【摘要】 采用高速定向凝固法(HRS)制备了含碳(0%～0. 130%(质量分数,下同))和硼(0%～0. 014%)的高铼(5%)镍基高温合金,利用SEM和EPMA研究了碳和硼含量对合金凝固组织和显微偏析的影响。结果表明:碳和硼的添加对一次枝晶间距无明显影响;但随碳含量的增加,共晶的体积分数和平均尺寸减小,碳化物的体积分数增多;随硼含量的增加,共晶的体积分数和平均尺寸增加,碳化物的体积分数减小。在200μm/s的抽拉速率下,碳化物的形貌主要以汉字体状为主,随碳含量的增加,汉字体碳化物的平均尺寸增大,汉字体网络分布变得密集;随硼含量的增加,汉字体状碳化物有部分向片状和大片状转化。随碳含量的增加,Re和W凝固偏析呈现先加重后减轻的趋势,其峰值出现在碳含量为0. 040%处;随硼含量的增加,Re和W的凝固偏析先稍微减轻然后又加重。碳和硼对Ta的凝固偏析影响不大。更多还原

【Abstract】 Nickel-based superalloys have been widely used in aircraft and industrial gas turbine. However,the casting characteristics of these modern high-refractory alloys are significantly worse than those of earlier alloys,such as a wider range of crystal orientations,the formation of grain defects,hot tearing and so on. To improve these properties of the alloys,minor elements of carbon( C) and boron( B) additions have been recognized one of effective methods. But unfortunately,few investigations were related with higher generation directionally solidified superalloys containing rhenium( Re) up to now. In this paper,the microstructure and dendritic segregation of Ni-based superalloy containing Re( 5 wt%) were investigated by directional solidification with withdrawal rates of 200 μm/s. The results showed that the addition of carbon and boron did not remarkably change primary dendrite arm apacing λ1. Carbon and boron additions varied the volume fraction of the γ/γ’ eutectic and the distribution of carbides. The volume fraction of γ/γ’ eutectic was reduced and the amount of carbides increased with increasing carbon content; when boron was added into the alloy,the volume fraction of γ/γ’ eutectic was increased and the volume fraction of carbides decreased. The morphology of carbides was mainly Chinese script-type. The average size of carbides became smaller and their distribution was sparse at lower carbon content.However,these carbides were much bigger and their distribution was denser at higher carbon content. The morphology of Chinese script-type carbides changed from a rod to a part sheet,then again to a larger sheet with the increase of boron content. The rise of segregation coefficients of Re and W was followed by the fall with the increase of carbon content,the peak value of segregation coefficient was found at 0. 040 wt% carbon content. The effect of boron on segregation was just opposite of carbon. For the element of Ta,there was not significant tendency of segregation variation with the increase of carbon and boron contents.更多还原