Fatigue Behavior of Nickel Based Super Alloy 718 in a Hot Corrosive Environment

    (Received 31 August 2013; accepted 29 January 2014)

    Published Online: 2014

    CODEN: MPCOAD

      Format Pages Price  
    PDF 16 $25   ADD TO CART


    Abstract

    Nickel based super-alloys when exposed to a combination of high temperature and low melting point fused corrosion products, result in early fatigue failure compared to their response in high temperature benign environment. The high cycle fatigue (HCF) (at 550 and 625°C) as well as fatigue crack growth (at 550°C) behavior of a nickel based super alloy 718 in hot corrosive environment (Na2SO4+NaCl salt coating), typical of marine engine environment, is presented in this paper. At least an order of magnitude decrease in fatigue life is noticed when the temperature is changed from 550 to 625°C at stress levels below 450 MPa. The statistical analysis of scatter in fatigue lives at different stress levels is performed and a Weibull–Inverse power law model is fitted to the stress–fatigue life data of alloy 718 in hot corrosive environment. Fracture surface examination of hot corrosion fatigue failures showed higher crack growth rates compared to uncoated high temperature HCF fracture surfaces. Fatigue crack growth rate at 550°C in a hot corrosive environment increases by an order of magnitude at 0.5 Hz in the Paris region compared to crack growth kinetics at 2 Hz in lab air environment at the same temperature. The fracture surface shows a mix of transgranular and intergranular mode of crack in the propagation region at 0.5 Hz. A fatigue failure diagram is proposed combining the thresholds of maximum stress level from endurance tests and maximum stress intensity factor from fatigue crack growth tests to demarcate the regions of propagating and non-propagating cracks during hot corrosion fatigue. The complexities in incorporating the effect of loading frequency in fatigue failure diagram are highlighted.


    Author Information:

    Prakash, Raghu V.
    Machine Design Section, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamilnadu

    Dhinakaran, Sampath
    Machine Design Section, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamilnadu

    Venkata Ramakanth, Jeyar
    Machine Design Section, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamilnadu

    Paulose, Neeta
    Gas Turbine Research Establishment, Bangalore, Karnataka

    Narendrababu, S. N.
    Gas Turbine Research Establishment, Bangalore, Karnataka

    Mannan, S. L.
    Gas Turbine Research Establishment, Bangalore, Karnataka


    Stock #: MPC20130039

    ISSN: 2165-3992

    DOI: 10.1520/MPC20130039

    ASTM International is a member of CrossRef.

    Author
    Title Fatigue Behavior of Nickel Based Super Alloy 718 in a Hot Corrosive Environment
    Symposium , 0000-00-00
    Committee E08