The Effect of B4c Additions on Mechanical Properties of Fe-Cu-Co Matrix Composites for Diamond Tools

K. Emre ÖKSÜZ 1,a, Yusuf ŞAHİN 2,b, Ebru Şahin YILDIRIM3,a, Yunus KAYIR

2b 1Cumhuriyet University, Department of Metallurgical and Materials Engineering, 58140, Sivas,

Turkey. 2 Gazi University, Department of Manufacturing Engineering, 06500, Ankara, Turkey.

3Cumhuriyet University, Faculty of Sciences, Department of Chemistry, 58140, Sivas, Turkey akerimemreoksuz@gmail.com,aebrusahinyildirim@gmail.com,

byusufsahin1954@gmail.com,bykayir@gazi.edu.tr

Keywords: Boron Carbide; Fe-Co matrix; Composite; Powder Metallurgy

Abstract.The effects of boron carbide (B4C) additions on characteristic of diamond impregnated Fe-Co-Cu matrix composites have been investigated using powder metallurgy (PM) method. For this purpose, samples of Fe-(30-60)wt. % Cu–20 wt. %Co alloys and1wt. % B4C additions of its matrix were processed by cold pressing at 350 MPa, followed by sintering at 1100°C. Microstructural examination, hardness and wear tests were performed.The microstructure of Fe–Cu–Co alloys was very sensitive to the Cu content and pore closure took place with increasing the Cu content.In addition, the addition of B4C particles increased Fe–Cu-Co hardness about 44% compared to samples without B4C particles. The experimental results showed that alloy Fe–60 wt. % Cu–20 wt. %Co-1 wt. % B4C presented the best results for use in diamond cutting tools.

Introduction

Fe–Cu–Co alloys are used in diamond cutting tools for cutting several types of stones. The choice of the matrix material that bonds the diamonds is vital to the eventual lifespan of these high-performance tools. The selection of the bonding metal in the impregnated diamond composite depends on the abrasiveness and hardness of the material to be cut [1]. In most commercial diamond cutting tools the matrix used is a metal alloy – very often based on cobalt sinceit combines good chemical compatibility with diamond at the processing temperatures, excellent diamond retention, associated with a satisfactory wear resistance after some cutting operations [2], Filgueira and Pinatti [3], and Barbosa et al. [4]. However, the price of cobalt has been fluctuating with a tendency to rise in recently [5]. Thus, researchers have proposed new alloys that have been extensively used as metal matrix in diamond tools, with the reduction of the Co content – exemplified by the Fe-Cu-Co alloys seen in Refs. [6-13], maintaining the Co mean content in approximately 20 wt. %. Fe can be used for bonding purpose and as a filling element since it is easy to apply, cheap and not a hazardous metal [14, 15]. The aim of this study is to improve in mechanical properties of diamond impregnated MMC’s by changing matrix composition of Fe-(30-60)wt.% Cu–20 wt. %Co alloysand and its 1wt.% B4C-reinforced composites,produced by powder Metallurgy (PM) and to investigate the wear behavior of composites under abrasive wear testing conditions.

Experimental

Fe (carbonyl iron powder) and B4C as reinforcement in MMCs were produced by blending certain metals, using powder metallurgy. A carbonyl iron powder with an average particle less than 75 µm (Bay-met Metal Industry Inc.), a cobalt powder with an average particle size of 40 µm (Umicore), a Cu powderless than 63 µm, and a B4C (H.C. Stärck) powder with average particle size less than 10 µm were selected as the starting materials for this study. Fe-(30-60)wt.% Cu–20 wt. %Co alloys and

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Fe-(30-60)wt.% Cu–20 wt. %Co and wt.%1 B4C mixtures were blended during 30 min. in an T2F turbula mixture, and zinc stearate % 0,5 was added in mixture before blending in order to obtain good and homogeny mixture. Cylindrical samples were cold compacted in a Shimadzu press – cap. 12 tons at 350 MPa using an uniaxial steel, and then sintered in an electrical furnace – Carbolite eurothermat 1100 ° C /30min. Samples with 30, 60 wt. % Cu were designated as A1, B1 and 30, 60 wt. % Cu and wt. 1% B4C A2, B2 respectively. Rockwell B hardness values were measured under a load of 62, 5 kgf for each sample and average of hardness was calculated. Microstructure of the composite was examined using optical microscope. After grinding and polishing, the composite samples were etched with %2 Nital.

