Crystallization Temperature and Hardness of New Type Cobalt-Based Amorphous Alloys

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Abstract
Amorphous alloys of a new type with excellent thermal stability and hardness have been found in extensive composition ranges in the alloy systems of cobalt-VIb group transition metals-carbon such as Co–Cr–C, Co–Mo–C, Co–W–C, Co–Cr–Mo-C, Co–Cr–W–C, Co–Mo–W–C and Co–Cr–Mo–W–C by a rapid quenching technique. Vickers hardness of these alloys increases with increase of chromium, molybdenum and tungsten and its maximum attains the value as high as about 1450 DPN. Also, the amorphous structure of these alloys is thermally more stable as compared with the other cobalt-based amorphous alloys reported so far. The highest crystallization temperature is 1042 K. The effectiveness of alloying elements on the increase in hardness and crystallization temperature becomes large in the order of chromium, molybdenum and tungsten. Such effects seem to take place by a stronger bonding force between alloying elements and carbon as compared with that between cobalt and carbon. These alloys are attractive materials because of their high hardness values with good ductility and high thermal stability.