copper tools in marble stones cutting

Journal Pre-proof Determination of wear parameters and mechanisms of diamond/ copper tools in marble stones cutting

Hedayat Mohammad Soltani, Morteza Tayebi PII:

S0263-4368(19)30936-9

DOI:

https://doi.org/10.1016/j.ijrmhm.2019.105172

Reference:

RMHM 105172

To appear in:

International Journal of Refractory Metals and Hard Materials

Received date:

24 November 2019

Revised date:

6 December 2019

Accepted date:

8 December 2019

Please cite this article as: H.M. Soltani and M. Tayebi, Determination of wear parameters and mechanisms of diamond/copper tools in marble stones cutting, International Journal of Refractory Metals and Hard Materials(2019), https://doi.org/10.1016/ j.ijrmhm.2019.105172

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© 2019 Published by Elsevier.

Journal Pre-proof

Determination of wear parameters and mechanisms of diamond/copper tools in Marble stones cutting Hedayat Mohammad Soltania and Morteza Tayebib,* [email protected] a

Mining and Metallurgical Engineering Department, Amirkabir University, Tehran, Iran

b

Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, Iran *

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Corresponding author.

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Abstract

In this paper, a type of soft metal binder of diamond tools (diamond segments) that was consisted

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of 78% Brass (Cu-10Zn) +16% Bronze (Cu-10Sn) +%6Co was investigated. The first, it was approved that the binder is a soft metal binder by a hardness test for diamond tools in natural

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stones cutting. Then, the effective factors on grinding efficiency such as specific energy (SE),

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Cutting force (FC), metal binder removal rate (MRR), grinding ratio (G-ratio), wear resistance and Mean free path (MFP) were evaluated by different formula and equations. On the other

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hand, the effect of different wear mechanisms on the metal binder and diamond grits of the tool was evaluated by the cutting of a type of very hard marble stone that calls Cappochino Beige

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Marble (CBM). The existence of wears of abrasive, surface fatigue, impact and erosive were confirmed by scanning electron microscopic observations. According to hardness 73 HRB

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(hardness of the binder) and the wears, there is a short tools life for the diamond tool due to low wear resistance of the metal binder but, the cutting rate was high. Novelty statement The rising price of decorative stones will increase the final price of the stones and will overshadow the global market of decorative stones. The presence of cobalt, iron, chromium and nickel powders increases the price of diamond tools because of their high price. On the other hand, due to the higher temperature and time of hot press to produce these tools by the mentioned powders, it will also increase the price. Therefore, in this paper, brass and bronze alloy powders, which are much cheaper than cobalt, iron, chromium and nickel powders, have been used as main metal binder powders to reduce raw material prices and manufacturing

Journal Pre-proof process costs. On the other side, due to the creation of a softer metal binder compared with the more expensive and harder binder of cobalt, iron, chromium and nickel powders, it can be affected to increase the cutting speed because of increasing wear of the binder. Therefore, mathematical calculations are essential for the efficiency of the tools' cutting.

Keywords: Diamond Tools; Wear; Soft Metal Binder; Marble Stone; Mean Free Path (MFP)

1. Introduction

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The composites based on synthetic diamonds due to their thermal stability, high hardness, impact

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resistance and etc. have excellent performance for decorative stones cutting tools in different systems. The composites quality is depended on diamond grits size, binder type, the interfaces

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properties, production parameters and etc. For the application, the diamond composites with metal binder have different wear mechanisms such as adhesive, abrasion, surface fatigue, and

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tribochemical reactions. Also different types of mating surfaces movements: sliding, rolling,

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oscillation, impact, and erosive wear. Adhesive wear occurs with the formation and breaking of interfacial adhesive bonds [1]. Abrasive wear happens with hard particles thus the binder cutting

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surface of the tool wears by hard protuberances such as hard stones particles (swarf). Surface fatigue occurs by cyclic surface stressing. On the other hand, synthetic diamond grits have high hardness and rigidity, low strength and large brittleness. Therefore, diamond grits are sensitive to

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surface fatigue. Tribochemical reactions carry out by frequent removal and new formation of

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reaction layers on the mating surfaces [1-3]. During stone cutting, contacting between diamond grits and stone surfaces is obvious that it results in an impact force on diamond grits. This force is more in circular blades and generates impact wear mechanism. By liquid in the environment that carries hard abrasives of tiny rock detritus, erosive wear occurs on metal binder surfaces in diamond tools [4-6]. Metal binders wear behavior in diamond tools is depended on wear environments and mechanisms, microstructure and chemical composition that they determine mechanical properties of binder such as hardness. Mechanical properties consist of hardness, fracture toughness, elastic modulus, tensile/compressive strength, and impact fatigue strength. Hardness is the main determinant in abrasive wear resistance. But, to mention of this point is necessary that microstructure can affect wear resistance without changing the chemical composition or mechanical properties. It means that many differences in wear occur at the same

