Influences of heat treatment on fatigue crack growth behavior of NiAl bronze (NAB) alloy
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ng Hu School of Nuclear Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
Liqiang Wang,a) Xiaoyan Xu, Yuanfei Han, and Weijie Lub) State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China (Received 10 June 2015; accepted 14 August 2015)
Fatigue crack growth tests of NiAl bronze (NAB) alloy heat treated at different temper temperature after quenching at 920 °C are performed using direct current potential drop method. The influences of heat treatment on the fatigue crack growth behavior of NAB alloy are investigated. The results show that the fatigue crack growth rate (FCGR) of NAB alloy decreases with the increase of temper temperature. A few large secondary cracks are obtained as the sample is tempered at 350 °C and the secondary cracks diminish with the increase of temper temperature. With further increasing temper temperature to 550 °C, a large number of small secondary cracks are obtained, which is responsible for its lower FCGR. The as-cast NAB alloy has a lower FCGR than that tempered at 550 °C at low stress intensity factor range (DK) region, and the lower FCGR is attributed to the crack deflection effect of the as-cast microstructure. At high DK region, the crack deflection effect diminishes, which leads to the higher FCGR of as-cast sample.
I. INTRODUCTION
Nickel–aluminum bronze (NAB) alloy is widely used for marine equipment such as propeller, pump, valve etc. due to the high mechanical properties and excellent corrosion resistance. As a quaternary system, NAB alloy typically contains 9–12 wt% Al and 6 wt% each of Fe, Ni, and Mn.1,2 The addition of alloying elements improves the mechanical properties and inhibits the formation of c2 phase (Al4Cu9), which is harmful to the corrosion resistance due to the high Al content.3 Typical microstructure of as-cast NAB includes ɑ matrix phase, martensite b phase (b9 phase), iron rich jⅰ, jⅱ, jⅳ, and nickel rich jⅲ phases. According to Nakhaie’s study, the anodic character of j phases with tens of millivolt higher than copper rich ɑ phase, which increases the galvanic corrosion of NAB alloy.4 The NAB alloy is also easily subjected to the selective phase corrosion in seawater.4,5 It is well accepted that the corrosion of NAB is initially confined to the ɑ phase within the ɑ 1 jⅲ eutectoid microstructure.6
Contributing Editor: Yang-T. Cheng Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2015.282 J. Mater. Res., Vol. 30, No. 20, Oct 28, 2015
To improve the corrosion and mechanical properties of cast NAB alloy, several techniques have been used such as equal channel angular extrusion,7,8 friction surfacing,9 and friction stir processing10–13 etc. It is commonly reported that these techniques significantly improves the corrosion and mechanical properties of as-cast NAB alloy due to the refined grains and simplified microstructure. However, it is difficult to use these techniques i
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