4. SCMV – Super chrome molybdenum vanadium steel
SCMV is a high strength low alloy steel of
composition (wt. %):
Round specimen, 499 ± 4 Hv
Flat 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
5. SCMV in aeroengine mainshaft spline coupling
Specimens 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.
6. 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
7. 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].
8. 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 parameter Value
Load, N 250, 450, 650
C 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, o
C 20 – 25
9. 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.
10. 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
• 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.
12. 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.
13. 4(c). Wear behaviour – SEM micrographs of wear scar
The wear scar profile of the flat specimen show decreasing width with
BSE of flat specimen wear scar (a) Room temperature, (b) 150, (c) 300 and
14. 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.
Room Temperature 150oC
15. 4(d) Wear behaviour – glaze layer
• The glaze layer as observed on the 450oC flat specimen.
Oxide glaze layer, about 5 microns thick
16. 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
17. 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
18. 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).
19. 5. Discussion
High 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,
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.
20. 6. Conclusions
The 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.
21. 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.