一、前言近二十年来,Ti-6Al-4V已成为国外航空工业中最广泛应用的合金,但以往主要用在发动机中所以不须考核断裂韧性。近年来由于将钛合金用于飞机骨架中,这样就突出了低应力脆断问题(即在弹性应力状态下发生灾难性的裂缝扩展问题)。因此,如何获得包括平面应变断裂韧性在内的最佳综合性能成为当务之急。众所周知,显微组织是影响断裂韧性的关键因素之一,因此在数年前洛克希德导弹与空间公司对Ti-6Al- I. INTRODUCTION In recent two decades, Ti-6Al-4V has become the most widely used alloy in the aviation industry in the world, but in the past, it was mainly used in engines so it did not need to evaluate the fracture toughness. In recent years, due to the titanium alloy used in the aircraft skeleton, thus highlighting the low-stress brittle fracture problem (that is, under the state of elastic stress in the crack propagation problem). Therefore, how to obtain the best comprehensive performance including the plane strain fracture toughness has become a top priority. As we all know, microstructure is one of the key factors affecting the fracture toughness, so a few years ago Lockheed missile and space company on the Ti-6Al-