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

在恒定应力下，压头在试样表面产生浅压痕，压痕深度随时间增加。这被称为“压痕蠕变试验”，原则上与热硬度测量相似。然而，与时间相关的硬度与蠕变速率没有很好的相关性，因为当硬度随时间降低时，应力也降低，并且不能达到稳定状态。而采用平头圆柱作为压头时，则可以得到一个稳态压头速度，它取决于温度、应力和压头尺寸。通过对稳态压痕速度的分析，可以推断出试件的蠕变特性。首先，我们将这种方法应用于Al和Al-5%Mg合金的蠕变研究。蠕变激活和n值与常规蠕变试验结果吻合较好，因此，该方法可作为一种简单的蠕变试验方法。蠕变机制可以通过了解压头尺寸对稳态压印速度的影响来分离。在CuZn的情况下<beta>，压痕蠕变是由位错的产生和运动引起的，因为稳态速度与压头半径成正比。最后，我们将此方法应用于<Ni_2AlTi><Co_2AlTi>金属间化合物的蠕变研究，这是一种良好的抗氧化表面防护材料。发现这些化合物具有高蠕变强度，其比NiAl和CoAl耐火化合物的蠕变强度强三倍。

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.