臺灣博碩士論文加值系統

鎳基超合金IN-738LC因具有優良高溫機械強度與抗腐蝕能力，因此常被用來作為
氣渦輪機內高溫部位材料（如渦輪葉片）。為了提升超合金在高溫下抗氧化以及
抗腐蝕能力，常在材料表面披覆一層鍍層（如鋁化、鉻化、電鍍白金鋁化等）。
本研究是將超合金IN-738LC先行電鍍鈀，再以粉浴鋁化或鉻化，藉以比較超合金、
超合金電鍍鈀、高鋁鋁化鍍層、電鍍鈀高鋁鋁化鍍層、低鋁鋁化鍍層、電鍍鈀低
鋁鋁化鍍層之高溫抗氧化及熱腐蝕性質。
粉浴鋁化過程中，以含鎳之粉浴配方，可以製得表面為(-NiAl之高鋁鋁化以及低
鋁鋁化鍍層。而在電鍍鈀之鋁化鍍層，表面則為(Ni,Pd)Al。四種鋁化鍍層厚度均
勻，並無孔洞與裂縫，而且與基材接合性也十分良好。高鋁鋁化以及低鋁鋁化反
應時均遵守拋物線法則，可知反應為固態擴散機構所控制。高鋁鋁化因鋁活性較
大，因此反應所需溫度以及時間都較低鋁鋁化少，鍍層厚度也較厚。而粉浴鋁化
過程中電鍍鈀之鋁化試片之重量增加量較未電鍍鈀處理之鋁化試片為高。顯示電
鍍鈀層在鋁化過程中有助於鋁之沈積與擴散。
鉻化鍍層以及電鍍鈀之鉻化鍍層，表面皆為Cr相，但在鍍層與基材界面處則有許
多孔洞，顯示鉻化鍍層結構較差。
將八種鍍層試片表面進行硬度測試，發現鉻化鍍層表面最硬，鋁化鍍層次之，基
材合金最差。證明了試片經過粉浴鉻化以及鋁化，可以提高合金表面硬度。然而
不同的鋁化鍍層比較，硬度並無差異。
將試片在900(C進行高溫循環氧化測試，鋁化鍍層並未剝落，而且試片重量趨於穩
定，由此可見，在900(C下，鋁化鍍層接合力依舊良好且能保護基材。而電鍍鈀鉻
化以及單純鉻化試片在循環氧化中，鍍層已有剝落情形，可見鍍層已不具保護性。
然而超合金及超合金電鍍鈀試片表面雖未有剝落情形，但試片重量仍緩緩上升，顯
示表面氧化層已逐漸失去保護性。
將試片在850~1200(C進行恆溫氧化測試，超合金、超合金電鍍鈀、鉻化、電鍍鈀鉻
化試片只在850(C時具有保護性。鋁化鍍層則在1100(C以下仍有好的保護性。當溫
度升到1200(C時，所有鍍層均不具保護性。依照氧化速率曲線圖及Arrhenius圖所
示，電鍍鈀有助於提升鋁化鍍層中鋁之活性。
將試片表面噴覆Na2SO4，在900(C空氣中進行高溫腐蝕測試，鋁化鍍層試
片經腐蝕後有嚴重剝落情形。電鍍鈀之粉浴鍍層在抗高溫腐蝕方面並沒有
明確效果，未能改善超合金之高溫抗腐蝕性。

Pack cementation coating process is an effective approach to raise the
resistance for oxidation and hot corrosion of superalloys. This research is
to electroplate palladium on the superalloy IN-738LC specimen, and then to
coat an aluminized or chromized layer on the superalloy IN-738LC by the pack
cementation process.

There are several different pack cementation processes carried out in this
study: high aluminization process, low aluminization process , chromization
process, Pd-modified aluminization and Pd-modified chromization process. By
the process with nickel contained in the pack and through the proper control
of the process, the main composition of the surface of the coated
aluminization layer is (-NiAl. As for the Pd-modified aluminization layer,
the main composition of the surface is (Ni,Pd)Al. The characteristics of the
aluminized coating layer is uniform, and has no voids or cracks. The coating
also owns good bonding with matrix. The coating temperature of the high
aluminization process is lower than that of low aluminization process due to
its high aluminium activity. In aluminization process, it has more aluminum
deposited on the Pd-plated aluminization process than that on the single
aluminization process. Obviously Pd plating is helpful for the deposition
and diffusion of aluminum in aluminization process. The main composition of
the surface of the coated chromization layer is Cr. There are some voids in
the interface between the coating layer and matrix.

The coating process parameters are optimized in this study to obtain a best
coating layer. The high temperature chemical properties of the aluminization
and chromization coatings are tested, and the results are shown as follows.
(I) The superalloy IN-738LC and chromization coating layer possess good
resistance of isothermal oxidation below 850(C, and four aluminization
coatings possess good resistance of isothermal oxidation at 850~1100(C. The
Pd-modified aluminization coating shows higher activity of aluminum than that
of pure aluminization at 850~1100(C. (II) The four aluminization coating
layers possess good resistance of cyclic oxidation at 900(C. But the two
chromization coatings have no resistance of cyclic oxidation at 900(C. (III)
The four aluminization and two chromization coatings have no resistance of
hot corrosion at 900(C. The Pd plating is unable to improve the resistance
of hot corrosion.