Study on the effect of 1.4-butynediol on the performance of electroplated diamond wire saw

In response to the problems of low production efficiency and short service life of electroplated diamond wire saws used in the photovoltaic industry, in order to improve the performance of electroplated diamond wire saws, electroplating solutions with different mass fractions of 1.4-butynediol (0.1 g/L, 0.3 g/L, 0.5 g/L) were prepared by using electroplating methods. Nickel coatings were obtained through customized electroplating tanks, and electroplated diamond wire saws were prepared through electroplating processes. The effect of 1.4-butynediol content (mass fraction) in electroplating solution on the performance of diamond wire saws was studied. A scanning electron microscope was used to observe the microstructure of the coating surface and wire saw section, and the hardness, tensile strength, and wear of the coating with different concentrations of 1.4-butynediol were measured. The results show that among the three ratios, when the mass fraction of 1.4-butynediol is 0.3 g/L, the nickel coating has the best bonding with the metal matrix, the wire saw performance is the best, the coating hardness is the highest (427 MPa), and the wire saw has the least wear (0.092 g).


Introduction
At present, the photovoltaic and semiconductor industries are developing rapidly, and the cutting and processing requirements for precious hard and brittle materials such as sapphire, monocrystalline silicon, and polycrystalline silicon are becoming increasingly high.Electroplated diamond wire saws are widely used due to their advantages such as narrow cutting seams, low loss, high cutting efficiency, and low environmental pollution [1][2][3][4][5].The electroplated diamond wire saw is a linear sawing tool that is made by reducing metal cations in the electrolyte to metal at the cathode, and coating the suspended diamond abrasive particles onto the coating during the deposition on the surface of the wire saw substrate.In the production process of electroplated diamond wire saws, a layer of metallic nickel is usually plated on the surface of diamond abrasive particles, giving them conductivity and metallicity [6,7].During the process of sanding and thickening, the nickel coating deposits and grows on the surface of the online substrate, as well as on the surface of the nickel-plated diamond and its interface with the nickel coating.The nickel-plated diamond is completely covered by the nickel coating on the surface of the online substrate, generating chemical bonds to firmly embed the nickel-plated diamond in the nickel coating.The strength of the wire substrate's grip on nickel-plated diamond depends on the mechanical properties of the nickel coating itself and the bonding strength between the coating and the wire substrate.Therefore, the study of the performance of nickel plating is particularly important.The performance of the plating is largely influenced by the composition of the electrolyte and process parameters, among which the type and amount of additives are crucial to the performance of the plating [8][9][10].According to the theory of electrodeposition, a high total number of adsorbed atoms, a high cathodic overpotential, and a low surface mobility of adsorbed atoms are necessary conditions for slowing down grain growth and increasing a large number of nucleations [11][12][13][14].Adding 1.4-butynediol as an additive to the electrolyte can increase the cathodic overpotential of nickel electrodeposition, slow down the exchange rate of discharge ions between the cathode surface and the plating solution, reduce the migration rate of adsorbed atoms on the cathode surface, and improve the mechanical properties, surface morphology, and bonding strength with the wire substrate of the nickel coating.This article introduces the addition of different proportions of 1.4-butynediol to the electrolyte and the preparation of nickel coatings and diamond wire saws, respectively.The hardness of the coating was measured by using a digital microhardness tester, the tensile strength of the coating was tested by using a universal testing machine, the morphology and microstructure of the coating were analyzed by using an electron scanning microscope, and the cutting performance of the electroplated diamond wire saw was tested through cutting experiments.The influence of different ratios of 1.4 butynediol on the coating performance and the electroplated diamond wire saw performance was explored.

Electrolyte composition and process conditions
The composition and process conditions of the nickel sulfamate electrolyte are shown in Table 1.The reagents used in the experiment were all analytical pure, and distilled water was used to prepare the electrolyte.The pH value of the electrolyte was adjusted by using sulfuric acid and sodium hydroxide.Electrolyte preparation method: 1) Dissolving the weighed nickel sulfamate and cobalt sulfate in deionized water, waiting for them to fully dissolve, and then pouring them into the electroplating tank; 2) Fully dissolving a certain amount of boric acid in heated deionized water and adding it to the plating bath under stirring conditions; 3) Mixing sodium dodecyl sulfate with deionized water to form a paste, then adding 100 times water to boil until fully dissolved, and adding the plating solution under stirring conditions; 4) Adding the plating solution to a fixed volume with deionized water, and finally adding 1.4-butynediol that has been fully dissolved in hot deionized water to obtain the prepared electrolyte.
The experimental power supply is a WLS digital constant current source with an anode of 150 mm × 100 mm × 10 mm metal nickel plate and a cathode of 100 mm × 50 mm × 0.2 mm back insulated stainless steel plate (replaced by treated metal wire substrate when preparing diamond wire saw), with an average coating thickness of 40 μ M.

