Measurement of residual strain of unidirectionally eutectic solidified ultrahigh temperature composite Al2O3/Y3Al5O12(YAG) by neutron diffraction method

This work is the first measurement of the residual strain of new unidirectionally eutectic solidified two phases single crystal ultrahigh temperature materials Al2O3/Y3Al5O12 (YAG) by a neutron diffraction method. The results showed that the amounts of strain of YAG phase were -0.73 x 10-3, -1.58 x 10-3 and -0.89 x 10-3 for the reflection (444), (521) and (431), respectively, under the condition of applying the spacing of lattice planes of sintered YAG to the reference value of distortionless state. They were all compressional states. On the other hand, we could not obtain the diffraction peak data set of Al2O3 phase to determine the amount of strain. One of the remarkable diffraction peaks of composite was an overlapping peak of two peaks such as the sintered Al2O3 and sintered YAG phase. This result showed that the spacing of lattice planes of two single crystal phases became equal after powder Al2O3 and Y2O3 (mol ratio 82/18) were melted and crystallized by the unidirectional solidification method. It corresponded to the results of HRTEM image of grain boundary of Al2O3 phase and YAG phase in the composite. The effective spacing of lattice planes corresponded to this overlapping peak was agreed with the estimated results used mol weight percent of two phases. The residual strain state formed in two phases single crystal composite materials Al2O3/Y3Al5O12 was very different from the strain state originated from ordinary polycrystal composite. The modeling of strain state of this sample needs a new method different from the micromechanical models. (S.Y.)