- 學位論文
Al-Cr-Ta-Ti-Zr-N 多元氮化物薄膜之製備與性質研究
Preparation and Characterization of Multi-element Al-Cr-Ta-Ti-Zr-N Coatings
摘要
本論文主要利用射頻磁控濺鍍法以單一等莫耳高熵合金靶材在Ar與N2混合氣氛下置備Al-Cr-Ta-Ti-Zr-N多元氮化物薄膜於Si晶片與WC-C基板上。藉由改變鍍膜參數與後退火溫度來研究此薄膜的微結構與機械性質。研究結果與討論主要分為四個部分。第一部份主要在不外加基板偏壓與溫度的條件下，置備 Al-Cr-Ta-Ti-Zr-N薄膜，探討N2流量比例的變化對於薄膜性質之影響。在純Ar的濺鍍情況下，薄膜呈現非晶態且具有相當平整的表面形貌；隨著逐漸通入N2流量比例超過14%時，氮化物薄膜呈現單一的FCC固溶結構並伴隨著較強的 (111) 晶向。氮化物膜呈典型柱狀結構，隨氮氣流量增加，其表面形態從三角錐狀變為由許多奈米顆粒團聚的圓頂狀。此氮化物薄膜具有高硬度 (26~32 GPa)，在氮氣流量比例為9%時，薄膜具有高硬度與低彈性係數，經TEM分析可能是因為形成奈米氮化物晶粒散佈於非晶基地的奈米複合結構而造成。第二部分探討基板溫度 (100-500°C) 對於Al-Cr-Ta-Ti-Zr-N薄膜的性質影響。在不同的溫度中，薄膜均呈現單一FCC結構；溫度上升則造成薄膜中N含量略為下降，(200)指向的強度逐漸升高，然而晶粒與晶格常數略微減小。薄膜的熱膨脹係數則藉由簡易的混合法則推算與溫度-應力之實驗曲線得到，此兩數值相當吻合，同時藉由得知膨脹係數可進一步推知薄膜的本質應力與熱應力之影響。薄膜的硬度與彈性係數似乎與基板溫度無明顯關係，分別維持在35 GPa與350 GPa左右。第三部分則研究基板偏壓對於薄膜性質之影響。添加基板偏壓造成離子轟擊現象增強，使得薄膜鍍膜速率、Al及N的含量略為下降。因添加基板偏壓，使得薄膜由具有狀柱間微孔的柱狀結構轉而變得緊實、柱狀邊界較不明顯的柱狀結構。隨基板偏壓的上升，薄膜仍呈現單一FCC結構，結晶指向由 (200) 為主轉變為 (111) 為主，晶粒尺寸與晶格常數也隨之增加。基板偏壓同時也造成殘餘應力、硬度與附著力的上升，而磨耗速率在-150至-200 V時達到最低。在最後一個部份則探討真空後退火處理 (500至1100°C, 2小時) 對於Al-Cr-Ta-Ti-Zr-N多元氮化物膜的微結構與機械性質之影響。經TEM與XRD分析，FCC結構的初鍍膜柱狀結構中，具有高度的缺陷(如大量的差排與晶界)；在退火後薄膜仍維持單一FCC結構，其高缺陷密度之柱狀結構仍與初鍍態相仿，同時經退火至1000°C後，薄膜的硬度也仍維持初鍍態約36 GPa的高硬度。此Al-Cr-Ta-Ti-Zr-N多元氮化物薄膜的結構與機械性質熱穩定性顯示在高速切削工具的保護性鍍膜上擁有很好的應用潛力。
並列摘要
The aim of this study is to prepare the Al-Cr-Ta-Ti-Zr-N multi-element coatings onto Si or WC-Co substrates in Ar+N2 mixed atmosphere by RF magnetron sputtering using a single euqimolar AlCrTaTiZr alloy target. The deposition parameters and post-deposition annealing temperatures were varied to investigate the change of structural and mechanical properties of these nitride coatings. The research is mainly divided into four sections. In the first section, Al-Cr-Ta-Ti-Zr-N films were deposited under various nitrogen flow ratios at room temperature without applying substrate bias. The AlCrTaTiZr alloy film exhibited an amorphous structure with smooth surface, while a face-center-cubic (FCC) solid-solution structure with strong (111) orientation, columnar structure and different surface features was observed in the nitride films prepared under different nitrogen flow ratios. The Al-Cr-Ta-Ti-Zr-N films exhibited high hardness as compared with conventional nitride and a nanocomposite structure was obtained for coatings deposited at nitrogen flow ratio of 9%. In the second section, the influence of the substrate temperature (100 to 500°C) on the properties of these Al-Cr-Ta-Ti-Zr-N coatings was investigated. A slight reduction of the N concentration is observed with increasing the substrate temperature. The Al-Cr-Ta-Ti-Zr-N coating of an FCC structure showed an increase in (200) peak intensity and a decrease in crystallite size and lattice parameter, for increasing substrate temperature. The coefficient of thermal expansion of coatings was determined from the rule of mixtures and the stress-temperature plot to see the contribution of thermal and intrinsic macrostress. An increase in substrate temperature results in a monotonic decrease of compressive residual macrostress from -3.2 to -2.0 GPa while the hardness and elastic modulus around 35 and 350 GPa, respectively, were obtained nearly independent of the substrate temperature. In the third section, Al-Cr-Ta-Ti-Zr-N coatings were deposited onto Si and WC-Co substrates to see the influence of substrate bias (0 to -200 V) on properties of these coatings. A reduction in the deposition rate and the concentration of N and Al was observed with increasing substrate bias. The application of substrate bias changed the coating from a voided to a dense columnar structure. The FCC-structured Al-Cr-Ta-Ti-Zr-N coatings showed an increase in both (111) peak intensity and grain size, for increasing substrate bias. The compressive residual macrostress, hardness and adhesion were enhanced with an increase of substrate bias. The lowest wear rate against 100Cr6 steel balls was obtained for the coating biased at -150 to -200 V. In the final section, the influence of post-deposition annealing (500 to 1100°C for 2 h) on the microstructure and mechanical properties for Al-Cr-Ta-Ti-Zr-N coatings was investigated. The coatings were found to retain their as-deposited single-phased FCC structure after all annealing temperatures. The columnar microstructure with a high defect density and the measured high hardness (~36 GPa) were observed to be unchanged after annealing up to 1000°C. The high thermal stability in structural and mechanical properties for this multi-element Al-Cr-Ta-Ti-Zr-N coating was considered as a promising candidate for application of cutting tools.