WEAR BEHAVIOR OF DUCTILE CAST IRONS WITH NANOPARTICLE ADDITIVES

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1 The 3 nd International Conference on DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS DIPRE 1 WEAR BEHAVIOR OF DUCTILE CAST IRONS WITH NANOPARTICLE ADDITIVES Julieta KALEICHEVA 1), Mara KANDEVA 1), Zdravka KARAGUIOZOVA ), Valentin MISHEV 1) 1) Technical University of Sofia, Sofia, BULGARIA 1) Space Research Institute, Bulgarian Academy of Sciences, Sofia, BULGARIA jkaleich@tu-sofia.bg, karazuzi@yahoo.com ABSTRACT The work in this study is focused on investigation of the structure and properties of ductile cast iron with nanoparticle additives: titanium nitride TiN; titanium nitride + titanium carbonitride and cubic boron nitride cbn. The nanoparticles are coated with nickel prior to addition to the iron melt to improve their wetting and uniform distribution in the volume of the casting. The metallographic observation and wear test are performed to study the influence of the nanoparticle additives on the microstructure and and cast iron tribological properties. Keywords: nanoparticle, metallographic observation, hardness, wear, cast iron. 1. INTRODUCTION Ductile cast iron is an engineering material characterized by high strength, toughness and wear resistance. Graphite present in the iron, provides resistance to mechanical wear and improves its processing. The wear resistance of the cast iron depends on the graphite morphology / shape, size, quantity, distribution / and the structure of the metal base. By alloying, heat treatment or combination of these two processes could affect the graphite morphology and the basis structure for receiving iron with optimum wear resistance [, 3, 5, 6]. Nanosized particles added to the melt in small quantities, change the graphite morphology, which in combination with a suitable heat treatment increases the cast iron wear resistance [4,7]. The aim of the present study is to investigate the microstructure and tribological properties of the ductile cast iron samples with different nanosized additives.. MATERIAL AND INVESTIGATION METHODS Four ductile cast iron compositions are casted, namely pure cast iron as well as cast iron with nanosized additives: titanium nitride TiN, titanium carbon nitride TiCN + titanium nitride TiN, cubic boron nitride cbn respectively (Table 1). Nanosized additive Hard-ness НВ Massive wear m [mg] Wear rate dm/dt[mg / min] Intensity of wear Table 1 Wear resistance I i ,6,5 0, , TiN ,8 1,43 0, , TiN + TiCN 01 18,4 1,57 0, , cbn ,4 1,39 0, ,

2 The composition of ductile cast iron is Fe-3.54 C-.47 Si-0.66 Mn-0.0 S-0.03 P-0.04 Cu-0.0 Cr Ni Mg wt%. The electroless nickel coating is deposited on the nanopowders prior to the casting by EFTTOM-NICKEL Method [1]. Nickel coating deposited on the nanosized particles improves their wetting and uniform distribution in the casting volume. The microstructure of the cast iron samples is observed by means of the optical metallographic microscope GX41 OLIMPUS. The samples were treated with % HNO3 - CH5OH solution. The hardness of the coating was performed by Brinell Method. The experimental testing of the wear is performed in conditions of a fixed abrasive by a cinematic scheme pin - disc using method and a device for an accelerated testing. The device functional diagram is shown in fig. 1. The tested cylindrical sample 3 (body) is fixed in a loading head 6 as its frontal surface contacts with the abrasive surface of a horizontal disc 1 (antibody). The antibody rotates with a constant angular speed around its vertical axis. The cycle s number is accounted with a cyclometer 5. The device allows alteration of the sliding speed changing the disc angular speed from a control unit and trough changing of the distance R between the rotation axis of the antibody 1 and the axis of the sample 3 toward the rotation axis of the disc. Fig. 1. Functional scheme of a device for wear testing of ductile cast iron samples with nanosized additives in a fixed abrasive. The abrasive surface of the antibody 1 is formed by impregnate corundum 60% harder then the tested materials. The used impregnate material in this study is Smirdex 330 Duraflex P SV. The methodology includes the following operations: 1. Preparation of same cylindrical samples 3 with an equal surface roughness R a 0. 5 [ m] avoiding structural and physical and chemical changes of the samples surface. The sample dimensions are: base radius r 4 mm and height 0 mm ;. Measuring of the weight of the sample before and after a determinate friction road S by an analytical balance WPS 180/C/ précised to 0,1 [mg]. The samples are treated with a special solution to neutralize the static electricity before the testing. 3. The sample 3 is mounted in a loading head, the desired normal load P and friction road S is assigned by a cycle counter The absolute massive wear m [mg] is measured as a difference between a sample mass before and after a definite cycle number N (friction road S). Test basic parameters: 1. Absolute massive wear m [mg] - difference between the samples weight before and after appointed number of friction road S.. Massive wear rate dm/dt [mg / min] - the lost weight of the sample surface for a minute. 3. Absolute intensity of the linear wear i - this is the lost thickness of the surface layer for a one friction cycle. It is a dimensionless number, which could be calculated by the formula having in mind the lost weight: m (1) i.aa.s where: is the density of the sample material / m kg ; A a is the nominal interaction contact surface, S is a friction road calculated by the number of cycles of the contact interaction N by the formula () S..R. N where R 4 [mm] 4. Absolute wear resistance I - it is determined as a reciprocal value of the wear intensity and respectively it is a dimensionless number etc. 1.Aa.S (3) I i m The specific wear resistance I s is a number presenting the friction road S in meters, covered by 1

