Technical Field

The invention relates to a boron nitride (BN) coating method using the Physical Vapor Deposition (PVD) method and the Inductively Coupled Plasma (ICP) method and the Magnetron Sputtering method.

Background

Boron nitride is a thermally and chemically resistant boron and nitrogen compound with the chemical formula BN. It exists in various crystalline forms that are isoelectronic, similar to a structured carbon lattice. The hexagonal form corresponding to the graphite is the most stable and softest among the BN polymorphs (h-BN) and is therefore used as a lubricant and additive to various products. The diamond-like cubic variety is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior. Rare wurtzite BN modification is similar to lonsdaleite but slightly softer than the cubic form. Due to its excellent thermal and chemical stability, boron nitride ceramics are used in high-temperature equipment. Boron nitride has potential use in nanotechnology [1],

In the article of Hacaloglu et al. on the technologies of determining the surface properties of boron nitride (BN) coatings, it is mentioned that Boron Nitride (BN), which is one of the coating methods, is widely used in the manufacturing industry and several new areas. As a result of the increase in efficiency and material-cutting speed in machining and the significant decrease in environmental factors caused by coolants the demand for machining is increasing day by day. In line with this increasing demand, there is a need for cutting tools that can be shaped according to harder and cutting process types that can withstand high temperatures. BN coating technology has been developed as similar needs arise for forming dies. It is possible to obtain a higher quality and qualified material by coating BN coating properties on existing materials in the medical sector, not only for the needs in the manufacturing sector. Boron Nitride has seven known allotropes. These are cubic BN (c-BN), hexagonal BN (h- BN), amorphous BN (a-BN), explosive BN (e-BN), rhombohedral BN (r-BN), wurtzite BN (w-BN) and turbostratic BN (t-BN). c-BN is the hardest material known after diamond. In addition, it comes to the forefront more than a diamond with its chemical stability against oxygen and ferrous materials at high temperatures. Implants used in the field of medicine are also coated with BN. In BN coating processes, the Magnetron Sputtering method is used with the Physical Vapor Deposition (PVD) Method. The Magnetron Sputtering method is preferred more because it takes place at low temperature, the possibility of obtaining very thin coatings, and magnification can be made on precise corners and complex geometries. Cutting tools, molds, dies and machine parts from industrial organizations and implants used in the field of medicine are coated with BN with a coating system whose technology, design and manufacturing are developed domestically. One of the purposes in BN coatings is to increase the coating hardness and durability by increasing the c-BN phase. Adequate ionization energy cannot be provided in the PVD method. For this reason, the c-BN phase, and the coating hardness and durability cannot be increased sufficiently.

Physical vapor deposition (PVD) is a thin film coating process that produces pure metals, metallic alloys and ceramic coatings, usually with a thickness of from 0.1 to 10 pm. Physical vapor deposition, as the name suggests, involves physically depositing the atoms, ions, or molecules of a type of coating onto a material (substrate) to be coated. In the PVD coating method, the material to be coated is placed in a high vacuum cabinet and coated with plasma ionized with high energy and formed with reactive gasses. In order for the coating to be homogeneous, maximum motion is provided to the material to be coated. The PVD method, which can find its place in the industry with the development of the semiconductor industry, is used in many different fields today. It is used in microelectronics, medicine, and decorative applications that require resistance to corrosion [2], In thin film coatings, the sputtering method is generally used as a vapor source. In this method, which offers many advantages over other methods, the solid material is bombarded with positive ions and the atoms are removed from the surface. If the material to be coated is bombarded with energetic particles such as accelerated ions, the scattered atoms form a film on the surface of the material (substrate) to be coated [3],

Inductively Coupled Plasma (ICP) is a plasma source in which energy is supplied by electric currents produced by electromagnetic induction, i.e., magnetic fields that change over time. The ICP is a power source that produces ions and plasma.

In the state of the art, the patent application WO2011083869A1 relates to a method for coating a substrate comprising an iron group transition metal, such as a tungsten carbidecobalt (WC-Co) super hard alloy, with a cubic boron nitride (c-BN) film comprising the preliminary step of forming boron or silicide from an iron c-BN film formation is performed using any of the methods of chemical vapor deposition (CVD) and physical vapor deposition (PVD). According to this method, c-BN is coated after boron or silica coating on the material (substrate) to be coated.

