摘要
使用Nd^(3+):YAG脉冲激光器产生的脉冲能量为12.5 J,频率10 Hz,波长1064 nm的脉冲激光研究了强激光冲击下的Ti-6Al-4V合金表面响应,用SEM和TEM及IFFT方法分析了激光冲击强化造成的微结构响应.结果表明,激光冲击可使Ti -6Al- 4V合金表面硬度增加80%以上,残余压应力达到500 MPa以上.在激光冲击产生的超高能量和超高应变率作用下,具有α/β两相结构的Ti-6Al-4V合金的激光冲击强化效应表现出明显的择优倾向.在较低冲击能量下,β相优先获得形变强化;在较高的冲击能量下,α和β相才能同时获得相当的形变强化,且优先强化相出现过饱和强化现象.位错增殖是冲击强化的主要微观机制,增殖形式多为定向发射和位错偶极子,α和β相则以半共格方式协调形变;在冲击强化区域内呈现应变屏蔽现象,其源于形变缺陷的自组织,是材料在激光冲击形变时的微观约束条件和激光冲击单点累积形变方式以及α/β两相的相间强度与结构差异共同作用所致.
Laser shock processing （LSP） is an effective and promising technology for improving surface mechanical properties of metals. The study of the strain behavior of individual phase of advanced engineering materials with polycrystalline and dual-phase microstructures subjected to laser shock processing is an important emerging frontier, which facilitates understanding of the relative roles of intrinsic and extrinsic attributes of microstructure upon strengthening, compared with the strengthening process of metals at the macroscopic scale of deformation. The influence of LSP on the surface layer properties and microstructures of a Ti-6Al-4V alloy has been investigated focusing on the microstructure response of the surface layer of the alloy by means of high efficient Nd^3＋ ： YAG ceramic pulse laser with 12.5 J per pulse at 1064 nm and 10 Hz repetition rate. The microstructures response of the alloy are analyzed and characterized with by FE-SEM, TEM and the inverse fast fourier transform （IFFT） algorithm, respectively. The experimental results show that the surface hardness of the laser shocked Ti-6Al-4V alloy can increase 80%, and the compressive residual stress can be over 500 MPa. Obvious preference effect between a and 13 phase is discovered upon strengthening of the alloy under the conditions of the ultra high energy and ultra-high strain rate of laser shock. With the lower shock energy, the deformation strengthening of β phase takes precedence over the other; as the shock energy increasing, both a and β are strengthened simultaneously, whereas, the previously strengthened β phase shows saturated strengthening effect. The results also reveal that dislocation multiplication is the main strengthen mechanism in the laser shocked region, including oriented dis- location projection and dislocation dipoles in the α phase with hcp crystal lattice, but diversified configurations, such as edge-dislocation, extended dislocations and dislocation dipoles presenting in the β phase with bcc crystal lattice. The semi coherent interface with misfit dislocations between α and β phase boundary is discovered, which plays a synergetic role upon deformation strengthening. Additionally, the strain screening manifestation within the laser shocked region is also discussed, which is regarded as a kind of self-organization phenomenon of deformation defects, and can be attributed to the synthetic effect of the confinement conditions upon laser shocking, the accumulative strengthening mode of single spot laser shocking process and the differences of strength and crystalline structure between the lamellar α and β phases.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第9期1116-1122,共7页
Acta Metallurgica Sinica
基金
国家自然科学基金项目50735001.50905080和51105179资助~~
关键词
激光冲击
材料响应
钛合金
表面强化
微结构
laser shock processing, material response, Ti-based alloy, surface strengthening, microstructure
作者简介
罗新民，男，1951年生，教授
