Closure Behavior of the Artificial Gas Pore inside the As-Cast Ti6Al4V Alloy during HIP: Constitutive Modeling and Numerical Simulation

Abstract

The isothermal compression tests of as-cast Ti6Al4V alloy specimens, with coarse grains obtained from the runner, were conducted at a strain rate range of 0.001–0.1 s−1 and a temperature range of 710–920 °C. The experimental results were used for constitutive modeling. A hyperbolic sine constitutive model was developed to predict the flow behaviors of the as-cast Ti6Al4V alloy. The experimental results agreed well with the predicted results by the above constitutive model. After the establishment of the constitutive model, the closure behavior of the gas pore inside the as-cast Ti6Al4V alloy during hot isostatic pressing (HIP) was studied by experiment and simulation. Through wire cutting, turning, drilling, and argon arc welding of the raw material, the HIP samples were obtained, with these being a cylindrical specimen (Φ15 mm × 13 mm) with a sealed pore (Φ2.5 mm × 4 mm) inside. Interrupted HIP experiments at 780 °C/102 MPa/0 min and 920 °C/120 MPa/20 min were designed, and a full-standard HIP experiment (920 °C/120 MPa/150 min) was also carried out. The HIP sample was simultaneously numerically simulated using the above constitutive model under the same conditions as the experiment. The simulation and the experimental results revealed that the pore begins to close in the first stage of HIP, and the closing rate is faster than in the second stage of HIP. The gas pore cannot be completely annihilated in a standard HIP cycle. Plastic deformation is the main mechanism for pore closure during HIP.