富鈦鈦鎳形狀記憶合金薄膜雷射退火之研究

Abstract

本實驗利用磁控濺鍍製備非晶富鈦鈦鎳形狀記憶合金薄膜。由於形狀記憶效應及超彈性只有結晶的薄膜才會出現，因此利用雷射雕刻機、連續二氧化碳雷射、脈衝UV雷射及脈衝IR雷射使薄膜產生局部區域結晶。由於設備的限制，使用雷射雕刻機及連續二氧化碳雷射分別遭遇了不均勻、雷射反射過大、熱影響區過大、氧化及試片損毀的問題。使用脈衝UV雷射，結晶深度僅有400 nm，並無法使用奈米壓痕測試其超彈性。使用脈衝IR雷射，雷射退火的參數及其退火區域的機械性質被系統化的研究。TEM結果顯示，退火後薄膜表面有約800奈米至1微米的奧斯田相結晶層，而其餘部分則為非晶層。退火薄膜的折減楊氏模數、微硬度及超彈性由奈米壓痕試驗檢測，可發現非晶薄膜經由雷射退火後，折減楊氏模數會由約127 GPa 降至 86 GPa，微硬度會由約7 GPa降至約5 GPa，符合試片表面為奧斯田相的結果。使用雷射在同一區域重複掃描數次以加深結晶深度，掃描次數重複太多超過臨界值會導致試片被燒毀。奈米壓痕的超彈測試結果顯示，隨著掃描次數的增加，誘發麻相的臨界應力會有些微的下降，但折減楊氏模數及微硬度並沒有明顯的改變。不同瓦數下的臨界掃描次數間的機械性質也在此研究中被比較，結果顯示，折減楊氏模數及誘發麻相所需要的臨界應力會隨著低瓦數/高掃描次數至高瓦數/低掃描次數有顯著的下降。此外，本實驗也顯示了掃描速率及雷射間的間距必須要有良好的匹配以達成最佳的超彈效果。另外，雷射退火時基板加熱會使得誘發麻相所需要的臨界應力下降，相轉更容易發生，但由於表面氧化的影響，壓痕後殘留的變形量也會增加。

Amorphous Ti-rich TiNi SMAFs were deposited using magnetron sputtering. Only crystallized films have shape memory effect and superelasticity. In this study, a normal laser engraving machine, continuous CO2 laser, pulsed UV laser and pulsed IR laser were used to anneal shape memory thin films. However, due to the limitation of the apparatus, problems like nonuniformity, high reflectivity of laser, heat affected zone, severe oxidation and damage occurred when using normal laser engraving machine and continuous CO2 laser. When using pulsed UV laser, the thickness of crystallized region was only 400 nm which is hard to measure their superelasticity by nanoindentation. In IR laser, the relationship between laser annealing parameters and the mechanical properties was studied. The cross-section of annealed-film showed crystallized surface layer of 800 nm to 1 μm in thickness and other region remained amorphous. The reduced Young’s modulus, micro-hardness and superelastic behavior of laser-annealed SMAFs were characterized using nanoindentation. After laser annealing, the reduced Young’s modulus decreased from ~127 to ~86 GPa and hardness decreased from ~7 to ~5 GPa indicating the formation of austenite phase on the sample surface. For the films scanned (i.e., annealed) by the laser beam multiple times in the same region, the film could be burned when the scanning times exceeded a critical number. This critical number decreased as the laser power increased. Without burning the film, the stress required to induce martensitic transformation decreased slightly with scanning times, while the reduced Young’s modulus and hardness didn’t show obvious change. The mechanical properties for films scanned at different laser powers for the corresponding critical times were also studied. Both the reduced Young’s modulus and stress required to induce martensitic transformation decreased drastically as the parameters changed from low power/high scanning times to high power/low scanning times. This study also indicates that the ratio between scanning speed and line spacing should match to reach a better superelasticity. For laser annealing films at an elevated substrate temperature, phase transformation will become easier and the plastic deformation increase. The increasing of plastic deformation comes from the effect of oxidation. The present results would be helpful in selecting laser annealing parameters to crystalize amorphous TiNi-based SMAFs.