a study on the effect of the change of tempering...

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:04 27

I J E N S August 2018 IJENS IJENS © -IJMME-5959-401806

A Study on the Effect of the Change of

Tempering Temperature on the

Microstructure Transformation of Cu-Ni-Sn

Alloy

Xuan Duong Pham1,*, Anh Tuan Hoang2,3, Duong Nam Nguyen1

1Vietnam Maritime University, Hai Phong, Vietnam 2 Ho Chi Minh city University of Transport, Ho Chi Minh, Vietnam

3 The Central Transport College VI, Ho Chi Minh, Vietnam

E-mail: [email protected]

Abstract— The copper alloys have been using in many

applications such as electrical devices, house wares, and others

due to their special properties. In this study, the changes in the

microstructure and hardness value of the alloy Cu-15Ni-8Sn after

heat treatment were investigated in the basis of Spinodal

decomposition theory and various analysis methods. After

quenching, an orderly microstructure (DO3) with low hardness

phase was formed in case of aging at 450oC within 2 hours. As a

result, an increase in the lubrication ability was shown for this

alloy. In addition, phase alpha that was considered as a solid

solution of Cu and Ni with high strength was formed by Spinodal

decomposition. Findings of this paper will orientate to produce a

new alloy for the fabrication of the small diesel engine bearing.

Index Term— Cu-15Ni-8Sn, bearing, Spinodal decomposition,

hardness

I. INTRODUCTION

Bearings are considered as the mechanical parts for

supporting the frictional portions in the vehicles, ships -

internal combustion engines (ICE) or compressors. The

bearing is a frictional bearing mechanical part, therefore, the

material for bearing fabrication has to meet the requirements

such as an embedding, a fatigue strength, a load and friction

resistant, and a wear resistant property [1]. Recently, based on

the demands of reducing the internal combustion engine size,

the bearing materials are usually used in order to meet the

higher loads with high speed, high friction, and high

temperature but low cost [2][3]. For this reason, bearing

materials grounded on the copper (Cu) system which contains

tin (Sn) as the main component instead of aluminum (Al)

system based materials. The bronze alloy contained up to

about 30% of Sn is considered as a kind of bearing material,

because up to about 14% of Sn content, the matrices of this

alloy are in the form of α+δ phase crystals [4]. This leads to

the load-resistant and the wear-resistant property. U.S. Pat.

No. 3,180,008 has presented a bearing material, the surface

layer of the multi-layer microstructure contains 2% to 10% of

In (Indium), 0.1% to 3% of Cu, 0.001% to 0.25% of Te

(Tellurium), 0.5% or less of Ag (silver) and/or 0.5% or less of

Sb (Antimon), and Pb (Lead) of remaining. However, about

5% to 35% of Pb and 20% or less of Sn, and Cu of remaining

to appear in the intermediate layer of the multi-layer

microstructure was shown [5]. This microstructure showed the

ability of high load resistance. The alloy contained 1% to 5%

or less of Ni (Nickel) and 0.5% to 3% or less of Sb, 8% to

20% or less of Pb and 4% to 10% by weight of Sn, and Cu of

remaining [6]. This material showed the incorporation of Sb,

the good combination between Ni and Pd, Cu to improve the

bearing performance. However, Ni and Sb are very expensive

thus this material is not suitable for the economy [7].

The materials for bearing fabrication have to meet the

requirements such as high fatigue strength, high seizure

resistance, high wear resistance (include abrasive wear,

adhesive wear, fatigue wear, corrosive wear erosive wear),

high conformability, high embed ability, high corrosion

resistance, high cavitation resistance, low cost and easy

fabrication [5][8][9].

