Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 111-122, Year 2012
TRIBOLOGICAL PERFORMANCE OF HIGHLY FINE NICKEL-
MOLYBDENUM DISULFIDE POWDERS ADDITIVE TO
LUBRICANT OIL
Dr. Haidar Akram Hussien
Lecturer
Technical College - Baghdad
Foundation of Technical Education
E-mail׃ drhaidar3@yahoo.com
ABSTRACT
Wear is a phenomenon which is surface materials damage or loss between two contact solids
surfaces in sliding, rolling, or impact movement. In most cases, wear is caused by the interaction of
surface asperities. To reduce the energy loss and equipment damage generated due to the
mechanical parts friction in the operation, around the world is stepping up developing appropriate
lubricants and lubrication technology. Molybdenum is one of the major refractory metals (metals
with very high resistance to heat and wear). As already noted, for lubricant compositions as
fillers can be used soft powder (anti-friction) of metals – nickel.
This work focuses on studying an urgency and favorable prospects of practical use of firm powder
additives on the basis of MoS2 which particles are coated with one layer of soft metal (Ni), and their
effect on tribological characteristics of lubricant oil (SAE 50) at a range of concentration (2 – 8)
wt%. Optimum lubricating effect concluded on the level of concentration of the composite additive
powder in the range of (3.5 – 4.5) wt %, by the formation of protective boundary layer between
sliding tribosurfaces that prevents wear.
Tribological characteristics significantly improved i.e.friction coefficient may drop about (1.5-2)
times, and the wear rate about (3-3.5) times compared with the case of usig the lubricant oil without
additives.
KEYWORDS: Tribological Properties, Additives, Coating, Lubricating Effect, Solid
Lubricant.
مليبدنيوم عالي النعومة على كبريتيد ال ثنائي–دراسة تاثير اضافة مسحوق نيكل
الخواص التريبولوجية لزيوت المحركات
حيدر اآرم حسين .د
مدرس
بغداد– الكلية التقنية /هيئة التعليم التقني
موجزال
لتقليل و،ء المتالمسه من الظواهر المهمه الجديره بالدراسه السيما بين اسطج االجزايعتبر االستهالك
بين بسبب التشغيل الميكانيكي واالحتكاك الحاصل واالنهيارات الحاصله الحاصلة في الطاقهالضياعات
الخواص التريبولوجيه لمواد بدا العلماء بالعمل اليجاد بعض البدائل والحلول لتحسيناالجزاء المنزلقه
Haidar Akram Hussien
ويعتبر عنصر المليبدنيوم من )وضغط عالييندرجة جراره (التزييت خصوصا في بعض الظروف الخاصه
يتناول هدا ·العناصرالرئيسيه في هدا المجال بسبب تركيبه البلوري ومقاومته العاليه للحراره واالستهالك
مسحوق مركب معامل ( عالي النعومه) نيومثنائي كبريتيد المليبد -نيكل (البحث دراسة تاثيراضافة مسحوق
،) النيكل –المعدن الناعم مغلفه بطبقه رقيقه منق مسحوق ثنائي كبريتيد المليبدنيوميث تكون دقائكيميائيا بح
– 2( وبتراكيز مختلفه تتراوح بينالخواص التريبولوجيه للزيتعلى ،)SAE 50 (الى زيت المحركات نوع
رت النتائج د اظه لق· من خالل حساب معامل االحتكاك بين السطوح المنزلقه ومعدل االستهالكلتر/غم)% 8
الطبقه بسببامكانيه عاليه في تحقيق هدف البحث المتمثل بتحسين الخصائص التريبولوجيه للزيت المستخدم
تعمل على زيادة المساحه السطجيه للسطوج المتالمسه وبالتالي التي ند االسطح المتالمسهالواقيه المتكونه ع
ومعدل االستهالك مره ) 2 - 1.5( بحدود االحتكاك فقد انخفضت قيمة معامل،نقليل االحتكاك واالستهالك
ثنائي كبريتيد -نيكل ( مسحوق لتر من/غم )%4.5 -3.5( على التوالي ودلك باضافة مره)3.5 -3( بحدود
· الى الزيت بالمقارنه مع الحاله عند استخدام الزيت بدون اضافات )المليبدنيوم
INTRODUCTION
Powder lubrication has been employed as a suitable dry lubricant in a variety of sliding contacts as
an alternative to conventional liquid lubricants. The essential postulate of this alternative approach
is that there are two operative elements, hydrodynamic and morphological. The hydrodynamic
element refers to the layered shearing of particles between sliding tribosurfaces, where as the