Journal Pre-proof hardness [1]. Co content is the main factor for wear resistance in metal composite tools. Generally, abrasion resistance decreases with increasing cobalt content. In 6-8% Co, there are optimum abrasion resistance and maximum impact wear resistance [7]. The effective way to improve diamond retention in the matrix is use of a coating such as Ti, TiN, Ni or Cr. On the other hand, the coating prevents surface graphitization and oxidation [8-11]. Pre-alloyed bronze and brass minimize the risk of segregation and still maintains acceptable sintered strength [1]. Generally, diamond concentration is C20-C40 for decorative stones cutting. WC carbides can add to the metal binders for increase of wear resistance of diamond tools. They enhance wear

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resistance of abrasive and erosive but decrease wear resistance of impact and surface fatigue.

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The wear resistance of diamond based materials such as copper alloy/diamond composites is better than WC-Co-diamond composites because the WC-Co binders do not support diamond

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grits as well as metal binders of without WC and the major wear mechanisms of the WC-Codiamond composites are exerted on diamond grits such as impact wear and surface fatigue wear

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[12, 13].

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In this investigation, low Co content +Brass +Bronze binder was approved as the soft metal binder for the diamond tool. Also, wear mechanisms were characterized for the soft binder of

life.

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diamond tools. This paper gives an overview of the correlation between hardness, wear and tool

The experiment aimed to investigate the wear of diamond tools (diamond segments) with brass

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(low zinc), bronze (low tin) and Co composition in hot pressed diamond–metal matrix tools for

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decorative marble stones cutting.

2. Experimental procedure 2.1. Materials Powders 78 wt.% Brass (Cu-10Zn, kymera international, USA), 16% Bronze (Cu-10Sn, Kymera international, USA) and 6 wt% Co (Standard, William Rowland, UK) used as matrix of the segments, and diamond grits with Ti coating (ZNZS-05), on the mesh 30/35 and 35/40, (Zhongnan Diamond, China) used as reinforcement. The cutting carried out on a type of beige marble (Cappochino Beige Marble, CBM) that figure of CBM is shown in Fig. 1a. The diamond concentration in the segments was C30 (7.5 vol %). Diamond grits sizes were two mesh 30/35

Journal Pre-proof and 35/40 (600/500 and 500/425 µm, ANSI B74.16 [14] (Fig. 1b). The summary of physical and mechanical properties of CBM are shown in Table 1. 2.2. Powder metallurgy and hot press The powders’ pre-alloyed have been hot pressed in graphite molds at 900 °C, with 50 MPa pressure for 240 s in graphite molds and produced sample size 24×9.2×10 mm3. 2.3. Mechanical Testing 2.3.1. Hardness Hardness tests were carried out by Rockwell B hardness (HRB) (model Leitz, England) under

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100 kgf load based on ASTM E18 standard. Vickers microhardness tests were carried out

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according to ASTM E384 standard by applying 0.3 Kg load. 2.3.2. Wear

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Wet cutting of the CBM carried out by large diameter circular saw blade with 108 pieces of marble segments, during 11520 min that 3200 m2 CBM was produced. Summarizes the

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measured performance of large diameter saw shown in Table 2.

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2.4. Characterization

Micrographs were obtained optical microscope (Country, model IMM-420) and scanning

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electron microscope (SEM) (Philips, model Xl30, Netherlands). Chemical composition was performed by EDS analysis (Philips, model XL30, Netherlands). Phase analysis was carried out by X-Ray diffraction (XRD) (Philips, model PW1800, Netherlands) with CuKα radiation

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(wavelength 1.540598 ˚A).

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3. Results and discussion

To prevent oxidation of copper a neutral atmosphere was used in hot press. Copper oxidation reduces the diffusion rate. In order to study and analyze the thermodynamic behavior and calculate the free energies of the copper oxidation reactions, the HSC Chemistry5 software was used. According to the copper oxidation reactions (Eq. 1, 2 and 3) and Ellingham diagram (Fig. 2), the free energy values for Eq. 1, 2 and 3 at hot press temperature (T=1173 K) are equal to 166.4, -103.6 and -40.8 kJ/mol, respectively. Since the ΔG values for reactions 1, 2 and 3 are negative. Therefore, neutral gas was required [15]. H2 was used as neutral gas. Accordance with reaction 4 and the amount of negative free energy (ΔG = -45 kJ/mol) at hot press temperature in Ellingham diagram (Fig. 2), H2 gas prevents oxidation and eliminates oxygen if it was presented in the binder metal powders.

