The characteristics of impression creep test and its application to intermetallic compounds.

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Under a constant stress, the indenter makes a shallow impression on the surface of the specimen, and the impression depth increases with time. This is called "Impression Creep Tests" which is, in principle, similar to the hot hardness measurements. The time dependent hardness, however, has not been related well to creep rate since when the hardness decreases with time, the stress decreases also and steady state can not be achieved. However, when a circular cylinder of flat end is used as an indenter, a steady state impression velocity can be obtained and it depends on temperature, stress and indenter size. Creep properties of specimens can be deduced analyzing the steady state impression velocities. First we applied this method to the investigation of creep in Al and Al-5%Mg alloys. The activation of creep and n value were in good agreement with those of conventional creep tests and therefore this method was found to be useful as a simple creep test. The creep mechanism can be separated by knowing indenter size effects on the steady state impression velocity. In the case of <beta> CuZn the impression creep was by generation and motion of dislocation since the steady state velocity was proportional to the indenter radius. Finally we applied this method to investigate the creep of <Ni_2AlTi> and <Co_2AlTi> intermetallic compounds which were expected as a good oxidation-resistance surface protective material. These compounds were found to have a high creep strength which was three times stronger than that of NiAl and CoAl refractory compounds.