TEMPERATURE-DEPENDENCE OF THE ATOM-DISPLACEMENT MECHANISM IN FCC METALS

The experimentally determined threshold energy for atom displacement, E(d), in fcc metals shows a particularly strong temperature dependence along the <111> direction. This is discussed paying special attention to the propagation of replacement collision sequences. Taking into account thermal effects, molecular dynamics calculations of such collision sequences along <100>, <110> and <111> are compared. Two mechanisms exhibiting a strong temperature dependence along <111> are found: First, by increasing the temperature, the energy loss caused by the opening of atomic windows decreases more rapidly for <111> sequences than for sequences along <100> and <110>. Second, a ''low-energy'' displacement mechanism along the <111> direction is found. Since this mechanism is effective mainly at high temperatures it causes a strong temperature dependence of E(d)<111>.