Journal Pre-proof 4(Cu) + (𝑂2) = 2 < 𝐶𝑢2 𝑂 > 1 2 < 𝐶𝑢 > + (𝑂2) = 2 < 𝐶𝑢𝑂 >

2

2 < 𝐶𝑢2 𝑂 > + (𝑂2) = 4 < 𝐶𝑢𝑂 >

3

< 𝐶𝑢2 𝑂 > + (𝐻2 ) = 2< 𝐶𝑢 > + (𝐻2 𝑂)

3.1.

4

Microstructure

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One of the most important effective factors on the life of a diamond cutting tool is the

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diamond/binder interface, i.e. the retention strength of the diamond grits. For this purpose, diamond particles were coated with titanium that elemental analysis of Ti-coated diamond grits

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is shown in Fig 3. The figure showed that the coating was not dissolved in the mixing and homogenizing process of metals and diamond powders as well as in the hot press. The

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matrix/diamond interface was evaluated with SEM. Ti-coated diamond grits had a great

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wettability with no crack in the diamond/matrix interfaces. On the other hand, due to the presence of the coating, the oxidation and decarburization of diamond grits at 900 °C were

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prevented. The distribution maps of elements Cu and C for diamond grits and the around areas of them is shown in Fig 3 that homogeneous distribution of Cu around the diamond grit has been demonstrated, i.e. the mixing process was successful before the hot press.

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The composite matrix after the hot press was investigated by SEM. In Fig. 4 it is evident that two

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phases with dark and light colors in the composite matrix were created. With EDX analysis on the marking phases, it is clear that there are copper and tin in the light phase and copper and zinc in the dark phase. The created phases in the composite matrix after the hot press were evaluated by XRD method. The results in Fig. 5 show that there were bronze and brass phases in the matrix, and no destructive phases were created during the hot press process due to the titanium coating of the diamond grits [16]. In solid solution, if the solute atom diameter is bigger or smaller than the solvent atom diameter, it will create a strain in the solvent atom network. The big solute atoms such as zinc and tin in copper (Atomic radii (r); rCu=0.128, rZn=0.133, rSn=0151 nm) expand the network around them and create a compressive stress field, and the small solute atoms such as cobalt (rCo=0.125 nm) in copper contract the network around them and create a tensile stress field. A reason for using

Journal Pre-proof brass and bronze powders instead of copper, zinc and tin powders was the presence of a solid solution that enhanced the slip resistant of dislocations with the presence of compressive stress fields and resulted in higher strength of the segments. Cobalt elements penetrated into the brass and bronze phases at temperature and time of hot press (900 °C, 4 minutes) and created the tensile stress fields in the compressive zones of the edge dislocations to minimize irregularities. The tensile stress fields locked the edge dislocations and increased the binder strength of the segment [17-19]. It should be noted that substitutional atoms such as cobalt due to the creation of a spherical

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hydrostatic field, only affect the motion of the edge dislocations and merely increase the strength

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of the brass and bronze phases approximately G/10 (G shear modulus) [17]. On the other hand, the presence of two phases of brass and bronze increased elastic strength of the matrix, the

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mechanical strength of matrix/diamond interface and retention strength of diamond grits in the matrix due to the high thermal expansion coefficient of the elements in them. The difference of

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the thermal expansion coefficients between the matrix and the diamond is very important in the

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mechanical adhesion of the diamond in the matrix. So that the thermal expansion coefficient of the diamond is very low compared to the metals. After hot press at high temperatures, the

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metallic matrix shrinks more than diamond grits during cooling and creates a suitable mechanical strength around diamond grits. Therefore, a greater difference in thermal expansion coefficients creates higher mechanical adhesion. The use of copper, zinc, and tin elements with high thermal

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expansion coefficients resulted in appropriate mechanical strength between the matrix and

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diamond grits after shrinkage [20, 21]. The mechanical strength of the matrix/diamond is created during the cooling operation after the hot pressing process. The mechanical strength of the matrix/diamond interface was created after the cooling. This effect greatly contributes to cobalt element which increases the adhesion strength of the diamond/matrix interface. Elemental use of copper, zinc and tin powders increases the separation of the metal phases and reduces strength on the metal binder after the hot press. Therefore, the use of pre-alloyed bronze and brass powders minimized the separation risk of metal phases [22]. On the other hand, the economical use of copper, zinc and tin powders compared with cobalt, nickel and iron powders in industrial applications is important for decreasing the price of diamond tools.

