Inertia Welding of Nickel Base Superalloys for Aerospace Applications G.J. Baxter 1, M. Preuss 2 and P.J. Withers 2 1 Rolls-Royce plc, UK 2 Manchester Materials Science Center, UMIST/University of Manchester, UK

Inertia Welding Project Operation temperatures are constantly increasing to improve engine efficiency High  ’ v / o nickel-base Superalloys (RR1000, Alloy 720LI) are replacing conventional nickel base Superalloys (Waspaloy, IN718) Only friction welding is capable of reliably joining RR1000 and Alloy 720LI  Characterization of residual stresses, microstructure and mechanical properties of inertia friction welded RR1000

Inertia Welding Process Welding Parameters: Rotational Speed Inertia Level Axial Pressure  no liquid phase during welding  join dissimilar metals/alloys

2000 ton force Inertia Welder Rolls-Royce plc. Compressor rotor factory (CRF) near Nottingham

Inertia Welding Process

143 mm specimen HOOP AXIAL (z) RADIAL (R)

calculated stress: with E = 224 GPa and = 0.27 for RR1000 average accuracy for the calculated stress: 60 MPa Residual Stress neutron diffraction strain:

All stresses are in the units of MPa a) as-welded, b) conventional and c) modified PWHT conditions Hoop residual stresses in RR1000 z is axial position from the weld line, R is radial position from the centre of weld

a) as-welded Hole drilling and neutron diffraction results Axial and hoop stresses of RR1000 as a function of R at the weld line

a) conventional PWHT Hole drilling and neutron diffraction results Axial and hoop stresses of RR1000 as a function of R at the weld line

a) modified PWHT Hole drilling and neutron diffraction results Axial and hoop stresses of RR1000 as a function of R at the weld line

Residual stresses in inertia welded RR1000 large stresses generated during welding largest stresses observed in the hoop direction, at the weld line and close to the inner diameter conventional PWHT reduces the residual stresses but not to an acceptable level modified PWHT gives acceptable level of residual stresses

Metallurgical characterization in inertia welded RR1000 what effect has the PWHT on the microstructure and the mechanical properties Microstructure in the heat affected zone  ’ volume fraction and particle size,  grain size, work hardening, coherency strain etc. how do the mechanical properties vary in the weld zone

Spatially resolved tensile testing modified PWHT

0.2% Yield stress variation 0.2% yield stress profiles (measured – nominal 0.2% yield stress) of the conventional and modified PWHT’d RR1000 samples as a function of axial distance from the weld line (z=0)

Hardness testing (RR1000) Hardness profiles of the as-welded and PWHT’d conditions

Synchrotron Integr. Intensity of the (100) superlattice reflection divided by the integr. Int. (200) reflection (RR1000)

FEG-SEM, low mag. images of  ’  ’ across a weld in RR1000 weld line2.5 mm away from the weld line 2.5  m

FEG-SEM images of RR1000 secondary and tertiary  ’ Secondary and tertiary  ’ across the weld modified PWHT weld line 250 nm 0.5 mm away from the weld line 250 nm 2 mm away from the weld line 250 nm 9 mm away from the weld line   ’ distribution only changes dramatically between the weld line and 2mm

Image Analysis Secondary and tertiary  ’ across the weld line modified PWHT

Coherency strain between  and  ’ Secondary and tertiary  ’ across the weld line As-welded

EBSD Euler-Maps of the as-welded sample (RR1000) weld line0.25 mm0.5 mm1 mm5 mm

grain size measured by EBSD Grain size across the weld line (RR1000)

EBSD + Synchrotron Comparing stored energy and FWHM of the (111) peak

between the weld line and 2mm dramatic microstructural changes between 2 and 4 mm from the weld line only increased coherency strain observable 20% increase of strength in the heat affected zone after PWHT New PWHT (conventional PWHT + 50°C) results in no overall significant loss of strength Microstructure in inertia welded RR1000 as-welded and PWHT

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