Performance testing
2.2.1 Coating performance testing.The microhardness of the coating was measured by using the MHV2000 digital microhardness tester.The loading speed was 30 mN/S, and the maximum load was 300 mN.After maintaining the maximum load for 5 seconds, the coating was automatically unloaded with an unloading load of 20 mN.Three sets of data were obtained from each group of samples and the average value was taken.
The tensile strength of the coating was tested on a WOW-50 universal testing machine, with a tensile speed of 5 mm/min.Three sets of data were obtained from each group of samples, with the minimum value not lower than the relevant standards, and the average value was taken.

Surface morphology and microstructure analysis of coating.
The surface morphology of the nickel coating was observed by using a FEI Phenom Prox electron scanning microscope, with a working voltage of 10 KV and a magnification of 4000 times.

2.2.3
Performance testing of diamond wire saws.The diamond wire saw was cut off with external force, the fracture morphology was observed by using an FEI Phenom Prox type electron scanning microscope, and the bonding ability between the coating and the substrate was analyzed.
The wear of the wire saw before and after cutting glass was weighed by using an analytical balance, the area of the cut glass was measured with a ruler, and the cutting ratio was used to characterize the cutting performance of the wire saw, as shown in Formula (1).
δ=∆m/S (1) In the formula: S is the area of cut glass, square meters; ∆M is the wear amount of a glass wire saw with a cutting area of S. As can be seen from the above formula, the higher the value δ is, the greater the wear of the wire saw is when cutting the same area of glass.To extend the service life of the wire saw, it is necessary to reduce the δ Value of the wire saw.

Coating hardness analysis
The hardness of coatings with different ratios of 1.4-butynediol was tested on a microhardness tester, and the results are shown in Figure 1.From the figure, it can be seen that as the mass fraction of 1.4-butylene glycol increases, the microhardness of the coating first increases and then decreases.The microhardness of the 2 # coating (427 MPa) is about 40% higher than that of the 1 # coating (298 MPa) and about 15% higher than that of the 3 # coating (371 MPa).The change in microhardness of the coating is related to the grain size and preferred orientation of the crystal plane.Within a certain range, as the mass fraction of 1.4-butynediol increases, it is beneficial for a large amount of nucleation to obtain a deposited layer with fine grains.The degree of preferred orientation of the coating (111) crystal plane increases, while the preferred orientation of the nano (111) crystal plane is beneficial for obtaining a high-hardness nanocrystalline coating [15][16][17].When the mass fraction of 1.4-butynediol continues to increase, the orientation density of the (200) crystal plane of the coating increases, and the microhardness of the coating decreases when it is lower than other crystal planes.When the mass fraction of 1.4-butynediol is less than 0.3 g/L, the grain refinement and microhardness of the coating increase with the increase of its concentration; When the mass fraction of 1.4-butynediol is higher than 0.3 g/L, the crystal density of the coating (200) increases and the microhardness decreases as its concentration increases.

Analysis of tensile strength of coating
The tensile strength of coatings with different ratios of 1.4-butynediol was tested on a universal testing machine, and the results are shown in Figure 2. From the figure, it can be seen that as the mass fraction of 1.4-butylene glycol increases, the tensile strength of the coating first increases and then decreases.The tensile strength of coating 2 # (564 MPa) is about 23% higher than that of coating 1 # (456 MPa) and about 41% higher than that of coating 3 # (398 MPa).1.4-butynediol contains unsaturated bonds and has a strong refining effect on grains.Within a certain range, as the mass fraction of 1.4-butynediol increases, the grain size decreases, the chances of coalescence increase, the coating shrinks, and the tensile strength increases [18].When the mass fraction of 1.4-butylene glycol continues to increase, the tensile stress of the coating significantly increases, leading to small cracks and a decrease in the tensile strength of the coating.When the mass fraction of 1.4-butynediol is less t h a n 0 .3 g / L , t h e g r a i n s i z e o f t h e c o a t i n g d e c r e a s e s a n d a g g r e g a t e s w i t h t h e i n c r e a s e o f i t s concentration, resulting in an increase in tensile strength; When the mass fraction of 1.4 butynediol is higher than 0.3 g/L, the tensile stress of the coating increases and the tensile strength decreases with the increase of its concentration.