Journal Pre-proof 3.2.

Hardness

Generally, metal binders based on brass and/or bronze are soft binders in diamond tools [23]. The hardness of the segments metal binder with 73 HRB confirmed soft binder of low cobalt + brass + bronze compared with high Co, Ni, Fe or a mixture of them. The hardness of the matrix phases, bronze/brass interface and surrounding the metal phases/diamond grits interface were evaluated. The hardness profile of the matrix is shown in Fig. 6, which shows the microhardness of the brass, the bronze, brass/bronze interface,

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surrounding the brass/diamond interface and surrounding the bronze/diamond interface were 206, 217, 228, 235 and 244 HV, respectively. The mentioned microhardnesses were due to the

and dislocations which are discussed below.

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influence of Co element, elastic interaction areas and structural defects such as phase boundaries

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Diffusion is the most important mechanism in the hot press process. The diffusion includes a

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lattice volume, a free surface, and a grain boundary diffusion. Surface diffusion and grain boundary diffusion are calculated by Fick's law (Equation 5 and 6) [15, 24]. −𝑄

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𝐷𝑠 = 𝐷0𝑠 exp ( 𝑅𝑇𝑠) −𝑄

𝐷𝑏 = 𝐷0𝑏 exp ( 𝑅𝑇𝑏)

(5) (6)

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Where Ds surface diffusion coefficient (cm2/s), Db grain boundary diffusion coefficient (cm2/s), D0s atomic frequency factor at surface (cm2/s), D0b atomic frequency factor at grain boundary

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(cm2/s), Qs activation energy for diffusion at the surface (kJ/mol), Qb activation energy for

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diffusion at grain boundary (kJ/mol), R universal gas constant (8.314 J/K.mol) and T are temperature (K) [15, 24]. In general, the activation energy for volume diffusion (Ql) is the highest and for surface diffusion the lowest. This means that at any temperature, diffusivity ratio Ds> Db> Dl (Dl, defect-free lattice diffusion coefficient) is maintained. But, at temperatures more than 0.75-0.8 Tm (the equilibrium melting temperature) due to the highest lattice expansion, the grain boundary diffusion portion is negligible compared with the lattice diffusion [24]. Therefore, according to hot press temperature (900 °C) for used the brass and bronze powders in the binder and their melting points, calculation of Co element grain boundary diffusion coefficient in the bronze and brass phases was not necessary. Because at high temperatures, the lattice diffusion is the highest and the fastest, the portion of dislocations like the boundaries in the atomic penetration can be ignored. In general, the effect of dislocations at temperatures

Journal Pre-proof below 0.5 Tm is important [24]. Therefore, only the surface diffusion coefficient of the Co element in the brass and bronze phases was very important. In the α-brass phase, the atomic radius difference of Cu and Zn (ΔrZn, Cu = 5 nm) is small. Both copper and zinc have similar FCC structure. In the α-bronze phase, the atomic radius difference of Cu and Sn (ΔrSn, Cu = 23 nm) is bigger. As well as, copper has FCC structure and tin has a tetragonal structure. Nevertheless, the formation of regular solid solutions of α-brass and αbronze had no problems, but the stress fields are larger in bronze [19, 24]. On the other hand, at

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the high temperatures, the arrangement in the atomic network disappears and at a critical temperature, the arrangement disappears in the long-range order. According to Brass (Cu-10Zn)

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solidus temperature (1020 °C), Bronze (Cu-10Sn) solidus temperature (845 °C) and hot press temperature (900 °C), more disorder at hot press temperature occurred in the bronze phase.

