Ni20Cr合金表面离子注入钇后氧化层的微观结构与氧化机制

MICROSTRUCTURE OF OXIDE SCALE AND OXIDATION MECHANISM OF Y^+ IMPLANTED ALLOY Ni20Cr

用SEM／EDS，XRD,TEM／EDS等对1000℃下的Ni20Cr合金及其离子注Y（剂量分别为1×1015，2×1016和1×1017ions／cm2）后的氧化膜表面形貌、微观结构和氧化产物进行观测分析，确认氧化膜由具有较大晶粒尺寸的NiO，NiCr2O4尖晶石和较小晶粒尺寸的Cr2O3氧化物组成，且在部分NiO三角晶界处发现有空洞产生，注入Y剂量大于2×1016ions／cm2后，Cr的氧化产物的体积分数明显增多，并在其中探测到Y，它大多以含Y的氧化物小颗粒存在于Cr2O3氧化物层内，根据实验结果，认为在氧化初始，Y优先氧化形成细小的氧化物颗粒（10—20nm），这些小颗粒在随后的氧化过程中，一方面促进Cr2O3氧化物的形核和生长，另一方面通过自身微量溶解产生Y3＋并向氧化膜晶界偏聚，这不仅阻挡Cr3＋沿晶界的短路扩散，而且增强了氧化膜晶粒间的粘结力，进而降低氧化速率，提高了氧化膜的力学性能。

The surface morphologies and microstructures as well as phase compositions of scale on the alloy Ni20Cr and the alloy implanted by Y+ (with the dose of 1×1O15,2×1016 and 1×1017 Y/ cm2 respectively) oxidized in air at 1000℃ have been investigated by means of SEM / EDS, XRD and TEM / EDS. It was found that all the scale of alloy Ni20Cr with and without yttrium implantation were composed of larger grained NiO, NiCr2O4 and finer grained Cr2O3, and among of which small pores were created at the triangular junctions of grain boundaries of NiO. The implanted yttrium ions over 2×1016/cm2 increased the volume fraction of Cr-containing oxide, in which yttrium, most of which formed small Y-containing oxide particles, was detected. According to the experimental results, it was believed that in the initial oxidation stage yttrium oxidized in preference to alloy elements and formed fine oxide particles (10-20nm), and sequentially the particles may not only promote the nucleation and growth for Cr2O3 also produce Y ions segregated to its grain boundaries due to the partial dissolution of the particles itselves, the latter was beneficial to decrease the scale growth rate as well as improve its mechanical properties for the reason that segragated Y ions may inhibit the Cr3+ out-diffusion along 'short-circuit' and enhance the cohesion between oxide grains.