617B镍基高温合金长期时效组织演变

Microstructure Evolution of Long-Term Aged 617B Ni-based Superalloy

摘要:

617B是一种固溶强化型镍基高温合金,是700℃先进超超临界火电站的候选材料之一,通常使用状态为固溶态,使用温度为700℃左右,因此研究其在近服役温度范围内的长期时效组织演变对其在实际应用中具有重要的意义。本文对617B合金在650℃、700℃、750℃分别时效至3000h并通过光学显微镜、场发射扫描电镜以及能谱分析其在时效过程中的组织演变规律。经研究发现,在时效过程中617B合金中主要的析出相为γ"相、富Cr、Mo的M23C6。650℃,600h后开始析出γ"相,且随着时效时间的延长以及温度的提高发生一定程度的粗化。低于700℃时效,γ"相的粗化满足传统的LSW理论,而大于750℃长期时效则转变为以团聚为主的粗化方式。晶界碳化由细小不连续分布的锯齿状逐渐粗化转化为连续的网状结构,晶内碳化物析出增多。750℃高温长期时效,碳化物可能存在与基体、γ"相之间的反应。

Abstract:

617B is a solid-solution strengthened Ni-based superalloy, a candidate material for 700℃ A-USC power plant. It is always used in solution-anneal at about 700℃. So it is significant to research its microstructure evolution during aging at its service temperature rang form 650℃ to 750℃. In this work, the 617B alloy was exposed prolonged approximately 3000h at 650℃, 700℃, 750℃ respectively. The microstructure evolution had been characterized by optical microscope (OM), field emission scanning electron microscope (FESEM) and energy dispersive spectrometer (EDS). γ" phase and Cr, Mo-rich M23C6 were the major precipitates during aging treatment. γ" phase precipitated at about 650℃,600h and got coarsening with a prolonged time and an increasing temperature. The coarsening of γ" phase met the LSW theory below 700℃ aging but when exposed higher than 750℃, it was priority to coarsen by agglomeration. The carbides along grain boundaries were transformed into continuous network structure by the gradual coarsening of small serration carbides. And carbides within grains increased during aging. When alloy undergone 750℃ long-term aged, there are reactions between carbides, matrix and γ"phase.