镍锗尖晶石位错域的高温蠕变实验研究

利用人工合成的多晶材料研究了镍锗尖晶石在位错域的高温蠕变性质.多晶材料的颗粒尺寸约8μm.单轴压缩试件为圆柱状,使用气体介质围压筒.常压蠕变试验过程中,围压为300MPa,温度为1373-1523K,应力在55-330MPa范围内.从实验结果得出了镍锗尖晶石在位错域的流动律,应力指数n=29±01,表明流动的微观机制为位错蠕变.与其他尖晶石进行对比可以发现一个力学同构群,虽然在正尖晶石和反尖晶石之间存在一定的差异.在位错蠕变域,尖晶石与橄榄石归一化的强度类似.由于尖晶石的剪切模量比橄榄石高50%,其实际强度也比橄榄石高.将橄榄石和尖晶石的蠕变数据外推到地球内部条件时,由于其高应力指数,橄榄石则有可能比尖晶石的强度高.

HIGH-TEMPERATURE DISLOCATION CREEP IN Ni2GeO4 SPINEL

HTWTRheological property of upper mantle materials is a critical factor for us to understand the geodynamic process of the earth. However, it is still very hard to perform the deformation experiment on earth material with high precision. Therefore the analogue material was used to model the deformation behavior of the earth material. In this study, high-temperature dislocation creep behavior in Ni 2GeO 4 spinel was investigated using synthetic polycrystalline aggregates with average grain-size about 8 micron. Cylindrical samples were deformed at constant load in a gas-medium apparatus at temperatures ranging from 1373 K to 1523 K and stresses ranging from 55 to 330 MPa. The deformation mechanism was identified, characterized by the flow law with the stress exponent: n=2.9±0.1. The flow law suggests deformation by dislocation creep. A comparison with other spinels shows that an isomechanical group can be defined for spinels, although some differences between normal and inverse spinels can be identified. When creep data for olivine and spinel are normalized, their normalized strengths are comparable. The actural flow stress of spinel is higher than that of olivine because of higher shear modulus. Spinel （ringwoodite） has a similar strength to olivine in the dislocation creep regime. When extrapolated to Earth-like conditions, olivine （n≈3.5） may be stronger than spinel （n≈3） due to it's higher stress exponent. HTH