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Therefore, the volume diffusion of the cobalt element in the bronze phase was higher than the

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brass phase and created more tensile fields in the bronze phase. Therefore, the microhardness of the bronze phase is higher than the brass phase [15, 24]. The mentioned surface diffusions that

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had the main portion of total diffusion were the phase boundaries between α-brass and α-bronze which are referred as phase boundaries. α -brass with lattice parameter 0.364 nm and α-bronze

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with lattice parameter 0.366 nm created a semi-coherent interface in the binder of the segment because the two phases had the same network structure (FCC) and low difference of their

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network parameters (Δa=0.002 nm). The disregistry or misfit (δ) between two lattices of α-brass

𝛿=

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and α –bronze phases in their semi-coherent interface was calculated by Eq. 7 [24, 25]. 𝑎𝐵𝑟𝑜𝑛𝑧𝑒 −𝑎𝐵𝑟𝑎𝑠𝑠 𝑎𝐵𝑟𝑎𝑠𝑠

(7)

According to Eq. 7, the value of δ was negligible and equal to 0.005. If there was a negligible misfit in the semi-coherent interface such as δ=0.005 in the semi-coherent interface of α-brass and α –bronze phases, matching in the interface is created by a series of edge dislocations. According to the high temperature of hot press and the presented description, the matching in the interface and the series of edge dislocations were occurred in the segments [24]. The edge dislocations distance (D, nm) is calculated by Eq. 8 [24]. 𝐷≈

𝑏 𝛿

(8)

Journal Pre-proof Where b (nm) is Burgers vector of the dislocations which is calculated by Eq. 9 [24]. 𝑏=

aBronze +aBrass

(9)

2

According to Eq. 8 and 9, D and b were equal 73 nm and 0.365 nm in the interface, respectively. The created edge dislocations in the phase boundaries are suitable sites for the diffusion of cobalt atoms. Due to the high temperature of hot press, Co atoms diffused into the phase boundaries and were located in the compressive zone of the edge dislocations and the stress fields in the phase

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boundaries were strengthened. It should be noted that the phase boundaries have a greater number of dislocations and empty spaces than inside the phases. Therefore, more Co atoms were

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diffused in the phase boundaries that resulted in higher microhardness in the phase boundaries

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than the brass and bronze phases. On the other hand, the metal matrix of the segment was strengthened by the phase boundaries

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The Ti coating of diamond grits has a HCP structure with lattice parameter 0.295 nm [20] and

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the α-brass and α-bronze phases have the FCC structure with the different lattice parameters. Therefore, the Ti-coated layer formed a semi-coherent interface with α-brass and α-bronze

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phases with δ = 0.23 and 0.24, respectively, due to the low density difference of the FCC and HCP lattices or a non-coherent interface due to high cooling rate and the differences in the type

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of structure and lattice parameters. Therefore, α-bronze/Ti layer and α-brass/Ti layer interfaces had more misfit, dislocations and empty spaces than the α-brass/α-bronze interface and α-

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bronze/Ti layer interface had more than α-brass/Ti layer interface. Therefore, diffusion rate of Co atoms in the α-bronze/Ti layer interface was higher than the α-brass/Ti layer interface and, the αbrass/Ti layer interface more than the α-brass/α-bronze interface, which resulted in the αbronze/Ti layer interface microhardness > the α-brass/Ti layer interface microhardness > the αbrass/α-bronze interface microhardness [17-20]. As well as, it should be noted that more diffusion rate of cobalt atoms in the diamond/matrix interface resulted in higher adhesion strength due to the chemical properties of cobalt and higher mechanical strength due to the creation of more tensile fields in the diamond/matrix interface. This increase in mechanical strength contributed to the caused mechanical strength by the high difference between the thermal expansion coefficient of the diamond and, the brass and bronze phases (Table 3).

Journal Pre-proof 3.3.

Wear parameter

The specific energy (SE, mJ/m3) for the cutting process was calculated through two modes according to Equations 10 and 11. The specific energy based on the Shore hardness (Eq. 10) and the specific energy based on uniaxial compressive strength (Eq. 11) for cutting of CBM were equal to 866 mJ/m3 and 782 mJ/m3, respectively. The specific energy indicates the rock sawability. In fact, the amount of energy needed to remove a volume of stone by a diamond tool [5, 26-29]. (10)

SE = 0.021 UCS 0∙775

(11)

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SE = 0.003 SH1∙377

Cutting force (FC, kN) was calculated by the Eq. 12 [5, 26-29]. Where SE is the specific energy

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(mJ/m3), Q is the volume of worn stone per unit length of cut (m3/km). The volume of removed

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material from the CBM is equal to total produced marble stone (3200 m2) × segment width (0.0092 m) = 29.44 m3. On the other side, the length of the cut is equal to total produced marble

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stone (3200 m2) ÷ slab width (0.5 m) = 6400 m. Therefore, Q is equal to 4.6 m 3/km. According

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to Eq. 12 and the specific energy values based on the Shore hardness and uniaxial compressive strength, Cutting forces (FC) were equal to 3984 kN and 3597 kN, respectively [5, 26-29]. (12)

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FC = Q. SE

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Peripheral speed and speed of rotation of a natural stones cutting system (stationary) are

V =

Dπn 60 ×1000

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calculated by the Eq. 13 [30].