With many advantages in terms of thermal conductivity,

corrosion resistance, durability, flexibility, lubricity, good

anti-friction, copper alloys are commonly used in a variety of

devices for silvering [8]. However, conventional copper alloys

work in heavy duty conditions, with low abrasion, corrosion,

and lubrication (such as swivel bits in drill bits), which work

after a short period of time [10]. These mechanical parts are

usually imported at very high cost or they are locally produced

but the quality is not guaranteed. Therefore, research on the

manufacture of copper alloys with good mechanical

properties, durability, and high abrasion resistant properties

are necessary [11][12]. One of the important requirements of

alloy for fabricating the bearing is to have a microstructure

consisting of high strength, high stiffness to load, alternating

with low hardness phase, which can wear out during work to

form a point containing lubricating oil [6]. The basis of high

durability copper alloy work in heavy load conditions is the

consequent application of Spinodal decomposition and phase

transformation during heat treatment [13]. Spinodal

microstructure are composed of a fine, homogeneous mixture

of two phases that form by the growth of composition waves

in a solid solution during a suitable heat treatment is called



Spinodal decomposition [14]. The phases of the Spinodal

decomposition differ in composition from each other and from

the parent phase but have the same crystal microstructure as

the parent phase [15]. The fineness of Spinodal microstructure

is characterized by the distance between regions of identical

composition, which is of the order of 50 to 1000 Ao [16].

With Cu-15Ni-8Sn alloys, many studies have introduced

microstructure models and explored mechanisms for

increasing durability and phase formation during aging [17].

Observed six types of phases formed during heat treatment: on

granules and in γ (DO3) granules; γ discontinuous (column

type); structured order form of DO22 (CuxNi1-x)3Sn; Order

microstructure L12 (CuxNi1-x)3Sn; Modular type, resulting

from Spinodal spinning and δ-orthogonal phase (β-Cu3Ti)

with a = 0.451 nm, b = 0.538 nm, c = 0.427nm. The

microstructures observed in the alloys are different and shown

in Figure 1 [18].

Fig. 1. Effect of tempering temperature on the phase changes of Cu-15Ni-8Sn alloy

Most authors report that in Cu-Ni-Sn alloys studied, the

increase in durability is due to the contribution of Spinodal

decomposition [12][19]. In many alloys, the sign of the

Spinodal decomposition is found in the solid solution. Even

some studies have found traces of Spinodal formation that

formed prior to the formation of a solid solution and the

Spinodal decomposition formed during my process. However,

authors such as Miki and Ogino [20] have concluded that

Spinodal decomposition does not increase the hardness of Cu-

20Ni-8Sn and Cu-15Ni-8Sn alloys. The main role of durability

is the networking between the Spinodal region and the new

phase.

In this study, a study of microstructure transformation of

Cu-Ni-Sn alloy with the change of tempering temperature

resulting in the change in hardness was conducted in the basis

of Cu-15Ni-8Sn alloy.

II. MATERIALS AND METHODS

The study alloy has component as Table I.

Table I

Composition of alloy

Cu Ni Sn Fe Others

75.2 15.4 8.95 0.28 exist

After casting, the alloy is heated to 850oC to keep heat 3h

and cool in the water. Next, be aged at different temperatures

of 250oC; 300oC; 350oC; 400oC; 450oC and 500oC and in

different time intervals.The samples after the test were

hardness measurement, microscopic examination, microscope

photography, SEM analysis, thermal analysis, and analysis.

Experiments were conducted at the Vietnam Academy of

Sciences and the Hanoi University of Science Techno

III. RESULTS AND DISCUSSION

A. Microstructure

The microstructures show that in the post-casting state

(Figure 2), the alloy is strongly biased. Arranging rough

branches is not just the middle of the hat but even the seed.

Obviously, the composition part is very uneven. The alloy

hardness measured in the molding state is 110HB. Cu-Ni-Sn

alloys are uniformized by incubation at 850°C (Figure 3).

After 3h annealing at 850oC, tree branches were removed, the

alloys were completely homogeneous, with a particle size

smaller than that of the molding. This is the right

microstructure for the next spinodal transformation. The

hardness behind quenching is 98HB.

