Microstructural and mechanical characterisation of the IW Ni-base superalloy RR1000

Simpson, Christopher (2015). Microstructural and mechanical characterisation of the IW Ni-base superalloy RR1000. University of Birmingham. Ph.D.

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Abstract

A high γ' volume fraction Ni-base superalloy (RR1000) has been studied and its microstructural and mechanical response to the inertia welding process assessed. The bond line microstructure has been characterised in terms of process parameters and associated modelled temperature distributions. The high temperature mechanical behaviour has been interrogated via sustained load crack growth testing in air and vacuum.

The weld microstructure is characterised by a uni-modal distribution of ultrafine γ' and a meta-dynamically recrystallised grain structure. The recrystallised grain size is determined by the width of the shear zone and the associated deformation behaviour, which varies with process parameter selection. Of particular importance is the welding pressure, which controls the upset rate, thereby limiting the shear zone width. A restricted shear zone can be related to increases in the peak bond line temperature and cooling rate.

The high temperature crack growth behaviour is controlled by grain boundary oxide formation and crack tip stress state. In inertia welded RR1000 this stress state is governed by the reprecipitated γ'. The steady state crack growth rate increases with temperature, which is due to an increased rate of oxide formation. Near threshold growth behaviour is also dependent on localised microstructural features.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):