A pin-on-disc type of apparatus was employed to evaluate the wear characteristics of composite. The pin specimens made from the composites were machined to approximately 5 mm in length. Wear test was performed under varied loads such as; 10, 20 and 30 N and at a constant speed of 1 m/s and a constant sliding distance of 60 m for each composite sample. After the test, the wear pin was cleaned in acetone prior to and after the wear tests, and then dried after being weighted on a micro-balance with 0.1 mg sensitiveness.

Results and Discussion

Microstructural analysis.Fig. 1a, b, c and d shows the microstructural aspects of the Fe-Cu-Co alloysafter sintering at 1100˚C. The dark phase is rich in Fe and the bright in Cu, pores are black. The microstructure of samples, where one can observe the influence of the Cu wettability within Fe grains, leaving behind regions of porosity. Porosity reduction, its spheroidization and microstructure refinement were observed in Fig.1b as the Cu content increased from 30 to 60 wt.%. It is worth noted that microstructures with higher Cu content presented the Fe rich phase well distributed into the Cu rich phase in a more homogeneous and refined manner. Fig.1b and d clearly show the presence of Fe rich phase 60 µm‘‘islands” along with well dispersed others. Strong CoFe solid solutions presence were observed for the composite alloys (Fig.1a and c). It is attributed to the presence of high content of Fe in these composite alloys. When Cu is added, Fe content is reduced by forming lower amounts of Fe–Co solid solutions.

(a) 30wt.%Cu(A1) (b) 60wt.%Cu (B1)

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(c) 30wt.%Cu%1wt.%B4C particle (A2) (d) 60wt.%Cu+1wt.%B4C particle (B2)

Fig.1. Microstructures of Fe-Co-Cu alloys.(a) 30wt.%Cu alloy, (b) 60wt.%Cu alloy,(c)30wt.%Cu+1wt.%B4C particle, (d) 60wt.%Cu+1wt.%B4C particle.

Fig.1dindicates the microstructure of 60wt.%Cu plus 1wt.%B4C particles added to alloys,sintered at 1100 ˚C. It can be observed that there was the presence of a liquid phase formed by Cu during the initial minutes of sintering. From then on, liquid Cu progressively penetrated in the Fe grain boundaries, forming a film between the Fe particles, thus promoting an efficient diffusion. As a consequence of this liquid Cu wettability, swelling might occur because the initial solid Cu regions became pore zones after the Cu melting. It is a well known phenomenon for the Cu–Fe system, as reported by Refs. [10 –12]. This can also be observed in Ref. [13], which shows the Fe–Cu phase diagram, where at 1150˚C the Cu solubility in Fe is by 9% and Fe solubility in the Cu is by 4.5%. This interesting microstructural features was responsible for the satisfactory values for the hardness and wear resistance for high contentsof Cu alloys.

Hardness.Table 1shows hardnessofthe Fe–Cu-Co and Fe–Cu-Co-B4C systems.The addition of60 wt.%Cu promoted an increase in hardness in the order of %16.6 when compared to samples with 30 wt. %Cu addition. Dispersed B4C particles increased Fe–Cu-Co (B2) hardness in 44% compared to samples without B4C particles(B1).This table showed that higher hardness values were found for samples with higher Cu and B4C content—sintered at 1100 ˚C. This property was of relevant importance when the metallic system was considered for use as a matrix in diamond cutting tools because hardness was commonly associated to wear resistance. The finely dispersed ceramic particles in the metallic bulk acted as the controller of the matrix wear rate and consequently it reduced the wear rate of the cutting tool [14].

Table 1.Rockwell B hardnessesfor the Fe–Cu-Co and its B4C reinforced MMCs, sintered at the temperature of 1100 ˚C

Material’s types A1 B1 C1 D1

Rockwell B Hardness

52.98 61.7 77.38 88.9

Wear Resistance.Fig. 2shows the results of wear resistance for the diamond composites, sintered at 1100 ˚C. It can be seen that the leastwear rate was found for the samplewith 60%wt Cu,and Fe–60%wt Cu–1%wt B4C, respectively. It suggests that its choice can be usefull as the bonding matrix for the diamond tools.Among the whole tested samples, the60%wt Cu–1%wt B4C reinforced MMCs showed the highest wear resistance due to its increased hardness (Table 1).The wear rate

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increased more or less linearly with increasing load for all tested samples, but it is more obvious for the A2 and B2 samples. The wear rate was slightly higher for the A1 samples due to decreased hardness and its microstructure. One can observe the influence of the Cu wettability within Fe grains, leaving behind regions of porosity (Fig.1a).