3 square millimetre contact ground in which 1 mg ground material is lost. The dimension respectively is [ m. mm / mg]. 5. Nominal contact pressure p a [ N / cm ] : is the normal load P, distributed per a unit of a nominal (geometrical) contact surface etc. P (4) pa [ N / cm ] Aa In this study the wear of three pieces of ductile cast iron samples is investigated. Their composition and designation are presented in Table 1. In Table, the values of some basic test parameters are shown. time are received (Table 3). The present tribological properties in Table 1 are for the same friction road S 659 [m]. In fig. 3 the dependence of the massive wear m on the cycles number N (friction road) and dependence of the massive wear rate dm / dt on the time of friction t are presented. In fig. 4 tablograms of the intensity of wear i (a), wear resistance I (b) and hardness HB (c) of ductile cast iron samples without (sample 1) and with (samples, 3, 4) nanomodifiers are presented. Table. Test parameters Parameters Nominal contact pressure, Value p 6 a [Pa] Average speed of sliding, V [ cm / s] Nominal contact surface, A [ mm ] Density 3 3 7,8.10 [ kg / m ] 3. EXPERIMENTAL RESULTS AND ANALYSIS The structure of the tested cast irons consists from ferrite, pearlite and graphite (fig. ). The manganese content is 0, 66 %, which is near the cast iron upper concentration limit between %. This influences significantly on the cast iron structure and properties increasing pearlite quantity. Ferritepearlite cast iron acquires higher hardness with pearlite quantity increasing. The main part in the investigated samples is pearlite structure (fig. c, f, i, l). This influences on the total hardness of the modified with nanosized particles cast irons and it is in the range between НВ (Table 1). Lowest hardness of 190 НВ has cast iron with nano modifier cbn, which structure consists of higher ferrite quantity compared to other samples (fig..l). Nanosized additives don t influence on the graphite form. It is observed an increase of the quantity and size of the graphite phase in the structure of sample number 3, containing TiCN+TiN nano modifier (Fig. g, h). The experimental results for the massive wear m, wear rate dm / dt, absolute intensity of wear i and absolute wear resistance I of the samples and their alteration in a contact interaction a Fig.. Microstructure of non - developed (a,b,d,e,g,h,j,k) and developed in % solution HNO 3 + CH5OH (c,f,i,l) ductile cast iron samples pure and with nanomodifiers: a c pure cast iron; d f with nanomodifiers TiN; g i - with nanomodifiers(ticn + TiN); j l with nanomodifiers cbn Graphite in the cast iron structure is of significant importance for their wear behavior, because of his lubricating ability therefore graphite performs a role of a lubricant. The wear resistance of the cast iron with TiCN + TiN modifier (sample 3) is 61% higher compared to pure cast iron (sample 1) and consists of bigger graphite quantity and size. 3

4 4 Table 3. Test results for massive wear m, wear rate dm/dt, intensity of wear i and wear resistance I. Friction road, S [m] Cycles number, N Time, t [min] Massive wear, m [mg] Wear rate, dm/dt [mg / min] Intensity of wear, i Wear resistance, I sample sample sample sample sample sample sample sample sample sample sample 3 sample sample sample sample sample Fig. 3. Dependance of the massive wear m on the cycles number N (a) and of the wear rate dm/dt on the friction time t (b). The wear resistance of the cast iron with nanosized additives TiN (sample ) and cbn (sample 4) is respectively 75% and 81 % higher than the pure cast iron (sample 1). The hardness of the samples and 4 are similar 195 and 190 НВ (Table 1), as well as the quantity and size of the graphite grains in their structure (Fig. d, e, j, k). The influence of the modifier on the graphite morphology is less marked in these cast irons. The wear resistance increase probably is connected to the nanomodifiers influence on the primary crystallization and surface strengthening during the friction. 4. CONCLUSIONS The wear performance, microstructure and hardness of pure ductile cast iron as well as the cast iron with nano additives are investigated. No change in the graphite form is observed in the presence of nano modifiers. The highest influence on the graphite morphology as an increase of the graphite quantity and size has nanomodifier TiCN + TiN. The metal matrix structure of the cast iron is ferrite-pearlite and the pearlite phase is dominant. The hardness is between НВ. The cast iron intensity of wear decreases in presence of nanomodifiers. The

5 wearresistance increases % compared to this one of the pure cast iron. ACKNOWLEDGEMENT The presented investigations are carried out and financed under the Project University Complex for research and development of innovations and knowledge transfer in the field of micro/nanotechnologies and materials, power effectiveness and virtual engineering, contract DUNK-01/3. REFERENCES 1. Gavrilov G. et al., 1985, Electroless Nickel and Composite Coatings, Tehnika, Sofia.. Haseeb A.S.M.A. et al., 000, Tribological behavior of quenched and tempered, and austempered ductile iron at the same hardness level, Wear, Vol. 44, pp Iacoviello F. et al., 008, Damaging micromechanisms in ferriticpearlitic ductile cast irons, Mater. Sci. Eng., Vol. A 478, pp Li J. et al., 001, Structures and Properties of Cast Irons Reinforced by Trace Addition of Modified SiC Nanopowders. Chinese Journal of Chemical Physics, Vol. 0, No 6, pp Sahin Y. et. al., 001, Wear behavior of austempered ductile irons with dual matrix structures, Mater. Sci. Eng., Vol. A 444, pp Xu W. et. al., 005, Influence of alloying elements on as cast microstructure and strength of gray iron, Mater. Sci. Eng., Vol. A 390, pp Wang Y. et al., 011, Sliding wear behavior of Cr Mo Cu alloy cast irons with and without nanoadditives, Wear, Vol. 71, pp Fig. 4. Hardness HB (a), intensity of wear I (b) and wear resistance I (c) of ductile cast iron samples without (1) and with (,3,4) nanomodifiers 5