【摘要】 等径角挤压（equal channel angular pressing, ECAP）因可制备出超细晶材料而受到界内广泛关注。其制备出块体超细晶材料具有优异的力学性能与耐腐蚀性能，目前已在航空航天、生物医疗、机械电子等领域得到率先应用，成为国内外材料学者研究的热点。然而，ECAP技术在发展和应用过程中仍然受到多重限制。对ECAP工艺进行优化与改进已成为发展趋势。初期，诸多学者通过实验研究证明：新型ECAP可达到“一次挤压，多次应变”的效果，晶粒细化更加明显，可制备出力学性能优异的材料。近年相关学者采用有限元模拟方法，探究新型ECAP技术的影响因素，从而对生产进行指导。本文评述了近年来国内外新型ECAP制备超细晶材料相关研究进展，从工艺原理出发，将新型ECAP工艺分为工艺优化与模具改进两大类，重点对7种不同新型ECAP工艺及研究现状进行归纳总结，对不同ECAP工艺后超细晶材料的显微组织、力学性能进行深入分析，最后对新型ECAP制备超细晶材料过程中存在的问题与今后的研究方向进行总结与展望，以期为开发晶粒细化效果更佳、生产效率更高的剧烈塑性变形技术提供参考。更多还原

【Abstract】 Equal channel angular pressing(ECAP) has received a lot of attention in the field due to its ability to produce ultrafine grained(UFG) materials. The advantages of ECAP deformation: firstly, the deformation does not change the cross-sectional size of the specimen and can be extruded in multiple passes. Secondly, the material loss is small and the utilization rate is high after ECAP. Finally, the block ultrafine grained material has excellent mechanical properties and corrosion resistance prepared by ECAP. The ultrafine grained materials have been applied in aerospace, biomedical, mechanical and electronic fields. Therefore, it becomes a hot spot of research for domestic and international material scholars. ECAP is a violent plastic deformation method to achieve ultrafine grained materials by deforming the material at the corner of the mold. The main influencing factors of ECAP deformation are extrusion pass, path, speed, temperature and other process parameters as well as die parameters. ECAP grain refinement can be divided into three stages. Firstly, coarse grains are elongated into slats along the shear direction to form sub-grains. Secondly, annihilation of small-angle grains occurs at grain boundaries and rotation of subgrains leads to an increase in orientation difference. Eventually, large-angle equiaxed grains appear at the grain boundaries. As the orientation difference continues to increase, the volume fraction of grains with large angular grain boundaries increases significantly. Grain can be refined to submicron or even nanometer level. However, there are some problems in the development and application of ECAP technology. Firstly, it is a problem of punch off-loading in the ECAP process. This problem will eventually result in uneven grain refinement of the specimen. Secondly, the inner corners of the dies are worn severely after repeated use, resulting in uneven deformation of the specimens. Thirdly, the size of ECAP specimen is limited, with the majority of specimens being only 150 mm in length, and it is also one of the most important reasons that limits the wider application of ECAP. Finally, ECAP needs to be completed under a large hydraulic press, which puts forward higher requirements for equipment. Therefore, the optimization and improvement of ECAP processes has become a development trend. The integration of ECAP technology with mass production has become a pressing issue now. In initial stage, many scholars have demonstrated that the new ECAP can achieve the effect of "one compression, multiple strain" through experimental studies, which can prepare materials with more ultrafine grains and excellent mechanical properties. In recent years, relevant scholars had adopted finite element simulation methods to study the influencing factors of new ECAP technology, which could provide a guidance for practical production. The investigation status of the preparation for ultrafine grained materials by ECAP in recent years was reviewed comprehensively. From the process principle, the new ECAP processes were divided into two categories: process optimization and die improvement. The process optimization includes extrusion-equal channel angular pressing(Ex-ECAP), cryogenic treatment-equal channel angular pressing(CT-ECAP) and ultrasonic assisted-equal channel angular pressing(UA-ECAP), mold improvements include rotary die-equal channel angular pressing(RD-ECAP), equal channel double angular pressing(ECDAP), double-equal channel double angular pressing(D-ECAP) and incremental-equal channel double angular pressing(I-ECAP). The research status of seven new ECAP processes was mainly summarized. The microstructure and mechanical properties of ultrafine grained materials after different ECAP processes were analyzed. The new ECAP was compared with the conventional ECAP process and the reasons why the new ECAP process optimized the overall performance of the material are analyzed. These new processes overcame the limitations of conventional ECAP deformation in terms of microstructure uniformity, grain refinement and sample size, and it had a great importance to the promotion and application of ECAP. Finally, the problems in the preparation of ultrafine grained materials by new ECAP and the future research directions were summarized and prospected. The new ECAP process of mold losses still existed. The ultrafine grained materials prepared by the new ECAP were mainly magnesium alloy, aluminum alloy and copper alloy. How to use the new ECAP to prepare ultrafine grained high-strength alloys remained to be studied. The channel friction coefficient tended to be idealized and the theoretical extrusion uniformity had some deviation from the actual value. At present, there were few experimental data and analysis results of new ECAP. In particular, new ECAP and conventional ECAP had few comparisons, which needed to be further strengthened and studied. The research idea of combining experiments and simulations would become an important method. The simulation was used to predict the manufacturing practice, and then the simulation was proven and expanded by using test. The mechanism of severe plastic deformation could be clearly revealed by studying the whole process of the new ECAP, and it could provide reference for the development of severe plastic deformation technology for better grain refinement and higher production efficiency.更多还原