A molecular dynamics study of temperature and depth effect on helium bubble released from Ti surface

Using molecular dynamics simulation, the effects of temperature and depth of helium bubble on volume, pressure and releasing process of helium bubble in metal Ti are investigated. First, through studying the states of helium bubble at different depths at room temperature, the variation regularities of volume, pressure and releasing process of helium bubble with its depth are acquired. The results show that with depth augmenting, the pressure of helium bubble increases gradually, while the volume decreases, but these two parameters are kept at some level when the depth is greater than 2.6 nm. Then, the evolutions of model system with helium bubble at various temperatures are simulated. The critical temperatures of helium bubble released from Ti surface at different depths are greatly different. On the whole, the critical temperature is in direct proportion to depth. But the releasing rates at different temperatures are almost unanimous. Finally, the mechanism of helium bubble released from Ti surface is explained on the basis of statistics and analyses of pressure of helium bubble and tensile strength of the metal thin film above the bubble. It is found that helium bubble would tear the Ti film above it when the pressure in helium bubble is greater than the strength of Ti film, and then helium atoms will be released from the metal.