(13)

Where n is the rotation speed, V is the peripheral speed, D is the outside diameter of the circular cutting tools. For very hard marble stones, suitable peripheral speed is 35 𝑚⁄𝑠 [31]. Base on Eq. 13 increase of the peripheral speed results in the speed of rotation and vice versa. On the other hand, harder marble stones need to lower peripheral speed [31]. Therefore, very hard marble stones have lower speed of rotation than other marble stones such as medium hardness marbles and hard marbles. Therefore, according to Eq. 13, the Optimum RPM Speed for the bridge saw blade was 418 RPM. It means that for medium hardness marbles and hard marbles, the Optimum RPM Speed is higher than 418 RPM. It means that for medium hardness marbles and hard marbles, the Optimum RPM Speed is higher than 418 RPM.

Journal Pre-proof Increase of speed of rotation results in an increase of material removal rate (metal binder removal rate in diamond segments) (MRR, mm3/min) [32]. MRR is calculated by the Eq. 14. MRR =

Volume of removed material of binder

(14)

time

Total cutting time

The diamond segment wore during 107 min (Number of segment =

11520 min 108

). For preventing the

damage of the blade, the cutting carried out until height 9 mm of the segment. Therefore, the volume of removed material is equal to 1987.2 mm3 (24×9.2×9 mm3). According to Eq. 14,

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MRR is equal to 18.6 mm3/min. It means that in the same conditions of cutting for different marbles and in the same diamond tool, very hard marble stones result in minimum wear

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(minimum MRR) of diamond tools. Tool life has a positive relation with MRR [33, 34].

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Therefore, tool life for cutting of very hard marbles is maximum in the same conditions of cutting for different marbles and in the same diamond tool [33, 34].

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The MRR, the grinding ratio (G-ratio) and wear resistance are the factors used to inspect the grinding efficiency. The G-ratio is calculated by the Eq. 15 [35-38].

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Volume of removed material from the stones Volume of removed diamond cutting tools

(15)

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G-RATIO =

The volume of removed material from the CBM is equal to 29.44×109 mm3. The volume of

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removed diamond segments (214617.6 mm3) is equal to the volume of worn segment (1987.2 mm3) × the number of segments in the saw blade (108). Therefore, according to Eq. 15, G-ratio

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is equal to 113877.

Wear resistance is calculated by Eq. 16 [39, 40]: Wear resistance (×103) =

𝐰𝐭 𝐰𝐨𝐫𝐧 𝐬𝐭𝐨𝐧𝐞 𝐰𝐭 𝐥𝐨𝐬𝐬 𝐭𝐨𝐨𝐥𝐬

=

𝝆𝒔𝒕𝒐𝒏𝒆 × 𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐫𝐞𝐦𝐨𝐯𝐞𝐝 𝐦𝐚𝐭𝐞𝐫𝐢𝐚𝐥 𝐟𝐫𝐨𝐦 𝐭𝐡𝐞 𝐬𝐭𝐨𝐧𝐞 𝝆𝒕𝒐𝒐𝒍𝒔 × 𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐫𝐞𝐦𝐨𝐯𝐞𝐝 𝐦𝐚𝐭𝐞𝐫𝐢𝐚𝐥 𝐟𝐫𝐨𝐦 𝐭𝐡𝐞 𝐭𝐨𝐨𝐥𝐬

(16)

Where wt worn stone is the weight of removed material from the stone (g); wt loss tools is the 𝑔 weight of removed material from the tools (g); 𝜌𝑠𝑡𝑜𝑛𝑒 is the density of stone ( ⁄𝑐𝑚3 ); 𝜌𝑡𝑜𝑜𝑙𝑠 is 𝑔 the density of tools ( ⁄𝑐𝑚3 ). The volume of removed material from CBM, the volume of removed diamond cutting tools, the density of CBM and density of the segments are equal to 29.44 × 106 cm3, 214.62 cm3, 2.86 𝑔 𝑔 ⁄𝑐𝑚3 , and 8.33 ⁄𝑐𝑚3 , respectively. Therefore, Wear resistance (× 103 ) is equal to 44.13×

Journal Pre-proof 103 . This is a low value of wear resistance for Brass + Bronze + low Cobalt binder compared with metal binders of high Co, Ni, and Fe and/or mixed them [39, 40]. The volume fraction of diamond grits, particle size, particle size distribution, mean free path (MFP) in the binder phase, and the ratio between MFP and abrasive particle sizes are microstructure factors that affect wear [1, 41]. The mean free path (MFP) was calculated by Eq. 17. 𝜆=4 ×

