Effect of dose rate and precipitates on irradiation damage structures

采用高压电子显微镜（HVEM）对SUS304不锈钢进行了2 × 10^<-3>、2.9 × 10^<-4>和1.7 × 10^<-4> dpa/sec三种不同剂量率的电子辐照，研究了剂量率和氦原子对SUS304不锈钢损伤结构的影响。试样由成分为Fe-18.2Cr-8.2Ni-1.3Mn的SUS304不锈钢制备。在1323K（固溶体处理）下热处理30分钟，在893K（敏化处理）下热处理24小时。在电子辐照前，在室温下用加速器（加速电压为70 keV）注入氦原子。在573和673K的HVEM中进行了高达7 dpa的电子辐照。除了在573K的高剂量率下溶液处理的样品外，其他都可以识别出空洞。随着损伤速率的增加，空洞数密度增大，空洞平均尺寸减小。随着温度的升高，空穴数密度和平均尺寸增大。在673K辐照下，样品中出现了镍富集和铬耗损等晶界偏析现象。随着损伤速率的降低，偏析的数量增加。溶液处理试样的孔隙数密度高于敏化试样。敏化试样的基体中细小的析出物可能受到抑制。在氦注入标本中，在辐照前未观察到空腔。在辐照过程中，高密度区形成了直径小于5 nm的氦泡。随着剂量率的降低，空腔数密度减小，平均尺寸增大。样品的数量密度和平均尺寸均低于未含氦样品。采用辐照法研究了Fe-Cr-Mn合金中析出相对损伤组织的影响。不同析出相的基体辐照结构差异较大。

Electron irradiations were performed in three different dose rates such as 2x10^<-3>,2.9x10^<-4> and 1.7x10^<-4> dpa/sec by using High Voltage Electron Microscopy (HVEM) to investigate the effect of dose rate and helium atoms on damage structures in SUS304 stainless steels.Specimens were prepared from commercial SUS304 stainless steel, which composition was Fe-18.2Cr-8.2Ni-1.3Mn. They were heat treated at 1323K (solid solution treatment) for thirty minutes and at 893K (sensitization treatment) for twenty four hours. Helium atoms were implanted by accelerator (accelerating voltage was 70 keV) at room temperature before electron irradiations. Electron irradiations were carried out in HVEM at 573 and 673K up to 7 dpa.Voids were recognized except for the solution-treated specimen in high dose rate at 573K.The void number density increased and the void mean size decreased as the damage rate increased. The void number density and the void mean size increased with increasing temperature. The grain boundary segregations, such as nickel enrichment and chromium depletion, were recognized in the specimens at 673K irradiation. The amount of segregations increased as the damage rate decreased. The void number density of solution-treated specimens were higher than that of sensitized specimens. The fine precipitates in the matrix of sensitized specimens might be suppressed void nucleation.In the case of helium implanted specimens, no cavities were observed before irradiations. During irradiations, helium bubbles ranging under 5 nm were formed in the high density. The cavity number density decreased and the mean size increased as the dose rate decreased. The number density and the mean size were lower than those of no helium specimens.Fe-Cr-Mn alloys were irradiated to investigate the effect of precipitates on damage structures. There were great differences of irradiated structures among the matrices with different precipitates.