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標題: 800H與825鎳基超合金銲接熱龜裂敏感性研究
A Study of Hot Cracking Susceptibility during Welding on Incoloy 800H and 825 Superalloys.
作者: 包景毅
Pao, Ching-Yi
Contributors: 吳威德
材料科學與工程學系所
關鍵字: 鎳基超合金;熱龜裂敏感性;熱裂紋;熱分析
Nickel superalloys;Hot Cracking Susceptibility;hot cracking;heat analysis
日期: 2012
Issue Date: 2013-11-18 11:31:39 (UTC+8)
Publisher: 材料科學與工程學系所
摘要: 本研究係以Incoloy 800H和825鎳基合金為基材,分別針對添加填料與未添加填料進行熱裂紋敏感性特性試驗。利用鎢極惰性氣體遮護電弧銲接法(Gas Tungsten Arc Weld, GTAW)銲接。最後使用鎢極惰性氣體遮蔽電弧銲接進行點狀變應變實驗(Spot Varestraint Test),觀察鎳基超合金在高溫下受到臨界應變量(CST)對裂紋的影響。另一方面藉由立體顯微鏡、光學顯微鏡觀察裂紋表面組織型態以及X光繞射分析銲道結構,由掃瞄式電子顯微鏡(Scanning Electronic Microscope, SEM)觀察龜裂型態及龜裂破斷面銲道及裂紋分佈之情形,並取合理範圍內並記錄最大龜裂長度(Maximum crack length, MCL)、最大龜裂距離(Maximum crack distance, MCD)及總龜裂長度(Total crack length, TCL)。並利用熱差分析儀(DTA)分析鎳基超合金液/固溫度差值(ΔT)範圍,探討熱龜裂敏感性。
結果顯示鎳基超合金添加填料在高溫下,龜裂敏感性低於未添加填料母材,其中以添加Inconel 82填料對熱龜裂敏感性影響較低,根據這些銲接數據可以得材料之熱龜裂敏感性與液/固溫度差值(ΔT)範圍相關性,裂紋總長度越長,熱分析顯示之液/固溫度差值(ΔT)範圍也越大,熱龜裂敏感性越高。裂紋形貌在金相上顯示分別有(a)熔池內沿晶裂紋,(b)熔池內之凝固裂紋,(c)銲道熱影響區之沿晶裂紋,(d)基材熱影響區之穿晶裂紋。根據裂紋形貌可推測出材料高溫下發生龜裂之過程與情形,在SEI與BEI圖像下觀察裂紋周圍可能產生之析出物,並以EDS分析周圍組織成分,結果顯示出Incoloy 鎳基合金在高溫下並無低溫相析出物產生,在在顯示出是由於變應變試驗將基材臨界應變提升至脆性溫度範圍區間,而高溫下脆性溫度範圍越大則代表熱龜裂敏感性越高,結果顯示Incoloy 800H鎳基合金熱龜裂敏感性最高。
In this study, the hot cracking susceptibility of the Incoloy 800H and 825 nickel-base alloy substrate was discussed with filler and without filler. And later nickel alloy of filler 52 and 82 Tungsten inert gas shielded arc welding in the specimen. Observation of nickel based superalloy at high temperature by the critical strain for crack. On the other hand by using a stereoscopic microscope, optical microscope observation of the crack surface type of organization, as well as X-ray diffraction analysis of the weld structure, observed by scanning electron microscopy. The maximum crack length, amount of cracks, and total cracks length were recorded. The difference of liquid and solid (ΔT) was analyzed in nickel-based superalloy using differential thermal analysis (DTA) and then examine the relationship between cracks and the hot cracking sensitivity.
The results showed that the hot cracking sensitivity of the nickel-based super-alloys with filler at high temperature was lower than that without filler base metal. The hot cracking sensitivity had a slight effect with the Inconel 82 filler addition. According to experimental data, the relationshop between the hot cracking susceptibility and the liquid-solid two-phase range can be obtained. When the crack total length was increased, the liquid-solid two-phase range is higher and then the hot cracking susceptibility was raised. The morphologies of cracks included the intergranular crack in the molten pool, the molten pool solidification cracking, the weld heat-affected zone of intergranular cracks, and the transgranular crack in the heat-affected zone. The occurrence of cracking in materials under high temperature can be inferred according to the morphologies of cracks. The results showed that no low temperature precipitates under high temperature incoloy nickel-based alloys. This was because that a critical strain increased to the range of the brittle temperature range rature in base metal during the varistraint test. When the brittle temperature range was higher under high temperature, hot cracking sensitivity was more obvious. The results displayed the hot cracking sensitivity was most evident in Incoloy 800H alloys of all the nickel-based alloys.
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