Surface morphology and microstructure analysis of coating
The surface morphology of nickel coatings with different ratios of 1.4-butynediol was observed by using an electron scanning microscope, as shown in Figure 3. From the figure, it can be seen that as the mass fraction of 1.4-butylene glycol increases, the grain size gradually decreases, and the microstructure of the coating gradually becomes flat and uniform.The microstructure of the 2 # coating is the best, and further increasing the concentration of 1.4-butynediol results in little change in the microstructure of the coating.During the deposition of metal nickel ions, 1.4-butynediol is adsorbed at the active point of crystal growth, hindering the continued growth of the crystal and reducing the size of the agglomerates.The lone pair electron pairs of 1.4-butynediol form stable coordination bonds with the empty d orbitals of nickel ions, making ion discharge more difficult.The overpotential of the reaction also significantly increases, promoting the formation of new crystal nuclei [19][20][21].The adsorption of 1.4-butynediol at the micro peak of the cathode surface is greater than that at the micro valley, and its inhibitory effect on nickel deposition at the micro peak is greater than that at the micro valley.Therefore, the deposition rate of metal nickel at the micro valley is greater than that at the micro peak, which can achieve a leveling effect and make the coating surface smoother.Therefore, as the concentration of 1.4-butynediol continues to increase, the surface microstructure of the coating becomes flat and uniform, and the grain size continues to decrease.When the concentration of 1.4-butynediol is 0.3 g/L, the surface morphology of the coating is optimal.

Analysis of the bonding ability between coating and substrate
The diamond wire saw was cut off with external force and the fracture morphology was observed by using a scanning electron microscope, as shown in Figure 4. From the figure, it can be seen that as the mass fraction of 1.4-butylene glycol increases, the bonding state between the coating and the substrate shows a trend of first strengthening and then weakening.The 2 # wire saw coating has good bonding with the metal substrate, and there are obvious cracks between the 1 # and 3 # wire saw coating and the metal substrate.Within a certain range, as the mass fraction of 1.4-butynediol increases, the coating becomes continuously dense and crystallizes uniformly, which is beneficial for improving the bonding ability between the coating and the substrate [22].As the concentration of 1.4-butylene glycol continues to increase, the orientation density of the coating (200) crystal plane increases, the mechanical properties weaken, and the bonding ability with the substrate weakens.As the concentration of 1.4-butylene glycol continues to increase, the bonding ability between the coating and the substrate increases, and the best effect is achieved when its concentration is 0.3 g/L.

Analysis of cutting performance of electroplated diamond wire saw
A reciprocating wire saw-cutting machine was used to cut ordinary flat glass.In the experiment, the thickness of ordinary flat glass was 5 mm, and the three formula wire saws were all cut into the same length, with a preliminary setting of 30 mm.All three types of wire saws exhibit good cutting performance and can smoothly complete the cutting of ordinary flat glass [23][24].The cutting performance analysis results are shown in Table 2. From the table, it can be seen that the cutting performance of wire saws varies depending on the mass fraction of 1.4-butynediol.When sawing ordinary flat glass of the same area, the weight loss of the 2 # wire saw is at least 0.092 g, while the weight loss of the 1 # and 3 # wire saw is more important than that of the 2 # wire saw, which is 0.168 g and 0.138 g, respectively.
After cutting, the wear of the saw blade was compared and analyzed by calculating the final reduction of the wire saw, as shown in Figure 5.As shown in the figure, after cutting 30 mm of glass, the wear of the 1 # wire saw is the highest, with a cutting ratio of 11.5 g/m 2 ; The wear of the 3 # wire saw is the second, with a cutting ratio of 9.2 g/m 2 ; The wear of the 2 # wire saw is the smallest, with a cutting ratio of 6.7 g/m 2 and the be st we ar re sistance .In summ ary , when the m ass fraction of 1.4-butylene glycol is 0.3 g/L, the wire saw has the smallest wear and the best cutting effect.

Conclusion
Diamond wire saws were prepared by using electroplating baths with different mass fractions of 1.4-butynediol (0.1 g/L, 0.3 g/L, 0.5 g/L), and nickel metal coatings were deposited in electroplating tanks.The effects of different mass fractions of 1.4-butynediol on the hardness, tensile strength, adhesion to the substrate, and wear resistance of the coatings were studied.The results show that the concentration of 1.4-butynediol has a significant impact on the hardness, tensile strength, adhesion to the substrate, and wear of the coating.When the mass fraction of 1.4-butynediol is 0.3 g/L, the nickel coating has the best adhesion to the metal substrate, with the highest microhardness of the coating being 427 MPa, the least weight loss of the wire saw being 0.092 g, and the minimum cutting ratio being 6.7 g/m 2 .

Figure 1
Figure 1 The Effect of 1.4-butynediol on the microhardness of coatings.

Figure 2
Figure 2 Effect of 1.4-butynediol on the tensile strength of coatings.

Figure 5
Figure 5 Diamond wire saw cutting ratio.

Table 1
Composition and process conditions of nickel sulfamic acid electrolyte.

Table 2
Diamond wire saw cutting performance.