[en] Displacement cascades are a fundamental aspect of the damage produced by fast neutron or heavy ion irradiation of metals. Recent molecular dynamic simulations of the evolution of the displacement cascade suggest that the energy deposited within the cascade region may be sufficient to induce a liquid-like state. The lifetime of this so called thermal spike phase appears to significantly affect the probability of a displacement cascade producing a vacancy type dislocation loop. Long thermal spike lifetimes are thought to increase the probability for vacancy loop formation. The present work examines the influence of the melting point and electron-phonon coupling on the probability for loop formation in a series of Cu-Ni alloys. The alloys investigated exhibit complete solid solubility across the full composition range and the constituent elements are of similar mass, reducing the influence of collisional factors on the observed microstructure. The method of Flynn and Averback has been used to calculate the degree of electron-phonon coupling