微量元素對超合金熱成型性影響之研究

Effect of minor elements on the hot deformation behaviours of a superalloy

張哲銘(Che-Ming Chang)

指導教授 ： 葉安洲

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

摘要

Incoloy A-286 為一鐵鎳基型超合金，其廣泛應用於渦輪及噴射引擊等。然而，A-286超合金雖然有其較長的應用歷史，對於A-286成型製程仍有其問題。其超合金之熱成形性質易受成份之影響，尤其以雜質元素(如：硫元素)較明顯。在此研究中，A-286合金在高溫輥壓下產生裂痕，並在仔細觀察下發現因為硫、磷、矽元素偏析在晶界造成共晶反應並產生富鈦液化相，促使材料產生沿晶斷裂之現象。同時發現有Ti(C,N)析出物在晶粒中。為了提升A-286之成形性，在合金設計中加入少許的鎂元素，同時也加入錳元素來觀察其成形性的影響。在研究中測試1050oC 及1175oC下拉伸試驗、900oC循環氧化實驗及使用OM, SEM-EDS,TEM-EDS,Auger及EPMA觀察其合金之微結構及破裂面。在結果中發現鎂元素添加在A-286中可減少富鈦液化相之現象及提升高溫下晶界延展之性質。

關鍵字

超合金 ； 雜質 ； 熱成形 ； 沿晶斷裂 ； 鎂

並列摘要

Incoloy A-286 is a Fe-Ni based superalloy and it is widely used in gas turbine industry, jet engines and other applications. Although A-286 has a long service history, the fabrication of A-286 is not without any challenges. The hot deformation property for this alloy is highly sensitive to its composition, especially the content of impurity such as sulfur (S). In present study, a batch of A-286 has suffered from cracking issue during rolling process at high temperature and detailed examinations have revealed that phenomena of liquation of Ti-rich phase induced by eutectic reaction with S appeared at grain boundary and caused intergranular fracture. To improve the hot deformation behaviors of A-286, alloy design has been performed with the minor addition of magnesium (Mg). Furthermore, its combined effect with manganese (Mn) has been examined. Experiments include tensile tests at 1050oC and 1175oC, cyclic oxidation at 900oC, detailed microstructure/fracture surfaces observations and composition analysis by OM, SEM-EDS, TEM-EDS, Auger, and EPMA. In conclusion, Mg addition can eliminate the phenomena of Ti-rich phase liquation, the high temperature deformation behaviours of A-286 can then be improved.

並列關鍵字

superalloy ； impurity ； hot deformation ； intergranular fracture ； magnesium

參考文獻

2. Rho, B.S., Hong, H.U. and Nam, S.W., Analysis of the intergranular cavitation of Nb-A286 alloy in high temperature low cycle fatigue using EBSD technique. Scripta Materialia, 2000. 43(2): p. 167-173.

3. Seifollahi, M., et al., The Mechanism of eta Phase Precipitation in A286 Superalloy During Heat Treatment. Journal of Materials Engineering and Performance, 2013. 22(10): p. 3063-3069.

6. Muhmond, H.M. and Fredriksson, H., An Investigation on the Effect of S and Al on the Austenite Growth Morphology in Gray Cast Iron, Using Thermal Analysis and Etching Technique. Transactions of the Indian Institute of Metals, 2013. 66(2): p. 185-192.

7. Ma, P. and Zhu, J., Magnesium Distribution in a Nickel-Based Superalloy. Metallography, 1986. 19(1): p. 115-118.

9. Tavakkoli, M.M. and Abbasi, S.M., Effect of molybdenum on grain boundary segregation in Incoloy 901 superalloy. Materials & Design, 2013. 46: p. 573-578.