Industrial pure titanium belongs to α Alloy, with a dense hexagonal (HCP) lattice structure, has excellent corrosion resistance, mechanical properties, and welding performance, and is widely used in fields such as aerospace, chemical industry, and marine engineering. Through ECAP deformation, the grain size can be significantly refined, the microstructure can be improved, and the mechanical properties of the material can be improved. Therefore, ECAP technology has received widespread attention from scholars both domestically and internationally in recent decades. At present, there are many literature reports that ECAP has successfully prepared ultra fine grained (UFG) materials, including face centered cubic structured metals, body centered cubic structured metals, and closely packed hexagonal structured metals.

Hardness is defined as the ability of a metal material's surface to resist the pressure of other hard objects, reflecting its physical and mechanical properties such as elasticity, plastic strength, toughness, and wear resistance. The commonly used hardness index, Vickers hardness, is widely used in precision industry and material science research, especially for measuring the hardness of metal thin film layers or surface layers after chemical treatment, as well as the hardness of smaller and thinner workpieces. There are many reports on the changes in material hardness after ECAP technology processing, but due to the fact that industrial pure titanium is a densely packed hexagonal structure metal with fewer slip systems and poor plasticity compared to cubic structure metals, ECAP deformation is difficult. Most foreign research is conducted at high temperatures, and room temperature extrusion is rare. Researchers mainly study the changes in the microstructure and hardness of industrial pure titanium after one ECAP extrusion of different molds at room temperature, and analyze the influencing factors to help improve the processing technology.

The experimental material is industrial pure titanium (TA1) in the hot-rolled state. Its chemical composition (mass fraction,%) is 0.10O, 0.001H, 0.01N, 0.007C, 0.03Fe. Average grain size 23 μ m. Having equiaxed single-phase tissue. The tensile strength of the experimental material is 407MPa, the Vickers hardness is 1588MPa, and the elongation is 35%. Cut the hot-rolled plate into 15mm × 15mm × 70mm ECAP sample with two channel angles Φ= 90 ° and Φ= 120 °, all rounded corners are Ψ= A 20 ° mold is subjected to one ECAP deformation at room temperature. mould Φ= At 90 °, a secondary effect becomes approximately 1.08; mould Φ= At 120 ° C, a secondary effect becomes approximately 0.635; Before the experiment, a self-made composite lubricant was applied to both the mold channel and the sample. The extrusion speed is all 120mm/min. Research results:

(1) At room temperature, one pass ECAP deformation of 90 ° and 120 ° industrial pure titanium dies was successfully achieved, and the lath like structures were obtained along one direction respectively.

(2) ECAP deformation of industrial pure titanium at room temperature can significantly refine grains and improve hardness, and there is no significant difference in hardness values after one pass extrusion using different molds (90 ° and 120 °).

(3) The hardness values on the upper and lower surfaces of the sample after 90 ° mold extrusion are slightly lower than the hardness values in the middle of the sample, while the hardness distribution on the surface of the sample after 120 ° mold extrusion is relatively uniform.

Hardness of CP-Ti original sample and sample after one ECAP deformation of different molds (MPa)