morphological element refers to the effects due to the mechanical, chemical, and tribological
surface phenomena characteristic of the mating materials [Zhang, 2010]. The term “powder
lubricants” is usually given to those lamellar solids that have low interlayer friction. Some of the
interesting attributes of powder lubricants that are worth noting are that they have been known to
adhere to surfaces forming a protective boundary layer that prevents wear, act like a lubricant in
sliding contacts by accommodating relative surface velocities, and are capable of lubricating at
high-temperatures. Several of these powder lubricants—molybdenum disulfide, tungsten disulfide,
titanium oxide, boron nitride, and boric acid— were evaluated for their lubrication behavior in
extreme-environments (i.e., high speeds ~ 45m/s, high temperature ~ 400°C) [Godloviski, 2008
and Taylor, 2000].
Wear is a phenomenon which is surface materials damage or loss between two contact solids
surfaces in sliding, rolling, or impact movement. In most cases, wear is caused by the interaction of
surface asperities. To reduce the energy loss and equipment damage generated due to the
mechanical parts friction in the operation, around the world is stepping up developing appropriate
lubricants and lubrication technology [Washida, 2003 and Hoshi, 1994]. Molybdenum is one of
the five major refractory metals (metals with very high resistance to heat and wear). The other
refractory metals are tungsten, tantalum, rhenium and niobium. Molybdenum's strength and
resistance to expanding or softening at high temperatures is particularly sought after in critical areas
where high temperatures are common, such as in nuclear power plants and aircraft engines
[Holinski, 2003 and Taylor, 1997]. Nickel-based sintered composites produced by powder
metallurgy processes are now widely used in tribological engineering parts, e.g. bearings and
bushes. Also composites based on nickel molybdenum disulfide alloys containing a solid lubricant
have been developed as self-lubricating materials under extreme conditions of load, atmosphere and
temperature. It is well known that the addition of molybdenum disulfide serves to reduce friction
and wear in nickel–molybdenum disulfide alloys. However it should be noted that the addition of
molybdenum disulfide (MoS2) has an adverse effect on the composites’ mechanical properties
[Godloviski, 2008 and Popczyk, 2006]. The lubricant MoS2 powder was coated with Ni to
Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 111-122, Year 2012 112
TRIBOLOGICAL PERFORMANCE OF HIGHLY FINE NICKEL-MOLYBDENUM DISULFIDE POWDERS
ADDITIVE TO LUBRICANT OIL
reinforce their bonding to the Ni particles in the composites during sintering. The hardness,
microstructure and bending strength of the sintered specimens were changed. The friction and wear
properties of the materials were clearly decreased. Although mechanical properties of the
composites decreased with increasing amount of added MoS2, the use of Ni-coated lubricant
powders improved the bending strength. Molybdenum disulfide was very effective in reducing the
wear and friction of the composites [Rafal, 2011 and Budniok, 2007].
This work focuses on studying urgency and favorable prospects of practical use of firm powder
additives on the basis of molybdenum disulfide which particles are coated with one layer of soft
metal (Ni), and their effect on tribological characteristics of lubricant oil.
EXPERIMENT PROCEDURE
The tribological characteristics of investigated metal-molybdenum disulfide additives to lubricant
oil with single-layered coating were received during wide range of experiments.
