Inertia Welding of Nickel Base Superalloys for Aerospace Applications

G.J. BaxterG.J. Baxter11, M. Preuss, M. Preuss22 and P.J. Withers and P.J. Withers22

1 Rolls-Royce plc, UK2 Manchester Materials Science Center, UMIST/University of Manchester, UK

Inertia Welding ProjectInertia 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 ProcessInertia 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 ProcessInertia Welding Process

Time

For

ce /

rpm

/ T

orqu

e / U

pset

Upset

Axial Force

rpm

Torque

I II III IV

Time

For

ce /

rpm

/ T

orqu

e / U

pset

Upset

Axial Force

rpm

Torque

I II III IV

143 mm specimen143 mm specimen

HOOP

AXIAL (z)

RADIAL (R)

.etc)],()1[()21)(1(

Eaxialhoopradialradial

• calculated stress:

with E = 224 GPa and = 0.27 for RR1000

• average accuracy for the calculated stress: 60 MPa

Residual StressResidual Stressneutron diffractionneutron diffraction

• strain:

0

0

d

dd

All stresses are in the units of MPa

a) as-welded, b) conventional and c) modified PWHT conditions

Hoop residual stresses in RR1000Hoop residual stresses in RR1000

z is axial position from the weld line, R is radial position from the centre of weld

0

200

400

600

800

1000

1200

140040

060

0

600

800

800

1000

1000

1200

2

1

0

-1

-2

R/m

m

0 1 2 3 4 5

z/mm

400

500

600

600

600

700

700

800

800

2

1

0

-1

-2

R/m

m

0 1 2 3 4 5

z/mm

200300

300

300

400

400 400

2

1

0

-1

-2

R/m

m

0 1 2 3 4 5

z/mm

a) as-welded

Hole drilling and neutron Hole drilling and neutron diffraction resultsdiffraction results

Axial and hoop stresses of RR1000 as a function of R at the weld line

-1500

-1000

-500

0

500

1000

1500re

sidu

alst

ress

/MP

a

-4 -2 0 2 4

R/mm

HOOP

AXIAL

hd hdnd

a) conventional PWHT

Hole drilling and neutron Hole drilling and neutron diffraction resultsdiffraction results

Axial and hoop stresses of RR1000 as a function of R at the weld line

-1500

-1000

-500

0

500

1000

1500re

sidu

alst

ress

/MP

a

-4 -2 0 2 4

R/mm

HOOP

AXIAL

hd hdnd

a) modified PWHT

Hole drilling and neutron Hole drilling and neutron diffraction resultsdiffraction results

Axial and hoop stresses of RR1000 as a function of R at the weld line

-1500

-1000

-500

0

500

1000

1500re

sidu

alst

ress

/MP

a

-4 -2 0 2 4

R/mm

HOOP

AXIAL

hd hdnd

Residual stresses in inertia Residual stresses in inertia welded RR1000welded 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 Metallurgical characterization in inertia welded RR1000in 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 testingSpatially resolved tensile testingmodified PWHTmodified PWHT

Spatially resolved tensile testingSpatially resolved tensile testingmodified PWHTmodified PWHT

0

200

400

600

800

1000

1200

1400

0.0 2.0 4.0 6.0 8.0 10.0 12.0strain/%

stre

ss/M

Pa

z=0mmz=0.5mmz=1mmz=2mmz=3mmz=4mmz=5mmz=6mm

0.2% Yield stress variation0.2% 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)

0

25

50

75

100

125

150

175

200

mea

sure

d-

nom

inal

0.2

%yi

eld

stre

ss/M

Pa

-6 -4 -2 0 2 4 6

z/mm

conv. PWHT

mod. PWHT

Hardness testing (RR1000)Hardness testing (RR1000)

Hardness profiles of the as-welded and PWHT’d conditions

420

440

460

480

500

520

540

HV1

0 1 2 3 4 5 6 7 8 9 10

z/mm

as-welded

conv. PWHT

mod. PWHTA

SynchrotronSynchrotron

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

IntegratedIntensity

0.005

0.010

0.015

0.020

0.025

I(10

0)/I(

200)

0 2 4 6 8 10

z/mm

as welded

conv. PWHT

mod. PWHT

FEG-SEM, low mag. images of FEG-SEM, low mag. images of ’’

’ across a weld in RR1000

weld line 2.5 mm away from the weld line

2.5 m2.5 m

FEG-SEM images of RR1000 FEG-SEM images of RR1000 secondary and tertiary secondary and tertiary ’’

Secondary and tertiary ’ across the weld modified PWHT

weld line250 nm

0.5 mm away from the weld line

250 nm 250 nm2 mm away from the weld line

250 nm9 mm away from the weld line

’ distribution only changes dramatically between the weld line and 2mm

Image AnalysisImage Analysis

Secondary and tertiary ’ across the weld line

400

425

450

475

500

525

550H

V1

0

10

20

30

40

vol.%

0 5 10

z/mm

0 5 10

HV1

vol% ( ' )sec

vol.%( ' )ter.

modified PWHT

Coherency strain Coherency strain between between and and ’’

Secondary and tertiary ’ across the weld line

As-welded

-1000

0

1000

2000

3000

4000

5000

stra

inbe

twee

nan

d'/m

icro

stra

in

0 1 2 3 4

z/mm

EBSDEBSD

Euler-Maps of the as-welded sample (RR1000)

weld line 0.25 mm 0.5 mm 1 mm 5 mm

grain size measured by EBSDgrain size measured by EBSD

Grain size across the weld line (RR1000)

0.45

0.50

0.55

0.60

0.65

0.70

0.75

D/

m-0

.5-0

.5

0 1 2 3 4 5 6

z/mm

EBSD + SynchrotronEBSD + Synchrotron

Comparing stored energy and FWHM of the (111) peak

0.5·106

1.0·106

1.5·106

2.0·106

stor

eden

ergy

per

unit

volu

me/

J/m

-3

0.018

0.019

0.020

0.021

0.022

0.023

0.024

0.025

FW

HM

/deg

ree

0 2 4 6 8 10

z/mm

0.0 2.5 5.0 7.5 10.0

stored energy

FWHM

as-welded

• 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 Microstructure in inertia welded RR1000welded RR1000as-welded and PWHTas-welded and PWHT

Questions ??