A Study of Residual Strain in a K 2O.6TiO 2W/Al Composite by Using Convergent Beam Electron Diffraction

Abstract

Metal-matrix composites (MMCs) offer many advantages in applications where low density, high strength and high stiffness are of prime concern. Whisker-reinforced MMCs offer the additional advantage of being machinable and workable. Potassium titanate whisker reinforced metallic matrix composite is a kind of newly developed materials. In the present paper, investigation on the interfacial residual strain in a K{sub 2}O.6TiO{sub 2}/Al composite in terms of the shifts of HOLZ lines is reported. To avoid the problem mentioned above in fitting the experimental HOLZ line patterns, the authors proposed a method to reduce the number of the independent changes of lattice parameters. Usually, when the electron probe is located very close to the interface, the HOLZ lines are split, and the positions of the HOLZ lines can hardly be measured. When the electron pore is slightly farther away from the interface, the HOLZ lines become relatively sharp, and the positions of the HOLZ lines are recognizable. In such a case, the lattice strain becomes approximately uniform with depth. Since the thickness of the TEM specimen is very small compared with the other two dimensions of the sample, and there are no external forces acting on the surfaces of the sample, the planemore » stress approximation can be used. With this approximation, the number of the independent components of the strain tensor is reduced from 6 to 3. The strain tensor in crystal coordinate system can be expressed with the changes of lattice parameters when the strain is less than 10{sup {minus}2}. Hence, the number of the independent changes of lattice parameters is reduced to 3 and the unique fit to the experimental HOLZ line pattern can be obtained. The experimental results and the fitting procedure are described in the present paper.« less