| Summary: | 博士 === 國立臺灣科技大學 === 材料科學與工程系 === 103 === Because of their unique properties, most recently, thin film metallic glasses (TFMGs) have been studied for various research and engineering applications, such as for medical tools, microelectromechanical system (MEMS) devices, and improving mechanical properties of materials. TFMGs to be used for a particular potential application, their electrical, mechanical, and thermal properties should be well known and thus, indentation recovery property of TFMGs following contact deformation must be considered. In this study, the effects of annealing temperature, holding time, free volume, indenter geometry, film composition, and film thickness on indentation recovery property of Zr50.3Cu28.1Al14Ni7.6, Cu48Zr42Al6Ti4, Hf45.9Cu44.8Al6.5Ti2.8, and Fe65Ti13Co8Ni7B6Nb1 (in at. %) TFMGs are examined.
The indentation recovery property of a sputtered Zr50.3Cu28.1Al14Ni7.6 (in at. %) thin film metallic glass upon heating is examined. Due to the surface tension-driven viscous flow, the shape of indentation appears to recover to different extents at various temperatures and holding times. It is found that a maximum of 59.8% indentation depth recovery is achieved after annealing within the supercooled liquid region (SCLR). The amount of free volume in the film is found to play a role in the recovery. Atomic force microscopy results reveal a decrease in film roughness to a minimum value after annealing within SCLR. To elucidate the experimentally observed shape recovery, a numerical modelling has been employed. It is evident that the depressed region caused by indentation is elevated after annealing.
The influences of indenter tip geometry, film thickness and film composition on indentation recovery of Zr-, Cu-, Hf-, and Fe-based TFMGs have been studied. Nanoindentations are performed at room temperature with two three-sided pyramidal indenters (Berkovich and cube-corner), followed by annealing performed within the supercooled liquid temperatures. The results reveal that the extent of recovery of indentation by Berkovich indenter is higher than that of cube-corner owing to higher compressive stress underneath of Berkovich tip and larger radius of curvature of the indent left behind after Berkovich indentation. The numerical modelling of depth profile of Zr-based TFMG shows the blunter the indenter tip is the higher the recovery. The thicker film also shows larger recovery. In addition, because of the bonding force difference between constituent elements, Zr-based TFMG exhibits larger recovery than Cu-, Hf- and Fe-based TFMGs.
Larger indentation recovery is achieved when TFMGs are annealed at around their corresponding crystallization temperature and longer holding time. In addition, films indented by blunter indenter, the thicker film, and the film that has lower glass transition temperature showed larger indentation recovery.
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