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Approximately 2 pm thick CrN and CrAlN coatings were synthesized on silicon and high speed steel substrate by multi-arc ion plating technology.The nanoindentation techniques,energy dispersive X-ray(EDX) analysis,scanning electron microscopy and X-ray diffraction were used to investigate the mechanical property and microstructure of the coatings.The XRD data showed that the CrN and CrAlN coatings exhibited Bl NaCl structure.Nanoindentation measurements showed that as-deposited CrN and CrAlN coatings exhibited a hardness of 21 and 32 GPa respectively.The thermal stability of the coatings was studied by heating the coatings in air from 500 to 900 ℃.The structural changes as a result of heating were studied using X-ray diffraction.The XRD data revealed that the CrAlN coatings were stable up to 800 ℃ and got oxidized at 900℃.On the other hand,the CrN coatings were stable up to 700℃ and got completely oxidized at 800℃.Nanoindentation measurements performed on the coatings after heat treament showed that CrN coatings retained a hardness of 13GPa at 700℃ and CrAlN coatings retained hardness as high as 20GPa upon annealing at 800 ℃.The results of tribological examination shows that the ternary CrAIN coating performs better than binary CrN as well as the conventional hard chromium plating.