Effects of Shot Peening on Fatigue Properties of Zr-based Amorphous Alloys Containing Ductile Crystalline Particles
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NTRODUCTION
AMORPHOUS alloys are considered as possible candidates for high-performance structural applications because of their properties such as strength, hardness, stiffness, and corrosion resistance.[1–4] However, they show limited plasticity at room temperature, which limits their practical applications to high-functional components such as electronic parts, sports goods, and those of the defense industry.[5] It has been suggested that the incorporation of crystalline particles within the amorphous matrix can improve plasticity.[6] The ex situ reinforcement of amorphous alloys with WC, SiC, W, or Ta particles was found to improve the ductility .[7] In contrast, amorphous matrix composites fabricated by the in situ formation of ductile crystalline particles demonstrated a dramatic improvement in ductility.[8] Zr-based monolithic amorphous alloys have high strength,[9] but their fatigue limits are 6 to 9 pct of tensile strength, which is a low level of fatigue limit, compared with 30 to 40 pct of tensile strength in conventional high-strength steels or aluminum alloys.[10] In general, damages during the fatigue crack initiation CHANGWOO JEON and CHANG YOUNG SON, Research Assistants, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea. CHOONGYUN PAUL KIM, Research Professor, is with the Stainless Steel Research Group, Technical Research Laboratories, POSCO, Pohang 790-785, Korea, and is also with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology. SUNGHAK LEE, Professor, is with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, and is also with the Materials Science and Engineering, Pohang University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted November 10, 2010. Article published online August 30, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
and propagation act as important factors in the fatigue life. Once a crack initiates in a Zr-based a monolithic amorphous alloy, the abrupt fracture occurs within limited fatigue cycles, thereby resulting in the lowered fatigue limit.[10,11] This implies that the damage during the fatigue crack initiation occupies most of the fatigue life. The fabrication of in situ amorphous matrix composites containing ductile crystalline particles is a good method for preventing or modifying the abrupt fatigue crack initiation and propagation.[6,12–15] Here in these amorphous matrix composites, the fatigue limit as well as ductility and fracture toughness are improved as ductile particles effectively block the propagation of shear bands formed in the amorphous matrix.[11,16–18] As another way for improving the fatigue limit in Zr-based amorphous alloys, Zhang et al.[19] suggested the formation of compressive residual stresses on the surface by shot peening. These compressive residual stresses helped the homogeneous deformation of the alloys, which led to a two-fold or three-fold improvement in ductility
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