First, the microstructure and properties of titanium alloy forgings are very sensitive to forging thermal parameters. The forging temperature range of titanium alloy is relatively narrow. During the forging process, as the deformation rate increases, its deformation resistance increases significantly, showing strong strain rate sensitivity.
Secondly, titanium alloy has poor thermal conductivity and is prone to local overheating during the forging process, resulting in a large internal and external temperature difference, exacerbating the uneven distribution of internal and external deformation of the billet, leading to cracking during the forging process, and in severe cases, causing the product to be scrapped.
Therefore, it is of great practical production significance to study the effects of different forging processes on the structure and mechanical properties of titanium alloys in order to find a reasonable forging process to form titanium alloy forgings.
The TC4 titanium alloy raw material used in the experiment is a forging billet with a size of Φ100mm×450mm. The (α+β)/β phase transformation point (Tβ) measured by the metallographic method is 990°C.
In order to study the influence of the forging process on the microstructure and mechanical properties of TC4 titanium alloy, the forging billet was divided into three sections, and conventional forging (Tβ-60℃), near-β forging (Tβ-20℃) and β forging were performed respectively. (Tβ+40℃) process test, the deformation is 50%. The forging equipment is a 3t free forging hammer. After forging, the forgings obtained by the three processes were subjected to dual heat treatment of 900℃×1h/AC+600℃×4h/AC. After heat treatment, metallographic samples, tensile samples and impact samples were taken from TC4 titanium alloy forgings, and their microstructures were observed under a metallographic microscope. Image analysis software was used to complete quantitative statistics of microstructural parameters such as equiaxed α phase content and secondary lamellar α phase thickness. The results showed that:
(1) After TC4 titanium alloy is forged by three processes: α+β forging, near-β forging and β forging, it obtains equiaxed structure, mixed structure and lamellar structure respectively.
(2) The strengths of TC4 titanium alloy bars after α+β forging, near-β forging and β forging are equivalent, while the plasticity of α+β forging and near-β forging is higher than that of β forging, but the TC4 titanium alloy bars after β forging have Best impact toughness. The TC4 titanium alloy bar shows the best comprehensive mechanical properties after near-beta forging.
(3) The fracture surfaces of the tensile specimens of TC4 titanium alloy bars under the three forging processes all show a ductile fracture mechanism. α+β forging and near-β forging have deeper and evenly distributed equiaxed dimples, while after β forging The alloy exhibits flatter and elongated dimples.
