氮化鋯硬膜破裂韌性量測

Fracture Toughness Measurement of ZrN Hard Coatings

陳郁翔(Yu-Hsiang Chen)

指導教授 ： 黃嘉宏 ； 喻冀平

國立清華大學/原子科學院/工程與系統科學系/碩士(2013年)

摘要

此研究的主要目的是測量氮化鋯硬膜的破裂韌性並探討織構對破裂韌性的影響。遵循Griffith準則與結合力區域模型，裂縫於薄膜內部生成前後，所造成的彈性應力與應變差可用於推導儲存應變能並進而計算出破裂韌性。在本團隊提出的方法中，彈性常數由奈米壓痕機量測、薄膜厚度由掃描式電子顯微鏡量測，而殘餘應力由光學曲率法或cos2αsin2ψ X光繞射方法測量。實驗結果顯示當氮化鋯硬膜的(111)織構為0.71時，其破裂韌性推估在23.9到42.4 J/m2範圍之間。氮化鋯的硬度並沒有隨著膜厚有趨勢性的改變，但應力梯度卻在破裂模型中扮演重要的角色。應力梯度由拉伸與壓縮應力彼此競爭造成，而裂縫可能起始於含大量缺陷和局部最大應力梯度的位置。當膜厚達4.2 µm以上，膜內(200)優選方向的晶粒增加而相對應的減弱(111)方向織構，推測與應力釋放有關。當氮化鋯膜內的儲存能量大於31.6 J/m2，此能量將隨著應力釋放而降低，而此釋放的儲存能可能是織構轉換的驅動力。

關鍵字

氮化鋯 ； 破裂韌性 ； 織構 ； 應力梯度

並列摘要

The objective of this study was to measure the fracture toughness of ZrN hard coatings and to investigate the effect of texture on the fracture toughness. Following Griffith's criterion and cohesive zone model, the stored elastic strain energy (Gs) inside the film derived from the elastic mismatch strain and the stress difference before and after cracking outset was used to evaluate the fracture toughness of hard coatings. For the proposed energy-based method, elastic constant was measured by nanoindentation, film thickness was determined from SEM cross-sectional image, and residual stress was obtained from the laser curvature method or XRD cos2αsin2ψ method. The results showed that for a ZrN coating with (111) texture coefficient of 0.71, the fracture toughness was estimated to be ranged from 23.9 to 42.4 J/m2. The hardness of the ZrN coatings was not changed with increasing film thickness. Stress gradient may play an important role in the fracture mode. Fracture of the ZrN coating may be initiated at a position of local maximum stress gradient accompanying with defects. The stress gradient in the ZrN coating may be originated from the competitive stress generation mechanisms. As the film thickness was above 4.2 µm, the (200) orientation increased in the strongly (111) textured ZrN coatings, which may be related to the stress relief. When the stored energy in the ZrN coating was higher than 31.6 J/m2, it was partly released accompanying with the stress relief. The release of stored energy was considered to be the driving force of texture inversion.

並列關鍵字

Zirconium nitride ； Fracture toughness ； Texture ； Stress gradient

參考文獻

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