纯钛搅拌摩擦焊晶粒细化机制

通过搅拌摩擦焊实现了5 mm纯钛的可靠连接，并对焊接接头组织进行了细致研究。通过光学、扫描电子显微镜和透射电子显微镜对纯钛搅拌摩擦焊组织进行了精细表征，对焊接过程中的再结晶机制进行了研究。结果表明：采用搅拌摩擦焊可以得到成型良好，组织致密的焊缝；焊缝组织可以分为焊核区( NZ)、热机影响区( TMAZ)、热影响区( HAZ)和母材区( BM)；根据各区组织形态和结构特点对纯钛搅拌摩擦焊动态再结晶过程进行了分析，揭示了纯钛搅拌摩擦焊焊缝细化机制；钛的层错能较大，搅拌摩擦产生的位错不能完全分解，遇到阻碍时，只能通过滑移和攀移继续运动，在多次搅拌摩擦作用下，位错缠结堆积，位错密度不断上升，产生新的晶界，从而形成细小晶粒，实现晶粒细化。

Mechanism of Grain Refinement of Pure Titanium by Friction Stir Welding

Reliable connection of 5 mm pure titanium was achieved by friction stir welding, and the microstructure of the welded joint was studied by optical microscopy( OM) , scanning electron microscopy( SEM) and transmission electron microscopy( TEM) . The re-sults show that the welded area can be divided into the weld nugget zone, thermo-mechanically affected zone, heat affected zone and base metal. According to the structure of each district, the dynamic recrystallization process of pure titanium during friction stir welding was analyzed. Because of high stacking fault energy, dislocations generated by friction stir of titanium cannot be completely decom-posed. When there is a hindrance, it can continue to move only through slip and climb. By the effect of friction stir repeatedly, the dislocation tangles are accumulated and piled up, so the dislocation density continuously increases, which will produce new grain boundaries and form fine grains, and then the grain refinement is achieved.