硼离子注入对多晶Ni力学性能及微观结构的影响

EFFECTS OF B^+ IMPLANTATION ON MECHANICAL PROPERTIES AND MICROSTRUCTURE OF POLYCRYSTALLINE Ni

用能量为50keV,剂量为3×10^(17)ions/cm_2的B^+注入多晶Ni,通过力学性能实验研究了多晶Ni注入前后表面硬度和疲劳性能的变化,以及多晶Ni表面层注入和疲劳前后化学成分、滑移特征、裂纹萌生、断裂方式和微观结构的变化。结果表明,B^+注入多晶Ni后,表面区域形成一个不同组织结构的由Ni-B非晶、Ni_3B和Ni_4B_3第二相以及辐照损伤组成的多层次的注入层,提高了多晶Ni的表面硬度,并使其疲劳极限提高16％。探讨了B^+注入影响多晶Ni疲劳极限的几种可能机制。

Polycrystalline Ni was implanted with 50 keV B^+ to a dose of 3×10^(17) ions/cm^2 at room temperature. The specimens with and without B^+ implantation were tested in micro-hardness and load or unload tensile fatigue under stress-controlled condition. The surface layer structure was observed with IMA, SEM and TEM before and after implantation and/or fatigue. The B^+ implanted surface region consists of amorphous Ni-B phase, Ni_3B and Ni_4B_3 second phases, and damage structure. The corresponding measurements indicate that both surface micro-hardness and endurance limit of the specimens have increased after implantation. Compared with unimplanted specimens under the same fatigue condition, all implanted specimens show the smallest overall fatigue damage. The cyclic loading at room temperature can lead to migration of implanted B^+ out of surface layer and recrysatallization of amorphous Ni-B phase. Possible strengthening mechanisms for these experimental results were discussed.