Synchroniser Ring 1

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Wear 254 (2003) 532–537

Microstructures and wear properties of brass synchroniser rings

H. Mindivan, H. Çimenoglu, E.S. Kayali∗

Metallurgy and Materials Engineering Department, Istanbul Technical University, 80626 Maslak, Istanbul, Turkey

Received 30 July 2002; accepted 6 January 2003

Abstract

In this study, the wear behaviour of synchroniser rings produced from a (+ ) high-strength brass was investigated under dry sliding

conditions by pin on disc and reciprocating wear tests. Pin on disc tests were conducted on M2 quality high speed tool steel and 120-mesh

Al2O3 abrasive papers. AISI 52100 quality steel balls were used in reciprocating tests as counterface. A correlation between microstructure,

hardness and wear resistance was established for the investigated synchroniser rings. An increase of -phase from 8 to 23 vol.% decreasedthe hardness from 281 to 250 HV and increased the wear resistance. Depending on the type of wear test and counterface, the increment in

wear resistance is found in between 15 and 80%.

© 2003 Elsevier Science B.V. All rights reserved.

Keywords: Abrasion; Brass; Synchroniser; Wear

1. Introduction

Synchronisers are used in almost all manual gear boxes

of vehicles. Synchroniser rings have been widely adopted in

manual transmissions to make gear shifting much smoother.

The synchromesh mechanism achieves speed matching bydragging the components to a matching speed with the syn-

chroniser rings. Since friction between the idler and syn-

chroniser ring is essential for the synchromesh mechanism,

synchronisers need machining of grooves on the friction sur-

faces. They perform the synchronising function very well

when new, but degrade with use because the grooves dis-

appear as a result of wear. Synchroniser rings are made

of brass or steels coated with molybdenum. Molybdenum

coated steel synchroniser rings have higher costs than brass

synchroniser rings [1].

In the automobile industry, particularly in the manufac-

turing of components, where resistance to wear is the chief

requirement, high-strength brasses are commonly used.

High-strength brasses are suitable mainly for engineering

areas where high strength to support heavy loads and/or

high resistance to wear and corrosion are required. The

main advantages of high-strength brasses are further im-

provement of mechanical properties by heat treatment as

well as their low cost [2–7].

∗ Corresponding author. Tel.: +90-212-285-3536;

fax: +90-212-285-3427.

E-mail address: [email protected] (E.S. Kayali).

High-strength brasses can be mainly classified as +

or brasses, depending on the phases present in their mi-

crostructures. In Cu–Zn binary system, -phase can dissolve

maximum 39% Zn at about 460 ◦C and has f.c.c. crystal

structure. -phase, which is stable between 45.5 and 49%

Zn, has disordered b.c.c. crystal structure at high temper-atures. At about 454 ◦C, an order/disorder transition takes

place [8]. Alloying elements such as aluminium, silicon,

iron, manganese, and tin are added to these brasses to ensure

high service performance by entering to the solid solution

and/or forming intermetallic compounds in the microstruc-

ture. In the case of alloys containing additions of silicon and

manganese, manganese silicide (Mn5Si3) intermetallic com-

pounds are formed. These intermetallic compounds have a

hexagonal crystal structure and high hardness and give the

alloy a high wear resistance [2,3,6].

In a Cu–Zn system, optimum wear behaviour is reported

for 25% Zn content, while an increase of Zn to 48% im-

proved the hardness without giving better wear performance

[9]. On the other hand, the lowest wear rate was obtained

when the microstructure was composed of -phase with

about 25% of -phase located mainly at grain boundaries [5].

According to Sadykov et al. [7], ultra fine grained (2–3m)

+ brass exhibits wear resistance higher than both heat

treated -phase and coarse-grained + phase brasses.

In this study, wear behaviour of synchroniser rings, which

are manufactured from a high-strength + brass in four

processing steps (sand casting, hot forging, machining and

tempering) was examined to establish the relationship be-

tween microstructure and wear performance.

0043-1648/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0043-1648(03)00023-1



H. Mindivan et al. / Wear 254 (2003) 532–537 533

Fig. 1. One of the synchroniser ring examined in this study. The outer

and inner diameters are approximately 130 and 112 mm, respectively.

2. Experimental procedure

This investigation was conducted on four synchroniser

rings having nominal compositions of 63% Cu, 8% Mn, 4%

Al, 1% Si and 20% Zn [10]. Fig. 1 shows one of the syn-

chroniser rings utilised in this investigation. The manufac-

turer declared that they are taken from the same batch but

their processing conditions are not exactly the same.

