單晶體銅奈米壓痕試驗之分子動力模擬

Milecular dynamics simulation for nanoindentation on Single crystal Cu films

張譯文(Yi-Wen Chang)

指導教授 ： 郭昌宏

國立暨南國際大學/科技學院/土木工程學系/碩士(2007年)

摘要

本研究係利用分子動力學理論模擬奈米尺寸單晶銅試體受剛性Berkovich式探針壓痕，觀察單晶銅變形過程及討論機械性質。於本研究之系統中，單晶銅試體於X、Y方向為週期邊界，內部銅原子鍵結以Morse Potential Function表示，壓痕主動控制項為壓痕深度，並利用Gear五階預測修正法作為系統數值積分方法。研究目的是藉由數值方法模擬單晶銅奈米壓痕過程，並探討系統溫度、單晶銅試體尺寸及探針壓痕速度、加速度、持壓時間、壓痕深度對於單晶銅試體機械性質影響。最後經由最小平方法回歸模擬所得之加載-卸載曲線方程式，利用Oliver-Pharr提出之壓痕理論求取初始卸載勁度並計算單晶銅於奈米壓痕下之硬度、楊氏係數等材料參數。研究結果顯示壓痕過程中，若系統溫度越高，則會軟化單晶銅試體，使其材料硬度、楊氏係數皆隨著溫度提升而降低。此外系統中之探針若壓痕速度過快，會嚴重影響所得卸載曲線之適用性。一般在200m/s以下、單次積分步階為 為本系統適合之壓痕速度。結果顯示壓痕速度越快所得之各項單晶銅材料參數值越高，若探針於到達壓痕預定深度前、後能有加速度假設則能獲得更加符合實際試驗之卸載曲線，且探針加速度越小則曲線越平滑。探針持壓時間對於單晶銅試體影響隨持壓時間增加而加劇，且會使單晶銅材料參數趨向一定值。另外，單晶銅試體在X、Y方項為週期邊界假設時，在探針與單晶銅試體邊界產生長程作用力之前，相較於試體平面尺寸，則試體厚度對於壓痕影響較大。

關鍵字

分子動力模擬 ； 奈米壓痕 ； 單晶銅

並列摘要

The research presents a molecular dynamics simulation of Berkovich nano-indentation test on a single crystal Cu film. The objective of this research is to apply MD simulation to simulate the nano-indentation process and to investigate the effects of system temperatures and the indenter’s tip on copper films. The Morse potential functions are applied to model the bonds between Cu atoms and the gear’s fifth predict-correct method is used for the numerical calculation where the boundary condition of copper films is assumed periodic in both X and Y directions. The tip of Berkovich indenter is rigid and perfect and the system is controlled by indentation depth. The least squares method is used to fit the unloading-curve and the O-P method is derived to determine the hardness and young’s modulus of Cu films. The simulation results show that the copper film could be softened by the higher temperature which leads to smaller hardness and Young’s modulus. The indenter with over speed will cause an inaptitude unloading-curve, and the indenter with higher speed could give greater Cu parameters. The indenter with well acceleration condition will obtain more adequate curve. As the indenter hold time increased, the plastic deformation and plastic energy increased. Furthermore, if the Cu films is in X,Y periodic condition, the Cu film’s area of horizontal doesn’t affect the outcome of indentation before the long-range force occurs.

並列關鍵字

MD simulation ； nanoindentation ； single crystal Cu

參考文獻

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