Industrial pure titanium belongs to alloy, which is a dense hexagonal (HCP) lattice structure with good corrosion resistance, mechanical properties and welding properties. It is widely used in aerospace, chemical industry, ocean engineering and other fields.ECAP deformation can significantly refine grain, improve structure and improve mechanical properties of materials.Therefore, ECAP technology has been widely concerned by scholars at home and abroad in recent decades.At present, many literatures have reported that ECAP has successfully prepared ultrafine crystal (UFG) materials, including face-centered cubic structure metals, volumetric centered cubic structure metals, and densely arranged hexagonal structure metals.
Hardness is defined as the ability of the surface of a metal material to resist the pressure of other hard objects, which can reflect the physical and mechanical properties such as the elasticity, plastic strength, toughness and wear resistance of the material.Vickers hardness, a commonly used hardness index, is widely used in precision industry and material science research, especially used to measure the hardness of metal thin film layer or chemically treated surface layer, as well as the hardness of smaller and thinner workpieces.There have been many reports on the changes in the hardness of materials processed by ECAP technology. However, due to the fact that industrial pure titanium is a closely arranged hexagonal structure metal, its slip system is less than that of cubic structure metal, and its plasticity is poor, ECAP deformation is difficult. Most studies abroad are conducted at high temperature, and successful extrusion at room temperature is rare.Researchers mainly studied the microstructure and hardness changes of industrial pure titanium after ECAP extrusion of different molds at room temperature, and analyzed the influencing factors to help improve the processing technology.
The experimental material is industrial pure titanium (TA1) in hot rolled state.Its chemical composition (mass fraction, %) is: 0.10O, 0.001H, 0.01N, 0.007C, 0.03Fe.Average grain size 23 m with equiaxed single-phase structure.The tensile strength was 407MPa, vickers hardness was 1588MPa and elongation was 35%.Hot rolled plate cutting into 15 mm * 15 mm * 70 mm of ECAP samples, using two channel Angle Φ = 90 ° and 120 ° Φ =, rounded corners are mould for Ψ = 20 °, ECAP deformation at room temperature for a time.A time when mould Φ = 90 °, equivalent strain is about 1.08;A time when mould Φ = 120 °, equivalent strain is about 0.635;Before the experiment, the mold channel and sample were coated with self-made compound lubricant.The extrusion speed was 120mm/min.Research results:
(1) One ECAP deformation of 90° and 120° industrial pure titanium mold was successfully realized at room temperature, and strip tissues elongated along one direction were obtained respectively.
(2) ECAP deformation of industrial pure titanium at room temperature can significantly refine the grains and improve the hardness, and the hardness value after one extrusion with different molds (90° and 120°) has little difference.
(3) The hardness values on the upper and lower surfaces of the samples after 90° die extrusion are slightly lower than those in the middle of the samples, while the hardness distribution on the surface of the samples after 120° die extrusion is more uniform.