Anisotropic growth in the olivine-spinel transformation of Mg2GeO4 under nonhydrostatic stress
Anisotropic growth in the olivine-spinel transformation of Mg2GeO4 under nonhydrostatic stress
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非静水应力下 Mg2GeO4 橄榄石-尖晶石转变的各向异性生长
DOI：
10.1016/0040-1951(84)90241-5
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发表时间：
1984
期刊：
影响因子：
2.9
通讯作者：
R. Coe
中科院分区：
文献类型：
--
作者：
P. Vaughan;Harry W. Greeen;R. Coe
mg2geo4中的橄榄石-尖晶石相变不是通过马氏体机制发生的。从格里格斯型固体介质变形仪中变形的样品中得到的证据是：1。(1)橄榄石相缺乏与马氏体机制相关的微观结构特征。(2)马氏体机制预测的两相取向关系不存在，相对取向也不存在明显的一致性。(3)对相变试样施加差应力导致尖晶石相的各向异性生长速率，表明生长受外部控制而非晶体学控制。尖晶石相的各向异性生长导致残余橄榄石相晶粒在与最大主压应力方向垂直的平面上伸长。通过对残余橄榄石晶粒的测量，确定尖晶石生长速率的速度比为1.7−0.7+5.4。在应力作用下，试样的相间晶界为尖晶石尖状指状，钝端由橄榄石细穗隔开。等静力变形的样品没有表现出这种特征，进一步证实了尖晶石的各向异性生长。尖晶石的择优生长符合非静水应力作用下的相变理论。根据这一理论预测的尖晶石手指形状除了钝端外，与观察到的形状基本一致。这种差异可能是由于这里没有考虑到的表面能，或者是由于施加宏观应力的局部偏差。
The olivine-spinel phase transformation in Mg2GeO4does not occur by a martensitic mechanism. The evidence, from samples transformed in a Griggs-type solid medium deformation apparatus, are:1.(1) lack of microstructural features in the olivine phase which can be specifically associated with a martensitic mechanism2.(2) the orientation relationship between the two phases that is predicted by the martensitic mechanism does not occur nor is there any apparent consistency of relative orientations3.(3) application of a differential stress to the transforming sample resulted in an anisotropic growth rate for the spinel phase indicating that growth was externally controlled rather than crystallographically controlled.Anisotropic growth of the spinel phase results in elongation of the residual olivine phase grains in the plane normal to the direction of maximum principal compressive stress. A velocity ratio of 1.7−0.7+5.4has been determined for the growth rate of the spinel from measurements on residual olivine grains. The interphase grain boundary in samples transformed under stress has cusp-shaped fingers of spinel with a blunt end separated by thin spikes of olivine. Samples transformed isostatically do not exhibit this feature providing further confirmation of anisotropic growth of the spinel. The preferred growth of the spinel is consistent with a theory of phase transformation under nonhydrostatic stress. The predicted spinel finger shape based on this theory is generally consistent with observed shapes except for the blunt end. The discrepancy may be due to surface energy which has not been considered here, or to local deviations of the applied macroscopic stress.