Ta-Ru and Mo-Ru alloy coatings with phases of intermetallic compounds are often used as protective coatings on die materials. After annealing under an oxygen containing atmosphere, the internal oxidation phenomenon resulted in the preferential oxidation of Ta or Mo in the coatings. This process created a phase separated structure consisting of continuous and alternative oxygen rich and deficient layers with a nano scale period beneath the free surface. The experiments in this study deposited Ta-Ru and Mo-Ru coatings with a Cr interlayer by direct current magnetron co-sputtering at 400 degrees C. Annealing treatments were conducted at 600 degrees C for short durations under controlled atmospheres consisting of 50 or 10,000 ppm oxygen with residual nitrogen or argon gas. The internal oxidation behavior in the initial stage was determined by evaluating the variations in crystalline structure, surface morphology and chemical composition. The laminated structure was examined by transmission electron microscopy. Results show distinct oxidation behaviors for Ta47Ru53 and Mo46Ru54 coatings. Internal oxidation phenomena appeared in Ta47Ru53 coatings annealed in both 50 and 10,000 ppm O-2 containing atmospheres. The Mo46Ru54 coatings exhibit external oxidation at 50 ppm O-2 containing atmosphere, and internal oxidation at 10,000 ppm O-2 containing atmosphere. Finally, this study proposes an internal oxidation mechanism for alloy coatings with an orientated structure. (C) 2011 Elsevier B.V All rights reserved.