In the state of the art, the patent application JP2010099916A relates to a method of obtaining a cubic boron nitride coating film composite material that can be applied to the material (substrate) to be coated, temperature resistant and high-insulating coatings, high-temperature electronic materials and the like. c-BN coating film preparation method is an ion-assisted physical vapor deposition method. In addition, the gas phase is activated by plasma formation and cubic boron nitride is deposited on the material (substrate) to be coated. One or both of hydrogen and a rare gas may be added for reaction and plasma control. Voltage is applied to the material (substrate) to be coated according to a reference electrode placed on the vacuum chamber wall. After a base material is formed on the material (substrate) to be coated before the coating, a layer of titanium (Ti), zirconium (Zr), hafnium (Hf) and vanadium (V), niobium (Nb), tantalum (Ta) groups are formed on it and then c-BN is coated. According to this method, total coating costs increase due to the process step of forming a base before coating. Although the PVD coating method has more advantages compared to the CVD method in terms of coating thickness and coating complex geometries in the state of the art, sufficient ionization energy cannot be provided with the PVD method used for BN coating. For this reason, the c-BN phase cannot be increased sufficiently, and the coating hardness and durability cannot be increased sufficiently. In addition, in BN coating methods, a base/layer is formed on the material before the coating. The process of creating a base causes extra costs. PVD has taken its place in the electronics, machinery-manufacturing industry, medical applications and applications that require resistance to corrosion. Although the PVD Magnetron Sputtering system successfully exhibits coating behavior on many materials, it sets limits in the use areas of the system due to its low accumulation rate and ionization effect in plasma.

In the state of the art, the limitations and inadequacies of the methods of boron nitride coating methods; due to the inability to provide sufficient ionization energy with these methods, the coating hardness and durability of the coated materials are not high, it is necessary to create a base/layer before the coating, therefore, it is necessary to make an improvement regarding the boron nitride coating methods due to the high processing costs. Brief Description and Objects of the Invention

The invention discloses a boron nitride (BN) coating method in which Physical Vapor Deposition (PVD), Magnetron Sputtering and Inductively Coupled Plasma (ICP) methods are used together. The invention provides a BN coating method that provides high coating hardness and durability, low cost and short-term processing.

It is an object of the invention to provide a method for making a BN coating having increased nano hardness and durability. In the invention, in addition to the Physical Vapor Deposition (PVD) method and the Magnetron Sputtering method, the Inductively Coupled Plasma (ICP) method is used. Here, ICP provides a high amount of ionization energy. Therefore, in the method according to the invention, the c-BN ratio is increased with a high amount of ionization energy, thereby increasing the coating's nano hardness and durability. Seven allotropes other than c-BN are also obtained.

Another object of the invention is to shorten the coating time and to reduce the cost. In the method of the invention, there is no need to form a base/layer on the material (substrate) to be coated before coating. Thus, the cost of coating is minimized since there is no cost of forming the base.

The invention provides a cost-effective BN coating method that provides high coating nano hardness and durability.

Description of the Figures

Figure 1. A graph showing the FTIR result of the boron nitride coating.

Figure 2.A graph showing the result of the adhesion (scratch) test of the boron nitride coating (A. Plunge depth during experiment, B. Permanent depth).

Figure 3. A graph showing the thickness measurement result of the boron nitride coating at 2168 nm wavelength.

Figure 4. A graph showing the friction coefficient test result of the boron nitride coating. Figure 5. A graph showing the result of the nano hardness test of the boron nitride coating.

Detailed Description of the Invention

The invention relates to a low-cost boron nitride (BN) coating method that provides high coating nano hardness and durability using the Physical Vapor Deposition (PVD) method and the Inductively Coupled Plasma (ICP) method and the Magnetron Sputtering method. The BN coating of the invention can be used in the coating of cutting tools in the manufacturing industry, in the coating of implants in the biomedical industry, or in the coating of lenses in the optical industry.

