非致密钨闭塞式背压变通道转角双向镦挤非平衡晶界形成及其对脆性的影响机理研究

Low temperature embrittlement, recrystallization embrittlement and irradiation embrittlement are the cruxes restricting the engineering applications of tungsten and its alloys. Severe plastic deformation (SPD) is an effective process of fabricating ultra-fine grained material to improve the embrittlement of tungsten. But the traditional severe plastic deformation technologies are not suitable for the porous tungsten with low plasticity and high strength. Based on the theory that severe shear deformation with high hydrostatic pressure can improve plasticity and refine grain, a new process which has good process plasticity and severe shear deformation, blocking varietal channel angular bi-directional upsetting-extruding with back pressure, is created by introducing blocking forging into traditional equal channel angular extrusion in this study based on floating die set to fabricate superior high density tungsten with ultra-fine grains from the porous tungsten material in relatively low temperature. Theoretical analysis, experimental research and multi-scale computer simulation are carried out to deeply investigate the deformation behaviour and the microstructure evolution of tungsten during the process such as dislocations, grain boundaries, impurities and vacancies．The mechanisms of both the formation of non-equilibrium grain boundaries and the effects on brittleness are revealed．Otherwise multi-objective optimization of key process parameters is performed to realize the optimum control of microstructure and properties. It has important theoretical and practical significances for improving the brittleness and promoting the industrial applications for tungsten.

低温脆性、再结晶脆性和辐照脆性是制约钨及其合金工程化应用的关键。大塑性变形工艺制备超细晶材料是改善钨的脆性的有效手段。但传统大塑性变形工艺在低塑性、高强度非致密钨的应用上均受到不同程度的限制。本研究基于具有高静水压力的大剪切变形工艺提高塑性、细化晶粒的原理，将闭塞式锻造技术引入传统等通道转角挤压工艺，提出一种基于浮动模架的工艺塑性好、剪切变形能力强的闭塞式背压变通道转角双向镦挤工艺，实现在相对较低的温度下性能优异的大尺寸块体高致密超细晶钨的制备。将理论分析、试验研究和多尺度计算机模拟相结合，深入分析钨在该大变形过程中的变形细化以及位错、晶界、杂质原子和空位等微观组织演变规律，揭示非平衡大角度晶界超细晶的形成及其对脆性的影响机理，并通过对主要工艺因素的多目标优化实现组织和性能的最优化控制。这对改善钨的脆性、促进其工程化应用具有重要的理论意义和实际价值。

聚变堆偏滤器等构件的极端服役条件对难熔金属钨提出了严苛的性能要求。大塑性变形工艺制备超细晶材料是改善非致密钨的低温脆性、再结晶脆性和辐照脆性的有效手段。采用一种用于难变形难熔金属的新型大塑性变形工艺，即闭塞式背压变通道转角双向镦挤工艺，实现了以粉末烧结体为原材料的大尺寸高性能致密化难熔金属钨超细晶块体材料的制备。通过对大塑性变形过程中晶粒剪切/动态转变细化、非平衡晶界形成以及相转变等组织演变进行理论分析、实验研究和宏微观多尺度模拟，阐明了由晶内滑移发展到晶界滑移的变形机理，非平衡大角度晶界超细晶形成机理，高能缺陷演变和形变诱导相变的微观物理机理，以及强韧性、热稳定性等服役性能的提升机理。这些研究为采用大塑性变形法制备大尺寸高性能致密化超细晶难熔金属材料提供必要的理论基础和实验依据，具有实际意义和科学价值。