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

在恒定应力作用下，压头在试样表面产生浅压痕，压痕深度随时间增加。这就是所谓的“压痕蠕变试验”，其原理与热硬度测量类似。然而，随时间变化的硬度与蠕变速率的关系并不好，因为当硬度随时间降低时，应力也会降低，不能达到稳定状态。然而，当使用平端圆柱作为压头时，可以获得稳态压头速度，该速度取决于温度、应力和压头尺寸。通过分析稳态压痕速度，可以推导出试件的蠕变特性。首先将该方法应用于Al和Al-5% mg合金的蠕变研究。蠕变活化和n值与常规蠕变试验结果吻合较好，是一种简便的蠕变试验方法。通过了解压头尺寸对稳态压痕速度的影响，可以分离蠕变机理。在< β > CuZn的情况下，由于稳态速度与压头半径成正比，压头蠕变是由位错的产生和运动引起的。最后应用该方法对<Ni_2AlTi>和<Co_2AlTi>金属间化合物的蠕变进行了研究，这两种化合物有望成为良好的抗氧化表面保护材料。这些化合物具有较高的蠕变强度，其强度是NiAl和CoAl耐火化合物的3倍。

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.