鎳基超合金Haynes 230放電表面合金化與高溫氧化性質研究

Studies of electrical discharge surface alloyed superalloy Haynes 230 and its high temperature oxidation behaviors

白清源(Ching-Yuan Bai)

指導教授 ： 顧鈞豪

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.00388

摘要

此研究主要探討放電合金化（EDA）的方法，對鎳基超合金Haynes 230表面改質（處理）的效果，並試圖了解放電合金化條件對合金化層組成與微結構及合金化材料表面整體性之影響。放電合金化期間，使鋁和鉬二種合金化元素融合於鎳基超合金Haynes 230表層，以形成富鋁及含少量鉬的合金化層。藉由微硬度量測及高溫氧化測試，以檢驗放電表面合金化對於超合金Haynes 230之表面機械與化學性質改良的成效。
放電合金化（EDA）製程設備採用傳統的雕模放電加工機。合金化材料為85 at% Al＋15 at% Mo均勻調和的Al-Mo混合粉末。部分Al-Mo混合粉末以粉末冶金方法製成生胚的Al-Mo複合電極。表面合金化的方法，係在放電合金化過程中；（1）採用Al-Mo複合電極，並以煤油或蒸餾水作為放電合金化之介電液（工作液體），或（2）採用銅電極，在介電液（煤油或蒸餾水）中添加/懸浮Al-Mo混合粉末。
以正極性之Al-Mo電極，在煤油（P-AlMo-Kero試片）或蒸餾水（P-AlMo-Water試片）中進行合金化，主要由NiAl相組成的合金化層形成於EDA試片上。P-AlMo-Kero的合金化層為NiAl、Al8Mo3、Cr23C6與Al4C3的混合物，P-AlMo-Water的合金化層則含有NiAl、AlCr2、Al5Cr與Al2O3等相。在所有EDA試片中，P-AlMo-Water呈現最高硬度值，P-AlMo-Kero則有最小的表面粗糙度與最佳的合金化效果。以負極性之Al-Mo電極，在煤油介電液中進行合金化（N-AlMo-Kero試片），許多不連續的堆積層（主要由AlMo3與Al8Mo3相組成）積聚在試片表面；但在蒸餾水介電液中進行合金化，則因在此EDA條件下難以正常放電而失敗。在煤油中添加Al-Mo混合粉末，並採用負極性銅電極的EDA試片（N-Cu-Kero(AlMo)），再鑄層含有Cr23C6、WC1-x與石墨等相；採用正極性銅電極的試片（P-Cu-Kero(AlMo)），除了超合金原材的γ相之外，並無新的合金相出現。若在蒸餾水中添加Al-Mo粉末（不論採用正或負電極極性），則因大量金屬氧化物的產生而干擾放電程序，因而無法進行放電合金化製程。
超合金Haynes 230與放電合金化試片，在1000 ~ 1200℃空氣中，恆溫氧化之結果顯示：（1）P-AlMo-Kero試片，在1000℃與1100℃空氣中氧化後，皆可形成連續且緻密的Al2O3氧化層，而提供基材良好的保護效果。（2）P-AlMo-Water試片在1000℃空氣中，具有良好的抗高溫氧化能力，但在1100℃或1200℃空氣中，則因放電造成的結構缺陷，使其合金化層失去保護能力。（3）N-AlMo-Kero、N-Cu-Kero(AlMo)與P-Cu-Kero (AlMo)等三種合金化效果不佳的試片，抗高溫氧化能力均劣於超合金 Haynes 230。因此，在所有放電合金化試片中，P-AlMo-Kero試片呈現最佳的抗高溫氧化能力，可將超合金 Haynes 230抗高溫氧化之溫度提升至1100℃。

