切削刀具上沈積鑽石和類鑽石薄膜之研究

Abstract

本研究利用熱燈絲及微波電漿化學氣相沉積法，進行鑽石薄膜沉積研究。使用基材包含燒結碳化鎢（鈷量，5%~27%，碳化矽和Si-Al-O-N等刀具材料。熱燈絲系統使用之沉積條件為：甲烷與氫氣之流量比，0.15/99.85~1.00/99.0；氣體總流量，每分鐘lOOcc；總反應氣壓，40torrs；基材溫度，T＝750~850℃：燈絲溫度，Tf＝2200~2350℃；燈絲功率，250~400 watts。微波電漿系統之沉積條件是：甲烷與氫氣之流量比，1.00/99.0；氣體總流量，每分鐘lOOcc；總反應氣壓，40 torrs；基材溫度，920~1050℃；微波功率，200~300 watts。 本研究針對基材前處理、沉積條件及基材種類等對於鑽石孕核及成長、薄膜之附著強度、薄膜之磨潤特性與沉積刀具切削性之問題加以探討。寶驗過程應用SEM, EDS, XRD. AES, XPS, RAMAN和TEM等分析儀器，來描析薄膜形貌與品質，缺陷與界面結構。並分別利用壓痕式附著性測定儀測量薄膜附著強度，表面粗度儀量測表面粗糙度及滑塊對環 (block-on-ting) 磨耗機決定薄膜之磨潤特性。從實驗結果，可獲得下列重要結論： (1) 燒結碳化鎢基材之表面粗糙度與表面屠台鈷量是控制鑽石薄膜附著強度的重 要因素。基材表面鈷元素有害於鑽石薄膜之孕核與成長。因此，利用化學浸 蝕方法除去鈷元素，成為碳化鎢基材沉積鑽石薄膜及提高附著性之必要步驟 。同時，基材之表面粗糙度控制Ra值範圍於0.06μm到 0.25μm之間，可得 到最佳附著強度。 (2) 鑽石薄膜之磨潤性質受薄膜結晶品質，表面粗糙度和結晶粒大小影響。在甲烷濃度為0.5%之沉積條件，薄膜具有 {100} 優選晶面及良好的結晶品質。因 此，可獲得較低的磨擦係數 (μ) 值，在乾式磨耗中，μ值約為0.23。 (3) 基材表面層之鈷量，經化學浸蝕除去，其表面粗糙度亦隨之變化，進而影響到鑽石薄膜之形貌及其抗破裂性。所以，一種正確的化學浸蝕處理方法去移除足夠的鈷量與維持基材表面粗糙度在最佳範圍內，是鑽石薄膜得到最佳附著強度的必要步驟。 (4) 由歐傑電子光譜 (AES) 分析得知，鑽石薄膜與碳化鎢基材之界面層存有大於50埃Ａ厚度之非鑽石碳層，此碳層之附著性可能是決定鑽石薄膜附著強度之指標。從穿透式電子顯微鏡 (TEM) 分析，亦得知微雙晶與差排是鑽石薄膜結構中最 主要的缺陷。所以，一種高級的製程必須先開發，以除去微雙晶及差徘缺陷，否則無法合成完美鑽石結晶。 (5) 鑽石薄膜沉積於燒結碳化鎢基材較優於碳化矽及Si-Al-O-N基材，是由於碳化鎢基材上沉積之鑽石薄膜，具有較高抗破裂強度及較低摩擦係數值。 (6) 在目前沉積條件下，沉積於碳化鎢基材之鑽石膜刀具，與已商業化陶瓷薄膜刀具相互比較，具有較佳之切削性。未來進一步改進仍有很大空間。

The diamond films deposited on various cutting tools by a hot filament assisted chemical vapor deposition (CVD) system and a microwave plasma CVD system were studied. The substrate tool materials include the cemented WC with 5% to 27% Co contents, SiC and Si-Al-O-N, etc. The deposition conditions for a hot filament CVD system are: CH4/H2 flow rate ratio, 0.15/99.85~1.00/99.0; total flow rate, 100 sccm; total pressure, 40 torrs; substrate temperature, 750~850℃; filament temperature, 2200 ~2350℃; power, 250~400 watts. The deposition conditions for a microwave plasma CVD system are: CH4/H2 flow rate ratio, 1/99; total flow rate, lOOsccm; total pressure, 40 torrs; substrate temperature, 920~1050℃; microwave power, 200~3OOwatts. Effects of substrate pretreatments, deposition conditions and substrate materials on diamond nucleation and growth, adhesion strength of the film, tribological behaviours of the film, and cutting performance of the coated tools were studied. SEM, EDS, XRD, AES, XPS, RAMAN and TEM were used to characterize the film morphologies and quality, defect and interface structures. Indentation adhesion tester, profilometer and block-on-ring tribotester were also used to determine the film adhesion, surface roughness and tribological properties, respectively. From the experimental results, the following conclusions can be drawn: (1) For cemented WC substrates, both surface roughness and surface Co content of the substrate are important factors controlling the adhesion strength of the films. The Co element on the substrate surface is detrimental to diamond nucleation and growth. Therefore, the removal of Co by chemical etching becomes a necessary step for a successful diamond deposition and adhesion. There exists an optimum surface roughness range (Ra=0.06~0.25μm) of the substrate for an optimum adhesion strength. (2) Tribological properties of the film generally depend on the film quality, surface roughness and particle size. At 0.5% CH4 concentration, the the film shows a predominant (100} facet and a better film quality, so gives rise to a lower friction coefficient (μ=0.23 under dry wear condition). (3) The removal of Co by chemical etching can change the surface roughness of the substrate, and so the final film morphology and its cracking resistance. Therefore, a proper etching treatment to remove enough Co from the surface and at the same time to maintain the surface roughness of the substrate in the optimum range are essential to reach an optimum adhesion strength of the film. (4) AES studies indicate that the interface layer between the film and the substrate is a carbon layer with a thickness >50A, which may be responsible for the adhesion strength of the film. The predominant defects in the film are microtwins and dislocations, therefore, a noble process must be developed to get rid of these defects before a perfect diamond crystal can be synthesized. (5) The cemented WC is a better substrate for diamond deposition than Si-AI-O-N or SiC materials due to a greater cracking resistance and a lower friction coefficient of the film on WC. (6) Under the present deposition conditions, the diamond-coated WC tools show a better cutting performance than the commercially available ceramic-coated tools. Further improvement can be made.