(1−𝑉𝑑𝑖𝑎 )

(17)

𝑆𝑑𝑖𝑎

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Where λ= the mean free path in the binder phase, Vdia = the volume fraction of diamond grits and

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Sdia = mean diamond grits size (µm). λ is a function of mean diamond grits size and volume fraction of diamond grits. On the other side, Mean free path is versus diamond grits size [1, 41,

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42]. Accordance with Eq., λ is approximately 0.0067 for the chemical composition. This is a low value for λ. On the other hand, in 6 Co content, λ (MFP) decrease results in transverse rupture

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strength decrease [41]. Therefore, transverse rupture strength is low value for the metal binder of

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tools. It means a low value of transverse rupture strength shows a soft metal binder. The 'contiguity' of the diamond grits is the fraction of the total surface of diamond grits that is shared

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with other diamond grits. This was investigated that the decrease of Co volume fraction increased contiguity. On the other hand, the increase of contiguity resulted in a decrease in

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transverse rupture strength. Therefore, according to 6% Co in the chemical composition of

tools [41, 42].

3.4.

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binder which is low value, transverse rupture strength is also low value for the metal binder of

Wear mechanisms

Abrasive wear, impact wear, surface fatigue wear and erosive wear occurred in the diamond segment that their schematic is observed in Fig 7. Abrasive wear includes microploughing, microcutting, and microcracking mechanisms on the surfaces of materials. Decorative stones cutting such as very hard marbles carries out with low stress. Very hard marbles cutting results in abrasive particles which are composed of hard and tiny abrasive minerals (swarf of stones) (Fig 8a) [1, 4, 43]. Therefore, the particles created scratches and crushed zones on the surfaces of the segments. Generally, abrasive wear occurred

Journal Pre-proof in the effect of friction between swarf and metal matrix [11]. Sign of abrasive wear is convexity and concavity of the surfaces (Fig 8b,d) [44]. Abrasive wear was observed on the surfaces of the segments. It should be noted that abrasive wear for diamond segments is essential. In diamond tools, diamond edges and diamond grits projection carry out stone cutting (Fig 8c). For creating the edges and the projections, abrasive wear is needed on the metal binder. On the other hand, excessive abrasive wear reduces the retention of diamond grits and segment life. Therefore, the abrasive wear rate is an important factor for diamond segments [45-49]. Diamond grits size and abrasive wear determine the height of protrusions on the binder surface.

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In this investigation, the metal binder was soft and diamond grits size was coarse. They were

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appropriate for very hard marble such as CBM [14, 50]. Therefore, cutting forces act on diamond grits created cyclical stress on them. Forasmuch as in diamond grits, there are pores [3, 4, 51].

-p

Therefore, surface fatigue wear was observed in some diamond grits (Fig 8d). Surface fatigue wear significantly reduced the cutting ability and created large particles of broken diamond grits

re

[51, 52].

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In circular blades, acts on diamond grits are constant. On the other side, the metal binder of diamond segments was soft. Therefore, macro-cracks were observed on the binder (Fig 9)

na

(especially around diamond/matrix interface) because of the plastic deformation around the diamond grits. On the other side, because of acts on diamond grits, the seat of the diamond slightly opened and deboning occurred for a few diamond grits (Fig 10a). For the reasons, impact

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wear or plucked off diamond grits was occurred. The impact wear is shown in Fig 10b. In this

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investigation, diamond grits had a Ti coating. Ti coating increases the level of interfacial adhesion by the crack network. It means that Ti coating promotes strong diamond–metal contact [8, 53, 54]. Therefore, a few diamond grits were plucked off. Sign of Erosive wear is crushed areas and cracks that formed when large hard mineral particles (Fig 11a) and large broken diamond grits rubbed on metal binder surfaces. Erosive wear is shown in Fig 11a, b. Generally, crushed areas in erosive have irregular orientation compared with abrasive wear (Fig 11c) [55]. As shown in Fig 10d, deep scratches were observed in the matrix due to the broken diamond particles which slithered between two surfaces of the segment and the stone. Therefore, surface fatigue wear can be another reason of erosive wear.

4.

