Microstructure Control in Self-lubricating CrAlN/VN Multilayer Coatings for Improved Mechanical Response and High-temperature Tribological Characteristics

藉結構調制具自潤滑之氮化鉻鋁/氮化釩奈米多層薄膜以強化機械性質及抗高溫磨耗特徵

王尹(Wang, Yin)

指導教授 ： 杜正恭

國立清華大學/工學院/材料科學工程學系/碩士(2016年)

摘要

表面改質工程係一項提升工件表面之機械性質、抗氧化、耐腐蝕與抗磨耗行為的新穎科技，在工業界中扮演著不可或缺的角色。然而，一些不可避免的問題仍限制表面改質技術於硬質塗層領域的發展，如在切削過程中，切削刀具表面會與工件表面產生極高之摩擦力，引起熱退化以及黏著反應等。為了克服這些缺陷，本研究嘗試開發一嶄新且具有卓越高溫抗磨耗性之自潤滑硬質薄膜系統。
本研究中，乃利用磁控濺鍍之方式製備出一新穎的氮化鉻鋁/氮化釩奈米多層薄膜，週期厚度控制在10至40奈米之間，而每一週期中，氮化鉻鋁與氮化釩之厚度相等。藉由穿透式電子顯微鏡之高解析模式、暗場影像，可驗證多層薄膜形成緊密之柱狀晶結構。由於大量介面引入之結構強化效應，使得此多層薄膜在適當週期厚度下，可展現出極為優異之抗塑性變型特性。當週期厚度控制於16奈米時，薄膜之最高抗塑性變型值可高達0.36。
此外，本研究分別於室溫及攝氏700度高溫下，利用ball-on-disc磨耗測試來檢驗薄膜之抗磨耗表現。室溫磨耗測試結果顯示，多層薄膜由於介面強化效果，其磨耗率均較單層之氮化鉻鋁低，而週期厚度為16奈米之多層薄膜具1.0×10−6 mm3N-1m-1之最低磨耗率。另一方面，在攝氏700度下，由於大量具有固態及液態潤滑效果的氧化釩於磨耗表面生成，氮化鉻鋁/氮化釩多層薄膜之摩擦係數更可大幅下降，而多層薄膜之磨耗率也因介面強化效應而明顯降低，當週期厚度控制為16奈米時，具最低之磨耗率1.6×10−5 mm3N-1m-1。研究中更可發現，經過攝氏700度之磨耗測試後，相較於單層氮化鉻鋁薄膜，氮化鉻鋁/氮化釩之多層薄膜較不易破裂、崩解，且磨道表面上存在較少之磨屑。藉由電子能譜儀、聚焦離子束及穿透式電子顯微鏡分析，更可進一步整合在不同溫度的條件下，此自潤滑薄膜之抗磨損機制。利用本研究中所提出結構強化及成分貢獻建構出之混成行為，可成功發展出一具抗高溫磨耗之自潤滑薄膜系統。

關鍵字

氮化鉻鋁/氮化釩奈米多層薄膜 ； 高溫磨耗試驗 ； 抗磨耗機制

並列摘要

The surface modification engineering is a useful technique to achieve desired properties of mechanical strength, thermal stability, anti-corrosion and wear-resistance onto the surface and thus plays an indispensable role in industry, especially in machining process. However, some inevitable problems restrict the continuous development of hard coatings in this field, such as high friction, thermal degradation and strong adhesive interaction at contact surface during the process. To overcome these drawbacks, the development of a novel self-lubricating hard coating with superior anti-abrasion at elevated temperature is compulsory.
In this study, a new CrAlN/VN multilayer coatings are fabricated by RF reactive magnetron sputtering. The bilayer periods are altered from 10 to 40 nm, and the individual layer thickness ratio of CrAlN to VN is kept at 1. Characterizations by TEM, dark-field images, and SEM reveal dense and coherent columnar in coatings. Owing to the interfacial strengthening with plenty of interfaces, CrAlN/VN multilayer coatings with appropriate bilayer period exhibit superior plastic deformation resistance, H3/E*2. With an appropriate bilayer period of 16 nm, the H3/E*2 boosts to a maximum around 0.36. Furthermore, the tribological properties are examined by a ball-on-disc wear test at room temperature and 700oC. At room temperature, the wear rates of CrAlN/VN multilayer coatings are lower than that of CrAlN due to structural strengthening. Particularly, the multilayer coating with a bilayer period of 16 nm reveals the lowest wear rate of 1.0×10−6 mm3N-1m-1. After wear test at 700 oC, it can be observed that the coefficient of friction (COF) values for CrAlN/VN multilayer coatings significantly reduce with increasing temperature, which is attributed to the formation of sufficient solid and liquid self-lubricating vanadium oxides at elevated temperature. Moreover, mechanical strengthening in multilayer coatings with numbers of interfaces is beneficial for lowering the wear rate. Especially, the value can be down to 1.6×10−5 mm3N-1m-1 for the one with bilayer period of 16 nm. In addition, the worn morphology after wear test at 700oC is much favorable with less spallation and debris on the wear track, as compared to CrAlN monolayer. The X-ray photoelectron spectroscopy (XPS), focused ion beam (FIB) and transmission electron microscopy (TEM) techniques are further used to examine the worn surface characteristics after wear test at elevated temperature to further probe the hybrid anti-wear mechanisms. A hybrid mechanism, including structural strengthening and elemental contribution, is proposed to highlight the favorable anti-wear property in CrAlN/VN multilayer coatings at elevated temperature.

並列關鍵字

CrAlN/VN multilayer coatings ； High-temperature tribological test ； Anti-wear mechanism

參考文獻

3. J.D. Kim, Y.H. Kang, “High-speed machining of aluminum using diamond endmills”, Int. J. Mach. Tools Manufact. 37 (1997) 1155.

4. R. Franz, C. Mitterer, “Vanadium containing self-adaptive low-friction hard coatings for high-temperature applications: A review”, Surf. Coat. Technol. 228 (2013) 1.

5. R.W. Hertzberg, “Deformation and fracture mechanics of engineering materials”, 3rd ed., Wiley, New York, 1989.

6. P.H. Mayrhofer, C. Mitterer, L. Hultman, H. Clemens, “Microstructural design of hard coatings”, Prog. Mater. Sci. 51 (2006) 1032.

7. I. Milosev, H.H. Strehblow, B. Navinsek, “Comparison of TiN, ZrN and CrN hard nitride coatings: Electrochemical and thermal oxidation”, Thin Solid Films 303 (1997) 246.