In the BN coating method, Physical Vapor Deposition (PVD) method and Magnetron Sputtering method are used. Cubic BN (c-BN), hexagonal BN (h-BN), amorphous BN (a- BN), explosive BN (e-BN), rhombohedral BN (r-BN), wurtzite BN (w-BN) or turbostratic BN (t-BN) allotropes are obtained using the Physical Vapor Deposition (PVD) method. Seven known allotropes of boron nitride are obtained at different rates depending on the coating parameter. Coating parameters play an important role in the crystal structure of the obtained film.

The PVD Magnetron Sputtering method is to increase the energy of the surface by using RF frequencies and to accelerate the detached ions to be adhered/deposited on the surface (substrate) to be coated. Basically, PVD allows for changing the physical and chemical properties on the surface of the material. High-quality coatings are also obtained on the surface of the material to be coated (substrate) without any restriction. PVD is the controlled bonding of the material (substrate) to be coated in the plasma environment formed by solid- state material ionization and reactive gasses. The most important advantage of the sputtering method is that it can be successfully deposited on the surface without changing the compositions with different evaporation rates at different vapor pressures. The noble gas ions used in the method of sputtering the obtained coatings on the substrate give the energy they have by hitting the target material surface to the material to be coated (substrate) and thus sputtering the atoms from the material surface. The PVD Magnetron Sputtering system has two RF power sources. One is the target plate, i.e., the power supply of the coating material, and the other is the power supply used to increase the energy on the material (substrate) to be coated. Here, the power limit of the target plate is 1200W and 900W is used. It is increased from 0 to 900W and fixed during coating. This power is used unchanged throughout the coating. The substrate RF power supply, on the other hand, plays a decisive role in the coating parameter. Here, it is called with the voltages corresponding to the power equivalent. Voltages that can be up to 0V-250V and can be applied individually. The set voltage value cannot be changed during the experiment. Argon gas is mostly used as an inert gas. Since the weight of argon gas is high, it leads to an increased sputtering environment. The nitrogen gas ionizes and penetrates the surface, forming nitrides that disperse into the structure in particles that are too small to be seen under a microscope and increase nano hardness. The boron nitride (BN) coating method subject to the invention comprises the following process steps: i. Cleaning the material to be coated on the surface, ii. Placing the cleaned material in a piece holder in the vacuum chamber contained in an RF Magnetron Sputtering system and whose pressure value is reduced to a base pressure lower than 5x1 O' ⁷ Torr with the pumping equipment, iii. Reducing the pressure in the vacuum chamber to 5xl0' ³ Torr with pressure valves, iv. Injecting argon gas into the vacuum chamber with a gas flowmeter to form plasma on the substrate, v. Providing the surface cleaning of the material at the atomic level, magnetic fields that can form plasma at lower working pressures can be created in the vacuum system with the increase of the ionization effect. By lowering the working pressure, the number of particles reaching the material to be coated (substrate) increases, as the sputtering of the target atoms in the gas phase will be less, and thus their deposition rates are comparatively higher. Plasma cleaning from the surface of the material to be coated by applying energy for this purpose, vi. The introduction of nitrogen gas into the vacuum chamber with a gas flowmeter and the initiation of heating, wherein the vacuum chamber temperature rises from 0°C to 300°C. vii. Directly increasing the magnetron power, starting to accumulate BN material on the material to be coated with coating material ionization, viii. ICP system, which is switched on at 300W at the same time; increasing ionization by using two different ICP power, 500W and 1500W, ix. Obtaining the final product boron nitride (BN) coated material.

The ICP power can be increased up to 3000W during the coating period. Thus, it is ensured that the h-BN molecules tom from the target plate are converted into c-BN and deposited on the substrate. The vacuum chamber pressure mentioned here is 0.005 Torr.

Within the scope of the invention, 6 experiments were conducted. The results obtained from these experiments are presented in items. Experiments were carried out using a rotary table and targeted experiments were carried out without using a rotary table.

