Industrial pure titanium belongs to α alloy, which is a close-packed hexagonal (hcp) lattice structure, has good corrosion resistance, mechanical properties and welding performance, and is widely used in aerospace, chemical industry, marine engineering and other fields. Through ECAP deformation, it can remarkably refine the grain, improve the structure, and improve the mechanical properties of the material. Therefore, ECAP technology has received extensive attention from scholars at home and abroad in recent decades. At present, there are many reports in the literature that ECAP has successfully prepared ultrafine crystal (UFG) materials, including face-centered cubic structure metal, body-centered cubic structure metal, and close-packed hexagonal structure metal.
Hardness is defined as the ability of the surface of the metal material to resist the intrusion of other hard objects, which can reflect the physical and mechanical properties of the material such as elasticity, plastic strength, toughness, and wear resistance. Among them, the commonly used hardness index Vickers hardness is widely used in precision industry and materials science research, especially for measuring the hardness of metal film layers or surface layers after chemical treatment, as well as the hardness of small and thin workpieces. There are many reports about the change of material hardness after ECAP technology processing, but because industrial pure titanium is a close-packed hexagonal structure metal, its slip system is less than the cubic structure metal, and the plasticity is poor, so ECAP deformation is difficult. At high temperature, room temperature extrusion is rare. The researchers mainly studied the changes in the structure and hardness of industrial pure titanium after ECAP extrusion with different molds at room temperature, and analyzed the influencing factors to help improve the processing technology.
Experimental material is hot-rolled industrial pure titanium (TA1). Its chemical composition (mass fraction,%) is: 0.10O, 0.001H, 0.01N, 0.007C, 0.03Fe. The average grain size is 23 μm, with an equiaxed single-phase structure. The tensile strength of the experimental material is 407 MPa, the Vickers hardness is 1588 MPa, and the elongation is 35%. The hot-rolled sheet was cut into 15mm × 15mm × 70mm ECAP specimens, using two channels with an angle of Φ = 90 ° and Φ = 120 °, and an external radius of Ψ = 20 °, and one ECAP at room temperature. Deformed. When the mold Φ = 90 °, the equivalent strain of one pass is about 1.08; when the mold Φ = 120 °, the equivalent strain of one pass is about 0.635; before the experiment, the self-made composite lubricant is coated on the mold channel and the sample. The extrusion speed is 120mm / min. Research result:
(1) A series of ECAP deformations of 90 ° and 120 ° mold industrial pure titanium were successfully achieved at room temperature, and lath-like structures elongated in one direction were obtained respectively.
(2) The industrial pure titanium ECAP deformation at room temperature can significantly refine the grains and increase the hardness, and the hardness values ​​are not much different after one extrusion with different molds (90 ° and 120 °).
(3) The hardness values ​​of the upper and lower surfaces of the sample after 90 ° die extrusion are slightly lower than the hardness values ​​in the middle of the sample, and the hardness distribution of the sample surface after 120 ° die extrusion is more uniform.
The hardness of the original CP-Ti sample and different molds after ECAP deformation (MPa).