Fig. 2. Microstructure after casting

Fig. 3. Microstructure after annealing and quenching



Fig. 4. Diagram of DSC analysis

To study the change in energy, to show the changes in

temperature change, the alloy after quenching was analyzed in

the laboratory of metal materials technology has the following

results:

From the thermal analysis diagram (Figure 4) found in the

temperature regions: 50oC; 418-482oC; 750-800oC the

appearance of the peak on the thermodynamic path. It can be

seen that from temperatures below 50oC began to show signs

of change, perhaps this is spinodal decomposition; Peaks in

the range of 418oC to 482oC correspond to the appearance of

the DO22 and L12 microstructures in the alloy, which are

formed when Sn is released from the Spinodal region,

preparing for new phase transformation. compared to theory,

with the results of the Roughen analysis and the results of the

change in temperature stiffness as discussed later. At 750-

800oC there is a discontinuous phase γ model with a DO3-like

microstructure.

Fig. 5. Microstructure after aging at 4500C (x13000)



Fig. 6. Microstructure after aging at 4500C (x200000)

The SEM image at a low magnification of 13,000 times

(Figure 5) of the sample after aging at 450oC shows phase

separation, corresponding to the microstructure. The

microstructure (Figure 6) shows that the inner grain has a

smoothly distributed microstructure, indicating that it is the

microstructure of the Spinodal decomposition (Figure 5) while

the grain boundary is structured in layers.

Fig. 7. Microstructure of Cu-15Ni-8Sn alloy quenching at 850oC-2.5h; aging at

450oC-2h

Fig. 8. The hardness measurement of the phase of the Cu-15Ni-8Sn alloy after

quenching at 850oC-2.5h; aging at 550oC-2h

a

b

Hardness

test

Phase γ

Phase α



c

d

e

f

g

h Fig. 9. Cu-15Ni-8Sn alloy after aging at 4500C within 2h

It can be seen from Figure 9 that SEM of Cu-15Ni-8Sn after

quenching uniformly and aging at 450oC within 2h (Fig. 9a

and Fig. 9b) with 13,000 of magnification shows the

microstructure of surface alloy in grain and grain boundaries.

However, SEM of Cu-15Ni-8Sn after quenching uniformly

and aging at 450oC within 2h (Fig. 9c to Fig. 9h ) with

150,000, 200,000, 13,000 of magnification shows the

microstructure of surface alloy in grain. The background SEM

shows the rich and poor microstructure of Sn which has the

Spinodal modules with the form of woven plaques. These

microstructures are evenly distributed on the ground, which is

the Spinodal structure of the Sn-rich microstructure. In order

to demonstrate the orderly microstructure, the Xray method

needs to be used.



Fig. 10. X-ray of Cu-15Ni-8Sn alloy after aging at 4500C within 2h

Position [°2Theta] (Copper (Cu))

10 20 30 40 50 60 70 80

Counts

0

400

1600

3600

6400

5.4

25 [

°];

16.2

9049 [

Å]

7.8

75 [

°];

11.2

2753 [

Å]

9.9

28 [

°];

8.9

0957 [

Å]

23.3

73 [

°];

3.8

0601 [

Å]

26.2

77 [

°];

3.3

9163 [

Å];

Cu N

i2 S

n

31.1

20 [

°];

2.8

7399 [

Å]

43.5

43 [

°];

2.0

7853 [

Å];

Cu

47.3

73 [

°];

1.9

1903 [

Å]

50.6

01 [

°];

1.8

0392 [

Å];

Cu

66.4

00 [

°];

1.4

0794 [

Å]

70.6

66 [

°];

1.3

3305 [

Å];

Cu N

i2 S

n

74.2

77 [

°];

1.2

7693 [

Å];

Cu

79.1

24 [

°];

1.2

0943 [

Å];

Cu N

i2 S

n

158R500



From Figure 10, it can be seen the location of the line

appearance such as:

Outside the copper background, the second phase also is

detected corresponding to the compound formula CuNi2Sn

with small content.

