Nature of the Microstructure and Interface Boundary Formation in Directionally Solidified Ceramic Boride Composites.

摘要

The goal of the present work has been the revealing of regularities/ patterns of structure formation of self-reinforced composite materials. For this was supposed to study the eutectic morphology transformation from fiber-like to platelet-like one with the increase of reinforcing phase content under conditions of directional crystallization. LaB6 (Tix,Cr1-x)B2 system has been chosen as the object for investigation on the assumption that of all previously studied eutectics the systems with titanium and chromium had minimal and maximal content of diboride phase, respectively. At the same time, on the initiative/suggestion of the project partner investigation of (LaxCe1-x)B6 and (Tix,Cr1-x)B2 single crystal growth has been carried out. Investigation of the directionally solidified LaB6 (Tix,Cr1-x)B2 composites fully confirmed the current theoretical understanding of the transition of the eutectic morphology with increasing Cr content, ie with the increase of the reinforcing phase volume. New results were obtained when attempting growing (Tix,Cr1-x)B2 single crystals: the existence of extreme melting temperature was discovered, which allowed to grow single crystals with x = 0, 0.2, 0.8 and 1. In order to grow single crystals with = 0,4-0.6 it is necessary to modernize the outfit. Simultaneously, in consultation with the partner investigation of LaB6 (Tix,Zr1-x)B2 system were continued. New studies show that even at =0.1 there is a significant increase in crack propagation resistance compared with x = 0. Investigations carried out by means of HRTEM and EBSD showed that the rotation the growth axis occurs at x = 0.25, and the crack propagation is significantly influenced by the stress field in the matrix caused by the influence of the reinforcing phase as well as the interaction energy on the phases interface. We can assume that it is the latter that determines the conditions of nucleation of eutectic colonies crystallization.