Abstract
There is a long pending dilemma, “strong and brittle” materials that still remains unsolved in materials development based on the discipline of Materials Science Engineering (MSE). To solve the dilemma a new concept of “Grain Boundary Engineering” (GBE) was proposed by one of the authors in the early 1980s. In recent years, GBE for toughening of brittle materials has been challenged by several groups including ours, drawing an increasing interest of many researchers. Extensive works have been successfully performed in order to produce “strong and tough” polycrystalline materials. In this article, we present the current progress in GBE, to confirm the situation to what extent the problem has been solved. We pay our special attention to two kinds of brittle materials, i.e. intrinsically and extrinsically brittle ones. These brittle materials can be transformed into “strong and tough” materials by GBE through controlling intergranular fracture under static and cyclic stressing fatigue conditions.

Key words
brittle materials, Grain Boundary Engineering (GBE), intergranular fracture, grain boundary microstructure, strong and tough materials

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