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用7075-T76航空铝合金进行激光冲击表层改性实验,借助SEM和TEM分析冲击层的微观结构、表层获得的非晶/纳米晶复合材料高熵合金层的演变过程和成因及力学性能与抗腐蚀性能.结果表明,激光冲击的超高能量、超快过程导致的绝热剪切热效应诱导材料表层合金体系发生熵增效应及重新配分.合金体系混合熵的增大促进组元间的混乱度增高,弱化了杂质原子的不良作用.激光冲击提供的外场能量促进熵的增量转化为合金中形成非晶态组织所需Gibbs自由能ΔGconf的降低.多组元铝合金在多次激光冲击强大的外场能量作用过程中,各组元间按照Boltzmann定律自发重组,动态析出的纳米晶组织则发挥过程中体系不平衡度的协调作用,使所获高熵非晶组织更符合Boltzmann关系的热力学要求.通过热力学自调整和微结构重组,激光冲击层最终由非晶/纳米晶颗粒复合组成.同时,激光冲击的超高应变率诱导的强烈微观应力使时效析出相发生整体塑性形变,产生平行分布的形变孪晶,协同吸收激光冲击能量.由于晶界强化消失和位错密度降低,激光冲击主要体现为结构重组效应.激光冲击表层的硬度在单次激光冲击后有所提高,随冲击次数增加,硬度逐步与基体硬度持平.激光冲击造成的强烈形变可使铝合金表层内纳米晶尺寸减小至2~3 nm.非晶态消除了在第二相周围的原电池腐蚀,从而使航空铝合金7075-T76表面激光冲击所获非晶/纳米晶复合材料表层的抗腐蚀性能明显改善.
The laser shock surface modification experiment was carried out by using 7075-T76 aviation aluminum alloy. The microstructure of the impact layer was analyzed by SEM and TEM. The evolution process, genesis and mechanical properties and resistance of the high-entropy alloy layer of the amorphous / nanocrystalline composite The results show that the adiabatic shear thermal effect induced by ultra-high energy and ultra-fast laser shock induces the entropy-increasing effect and re-partitioning of the surface alloying system.Improvement of the mixing entropy increases the chaos between the components, , Weakened the adverse effects of impurity atoms.The external field energy provided by laser shocks promotes the increment of entropy to reduce the Gibbs free energy ΔGconf required for the formation of amorphous structures in the alloy.Multiple aluminum elements in a number of laser shock strong In the process of external field energy, the components are spontaneously recombined according to the Boltzmann law, and the dynamically precipitated nanocrystalline structure plays a coordinating role in the imbalance of the system, and the obtained high entropy amorphous structure more meets the Boltzmann relationship thermodynamic requirements. Through thermodynamic self-tuning and microstructure recombination, the laser impact layer is finally composed of amorphous / nanocrystalline particles. At the same time, laser shock The intense micro-stress induced by the ultra-high strain rate causes the whole plastic deformation of the precipitated phase, resulting in twins parallel to the deformation and synergistically absorbing the laser shock energy. Due to the disappearance of the grain boundary strengthening and the decrease of the dislocation density, the laser shock mainly manifests as structural recombination The hardness of laser shocked surface layer increased after single laser shock, and the hardness increased gradually with the hardness of the substrate with the increase of the impact frequency.The intense deformation caused by laser shock could reduce the size of nano-crystal in the surface of aluminum alloy to 2 ~ 3 nm. The amorphous state eliminates the galvanic corrosion of the secondary battery around the second phase, so the corrosion resistance of the surface layer of the amorphous / nanocrystalline composite obtained by the laser shock on the surface of the aluminum alloy 7075-T76 is remarkably improved.