Study of tribological characteristics of the developed lubricant compositions was performed on a
friction machine model CMT-2. A simplified diagram is shown in Figure 1 [Godloviski, 2008].
Friction moment on the shaft (rotating disk) was measured using an inductive sensor. Electrical
signals werefed into the electrical circuit and then compared to the potentiometer readings, mounted
in anelectrical controlcabinet.
Testing samples were made of steel 45, hardness 40-42, dimensions l x b x h = (10 x 10 x10
mm). All samples had a same surface roughness. The roller was d = 40 mm diameter, 15 mm thick,
made of steel 45, hardness 35─ 40.
Friction conditions [Godloviski, 2008]: the rate of slip-(2m / s) was not changed during the tests,
the load on the sample increased stepwise from 0.2 kN to a sharp increase in friction moment.
Contact area of friction pairs - about 1 cm². Lubricating compositions were administered in the
friction zone on the metal surface for 2km sliding path. During the study recorded the friction
coefficient and wear rate.
MATERIALS USED
In this study, the basic lubricant oil used was SAE 50. Investigated lubricant composition additives
powders consist of ׃ molybdenum disulfide powder (particle size 4 - 53µm) at a range of
concentration (2 – 8) wt%, soft metal powder, nickel powder,( particle size 4 - 53µm ) at a range of
concentration(2 – 8) wt% and nickel-molybdenum disulfide powder with single-layered coating
4wt% [Godloviski, 2008 and Rafal, 2011].
MEASUREMENTS
COEFFICIENT OF FRICTION׃
Coefficient of friction was measured by using the formula [Godloviski, 2008]׃
µ ═ 2T/ P. D (1)
where µ ═coefficient of friction
T ═moment of friction(N.m).
P ═load (N).
D ═roller diameter(m).
WEAR RATE׃
Measurement of linear wear was carried out by the "artificial bases" method by the establishment of
an impression on the contacting friction surfaces using the hardness device TCS - 1M. The
diameters were determined from the impression using a microscope MBS - 10.
The wear rate was determined by the formula [Godloviski, 2008] ׃
Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 111-122, Year 2012 113
Haidar Akram Hussien
W = 0.004(d2 – d1) / S (2)
Where W ═ wear rate (µm / km)
d1 ═diameter of impression before wearing (mm)
d2 ═diameter of impression after wearing (mm)
S ═ sliding path (km)
RESULTS and DISCUSSION
The tribological properties of lubricating compositions based on the lubricant oil SAE 50, filled
with powders of various grades of MoS2 as well as soft metal(Ni) were studied.
EFFECT of MoS2 POWDER׃
Effect of MoS2 powder addition on the tribolorgical characteristics of lubricant oil based on SAE 50
was studied at a range of concentration (2 – 8) wt% [Holinski, 2003] as shown in Figure 2. The
lubricating properties of MoS2 have been explained by the strong polarization of the sulfur atoms
which produce a layer structure, good adhesion to metal surfaces, adhesion between MoS2 basal
planes, easy sliding of MoS2 and the formation of a homogeneous continuous film. The load
carrying part of the MoS2 film lies only on the asperities of the metal surface. The results can
be explained by the fact that MoS2, as a solid lubricant helped to form, through the process, a solid
lubricant layer helps to reduce friction losses in the relative sliding of solid bodies. It was evident
that (2 wt%) MoS2 in the lubricant composition is not enough to form a solid lubricating film on the
metal surfaces that separates from the rubbing surfaces. However, increasing the amount of
MoS2 over (6 wt%) results in a thick loose film, deleted in wear action with an increase in friction
moment. Results also revealed that minimum friction coefficient was obtained at (4 wt%) of MoS2
addition . In Figure 3 results had revealed that, an addition of (4 wt%) of MoS2 powder to
lubricant oil based on SAE 50 would help to reduce friction losses, i.e. reduce the coefficient of
friction to reach 0.095 at the load of 0.4 kN, this related to the formation of a solid protective
lubricating film of MoS2 on the sliding metals surfaces which increased the contact surface area
between the sliding bodies, MoS2 powder has the characteristics which are crystal structure, fine
particle and large specific surface area. In Figure 4 results revealed little influence of MoS2 powder
adding to the lubricant oil based on SAE 50, on the wear rate at these operating conditions
[Godloviski, 2008 and Holinski, 2003]. This is because of little changing in wear rate values.
