[en] The surface composition and room temperature oxidation of atomically clean single crystal Ni-15%Cr(110) and polycrystalline Ni-23%Cr alloy have been studied using Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), Ion Scattering Spectroscopy (ISS) and Electron Stimulated Ion Desorption (ESID). It was found that Ni segregated preferentially to the surface of Ni-15%Cr(110) in vacuum at temperatures between 500 to 650 degree C, and the heat segregation was 2550 cal/mole. The surface region of the Ni-Cr alloy was depleted in Ni during Ar ion bombardment at temperatures above 200 degree C, which is an agreement with the model of preferential sputtering of Ni caused by radiation-enhanced surface segregation of Ni. But the subsurface region of room temperature sputtered Ni-Cr alloy was depleted in Cr. Possible causes for this observation were discussed