- 學位論文
鈷-28鉻-5鉬合金顯微結構分析
Analysis of the Microstructures on the Co-28Cr-5Mo Alloy
摘要
本文主要探討鈷-28鉻-5鉬合金鑄件，分析合金經不同退火處理之顯微結構，以及合金元素對析出的影響。研究結果，如下所示：合金薄片鑄件，主要為具疊差與雙晶之α鈷(F.C.C)結構，同時存在高鉬團狀析出物與顆粒狀析出物，經電子顯微鏡分析結果，此析出物皆為M23C6碳化物，晶格常數為a=1.056nm。合金1200℃/10小時高溫處理後，可消除顆粒狀析出物，惟仍可觀察到團狀析出物。合金經450~550℃時效處理後，基地為鈷結構，另可觀察到M23C6碳化物於雙晶邊界與基地析出。於650~850℃高溫時效時，M23C6碳化物於基地、雙晶邊界與疊差處析出，晶粒邊界存在α鈷→β鈷(HCP)+ M23C6相變態。β鈷與M23C6方向關係為(111)M23C6//(0001)β、[110]//[112 ̅0] β。研究發現：α鈷/β鈷轉換溫度介於550~650℃，較低於其他學者所觀察之結果。另M23C6碳化物，其[001]擇區繞射圖形中，繞射點強度呈現4種分佈，顯示其結構型態有F.C.C.、L12、鑽石和D85排列。此外，STEM-EDS分析顯示：鉬元素為高溫團狀析出物存在之影響主因，鉻元素為時效析出物形成之影響主因，碳元素將影響α鈷→β鈷(HCP)+ M23C6相變態的過程。此結果，並未被其他學者觀察到。
並列摘要
The purposes of the studies are to investigate the microstructures and effects of alloy elements on the precipitation of as-cast Co-28Cr-5Mo alloy annealed at various temperatures. Some results are described as following: Being heated at 1200℃/10hrs, the microstructure of the alloy is a αCo (FCC) + clustering precipitates structure. After aging at 450~550℃, some M23C6 precipitates could be observed on the twin boundaries and within the matrix. When aged at 650~850℃, some M23C6 precipitates could be observed either on stacking faults or twin boundaries. Moreover, a αCo → βCo (HCP) + M23C6 phase transition was occurred on the boundaries. The orientation relations between the βCo and M23C6 carbide is (111)M23C6//(0001)β, [110]M23C6//[112 ̅0]β. It is noted that the temperature of the αCo/βCo transition is in range of 550~650℃, which being lower than other workers. In addition, the intensity distribution of the reflection spots in [001] SADP divided four types, it implies that the structure of M23C6 carbide is belonging to F.C.C., L12, diamond cubic or D85 structure which of lattice parameter being a=1.056nm. Based on STEM-EDS, the Mo element will play an important role on occurrence of the clustering the precipitates, and of Cr element on the precipitation of M23C6 carbide. Moreover, the carbon element would be major influenced on a αCo → βCo + M23C6 phase transition.