新型鈷基超合金之熱處理

The heat treatment of a new Co base superalloy

羅璟元

指導教授 ： 張士欽

國立清華大學/工學院/材料科學工程學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00360

摘要

本研究以改良合金成分之新型鈷基超合金(X 合金)為對象，探討不同熱處理條件對於X 合金碳化物二次析出的影響以及碳化物二次析出對於材料性質的影響。研究發現鑄造態X 合金在樹枝間區域中有M(Cr, Co)7C3 和 M(Cr, Co, W, Mo)6C 碳化物；在樹枝狀區域中有中國文字形貌的碳化鈮(NbC)。經1000 ℃時效4小時，可發現大量碳化物M23C6 和M6C顆粒二次析出。經1106 ℃時效4小時，可發現有大量碳化物M7C3和M6C顆粒二次析出。經1200 ℃固溶12小時後中國文字形貌碳化鈮(NbC)尺寸會成長並觸及樹枝間區域的共晶相，再經時效1000 ℃時效4小時，與未經固溶熱處理而直接1000 ℃時效4小時相比，可發現固溶熱處理反而使試樣具有較寬的無析出區，及數量較少並且尺寸較大的二次析出碳化物，不利於合金的強度、抗腐蝕和磨耗性質。
鑄造態X合金經過1000 ℃ / 4 h和1106 ℃ / 4 h熱處理後，碳化物二次析出可有效地提升合金的強度和磨耗性質，但同時會降低合金基地相的鉬和鉻含量，因此X 合金對於室溫3.5wt% NaCl (pH=7) 和0.5 M (1 N) H2SO4水溶液的抗蝕能力也會變差。經1106 ℃ / 4 h熱處理後，再經1200 ℃固溶2小時，可提升鑄造態X 合金在室溫3.5wt% NaCl水溶液中的抗蝕能力，同時提升其抗磨耗性質。在室溫1 M (1 N) KOH水溶液極化試驗測試後，可發現原本在合金內作為強化相的碳化物會被優先腐蝕。

關鍵字

鈷基超合金 ； 熱處理 ； 碳化物

並列摘要

This work studied the effect of heat treatment on precipitation of secondary carbides and their effects on the properties of a new cobalt base superalloy–X alloy. The X alloy is strengthened by carbide precipitations. The as-cast alloy have three kinds of primary carbides: M(Cr, Co)7C3 and M(Cr, Co, W, Mo)6C in the interdendrite region, and Chinese script-like NbC in the dendrite. Since M7C3 carbides are stable only in the high temperature range, heat treatment at 1000 ˚C for 4 hours would cause the dissolution of the M7C3 carbides and the precipitation of secondary carbides M23C6 and M6C. When aged at 1106 ˚C for 4 hours, the precipitation of secondary carbides M7C3 and M6C were observed. If solution heat treated at 1220 ˚C for 12 hours, the area fraction of Chinese script NbC phase would increase and some of the NbC arms extend to touch the interdendrite eutectic area. By the following aging treatment at 1000 ˚C for 4 hours, wider precipitate free zone and coarser secondary carbides in less number were observed that would detrimental to the corrosion resistance and mechanical properties.
The precipitation of the secondary carbides increases the strength and wear resistance of the alloy. However, the precipitation of the secondary carbides decreases the corrosion resistance of X alloy in 3.5wt% NaCl (pH=7) and 0.5 M (1 N) H2SO4 aqueous solution at ambient temperature by reducing the Mo and Cr content in the matrix. The corrosion resistance of X alloy can be improved by the 1200 ˚C / 2 h solution heat treatment following the 1106 ˚C / 4 h aging. When tested in 1 M (1 N) KOH aqueous solution at ambient temperature, all the carbides in the alloy were preferentially attacked no matter how it was heat treated.

並列關鍵字

cobalt superalloy ； heat treatment ； carbide

參考文獻

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