EFFECT of SOFT METAL(Ni) POWDER׃
As already noted, for lubricant compositions as fillers can be used soft powder (anti-friction) of
metals - nickel, tin, lead, etc.[Aurelian, 1989]. Effect of Ni powder addition on the tribolorgical
characteristics of lubricant oil based on SAE 50 was studied at a range of concentration (2 – 8) wt%
[Godloviski, 2008] as shown in Figure 5. It was noted that an addition of Ni powder to the
lubricant oil at a range of 4wt% would help to reduce friction losses, i.e. reduce the coefficient of
friction to reach its minimum value under experiment conditions. This related to the formation of
thin plastic film of nickel on steel surfaces, that increased the contact surface area. In Figure 6
results had revealed that an addition of (4wt%) soft powder (anti-friction) of metals – nickel to the
lubricant oil based on SAE 50 would help to reduce friction losses, i.e. coefficient of friction
reduced from 0.122 for lubricant oil SAE 50 without additives at a load of 0.4 kN to 0.116 for the
lubricant oil SAE 50 with 4wt% addition of Ni powder at the same load. In Figure 7 results had
revealed that an addition of (4wt%) soft powder (anti-friction) of metals – nickel to the lubricant
oil based on SAE 50 would help to reduce the wear rate under these experiments conditions, i.e.
wear rate reduced from 6.5µm/km for lubricant oil SAE 50 without additives at a load of 0.4 kN to
3.8 µm/km for the lubricant oil SAE 50 with 4wt% addition of Ni powder at the same load. This
may related to the formation of thin plastic film of nickel on steel surfaces, that increased the
contact surface area, then the pair of friction steel – steel gradually in some areas on the sliding
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TRIBOLOGICAL PERFORMANCE OF HIGHLY FINE NICKEL-MOLYBDENUM DISULFIDE POWDERS
ADDITIVE TO LUBRICANT OIL
surfaces, was replaced by a pair of energetically favorable friction steel – nickel, so wear and
friction at the same time significantly reduced.
EFFECT of NICKEL MOLYBDENUM DISULFIDE COMPOSITE POWDER׃
Significantly improve the lubricating effect of the fillers can be pre-modification of their surface,
i.e. modifying the layered filler powders by reduction of the particles of powder metal films by
chemical method [Washida, 2003 and Popczyk, 2006]. Effect of addition of nickel molybdenum
disulfide composite powder, i.e. use of firm powder additives on the basis of molybdenum disulfide
which particles are coated with one layer of soft metal(Ni), on the tribolorgical characteristics of
lubricant oil based on SAE 50, was studied as shown in Figure 8 and Figure 9. It was noted that an
addition of (4wt%) nickel molybdenum disulfide composite powder to the lubricant oil would help
to reduce friction losses, i.e. the friction coefficient was reduced in (1.5 – 2) times under a load
of 0.4 kN(Fig.8), the wear rate was lowered to (3 – 3.5) times (Figure 9) and load capacity of the
friction pair was increased by 1.5 times, by compairing with the case of lubricant oil without
additives at the same conditions. Since MoS2 powder as a filler, reducing the coefficient of friction,
and nickel powder - the wear rate under the same regimes of friction and lubrication , which
should lead to reduce friction and wear. Then the formation on the contacting friction surfaces of
nickel films abled to express anti-friction and wear effects [Godloviski, 2008 and Holinski, 2003].
