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    STP1580

    Mechanical Twinning in Aircraft Engine Bearing Steel

    Published: 2014


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    Abstract

    A new mechanism is proposed for rolling contact damage involving mechanical twinning in an aircraft gas–turbine engine bearing steel AISI M50NiL. These heavily tempered bearing steel components display prominent mechanical twinning not only in serviced material, but also within virgin samples in the heat-treated condition. The twins seem to initiate at inhomogeneities in the case-carburised zone beneath the grooved contact surface, where the tempered martensite contains fine dispersions of carbides rich in the substitutional solutes Mo, Cr, and V. The occurrence of twins in this hardened carbide-rich zone may coincide with the fact that the carburised region is designed to resist plastic deformation. There are surprising features associated with localised deformation via a twinning shear at interfaces where strains may become concentrated; for example along the prior-austenite grain boundaries and at incoherent interfaces around carbides. The consequences of these observations on rolling contact fatigue have yet to be addressed, but localised damage in the microstructure should promote crack initiation in bearing steels.

    Keywords:

    mechanical twinning, bearing steels, carburised m50nil, strain localisation, rolling contact fatigue, microstructure, damage mechanisms, aircraft engines


    Author Information:

    Nygaard, J. R.
    Univ. of Cambridge, Cambridge,

    Vegter, R. H.
    SKF Engineering & Research Centre, Nieuwegein,, MT

    Rawson, M.
    Rolls-Royce, Derby,

    Danson, P.
    Rolls-Royce, Derby,

    Bhadeshia, H. K. D. H
    Univ. of Cambridge, Cambridge,


    Committee/Subcommittee: A01.28

    DOI: 10.1520/STP158020140069