Inertia Welding of Nickel Base Superalloys for Aerospace

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 (RR 1000, Alloy 720 LI) are replacing conventional nickel base Superalloys (Waspaloy, IN 718) • Only friction welding is capable of reliably joining RR 1000 and Alloy 720 LI Ø Characterization of residual stresses, microstructure and mechanical properties of inertia friction welded RR 1000

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

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

Inertia Welding Process

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

Residual Stress neutron diffraction • strain: • calculated stress: with E = 224 GPa and = 0. 27 for RR 1000 • average accuracy for the calculated stress: 60 MPa

Hoop residual stresses in RR 1000 a) as-welded, b) conventional and c) modified PWHT conditions All stresses are in the units of MPa z is axial position from the weld line, R is radial position from the centre of weld

Hole drilling and neutron diffraction results a) as-welded Axial and hoop stresses of RR 1000 as a function of R at the weld line

Hole drilling and neutron diffraction results a) conventional PWHT Axial and hoop stresses of RR 1000 as a function of R at the weld line

Hole drilling and neutron diffraction results a) modified PWHT Axial and hoop stresses of RR 1000 as a function of R at the weld line

Residual stresses in inertia welded RR 1000 • 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 RR 1000 • 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

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 RR 1000 samples as a function of axial distance from the weld line (z=0)

Hardness testing (RR 1000) 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 (RR 1000)

FEG-SEM, low mag. images of g’ 2. 5 mm weld line 2. 5 mm away from the weld line ’ across a weld in RR 1000

FEG-SEM images of RR 1000 secondary and tertiary g’ 250 nm 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 Secondary and tertiary ’ across the weld modified PWHT ’ distribution only changes dramatically between the weld line and 2 mm

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

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

EBSD weld line 0. 25 mm 0. 5 mm 1 mm 5 mm Euler-Maps of the as-welded sample (RR 1000)

grain size measured by EBSD Grain size across the weld line (RR 1000)

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

Microstructure in inertia welded RR 1000 as-welded and PWHT • between the weld line and 2 mm 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

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