Mechanical properties and deformation behavior of amorphous nickel-phosphorous films measured by nanoindentation test

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ated Ni-P ﬁlms with good mechanical and anticorrosion properties have been widely studied and used in molding, tool, and many other industries, including microelectromechanical systems as wear- and corrosionresistant coatings.[1–4] The effects of processing parameters, such as the composition and pH value of plating solution, on the P content, and consequent structure and properties of the plated Ni-P ﬁlms have been studied.[4,5,6] To enhance further the mechanical properties and application variety of the coatings, especially at elevated temperatures, transition metals like tungsten and cobalt have been incorporated in the Ni-P ﬁlms, and the mechanical properties of these ﬁlms have been reported.[7,8] Generally, the Ni-P ﬁlms with high P contents have an amorphous structure,[1–8] and amorphous materials are observed to exhibit better mechanical properties than crystalline ones because ductile deformation accounting for dislocation activity (formation and sliding) is no longer valid for amorphous structures.[9–12] However, the deformation mechanism based on bulk metallic glasses has been primarily investigated.[10,11,12] Limited experimental observations on the deformation behavior of thin amorphous ﬁlms on a nanometer scale have been reported.[13–17] Because the deformation behavior signiﬁcantly affects the mechanical properties of materials, the inﬂuence of microstructure on the deformation behavior on a nanometer scale needs to be clariﬁed, especially for thin, amorphous Ni-P coatings, because their application extends to micro- and nanometer scales as seen in microelectromechanical systems. An instrumented nanoindentation test has been widely applied for the measurement of the mechanical properties SHOU-YI CHANG, Assistant Professor, YU-SHUIEN LEE, Graduate Student, HSIANG-LONG HSIAO, Graduate Student, and TING-KUI CHANG, Graduate Student, are with the Department of Materials Engineering, National Chung Hsing University, Taichung, Taiwan, Republic of China. Contact e-mail: [email protected] Manuscript submitted December 8, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A

of thin ﬁlms.[18,19] However, only the hardness and elastic modulus of electroless plated Ni-P ﬁlms have been obtained with this test.[7,8] These basic experimental data do not sufﬁciently represent the mechanical stability or failure model of the Ni-P ﬁlms in practical applications. Analyses of the mechanical behaviors of the ﬁlms relating to the deformation mechanism need to be further performed. Actually, by using nanoindentation, much more information can be obtained through which critical shear stress and fracture toughness can be extracted to reveal more representative mechanical properties of the ﬁlms.[20–25] Therefore in this study, the instrumented nanoindentation test is applied not only to measure the mechanical properties of the electroless plated Ni-P ﬁlms, but also to calculate the critical shear strength and energy release rate required for the initiation of early-stage plastic yielding on a nanometer scale. The Ni-P ﬁlms

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