MSc Thesis Presentation

Effect of Temperature on Fretting Behaviour of SCMV

Julius Oluwatayo Abere(4057159)

Table of Contents• 1. Introduction• 2. Elevated temperature fretting of SCMV• 3. Friction behaviour – COF, fretting loops• 4. Wear behaviour – glaze layer/temperature• 5. Discussion• 6. Conclusions• 7. Future works

1. Introduction• Aeroengines mainshaft spline couplings and fretting.

LP spline coupling

Cylinder-on-flat fretting contact geometry

Internal and external splines

SCMV – Super chrome molybdenum vanadium steelSCMV is a high strength low alloy steel of

composition (wt. %):

Tempered martensite.

Vickers Hardness:Round specimen, 499 ± 4 HvFlat specimen, 482 ± 5 Hv

C Si Mn P S Cr Mo Ni V Fe

0.35-0.43 0.1-0.35 0.4-0.7 <0.007 <0.002 3.0-3.5 0.8-1.10 <0.3 0.15-0.25 Remainder

SCMV in aeroengine mainshaft spline couplingSpecimens supplied by

Weight reduction on both LP and IP shafts.Weight of the coupling reduced by about 1.5kg.Shaft weight per unit of torque transmitted reduced

by 25% and torque capability per unit shaft diameter doubled relative to earlier engines.

Spline life increased.

2.Elevated temperature fretting of SCMV

Fretting (micro-slip) in quasi-static contacts, e.g. splines, shrink fits, bolted parts, rivets, etc.

SuperCrMoV operating temperature up to 450oC Elevated temperature fretting of some steels, Ti &

Ni superalloys etc.

Oxidation, tribo-oxidation, tribo-sintering, glaze layer and severe-to-mild wear transition in metals

Transition temperature• Transition temperature for SCMV in fretting yet unknown.

• Friction and wear behaviour at RT, 150, 300 and 450oC under fretting conditions in air.

Transition temperature (220oC) for a steel/steel tribo-system in GSR fretting [Rybiak, etal., 2010].

Fretting wear tests

• Bespoke fretting wear test rig.– Lower stationary, while upper specimen oscillates.– Data logging system– Electrical heating system– Temperature maintained during test.

Test Conditions:Test parameter Value

Load, N 250, 450, 650

Temperature, oC 20 (Room), 150, 300, and 450.

Humidity, % 20 - 50

Slip amplitude, μm 25 and 50

Frequency, Hz 20

Number of cycles 100,000

Room temperature, oC 20 – 25

3(a). Friction behaviour - COF • COF vs Temperature for 250 N, 25 um, 100,000 cycles

and 20 Hz.

• COF decreased with temperature increase due to oxidation, tribo-oxidation and sintering of oxide particles to

form glaze layer.

3(b) Fretting loops• Gross slip regime fretting loops for 10,000 to 25,000 cycles at (a) room

temperature (RT), (b) 150, (c) 300 and (d) 450oC.

• Tangential force peaks, especially in 300oC test, are characteristic of ductile materials.

• It is related to a ploughing effect induced by the lateral interactions between the cylindrical specimen and the worn fretting scar borders when displacement reaches the amplitude positions.

RT

300oc

150oC

450oC

4(a). Wear behaviour –wear rates

• Wear rates reduced greatly at elevated temperatures.

4(b). Wear behaviour – wear scar profiles

• The wear scar profiles of the flat specimen of test at 450oC show material build up due to tribo-oxidation and glaze layer thickness.

4(c). Wear behaviour – SEM micrographs of wear scar

The wear scar profile of the flat specimen show decreasing width with increasing temperature.

BSE of flat specimen wear scar (a) Room temperature, (b) 150, (c) 300 and (d) 450oC.

150oCRoom Temperature

450oC300oC

4(c). Wear behaviour – SEM micrographs• The glaze layer on flat specimens increased with increasing temperature.

• The oxide glaze layer on elevated temperature specimens (150oC upward) compared to loose wear debris on room temperature specimen.

c d

Room Temperature 150oC

300oC 450oC

4(d) Wear behaviour – glaze layer• The glaze layer as observed on the 450oC flat specimen.

Oxide glaze layer, about 5 microns thick

450oC

450oC

4(e). Wear behaviour: X-SEM micrographs• The cross-section BSE of wear scar on the flat specimen show increasing oxide

glaze layer thickness with increasing temperature: (a) room temperature, (b) 150, (c) 300 and (d) 450oC.

Room Temperature 150oC

450oC300oC

4(f). Wear behaviour: occuring oxides, XRD patterns

• The XRD patterns show that haematite (H) and magnetite (M) occur in the Fe oxidation process during fretting of SCMV, especially on the 450oC flat specimen (e). (a) is unfretted, (b) room temperature, (c) 150oC and

(d) 300oC.

Unfretted

Room Temperature

150oC

300oC

450oC

4(g) EDX analysis of fretting contact at 450oC

• The EDX spectrum of the bright spots on 450oC flat specimen show thinner layers of new oxides (regrowth).

450oC

450oC

5. DiscussionHigh COF in RT test due to adhesion, reduced by

oxidation in ET tests.Steady state gross slip regime (GSR) fretting loops are

observed with tangential force peaks. Static oxidation before, and tribo-oxidation during, ET

fretting.

Sintering to form the glaze layer starts from 150oC.The oxide glaze layer is thin at 150, breaks up at 300

and builds up at 450oC.

6. ConclusionsThe COF of SCMV pair in fretting at ET, from 150oC, is

much lower compared to that at RT.

Mild wear at 150oC and higher.

Material removal turned to oxide layer build-up at

450oC, harder oxides support load and reduce wear.Tribo-oxidation may have healing effects on ET

fretting for SCMV similar to mild steel.

7. Further work The severe-to-mild wear transition temperature of SCMV

has yet to be determined, more tests are necessary.

Micro-hardness of the oxide layer.

Thermal cycle fretting wear tests.

The glaze layer chemistry – XPS, SAM, ESCA., etc.

ET fretting wear map for SCMV.

Tests with other representative contact geometries.

Controlled environment tests.

Thank you