Fig. 2. Average volumetric wear rates of the alloys and its MMCs after wear tests.

Conclusions

The experimental study showed that Cu and B4C particle additions affected the hardness and wear resistance Fe–Cu alloys for impregnated diamond cutting tools.(a) Microstructure of Fe–Cu–Co alloys was found to be very sensitive to the Cu content and pore closure took place with increasing the Cu content. (b) The addition of60 wt.%Cu promoted an increase in hardness in the order of %16.6 when compared to samples with 30 wt.%Cu. The addition of B4C particles increased Fe–Cu-Co (B2) hardness in 44% compared to samples without B4C particles (B1). (c) The best wear resistance was obtained for the1wt.% B4C reinforced-Fe–60wt.% Cu–samples among the others because of its increased hardness.

References

[1] M.Filgueira, D.G.Pinatti, Production of diamond wire by Cu–15%vol. Nb in situ process. In: Proceedings of the 15th Int. Plansee Seminar, Reutte, Austria, Plansee Holding, AG, (2001) 360–374.

[2] K.Przyklenk, Diamond impregnated tools – uses and production, Toolmaking ID 4 (1993) 192–195.

[3] M.Filgueira, D.G.Pinatti, Processing of diamond composites by powder metallurgy and rotary forging. J Mater Sci Forum 416-418 (2003) 228–34.

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[4] A.P. Barbosa L.J. Oliveira, Guerold Sergueevitch Bobrovinitchii, R.S. Guimarães, S. Crespo, Marcello Filgueira , Processing and mechanical properties of PM processed

Fe– Cu–Co alloys, Mater. Sci. Forum591-593 (2008) 247–51.

[5] I. E.Clark, B.J.Kamphuis, Recent advances in prealloyed powders for diamond tooling, Proc. Conf. EPMA, Lausanne, 2002, pp. 35-42.

[6] B. Kamphuis, A.Serneels, Cobalt and nickel free bond powder for diamond tools: Cobalite CNF, Ind. Diamond. Rev. 1(2004) 26–32.

[7] M.Del Villar, P. Muro,J.M. Sánchez, I. Iturriza, F. Castro, Consolidation of diamond tools using Cu–Co–Fe based alloy as metallic binders, Powder. Metall.1-44 (2001) 82–90.

[8] I.E. Clark, B-J. Kamphuis, Cobalite HDR, A new prealloyed matrix powder for diamond construction tools, Ind. Diamond Rev. 3 (2002) 177–182.

[9] G.Weber, C.Weiss, Diamix – a family of bonds based on diabase – V21. Ind. Diamond Rev. 2 (2005) 28–32.

[10] W.A.Kaysser, G.Petzow, Basic mechanisms of liquid phase sintering. In: G.S. Upadhyaya, Editor, Sintered Metal-Ceramic Composites, Elsevier Science Publication; 1984. p. 51–70.

[11] F.Thümmler, R.Oberacker, Introduction to Powder Metallurgy, Ed. by The Institute of Materials. London. 1st ed, 1993; p. 220–222.

[12] W.J.Huppmann, The elementary mechanisms of liquid phase sintering: II-Solution—reprecipitation, Zeitschrift für Metallkunde70 (12) (1979) 792–797.

[13] ASM HANDBOOK, Alloy Phase Diagrams, 3rd ed. 3 (1979) p. 168.

[14] M.Şimşir, E.Kerim Öksüz, Y.Şahin, Mechanical behaviour of diamond reinforced metal matrix composites, 11st Inter.Conf.on Mechanical Behaviour of Materials, ICM-11, M.Guagliano (Editor), Cerobbi, Lake Como, Milano, Italy, June 5-9, 2011.

[15] Y.Şahin, K.Emre Öksüz, Wear studies on diamond reinforced Fe-Co based metal matrix composites, 6thInternational Powder Metallurgy Conference and Exhibition, organized by Turkish Powder Association Middle East Technical University,Editor (M.Turker), 5-8 Oct.2011.

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Advanced Materials Research III 10.4028/www.scientific.net/AMR.685 The Effect of B4C Additions on Mechanical Properties of Fe-Cu-Co Matrix Composites for Diamond

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