René77合金渦輪噴嘴鑄件表面狀況及擺放方式對氣相鋁化鍍層品質之影響研究

Effects of Surface Condition and Part Orientation on the Quality of Vapor Phase Aluminized Coating for Nozzle Segment Casting of René77 Alloy

何堃森(K. S. Ho) ； 黃文星(W. S. Hwang) ； 曾清暉(C. H. Tseng)

《材料科學與工程》 36卷1期 (2004/03) Pp. 36-47

https://doi.org/10.6409/JMSE.200403.0036

摘要

本研究是針對非接觸式包覆(Out of Pack or Above Pack)氣相法沛鋁化René77合金渦輪噴嘴鑄件表面的製程，探討製程中鑄件表面粗糙度及鑄件擺放方式對鋁化鍍層厚度及鍍層內鋁含量之影響，同時也是討鑄件表面缺陷，如夾渣物(Inclusion)，凸出物(Positive Matter)，凹陷(Negative)，孔洞(Open Void)等，對鍍層氣態之影響。
本研究以尺寸為230mmL×180mmH×51mmW，6片一組之René77合金渦輪噴嘴鑄件為對象，在氣相鋁化爐內使用4種不同的籌件擺放方式，5種不同表面粗造度，在氬氣之保護氣氛下，升溫至1080ºC溫度，保持6小時，使爐內預先放置之顆粒鉻鋁合金與定量之AlF3活化劑作用，讓鑄件得到不同厚度與鋁含量之鍍層。每一鑄件選取相同位置，經電鍍、切割成9個部份，再進行鑲埋、研磨、拋光等步驟，由光學及扭瞄式電子顯微鏡觀察及量測鍍層之厚度與鋁含量後，進行數據分析。
實驗結果顯示，鑄件之擺放成式將影響鍍層厚度之均性，但對鍍層外層鋁含量之影響則無規則性，而以類型3之擺放方式(方向為內護環(Inner Shroud)朝內，後緣(Trailing Edge)朝，翼形面凹面(Concave)朝上)可符合規格要求及得到較均勻之鏡層厚度。鑄件表面粗糙度Ra高於1.89μm時，表面粗糙度對鍍層厚度及品質有相關大影響，而Ra 低於1.40μm時，表面粗糙度對鍍層厚度及品質則沒有明顯的影響。鑄件表面有凸出物或凹陷等缺陷將容易附著氧化物並造成鍍層形態之變變，而夾渣物及孔洞則會阻擋擴散之進行，造成鍍層出現缺口，這此鍍層型態皆會影響高溫抗氧化性質。

關鍵字

氧相鋁化鍍層 ； 非接觸式包覆法 ； René77合金 ； 攘散鍍層 ； 超合金鑄件

並列摘要

In this study, the effects of surface roughness and part orientation on the quality of vapor phase aluminized coating with the out of pack/above pack process for a nozzle segment casting of rené77 alloy are investigated. The morphology and quality of the coating are also studied when surface defects of the casting; such as inclusion, positive matter, negative surface and open void,exist.
The casting under investigation is a 6-vane turbine multi-nozzle segment with item dimensions of 230mmL×180mmH×51mmW. Five casting surface roughnesses, which are obtained by different surface pretreatment, and four part orientations, where castings are placed differently in the vertical vapor phase aluminized coating furnace, are considered in this study. The furnace is heated up to 1080ºC and held for six hours under argon atmosphere. Cr/Al alloy pellets originally placed in the furnace react with the AIF3 activator to produce aluminum subhalide vapor. The vapor is attached on the casting surface and in turn react with the nickel element in the casting alloy to from an aluminide coating layer on the casting surface. Nine samples are cut from the coated casting and the thicknesses aluminum contents of the coatings are observed and measured through an optical microscope and a SEM.
The results show that the part orientation significantly effects the thickness uniformity of the coating. However, it has little influence on the aluminum content of the coating. The part orientation #3, where the casting is placed in the chamber with inner shroud inward, outer shroud rightward and concave side of the airfoil upward, can not only meet the specifications on the thickness and aluminum content of the coating but obtain the most uniform coating. Surface roughness of the casting, Ra, has an obvious effect on the coating thickness when it is above 1. 89μm. However, the effect on coating thickness becomes insignificant when the surface roughness is below 1.40μm. The surface defects of positive matter and negative surface result in the attachment of oxides and subsequent change of coating morphology. Inclusion and open void, however, retard the diffusion process and generate discontinuity in the coated film. These irregular coatings weaken the high temperature resistance properties of the coated casting.

並列關鍵字

Vapor Phase Aluminized Coating ； Out of Pack/Above Pacek ； Rene77 Alloy ； Diffusion Coating ； Superalloy Casting