Inconel 740H蠕变过程中晶界M23C6的粗化行为

为了解700℃超临界电站锅炉过/再热器用主要候选材料Inconel 740H晶界M_(23)C_6相在蠕变过程中的粗化行为,对通过真空感应熔炼和真空电弧重熔双联工艺制备的合金,在750℃/200 MPa条件下分别开展蠕变中断与蠕变断裂试验,并利用扫描电镜、透射电镜、能谱分析仪等测试方法对晶界M_(23)C_6相进行表征.采用Image-Pro Plus软件对相参量进行定量统计,进而分析其变化趋势.研究表明:在所研究温度、应力及时间范围内,随着蠕变时间的延长,晶界富Cr的M_(23)C_6相逐渐由粒状、短棒状发展成为长条、半连续的链状分布;粒子沿平行于晶界方向的长大速率明显高于沿垂直于晶界方向的长大速率,但二者的粗化均表现出尺寸三次方与时间之间呈线性关系的规律;相数量的增加与蠕变时间亦呈线性关系;与尺寸的粗化相比,相数量的增长较为缓慢,外加应力在一定程度上促进了M_(23)C_6的析出.

Coarsening behavior of grain boundary M23C6 in Inconel 740H during creep

To understand the coarsening behavior of grain boundary M23 C6 in Inconel 740H, which is a new Ni-Co based superalloy developed for superheater/reheater of 700 ℃ ultra super-critical boiler, creep interrupted and creep rupture tests of the Inconel 740H obtained by vacuum melting and vacuum arc remelting were performed under the conditions of 750 ℃ and 200 MPa up to 3000 and 5879 h, respectively. The evolution of M23 C6 precipitates along grain boundaries were investigated as a function of creep time by SEM, TEM and EDS technologies and Image-Pro Plus software. The result shows that the M23 C6 phase of Cr-rich Cr is gradually grown from granular and short rods into long and semi-continuous chain-like distribution with the creep time prolonged in the studied temperature, stress and time range. The growth rate in the grain boundary direction is obviously higher than that in the direction perpendicular to the grain boundary direction, but the coarsening of the two shows the linear relationship between the cube of average size of M23 C6 particles and the creep time. Compared with the coarsening rate of phase size, the increasing of phase amount is relatively slow, and it also presents a linear relationship between the amount of phase and creep time. In addition, the applied stress can promote the precipitation of M23 C6 to a certain extent.