SEM images were taken. The results showed that the average initial grain size of 18385 nm decreased to 729 nm after 4 passes of ECAP. Furthermore, it was revealed that after ECAPing the fine dimples with uniform distribution were created indicating homogeneous structure.