Improved Fatigue Properties of 316L Stainless Steel Using Glass-Forming Coatings
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Improved Fatigue Properties of 316L Stainless Steel Using Glass-Forming Coatings F. X. Liu*, C. L. Chiang*,**, L. Wu*, Y. Y. Hsieh**, W. Yuan*, J. P. Chu**, P. K. Liaw*, C. R. Brooks*, and R. A. Buchanan* *Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA ** Institute of Materials Engineering, National Taiwan Ocean University, Keelung 202, Taiwan
Abstract The effects of the glass-forming coatings on the fatigue behavior of 316L stainless steel were investigated. Films consisting of 47%Zr, 31%Cu, 13%Al and 9%Ni (atomic percent) were deposited onto the stainless steel by magnetron sputtering. The influences of the substrate condition, the surface roughness, the adhesion, and the compressive residual stresses on the fatigue behavior were studied. The applications of the glass-forming coating gave rise to significant improvements in both the fatigue life and the fatigue limit, in comparison with the uncoated steel. Depending on the maximum stress applied to the steel, the fatigue life can be increased by at least 30 times, and the fatigue limit can be elevated by 30%. Introduction Bulk-metallic glasses (BMGs) possess desirable properties, including extraordinarily high strengths, high hardness, low friction coefficients, and excellent wear and corrosion resistance, good bending ductility in the form of thin films, which makes them good candidates for coating materials to improve materials properties, such as fatigue and wear resistances [1,2]. The wide applications of BMGs are limited by the relatively small sample size and high cost [3]. Thus, the deposition of thin glass-forming coating materials onto structural materials to enhance the fatigue behavior becomes a challenging area for scientific studies. The Zr-based metallic glasses with the composition of Zr-31Cu-13Al-9Ni (in atomic percent) have good glass-forming abilities and high strengths. The annealing treatment of Zr31Cu-13Al-9Ni films results in crystallization and amorphization [4]. The Zr-based glassforming coating with this composition was deposited on 316L stainless steel by magnetron sputtering. The effect of the glass-forming coating on the fatigue behavior of the 316L stainless steel was investigated by four-point-bend fatigue tests. Atomic-force microscopy (AFM) and scanning-electron microscopy (SEM) were employed to measure the surface roughness and study the fractography, respectively. Fatigue results such as fatigue life and
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fatigue-endurance limit were compared with those reported from similar steels coated with other hard coating materials [5, 6]. Experimental procedure 316L stainless steel with 20% cold work was used as the substrate material with the composition listed in Table 1. The samples, with the geometry of 3 x 3 x 25 mm3 were ground with 800-grit sand paper, followed by electrical polishing to ensure a smooth surface. The bottom of the 316L specimen was coated with the Zr-based amorphous film to avoid the crack initiation and propagation in the tensile stresses, a
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