Conclusion

Journal Pre-proof From the foregoing results and discussion, the following conclusions have been drawn: 1. The prediction of CBM sawability by specific energy (SE) shown a suitable sawability. On the other hand, very hard marbles such as CBM had minimum RPM than hard marbles and medium marbles. Therefore, tool life for cutting of very hard marbles compared with hard marbles and medium marbles is maximum (in the same conditions of cutting for different marbles and in the same diamond tool). 2. Amounts of the grinding ratio (G-ratio) and wear resistance shown low values of G-ratio and wear resistance for Brass + Bronze + low Cobalt binder compared with metal binders of high

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Co, Ni, and Fe and/or mixed them.

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3. Increase of diamond grits size, the volume fraction of diamond grits and contiguity, also decrease of mean free path, Co volume fraction and hardness resulted in the decrease of

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transverse rupture strength and, creating a soft metal binder.

4. In diamond marble tools occurred the following wears by marble stone cutting:

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 Abrasive wear happened because of a group of abrasive particles that were composed of

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hard and tiny abrasive minerals. The tiny particles created convexity and concavity of the surfaces which were the sign of abrasive wear.

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 Surface fatigue wear happened because of cutting forces act on diamond grits which created cyclical stress on them.

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 Impact wear happened because of acts on diamond grits were constant in circular blades and macro-cracks specially created around diamond/matrix interface on the metal binder.

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Of course, Ti coating on diamond grits increased the level of interfacial adhesion by the crack network.

 Erosive wear happened because of individual large hard mineral particle and broken diamond grits. Erosive wear had irregular orientation compared with abrasive wear.

We have no conflict of interest to declare.

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Fig. 1 (a) CBM and (b) Diamond grit size Fig. 2 Free energy of copper oxidation reactions in Ellingham diagram at hot press temperature Fig. 3 Elemental analysis of Ti-coated diamond grits and element distribution map Fig. 4 The diamond segment SEM and EDS Fig. 5 XRD paterns of Brass and Bronze phases in the diamond segments.

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Fig. 6 Microhardness of the brass, the bronze, bronze/brass interface, surrounding the brass/diamond interface and surrounding the bronze/diamond interface in the diamond segments

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Fig. 7 Schematic of Abrasive wear, impact wear, surface fatigue wear and erosive wear in diamond segments

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Fig. 8 a) Hard and tiny abrasive minerals of CBM, b) Convexity and concavity of the cutting surfaces (Abrasive wear), c) Diamond grits projection, d) Broken diamond grit (surface fatigue wear)

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Fig. 9 Seat of diamond grit and macro-crack.

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Fig. 10 a) The seat of the diamond is slightly opened and debonding is occurred, b) Impact wear or plucked off diamond grits

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Fig. 11 a) Crushed areas and large hard mineral particles b) Erosive wear with irregular orientation, c) crushed areas, d) Effect of broken diamond grit or deep scratch

Sample Color

CBM

Beige

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Table 1 Summary of physical and mechanical properties of CBM Grain Size (mm)

Density 𝑔 ( ⁄ 3) 𝑐𝑚

C-2 type Shore sclerescope hardness

˂ 0.1

2.68

61.2

Compressive Strength (MPa)

E (GPa)

Saturate-toDry Ratio

Dry

Saturate

Dry

Saturate

106.4

86.8

41.8

38.9

Table 2 Measured performance of large diameter saw

Stone

Machine weight (ton)

Saw diameter (mm)

Number of the tool in the saw

Vertical saw motor power

Horizontal saw motor power (kw)

Advance rate of saw (cm/s)

Slab dimension (cm)

Sawing length (cm)

0.93

Journal Pre-proof

CBM

18

1600

blade

(kw)

108

190

22

2.5

2×220×50

220

Table 3 Melting point and coefficient of expansion Co, Cu, Zn, Sn, Brass and Bronze [15, 20,

Co

1495

At 20 – 400 °C ------ 14

Cu

1084

At 20 – 500 °C------ 18.3

Zn

420

At 20 – 300 °C------ 34

Sn

232

At 20 – 200 °C------24.2

Brass (Cu10Zn)

1065

At 20 – 300 °C------18.4

Bronze (Cu10Sn)

1000

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At 20 – 300 °C ------ 1

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Synthetic singlecrystal diamond

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Coefficient of expansion × 10-6

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Elements

Melting point (°C)

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21].

At 20 – 300 °C------18.4

Highlight 

Creating a soft metal binder for diamond tools by Brass/Bronze + low cobalt.

 

Grinding efficiency calculations of diamond tools by cutting of very hard marble stone. Existence of wears of abrasive, surface fatigue, impact and erosive in diamond tools for cutting of beige marbles.