In targeted experiments where RF power (100+0)V was applied without the use of a turntable, there was a decrease in thicknesses as a result of the use of ICP power. In the experiments in this parameter, c-BN conversion at 1500W ICP power is seen. In addition, in this experiment, h-BN was suppressed on Si, which was a different substrate, and the a-BN structure emerged as dominant. In experiments where ICP power was applied, the same nano hardness was obtained. Coatings are soft. In addition, in the experiment using 1500W ICP power, the coating with the highest adhesiveness was obtained. In targeted experiments where OV was applied without the use of a turntable, there was a decrease in thicknesses as a result of the use of ICP power. In the experiment where 1500W ICP power was applied; a-BN (1263-350 cm' ¹ ) peak shifted to the left, w-BN (960 cm' ¹ ) peak shifted to the right and approached t-BN, w-BN, c-BN peaks at 1162.32 cm' ¹ . In the experiment where 1500W ICP power was applied, the highest nano hardness (3.4GPa) was obtained. In addition, the stickiest coating was obtained in this experiment. In targeted experiments where 250V is applied without the use of a turntable, the hardest coating with an ICP power of 500W is achieved. Although the thickness of this coating is not known, it is thought that the nano hardness of the coating is measured correctly due to the fact that the nano hardness depth is close to the surface. Coating adhesives exhibit similar behavior.

In experiments where (100+0)V was applied using a rotary table, coating thicknesses decreased. However, no increase in thickness was observed in this parameter no matter how much we increased the ICP power. It is thought that this is due to the fact that the energy given to the substrate was cut off at the end of 1 hour. It is thought that this energy may be effective in thickness formation. In the FTIR examinations, the peaks were almost at the same place. In all three experiments, h-BN peaks were observed. However, the e-BN seen in the reference experiment was converted to a-BN at an ICP power of 1500W and the second peak of h-BN was formed. The coating was soft, and the nano hardness value was increased in the ICP-applied experiments. The experiment with the best coating adhesion is the 500W ICP experiment. In experiments where 0V was applied using a turntable, the coating thicknesses were reduced, and the amount of reduction was low. In the FTIR examinations, the peaks were almost at the same place. In all three experiments, h-BN, a-BN, and e-BN peaks were observed. The coating is soft, and the nano hardness value is almost identical in the experiments where ICP is applied. Coating adhesion is almost the same in all three experiments. In the experiments where 250V was applied using a turntable, the coating thicknesses were reduced, and the amount of reduction was low. In the FTIR examinations, the peaks for the D2 sample were almost in the same place. c-BN was observed as a low peak. The coatings are hard and the nano hardness values are close to each other. Although the coating thicknesses are unknown, measurements were taken close to the surface. Coating adhesion is almost the same in all three experiments. As can be seen in Figure 1 and Table 1, c-BN peak was seen predominantly in the OV experiment using Spindle. As can be seen from Figure 2, BN adhesion on D2 steel using 500W ICP power and using Spindle and in (100+0)V experiment withstood up to 55.83 N. In the OV experiment using 500W ICP power, it is seen in Figure 3 that the RN film thickness formed on D2 steel is 2168 nm. In addition, while the initial value of the friction coefficient on D2 steel was 0.5 in the OV experiment using 1500W ICP power, as seen in Figure 4, the average value was 0.6. Figure 5 shows that the RN coating hardness on D2 steel in the 250V experiment using 500W ICP power is 30.5 GPa. According to the coating characterization results of BN-coated substrates using ICP, there is an increase in nano hardness values, a decrease in friction coefficient and an improvement in the adhesion of the coating to the substrate surface. In addition, the nano hardness, friction and adhesion properties of the coating are positively affected by the increase in ICP power.

Table 1. Literature comparison of peaks in the graph showing the FTIR result of boron nitride coating

The BN coating of the invention can be used in the coating of cutting tools in the manufacturing industry, in the coating of implants in the biomedical industry, in the coating of lenses in the optical industry, in the nuclear or food industry. References

[1] Boron Nitride: Properties, Manufacturing and Applications . (2018). Matmatch, http s : //matmatch . com/1 earn/ materi al/b oron-nitri de [2] What is physical vapour deposition (PVD)? (2022). TWI. https://www.twi- global.com/technical-knowledge/faqs/faq-what-is-physical-vap our-deposition-pvd

[3] Magnetron SA T1RMA prensibi. (2018). IKS PVD Teknolojisi (Shenyang) A.§. http://rn.tr.iksvacuum.com/info/magnetron-sputtering-2436696 2.html