Metallographic studies, X-ray diffraction (XRD) analysis

and microhardness measurements were carried out for the

synchroniser rings to characterise their microstructures. Mi-

crostructures of the investigated synchroniser rings were ex-

amined by light optical microscope (LOM) after grinding,

polishing, and etching in standard manner. The etchant wascomposed of 5 g FeCl3, 95 ml alcohol (methane) and 2 ml

HCl. XRD with Cu K radiation was used to analyse the

constituent phases in the microstructure. Volume fraction of

the microstructural constituents was quantified on metallo-

graphic samples prepared from five different regions of each

synchroniser rings by Zeiss Apiotech Vanio optical micro-

scope in conjunction with a computer having KS 400 im-

age analysis software program. Microhardness measurement

was also carried out on metallographic samples under the

load of 200 g with a Vickers indenter. For each synchroniser

ring, ten hardness measurements were made on the samples.

Room temperature dry sliding wear behaviour of the syn-

chroniser rings was examined by a pin on disc and a recip-

rocating wear tester. Pin on disc wear tests were carried out

under metal–metal and metal–abrasive testing configurations

with a normal load of 27 N, where the relative humidity of

the environment varied between 50 and 60%. M2 quality

high speed tool steel disc (65 HRC) and 120-mesh Al2O3

abrasive papers were used as counterfaces for metal–metal

and metal–abrasive test configurations, respectively. During

metal–metal tests, pins were continuously in contact with the

same circular path on the disc, whilst they followed a spiral

path on the abrasive paper so that they always passed over

fresh abrasive grains throughout the metal–abrasive wear

tests. Pin on disc wear test specimens (pins) were machined

from the thick sections of the synchroniser rings with 4 mm

tip diameter. Contact surfaces of the pins were finished with

1m Al2O3 paste after grinding. Metal–metal wear tests

were performed for a sliding distance of 10 km with a slid-

ing speed of 0.3 m/s. The sliding distance and speed of the

pins on the abrasive paper was 3 m and 0.15 m/s, respec-tively. The results of the wear tests were analysed according

to weight loss. Weight losses of the pins were determined

by measuring the weights before and after the wear tests,

nearest to 0.1 mg.

Reciprocating wear tests were carried out at room tem-

perature by applying normal loads of 1.3 and 3.4 N to the

plate samples with a 10 mm diameter steel (AISI 52100)

ball. Humidity of the environment varied between 70 and

80% during the tests. The surfaces of the plate samples

machined from the synchronising rings were polished with

1m Al2O3 paste after grinding. During the tests, sliding

speed was 0.02 m/s for the total sliding distance of 240 m.

The stroke of the balls on the plate samples was 12 mm. Af-ter the tests, the wear tracks developed on the surfaces were

detected by a profilometer. The results of the reciprocating

wear test were based on 2D profile images of the wear tracks.

Wear performance of the examined synchroniser rings

were evaluated by taking the average of two successive pin

on disc (metal–metal and metal–abrasive) and reciprocating

wear test results. After the wear tests, the worn surfaces of

the specimens were examined by a scanning electron micro-

scope (SEM).

3. Results and discussion

LOM photographs and XRD pattern of the examined syn-

chroniser rings are depicted in Figs. 2 and 3, respectively.

The XRD pattern consists of a Cu rich -phase, a Zn rich

-phase and a Mn5Si3 type intermetallic compound. Mi-

croscopic examinations revealed that, in the microstructures

light coloured needle shaped -phase precipitated in dark

coloured -phase matrix. Mn5Si3 intermetallics are gray

in colour. Volume fractions of Mn5Si3 intermetallics were

about 4% for all of the investigated synchroniser rings, while

-phase volume fractions are listed in Table 1. The balance

was -phase. Microhardness measurements revealed that theaverage hardness of the investigated synchroniser rings var-

ied in the range between 250 and 281 HV depending on

the volume fraction of -phase. As can be seen in Table 1,

Table 1

Image analysis and hardness results of the investigated synchroniser rings

Sample Volume fraction of -phase (%) Hardness, HV (kg/mm2)

1 8.4 ± 2.5 281 ± 2

2 14.1 ± 1.0 267 ± 4

3 19.3 ± 2.0 260 ± 3

4 23.0 ± 1.5 250 ± 4



534 H. Mindivan et al./ Wear 254 (2003) 532–537

Fig. 2. LOM photographs of the examined synchronising rings: (a) Sample 1, (b) Sample 2, (c) Sample 3 and (d) Sample 4.

the higher the amount of -phase in the microstructure, the

lower is the hardness of the synchroniser rings.

