| Summary: | 博士 === 國立臺灣科技大學 === 應用科技研究所 === 102 === In this study, we propose the use of the Zr-based thin film metallic glass (TFMG) as a promising coating for enhancing fatigue property of Ti6Al4V alloy and 316L stainless steel. 200 nm-thick Zr50Cu27Al16Ni7 and TiN thin films are prepared by sputtering on Ti6Al4V substrate. The four-point bending fatigue life is improved from 3.1 x 10^5 cycles for the uncoated sample by ~17.3 times to 5.3 x 10^6 cycles at a stress level of 675 MPa. The improvement in fatigue limit increases from 575 to 675 MPa as well. TFMG has a better performance than the TiN coating. On the other hand, the fatigue life of tension-tension fatigue 316L stainless steel is increased by ~25 times from 2.3 x 10^5 cycles of the bare sample to 6.0 x 10^6 cycles of TFMG coated sample at a loading stress of 350 MPa. The fatigue property improvements could be attributed to the several reasons, for instance, good mechanical property of Zr-based TFMG, specifically high strength and flexibility. After coating, Zr-based TFMG yields a decrease in surface roughness of substrates, hence reducing the crack initiations and propagations on the surface. Furthermore, the good adhesion property of TFMG also plays an important role. The mechanism of the film to prolong the fatigue life is examined by FIB and TEM. It has been proven that the coatings restrain the defects propagate to the surface during the fatigue cycles. The above-mentioned are the key factors that improve the fatigue resistance of the coated materials. Thus, this study demonstrates the metallic glass film as a promising coating material for improving the fatigue properties of materials.
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