Multiscale Characterization of Deformation Mechanisms in the Weld Joint of a Nickel-based Superalloy
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EE4.11.1
Multiscale Characterization of Deformation Mechanisms in the Weld Joint of a Nickel-based Superalloy O.M. Barabash, J.A. Horton, S.S. Babu, J.M. Vitek, S.A. David, G.E. Ice and R.I. Barabash* Metals and Ceramics Div., Oak Ridge National Laboratory, Oak Ridge, TN Abstract Multiscale plastic deformation in the heat affected zone (HAZ) of a Ni-based single crystal superalloy has been characterized using white microbeam synchrotron diffraction measurements together with OIM imaging, electron and optical microscopy. Characteristic length scales on the macro, meso and nano scale are determined. Dissolution of the γ' - phase particles during heating and secondary precipitation of γ' – phase during cooling is found, as well as formation and multiplication of dislocations. This process is more intense as one approaches the fusion line (FL). In the regions immediately neighboring the FL, γ' - phase particles dissolve completely and reprecipitate from the solid solution in the form of very small (50-70nm) particles. In the immediate vicinity of the FL, the temperature gradient and the rate of it’s change reaches maximal values and causes the formation of large amounts of dislocations. Dislocations are concentrated in the γ matrix of the single crystal superalloy. X-ray Laue diffraction (both conventional and microbeam) and electron microscopy show that alternating dislocations slip systems dominate in the HAZ with typical Burgers vector b=[110]. Local lattice rotations in different zones of the weld joint are linking with the microslip events in different zones of the weld. Introduction Microstructural stability of blade materials used in turbine systems has become a critical issue for the reliability and economy of entire power generation systems. When manufacturing fusion welds, the potential exists for defects to be introduced: dissolution and re-growth of nanosize L12 ordered particles influences phase and microstructure stability; centerline grain boundaries may appear; interdendritic microporosity, liquation and solidification cracking may form; plastic deformation may cause cracking in the heat affected zone (HAZ). The HAZ is located in the immediate vicinity of the fusion zone (FZ). It forms as a result of heating up to below the melting temperatures and subsequent cooling. The HAZ is an important part of the weld and determines many of the weld properties. The HAZ which is formed during welding of a single crystal nickel-based alloy has some specific features1, 2 as a consequence of the absence of grain boundaries and the presence of strengthening γ' phase particles with the volume fractions up to 75%. Experimentals The structures of the HAZ, fusion zone (FZ) and base material (BM) formed during welding of TSM 75 and RENE N5 nickel based single crystals were analyzed. The initial
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Contact author: Rosa Barabash
EE4.11.2
single crystals had a dendrite microstructure that was a result of its original casting. Dendrites were oriented along the [001] sample axis (± 2.50). The spot welding experiments for T
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