The results of pin on disc wear tests of the examined

synchronising rings are presented in Fig. 4 with respect to-phase content. Both metal–metal and metal–abrasive wear

test results reveal that weight loss decreases with increasing

Fig. 3. XRD pattern of sample 4.

-phase volume fraction. According to Fig. 4, increase of

-phase from 8 to 23 vol.% increased the metal–metal and

metal–abrasive wear resistance of the synchronising rings

about 25 and 15%, respectively.Worn surfaces of the samples after metal–metal and

metal–abrasive tests are shown in Figs. 5 and 6, respectively.

Wear surfaces of the samples worn on M2 quality steel

Fig. 4. Results of pin on disc wear tests as a function of -phase volume

fraction.




Fig. 5. SEM photographs of the surfaces of the pins worn on M2 quality tool steel: (a) Sample 1 and (b) Sample 4.

Fig. 6. SEM photographs of the worn surfaces of the pins worn on Al 2O3 abrasive papers: (a) Sample 1 and (b) Sample 4.

disc are smooth. On the metal–metal contact surfaces, lim-

ited plastic deformations with narrow and shallow parallel

grooves are evident. Electron probe microanalysis has not

revealed any iron and chromium elements detached from

the counterface steel disc on the contact surfaces of brass

pins. Local adhesion of pin material to the surface of the

disc might be responsible for these fine grooves. Relatively

Fig. 7. 2D profile images of the wear tracks produced on the surfaces of: (a) Sample 1 and (b) Sample 4 under normal load of 1.3N.

wider and deeper grooves were observed on metal–abrasive

contact surfaces with some embedded abrasive Al2O3 par-

ticles. Abraded surface topographies indicate the dominant

wear mechanism as ploughing.

The results of reciprocating wear tests are given in Fig. 7

as 2D profile images of the wear tracks. Wider and deeper

wear tracks were developed on the surfaces with decreasing



536 H. Mindivan et al./ Wear 254 (2003) 532–537

volume fraction of -phase. The performance of the syn-

chroniser rings during reciprocating wear tests were quanti-

fied by measuring the area of the wear tracks. The variation

of the wear track area with the volume fraction of -phase is

shown in Fig. 8. As for the pin on disc tests, the reciprocating

wear tests also give similar trend between wear resistance

of synchronising rings and volume fraction of -phase. Theincrease of -phase from 8 to 23 vol.% increased the recip-

rocating wear resistance about 45 and 80% for test loads of

1.3 and 3.4 N, respectively.

Figs. 9 and 10 depict the SEM photographs of the cen-

tres of the wear tracks produced on the surfaces of the syn-

chronising rings by the steel ball under the normal loads of

1.3 and 3.4 N, respectively. During reciprocating wear tests,

wear was progressed by ploughing action of the ball by form-

ing grooves in the wear tracks aligned parallel to the recip-

rocating sliding direction. In some regions of wear tracks,

microcracks perpendicular to the sliding direction were ob-

served. These microcracks, which indicate the possible wear

mechanism as fatigue, were much more apparent for low

Fig. 9. SEM photographs of the wear tracks produced on the surfaces of: (a) Sample 1 and (b) Sample 4 under normal load of 1.3N.

Fig. 10. SEM photographs of the wear tracks produced on the surfaces of: (a) Sample 1 and (b) Sample 4 under normal load of 3.4 N.

Fig. 8. Results of reciprocating wear tests as a function of -phase volumefraction.




volume fractions of -phase. Microcracking was more fre-

quently observed with the increase of test load, especially

when the -phase volume fraction is low.

The results of pin on disc (metal–metal and metal–abrasive)

and reciprocating wear tests carried out in this study are in

good agreement with the result of Waheed and Ridley [6],

who studied dry sliding wear behaviour of a Cu–41%Znbinary alloy. These researchers attributed the reduction in

wear rate with increasing volume fraction of -phase to

toughening of the material due to blunting of cracks when

they reach the -phase.

4. Conclusion

In this study, room temperature dry sliding wear be-

haviour of synchroniser rings manufactured from a +

high-strength brass was investigated by pin on disc (for

metal–metal and metal–abrasive configurations) and recip-

rocating wear tests.

Increase of -phase present in the microstructures of syn-

chroniser rings from 8 to 23 vol.%, decreased the hardness

from 281 to 250 HV, but increased the wear resistance. De-

pending on the type of wear test and counterface the incre-

ment in wear resistance of synchroniser rings is found in

between 15 and 80%.

Acknowledgements

The authors wish to thank Dr. H. Kazdal Zeytin for her

help in image analysis. The assistance of Mrs. Candan Ayhan

in SEM examinations is also appreciated.

References

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