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借助X射线衍射仪、透射电镜及显微硬度仪等先进仪器,研究了经超音速微粒轰击(SFPB)形变热处理Ti-6Al-4V合金表面自身纳米化晶粒尺寸演化及纳米化机制。研究结果表明:超音速微粒轰击使Ti-6Al-4V合金表面获得了纳米组织,并发生显著的加工硬化,表面显微硬度比基体硬度提高了1倍多;随着SFPB处理时间的延长,纳米结构层厚度不断增加,晶粒尺寸逐步细化,当SFPB处理30 min后晶粒尺寸趋于稳定,在表层形成了晶粒尺寸约为20 nm具有随机取向的纳米等轴晶。Ti-6Al-4V合金表面自身纳米化是由于位错运动、孪晶的形成及交割共同作用的结果;在多方向载荷的重复作用下,在塑性变形区产生了大量的由位错线和高密度位错缠结分割的位错胞,并在位错塞集处产生应力集中,进而形成孪晶;孪晶自身相互交割和位错的滑移相互协调,形成了细小的孪晶和胞状组织;晶胞组织转变为细小多边形亚晶;当孪晶尺寸细化到亚纳米级时,位错的滑移起主导作用,最终通过位错的湮灭和重组形成了具有随机取向的等轴状纳米晶粒。
With the help of XRD, TEM and microhardness tester, the nano-scale grain size evolution and nano-scale mechanism of Ti-6Al-4V alloy surface treated by supersonic particle bombardment (SFPB) heat treatment were studied. The results show that supersonic particle bombardment makes the surface of Ti-6Al-4V alloy get nanostructures and undergoes significant work hardening. The surface microhardness is more than double that of the matrix; with the extension of SFPB processing time, The thickness of the structural layer increases continuously, and the grain size is gradually refined. When SFPB treatment for 30 min, the grain size tends to be stable, and a randomly oriented nano-equiaxed grain with a grain size of about 20 nm is formed on the surface. The self-nanocrystallization of Ti-6Al-4V alloy surface is the result of dislocation movement, twin formation and delivery interaction. Under the repeated action of multi-directional load, a large number of dislocation lines and high Density dislocations entangle the dislocated cells and generate stress concentration at the dislocations, forming twins. The twins themselves interact with each other and slip dislocations to form tiny twins and cells ; The unit cell structure transforms into small polygonal subgrains; when the twin size is subdivided to the sub-nano level, the slip of dislocation plays a dominant role, and finally the disordered annihilation and recombination form a randomly oriented equiaxed nano Grain.