In Figure 10 friction surfaces was carried out before and after 20 (km) path of friction in the
lubricant oil SAE 50 with newly developed nickel molybdenum disulfide composite powder at a
load of the working surface of 0.4 (kN). Photographing the surfaces was carried out using an
electron microscope with an increase of 2,000 times, obtained profilograms and photos were
presented in Figures 10 – a and b and 11. It was noted the sharply difference between
profilograms surface friction for lubricant oil SAE 50 without additives (fig.10 - a) and with 4wt%
nickel molybdenum disulfide composite powder (Figure10 - b). This may related to the formation
of solid lubricant and metallic film on the contacting friction surface, abled to improve tribological
properties of the lubricant oil composition.
CONCLUSION
1. The experiments observed an increase in the efficiency of the lubricating medium in sliding steel-
steel pair with the addition of additives to the lubricant oil SAE 50, i.e. addition of molybdenum
disulfide powder-coated metal (Ni) in comparison with the case of separate administration of the
same amounts of molybdenum disulfide powder and soft metal, entered separately.
2. Put forward a theoretical concept that the introduction of a lubricating base medium of
molybdenum disulfide powder and metal as thin layer coating of molybdenum disulfide powder
particles should lead to an increase in anti-friction efficiency and anti-wear performance in
comparison with the case of separate administration of the same amounts of molybdenum disulfide
powder and soft metal, entered separately.
3. Obtained tribological characteristics of composite molybdenum disulfide -metal additives in the
lubricant oil with a single layer coating. It was shown that in monolayer nickel coating the friction
coefficient may drop about (1.5-2) times, and the wear rate about (3-3.5) times compared with the
case of usig the lubricant oil without additives.
4. Established for the friction pair steel-steel that the introduction of molybdenum disulfide,
nickel and composite additives powders observed optimum lubricating effect on the level of
concentration of the additive in the range of 3.5 – 4.5 wt. %.
5. Metallization of powders - filling lubricant compositions help to solve important issues such as:
a - reducing the amount of powder fillers.
b - alignment specific gravity (density) of the powders.
6. Use as a filler nickel coated molybdenum disulfide powder leads to the formation of
nickel films on the contacting friction surfaces able to express anti-friction and wear effects.
Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 111-122, Year 2012 115
Haidar Akram Hussien
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metal”, Collection of scientific proceeding of the VIII international conference, Saint Petersburg –
Russia, 2008.
3. K. Washida, Y. Sasaki ”Wear and mechanical properties of sintered copper – composites
containing molybdenum disulfide”, paper, industrial technology center, Japan, 2003.
4. R. Holinski, J. Gansheimer “A study of the lubricating mechanism of molybdenum disulfide”.
Journal, Advanced Materials Research, Volume 3, P.145-151. Germany 2003.
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Containing Molybdenum, ” journal, Materials Science, № 3, vol. 514, pp.182-185, 2006
6. Galda, Pawel, Rafal. Improvement of Tribological Properties of Coating Elements by Oil Pockets
Creation on Sliding Surfaces”. Journal Meccanica, № 3, vol. 46, pp.523-534, 2011, Poland.
7. A. Budniok, A. Lasia ”Study of The Hydrogen Evolution Reaction on Nickel-Based Composite
Coatings Containing Molybdenum Powder”. Journal, Materials Science, Vol. 2, PP.43-47, 2007.
8. Aurelian C.,” Electrodeposition of Metal Powders”, Vol. 3, Elsevier Scientfic Publishing
Company, Amsterdam, Oxford, New York, pp. 336, 1989.
9. R.I. Taylor, R.C. Coy, “Improved Fuel Efficiency by Lubricant Design: A Review”, Proc. Instn.
Mech.Engrs., Vol 214, Part J, pp 10-15, 2000.
10. M. Hoshi, “Reducing Friction Losses in AutomobilEngines”, Tribology Int., 17, pp 185-189,
1994.