關鍵字

放電合金化 ； 鎳基超合金 ； Al-Mo電極 ； 高溫氧化

並列摘要

This research is to examine the surface modification (treatment) of the Ni-based superalloy Haynes 230 through electrical discharge alloying (EDA) method. The effect of EDA parameters on the alloying surface conditions; such as the composition, the microstructure, and the surface integrity of the superalloy are all investigated. In the EDA process, the alloying elements, Al and Mo, would be blended into the surface layer of the superalloy. Therefore, an alloyed layer with rich Al and minor Mo is expected to form on the surface of the superalloy. The micro-hardness test and the isothermal oxidation examination at high temperature are performed to inspect the EDA results on the mechanical and chemical properties of the alloy surface layer.
The EDA process is carried out with a conventional die-sinking electrical discharge machine. A uniform mixture of the powders with 85 at% Al and 15 at% Mo is applied for the surface alloying materials. The Al-Mo powder mixture is made to be a green-compact composite electrode by the powder metallurgy process. To reach the purpose, the surface alloying treatments may employ two different ways: (1) By using the Al-Mo composite electrode and utilizing the pure kerosene or the distilled water as the dielectric (working fluid), or (2) By using the electrolytic copper electrode and adding/suspending the Al-Mo powder mixture in the dielectric (kerosene or distilled water), during the EDA process.
For employing the Al-Mo electrode with positive polarity, the alloyed layer constituted mainly of the NiAl phase is formed on the EDA specimen, in either the kerosene (P-AlMo-Kero specimen) or the distilled water (P-AlMo-Water specimen). The alloyed layer of P-AlMo-Kero contains a mixture of NiAl, Al8Mo3, Cr23C6, and Al4C3; while that of P-AlMo-Water consists of NiAl, AlCr2, Al5Cr, and Al2O3 phases. The P-AlMo-Water exhibits the highest hardness, whereas the P-AlMo-Kero owns the smallest surface roughness and with the best alloying efficiency among all the EDA specimens. Employing the Al-Mo electrode with negative polarity and alloying in kerosene (N-AlMo-Kero specimen), a lot of discontinuous piled-layers comprised mostly of Al3Mo8 and AlMo3 phases are accumulated on the surface of the specimen; while alloying in distilled water fails owing to the difficulty of discharging under such an EDA condition. For suspending Al-Mo powder mixture in kerosene and utilizing the Cu electrode with negative polarity, the Cr23C6, WC1-x, and the graphite phase may exist in the recast layer of the EDA specimen (N-Cu-Kero(AlMo)). While applying the Cu electrode with positive polarity, the EDA specimen, P-Cu-Kero(AlMo), exhibits no alloying phase. For using the Cu electrode and adding Al-Mo powder mixture in distilled water, the electrical discharge alloying (EDA) cannot be proceeded. Doesn't matter with positive or negative electrode polarity, the discharging procedure is always disturbed by a lot of metal oxides.
The superalloy Haynes 230 and the EDA specimens are subjected to isothermal oxidation at 1000 ~ 1200℃ in static air. Experimental results of the oxidation at 1000℃ and 1100℃, respectively, indicate that a dense and continuous oxide scale composed of Al2O3 forms on the surface of the P-AlMo-Kero specimen and protects the substrate of the superalloy from oxidation. The P-AlMo-Water specimen shows a superior oxidation resistance at 1000℃, but lose its protective ability at 1100℃ or 1200℃, respectively, in static air, because of the structure defects in its alloyed layer by electrical discharge process. The oxidation resistance of the N-AlMo-Kero, N-Cu-Kero(AlMo), and P-Cu-Kero(AlMo) specimens with invalid alloying results is even worse than that of unalloyed superalloy Haynes 230. In summary, the P-AlMo-Kero specimen is more resistant to the oxidation than the unalloyed superalloy and the other EDAed specimens, and its effective anti-oxidation temperature can be elevated to 1100℃.

並列關鍵字

Electrical discharge alloying ； Ni-based superalloy ； Al-Mo electrode ； High temperature oxidation

參考文獻

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