Effect of Microstructures on Fatigue Crack Growth Behavior of Friction Stir Processed NiAl Bronze Alloy
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NICKEL-ALUMINUM bronze (NAB) alloy is widely used in marine engineering materials of propeller, pump, valve, etc. due to its excellent combination of high strength and corrosion resistance.[1] With the development of ocean engineering around the world, NAB alloy has been paid more and more attention by many material scientists.[1–3] Typical microstructures of the as-cast NAB include a phase, retained b (b¢) phase, and several precipitation phases (ji, jii, jiii, and jiv).[4] The complex microstructures are disadvantageous to the mechanical properties and corrosion resistance of the as-cast NAB alloy.[5] For example, Xu et al. reported that high interphase stress was formed between a matrix YUTING LV is with the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P.R. China, and also with the Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, P.R. China. YANG DING and YUANFEI HAN are with the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University. LAIZHI Wu is with the Jiujiang Brand of 707 Institute of China Shipbuilding Industry Corporation, Jiujiang 332007, P.R. China. LIQIANG WANG and WEIJIE LU are with the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, and also with the Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, No. 800 Dongchuan Road, Materials Science and Engineering Building D329, Minhang District, Shanghai, 200240, P.R. China. Contact emails: [email protected], [email protected] Manuscript submitted October 13, 2016. Article published online January 13, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
and j phases when NAB alloy was deformed in elastic–plastic region (about 300-450 MPa). Fracture might initiate from the a/j phase boundaries due to the high interphase stress.[6] Fonlupt et al. found that NAB alloy containing more second phases had higher stress corrosion cracking susceptibility.[7] In addition, porosity defects are also formed due to gas evolution during solidification and fatigue crack can initiate and propagate from these defects, which are also adverse to the mechanical properties of NAB alloy.[8,9] Recently, several techniques have been adopted to improve the mechanical properties and corrosion resistance of the as-cast NAB alloy such as ion implantation,[10] laser surface melting,[11,12] friction stir processing (FSP),[13,14] and friction surfacing (FS).[15] Among them, FSP has been rapidly developed due to its energy efficiency, environmental friendliness, and versatility.[16] Although this technique is originally intended for aluminum alloys, the applications have now been extended to various alloys such as magnesium, copper, titanium, and steels.[16] One important advantage is that only the component surface is modified, while for NAB component used in ocean engineering almost all the damages occur on the surface. Thus, FSP is a suitable technique to make uniform the surface microstructures of the as-cast
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