11. C.M. Taylor, “Engine Tribology”, Tribology Series, 26, Vol. 211, Part J, pp 91-106, 1997.
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TRIBOLOGICAL PERFORMANCE OF HIGHLY FINE NICKEL-MOLYBDENUM DISULFIDE POWDERS
ADDITIVE TO LUBRICANT OIL
Figure 1 Simplified diagram of the friction machine CMT - 2
1 - bottom (rotating) shaft, 2 - upper (stationary) shaft; 3- loading device, 4- sample,
5 – Rider (roller); 6 - bath for lubrication [Godloviski, 2008] .
2 3 4 5 6
0 .0 0
0 .0 2
0 .0 4
0 .0 6
0 .0 8
0 .1 0
0 .1 2
0 .1 4
2 % M o S 2
4 % M o S 2
6 % M o S 2
8 % M o S 2
µ
P x 1 0 2 (N )
Figure 2 Effect of MoS2 powder concentration at various loads on friction coefficient(µ) for
lubricant oil composite based on SAE 50
Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 111-122, Year 2012 117
Haidar Akram Hussien
2 3 4 5 6
0.08
0.09
0.10
0.11
0.12
0.13
0.14 Oil SAE 50 without additive
Oil SAE 50 with 4% MoS2
µ
Px102(N)
Figure 3 Effect of load (P) on friction coefficient (µ) for lubricant oil composite based on SAE 50
2 3 4 5 6
4.5
5.0
5.5
6.0
6.5
7.0
7.5
Oil SAE 50 without additives
Oil SAE 50 with 4% MoS2
W, µm/km
Px102(N)
Figure 4 Effect of load (P) on wear rate (W) for lubricant oil composite based on SAE 50
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TRIBOLOGICAL PERFORMANCE OF HIGHLY FINE NICKEL-MOLYBDENUM DISULFIDE POWDERS
ADDITIVE TO LUBRICANT OIL
2 3 4 5 6
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
2% Ni
4% Ni
6% Ni
8% Ni
µ
Px102(N)
Figure 5 Effect of Ni powder concentration at various loads on friction coefficient(µ) for lubricant
oil composite based on SAE 50
2 3 4 5 6
0.105
0.110
0.115
0.120
0.125
0.130
0.135
0.140
0.145
Oil SAE 50 without additives
Oil SAE 50 with 4% Ni
µ
Px102(N)
Figure 6 Effect of load (P) on friction coefficient (µ) for lubricant oil composite based on
SAE 50
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Haidar Akram Hussien
2 3 4 5 6
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
Oil SAE 50 without additives
Oil SAE 50 with 4% Ni
W, µm/km
Px102(N)
Figure 7 Effect of load(P) on wear rate(W) for lubricant oil composite based on SAE 50
2 3 4 5 6 7 8
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
Oil SAE 50 without additives
Oil SAE 50 with 4% Ni-MoS2
µ
Px102(N)
Figure 8 Effect of load (P) on friction coefficient (µ) for lubricant oil composite based on SAE 50
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TRIBOLOGICAL PERFORMANCE OF HIGHLY FINE NICKEL-MOLYBDENUM DISULFIDE POWDERS
ADDITIVE TO LUBRICANT OIL
2 3 4 5 6 7 8
1
2
3
4
5
6
7
Oil SAE 50 without additives
Oil SAE 50 with 4% Ni-MoS2
W, µm/km
Px102(N)
Figure 9 Effect of load(P) on wear rate(W) for lubricant oil composite based on SAE 50
(a) ( b)
Figure 10 Profilograms surface friction for lubricant oil SAE 50 without additives (a) and
with 4wt% nickel molybdenum disulfide composite powder (b).
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Haidar Akram Hussien
Figure 11 Surface friction photo for lubricant oil SAE 50 with 4wt% nickel molybdenum disulfide
composite powder (increasing x 2000).
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