The background includes bars:

d1(111)= 2,07853 A0, corresponding to angle 2 = 43,5430

d1(200) = 1,80392A0, corresponding to angle 2 = 50,6010

d1(220) = 1,27693 A0, corresponding to angle 2 = 74,2770

The second line system for the positions:

d2(111)= 3,39163 A0, corresponding to angle 2 = 26,2930



Besides three α phase bars, the apperance of and phase

with small content also can be seen in Figure 11. Moreover,

the transformation of orderly bridging phase ’ (DO22và L12)

with FCC to phase (CuxNi1-x)3Sn with DO3 (BCC) with

lattice parameter of 5,926 Å, the phase of with formula

(CuxNi1-x)3Sn and lattice parameter such as a= 4,51 Å ; b=5,39

Å ; c= 4,29 Å can be analyzed.

B. Hardness

Aging for longer periods of time and higher temperatures

indicate that there are black phases in the grain boundaries.

This phase is the γ shown in Figure 7 and Figure 8 and has a

lower hardness than the background phase. The measurement

of the phase hardness included base phase (light color with

high hardness, and black with lower hardness) is given in

Table 2.

Table II

Hardness of phase

From Table 2, it can be seen that the hardness of the base

phase α is very high on average 387 HV, the hardness of the

base phase α is much higher than the α background after

quenching. This proves that there may be a process of

Spinodal decomposition in the background, which increases

the hardness of the background. The relationship between Cu-

15Ni-8Sn alloy hardness and aging temperature is shown in

Figure 11, and between Cu-15Ni-8Sn alloy hardness and time

is shown in Figure 12.

Fig. 11. The relationship between Cu-15Ni-8Sn alloy hardness and

temperature

Fig. 12. The relationship between Cu-15Ni-8Sn alloy hardness and time

When aging at different temperatures, the hardness of the

alloy at temperatures of 250oC and 450oC is quite higher than

20HRC. The highest hardness at 350oC is 32HRC, equivalent

to C45 steel hardness in the well-tempered state, equivalent to

attainable strength up to 900MPa. This hardness value is quite

high compared to copper alloys in general. At this

temperature, the microstructure of the alloy has a net

microstructure between the Spinodal region and the new

phase. When aging at higher temperatures, coupled with the

presence of γ phase (black), the hardness of the alloy

decreased sharply.

The behavior of the hardness curved when increasing the

aging time is the same as when changing the temperature. Fix

aging at 350oC Cu-15Ni-8Sn alloys tested at 0.5h were given a

high hardness of 30HRC, however as the aging time is 1.5

hours, hardness is about 34HRC. This value is quite high and

suitable for many applications such as abrasion and high

elasticity mechanical parts. The aging time is about 2-3 hours

hardness slightly reduced but at about 3 to 3.5 hours hardness

increased and then dropped sharply. In the early stages, the

solid solution breaks down into fine, fine Spinodal regions

increase hardness. Thus, it may understand that, the longer the

22.6

26.4

32

24.123

11.1

0

5

10

15

20

25

30

35

250 300 350 400 450 500

Ha

rdn

ess,

HR

C

Temperature, oC

30 29.4

33.6

28.329.6

34 34.3

26.4

0

5

10

15

20

25

30

35

40

0.5 1 1.5 2 2.5 3 3.5 4

Har

dn

ess

, HR

C

Time, h

Phase Hardness (HV)

α

390 Average

387 382

387

γ

238 Average

235 230

237



aging time is, the more increasing the Spinodal regions are,

and lead to increase the hardness. But if prolonged aging

occurs, when new phases appear, the hardness decreases. In

the basis of the combination of temperature and treatment

time, found that the aging temperature at 350oC and the aging

time from 1.5h-2h alloy for highest hardness.

IV. CONCLUSIONS

From the results of the analysis above can be concluded

about the organization and mechanical alloy change as

follows: At the beginning of the increase in the body

corresponds to the Spinodal spinning phase. The main

strengthening mechanism of the alloy is the Spinodal spinning

mechanism. When the temperature is too high or the time is

too long, the new phase is created as the hardening decreases.

Perform aging at 350 – 450oC for about 2 hours, receiving a

consistency consisting of a high hardness substrate, intermixed

with soft γ phase, in accordance with the requirements of the

heavy load-bearing of the engines.

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a study on the effect of the change of tempering...

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