AlCrNbSiTi高熵合金與其氮化物薄膜微結構、機械性質與高溫氧化行為之研究

Study on Microstructures, Mechanical Properties and Oxidation Behavior of High-Entropy (AlCrNbSiTi)Nx Metallic and Nitride Films

沈宛叡(Wan-Jui Shen)

指導教授 ： 葉均蔚 ； 張一熙

國立清華大學/工學院/材料科學工程學系/博士(2014年)

摘要

本實驗利用真空電弧熔煉法製備Al0.34Cr0.22Nb0.22Si0.11Ti0.11六元非等莫耳高熵合金靶材，再利用反應式直流磁控濺鍍法製備其高熵金屬及氮化物薄膜，藉由調整氮氣流率與基板偏壓，探討此二參數對薄膜微結構與機械性質的影響。此外，為了解薄膜抗氧化性質，選擇氮氣流率50% 與基板偏壓 -100 V所鍍製之薄膜，在不同條件下進行大氣退火，研究此高熵合金氮化物薄膜的抗氧化性質及機制。為瞭解附著性，則以Ti, Cr, 與自身合金作為中間層，研究此最佳化高熵氮化物薄膜在WC/Co基板上的附著性質。最後，以此高熵氮化物膜搭配適宜的中間層鍍覆在WC/Co商用三角銑刀上，對304不銹鋼以及SKD11 工具鋼進行切削測試，並與商用TiN 及TiAlN互相比較。

實驗結果發現(Al0.34Cr0.22Nb0.22Si0.11Ti0.11)50N50氮化物薄膜在氮氣比例50 %、基板偏壓 -100 V的製程條件下，擁有最高的硬度值36 GPa與楊氏係數340 GPa。除合金膜為非晶質結構外，高熵氮化物薄膜呈現單一的FCC結構，為二元氮化物的固溶相，其薄膜結構呈現緻密的細纖維結構。此外，此製程條件下製備之高熵氮化物擁有非常優秀的抗氧化性質，在900 °C 50小時的大氣退火下，表面只有約 290 nm厚的氧化物生成；而氧化增重測試中，由室溫以每分鐘上升10 °C到1300 °C，每cm2也只增重0.015 mg，皆遠優於商用TiN與TiAlN的表現。此絕佳抗氧化表現經TEM及EDX分析，應歸因於表面緻密氧化鋁層與豐富的非晶氧化物層形成了良好的擴散阻絕層。而附著測試中，以100 nm厚的Ti作為中間層可在WC/Co基板上提供最佳的附著性質，其臨界應力大於100 N，超過商用標準。以此(Al0.34Cr0.22Nb0.22Si0.11Ti0.11)50N50氮化物薄膜搭配Ti中間層鍍覆在商用WC/Co銑刀上進行切削測試，並與與商用TiN與TiAlN薄膜相較，高熵合金氮化物擁有更優秀的切削性質。綜合本研究成果，可瞭解(Al0.34Cr0.22Nb0.22Si0.11Ti0.11)50N50高熵氮化物在刀具保護上具有優秀的應用潛力。

關鍵字

高熵氮化物 ； 機械性質 ； 抗氧化 ； 切削性質

並列摘要

High-entropy nitride (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)100-xNx coatings were sputter-deposited from an alloy target Al0.34Cr0.22Nb0.11Si0.11Ti0.22. The effects of nitrogen flow ratio and substrate bias on film structure and properties were studied. Stoichiometric nitride coatings with the best hardness were then annealed at various conditions to investigate the oxidation properties. This (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coatings were also deposited onto WC/Co substrate with Ti, Cr, and Al0.34Cr0.22Nb0.11Si0.11Ti0.22 metallic interlayers to study the adhesion properties. The cutting test of (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coated inserts with optimal interlayer and oxidation resistance was performed on 304 stainless steel and SKD11 tool steel. For comparison, TiN and TiAlN coatings were also prepared for oxidation and cutting tests.
The results show that (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coatings deposited at nitrogen flow ratio 50% and substrate bias -100 V have the highest hardness of 36 GPa and Young's modulus of 340 GPa. The metallic films exhibit amorphous structures, while all other nitride films are in single FCC structures. This hard coating also possesses outstanding oxidation resistance. The oxide layer on the coating surface was 290 nm after 50 h annealing at 900 °C. The weight gain after thermal ramping to 1300 °C was merely 0.015 mg cm-2. Such an oxidation resistance is superior to other reported nitride coatings. Eight layers of oxides with different compositions were observed in the scale by TEM. The superior oxidation resistance is owing to the protection of the dense Al2O3 layer and inter-connected Si-rich amorphous network.
In adhesion test, (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coatings with 100 nm Ti-interlayer demonstrate the best adhesion property. The critical load exceeds 100 N, which is better than the commercial demand (60 N). The cemented inserts coated with (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 and Ti-interlayer show a better milling performance than commercial TiN and TiAlN-coated inserts. This research demonstrates the great potential of application of this high-entropy (Al0.34Cr0.22Nb0.22Si0.11Ti0.11)50N50.coating for cutting tools.

並列關鍵字

High-entropy Nitride ； Mechanical Properties ； Oxidation Resistance ； Machining Performance

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