Investigation on the crystallographic orientation relationships and interface atomic structures in an in-situ Ti₂AlN/TiAl composite

In this research work, 15 vol% Ti₂AlN particles reinforced TiAl alloy matrix composite was prepared by an in-situ reactive hot processing method using Ti, Al and TiN powders as raw materials. Transmission electron microscope (TEM) coupled with energy-dispersive spectroscopy (EDS) was utilized to investigate the morphology characteristics of Ti₂AlN particles. The crystallographic orientation relationships and interface atomic structures between various shaped Ti₂AlN particles and TiAl matrix were investigated by the means of selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The results show that four kinds of Ti₂AlN particles presented in the composite, which include vast majority of elliptical and polygonal Ti₂AlN particles with the sizes of 4 μm, few hexagonal Ti₂AlN particles with the sizes of 4 μm and small plate Ti₂AlN particles with the sizes of 0.4 μm. The elliptical and polygonal Ti₂AlN particles have no fixed crystallographic orientation relationship with TiAl matrix, the elliptical and polygonal Ti₂AlN/TiAl interfaces are incoherent interphase boundaries composed by many atomic-scale microfacets. The hexagonal and small plate Ti₂AlN particles have a fixed orientation relationship with TiAl matrix. Both the hexagonal and small plate Ti₂AlN particles have a ledge and terrace coherent interface with TiAl matrix.