Influence Of Titanium Forging On The Properties And Organization Of TC4 Titanium Rods And Titanium Alloy Rods

TC4 titanium alloy is a widely used a + β type titanium alloy at home and abroad, due to its high specific strength, good corrosion resistance and superior overall performance, it is widely used in aerospace, chemical machinery, pharmaceutical engineering and other industries.TC4 titanium alloy common defects are alloying element segregation and inclusions, casting organization of the residue, brittle layer, hydrogen embrittlement, and brittle and forging cracks. China in the "Tenth Five-Year Plan" period began independent research and development of a medium-strength high damage tolerance type titanium alloy, compared with other medium-strength titanium alloy titanium rods, its strength, plasticity level under the conditions of comparable conditions, with higher fracture toughness and crack resistance to the expansion of the ability to be widely used in our country's four generations of aircraft, aircraft and other important models of the key load-bearing components. Using two-phase zone annealing, two-phase zone solid solution + aging, single-phase zone solid solution + aging heat treatment process, the effect of different heat treatment processes on the microstructure and mechanical properties of TC4 titanium alloy rods was investigated in order to obtain a heat treatment process that best matches the strength, plasticity and toughness of the alloy.
(1) TC4 titanium alloy in the two-phase region of the ordinary annealing and recrystallization annealing treatment occurs after recrystallization, the a-phase size increases, and the higher the annealing temperature, the slower the cooling rate, the more fully recrystallized, and the a-phase aggregation growth occurs, resulting in a significant decrease in the strength of the alloy and an increase in plasticity.

(2) in the two-phase region solid solution + aging treatment to get the bimodal organization, with the aging temperature increases, the secondary a-phase content decreases, the a layer size increases, the alloy's strength and fracture toughness decreases, the plasticity is improved. And when the cooling rate is elevated during solid solution, the secondary lamellar a-phase generated during aging is finer, resulting in an increase in the strength and a decrease in the plasticity and fracture toughness of the alloy.

(3) In the single-phase zone solid solution water cooling to obtain martensitic organization, followed by aging treatment, the plasticity of the alloy deteriorates sharply, are brittle fracture. And when the aging temperature increases, the lamellae are thickened, but the precipitation of secondary a-phase content is reduced, the strength and fracture toughness of titanium alloy titanium rods decreased. In the single-phase zone solid solution air cooling to obtain the Weiss organization, followed by high-temperature aging treatment, will make the a lamellae thickness further increase, and chaotic intertwining degree is reduced, resulting in a decrease in strength, plasticity and fracture toughness are improved.

(4) TC4 titanium alloy bar by 950C/1h/WQ+550C/6h/AC heat treatment, can realize the strength, plasticity, toughness of the optimization of the match, so as to obtain excellent comprehensive mechanical properties.

TC4 titanium bar reforging ring piece process is at 950 degrees two fire times heating, forging into cake material, cake material flaring into ring material, the defects may be due to improper reforging process caused by cracking, but also may be the bar itself exists in the metallurgical defects such as inclusions, segregation, porosity, etc., and in the subsequent reforging process by the metallurgical defects caused by cracking. Through theoretical calculations, it is concluded that the design of this set of computerized flat knitting machine catwalk fixture is fully in line with the theoretical design requirements. So the author made this set of fixtures in kind, and will be installed into the Vcentei-70 high-precision CNC machining center workbench for actual processing verification. Then the processed parts of the bridge to the three coordinate measuring machine for the accuracy of the measurement of the two angles of the angle error in the range of 0.2 ° ~ 0.6 °, in line with the technical requirements. Because this set of fixtures can be very convenient and fast to realize the processing positioning of the flyover parts, without the need for other ways to find the right, so it is suitable for the mass production of flyover parts.

The forging temperature determines the organization of titanium alloy, and it is inevitable to produce β-phase transformation in the forging process of titanium alloy, and the following conclusions can be drawn through the research of this paper:

(1) There is no difference in the main chemical composition between the black spot area and the normal area of TC4 titanium bar, and there is no segregation of components, so the black spot is not a phase change organization caused by segregation of chemical composition.

(2) TC4 titanium rod black spot area of p-phase morphology and the normal area has a big difference, for the formation of single-phase region of the abnormal phase change organization.

(3) The black spot organization of TC4 titanium rods is an uneven organization formed by different phase transformation of titanium rods due to uneven deformation in the forging process. Excluding the influence of experimental errors, according to the test results, it shows that there is no significant difference in the content of Al, V, Fe and titanium matrix elements between the low-fold black spot area and the normal area of titanium rods, which indicates that there is no segregation of components in the black spot area. Therefore, there is no direct relationship between the organization of low-fold black spots and the segregation of the chemical composition of titanium rods.