**1. Introduction**

Boron is a very useful element that exists in compounds such as borates. Generally, boron is a non-metallic element and can be extracted into pure crystalline boron that is black in colour and conduct electricity at higher temperature and insulator at low temperature. It is as hard as carborundum but too brittle to be used as a tool. Boron is used in medicine, agriculture, decarbonisation purposes and industrial uses.

One of the outstanding compounds of boron is Cubic Boron Nitride (CBN). CBN is a synthetic abrasive material made of Cubic Boron Nitride grains bonded in ceramic material and is commonly known as Borazon™ [1]. CBN is an allotropic crystal of boron nitride (B4N) and has a hexagonal crystal. It is the second hardest material after diamond but more chemically and thermally stable than diamond and is extensively used in cutting tools [2]. CBN has excellent thermal stability, with oxidation starting at 1000°C and finishing around 1500°C. This is aided by the presence of boron oxide layer, which allows the use of high speed of 30.5–61 ms−1 [3]. Polycrystalline cubic boron nitride (PCBN), an extended version of CBN, is developed for machining, superalloys, and high-temperature alloys. Besides having high-temperature resistance, it has a low coefficient of friction but low fracture toughness [4].

Cubic boron nitride (CBN) is very well known in many machining industries. CBN is man-made material that having a hardness that is second to diamond [5]. Since CBN has hardness after diamond, it has outstanding mechanical and thermal properties, for examples, having high temperatures strength and wear resistance. Multilayer CBN coatings represent a new deposition method that can improve adhesion on metal substrates. Even with high residual stress, this multilayer CBN structure showed outstanding adhesion in atmospheric conditions. A study found that the multilayer CBN films in comparison to monolayer CBN, has lower elastic moduli, but twice as high to their critical loads [6]. In recent years, the performance of CBN tools has been researched [7, 8].

Instead of pure CBN, composite coating of CBN-TiN also being used as machine cutting tools [9]. It is found that, this composite has outstanding CBN-to-TiN as well as the adhesion of composite coating-to-carbide substrate. The characterisation analysis indicates an evenly distributed CBN particles in TiN matrix [10].

## **1.1 Electroless nickel**

Electroless nickel (EN) is an in-situ chemical reaction process where a metallic nickel is deposited onto a surface. This process is different from nickel electroplating that uses an applied current in the electrolytic bath which has effect on the current density, electrolyte composition, pH, bath agitation on the physicochemical and mechanical properties of the deposits [11, 12]. The main ingredients of EN are electroless bath, reducing agents, complexing agents, bath stabilisers and accelerators. **Table 1** describes the function and type of each EN ingredients.

**Table 1** lists the three types of available EN baths, pure nickel, acid-based and alkali-based chemicals. The pure nickel bath provides pure nickel metallic deposition for semiconductor application purposes. The acid and alkali-based chemicals either produce Ni-P or Ni-B alloy deposition depending on the reducing agent used. The properties of the EN deposits strongly depend on the content of phosphorus or boron in the alloys. As seen in **Table 2**, the deposit structure changes because the phosphorus or boron content changes. EN bath concentration, temperature, pH, agitation, and bath loading effect the EN process [14].

It is known that the EN process provides exceptional standardisation and impenetrable deposition even with a coating thickness of fewer than 10 μm [15]. In manufacturing, EN deposition has been widely used for it provides excellent corrosion, lubricity, ductility, wear and abrasion resistance, high hardness, and electrical properties [16].

*Characterisation and Application of Nickel Cubic Boron Nitride Coating via Electroless Nickel… DOI: http://dx.doi.org/10.5772/intechopen.105364*


#### **Table 1.**

*EN process chemicals and their functions.*

#### **1.2 Electroless nickel composite**

When incorporated with particles or powders of different materials, EN deposition becomes an EN composite and the process is called EN co-deposition. This incorporation of particles or powders in the EN deposit has remained extensively explored. Similar to the EN deposit, there are two EN composites upon particles incorporation, either Ni-P or Ni-B, depending on the EN reducing agent used. The particles that have been studied include ceramic, polymer and metal particles. **Table 3** summarises the particles that have been investigated for various applications. Incorporating ceramic particles into EN deposit produces a composite name cermet, which is the current issue discussed by using CBN particles for cutting tool applications.

#### **1.3 Application of Ni-CBN**

The coating technology is more demanding due to the increase in productivity rates for industry consumption, especially for cutting tool purposes. It shows the growing market of cutting tools has been developed [31]. The coated tools application is becoming more important in the machining process. These tools are produced using thermal spraying processes such as physical vapour deposition (PVD) and chemical vapour deposition (CVD). Thermal spraying processes are very reliable; however, they are costly, and the high temperature causes materials properties to degrade [32].


#### **Table 2.**

*Summary of EN baths, reducing agents and their properties [13].*


#### **Table 3.**

*Investigation of various particles for EN composites and their applications.*

#### *Characterisation and Application of Nickel Cubic Boron Nitride Coating via Electroless Nickel… DOI: http://dx.doi.org/10.5772/intechopen.105364*

In hard milling, the most acceptable significant representation is the cutting tool's thermal property of the material, such as thermal conductivity. The cutting tool's function ability can only be estimated via temperature tool measurements. For ferrous materials, cubic boron nitride (CBN) is one of the most demanding cutting tools. Multilayer CBN coatings provide a unique deposition method when applied to metal surfaces. Even under extreme conditions of high residual stress, the adhesion of this multilayer CBN structure was remarkable. Their heavy loads were twice as extraordinary compared to the monolayer CBN coatings, which had lower elastic moduli. It showed that stress relaxation significantly impacts the multilayer CBN structure [33]. This type of cutting tool is essential for cutting ferrous materials in a wide range of industries because of the advantages of suitable coating materials. Some of the most challenging materials to mill, such as aerospace alloys, die steels, and toughened steels, required the employment of CBN cutting tools [34, 35].

The diamond's remarkable mechanical and thermal capabilities, such as strength at elevated temperatures, abrasion resistance, and hardness, are the second property that the diamond possesses. Thus, numerous sorts of research have been undertaken in the last few years on the performance of CBN tools [36, 37]. The application of CBN as a cutting substance is a suitable method that may affect production. Nonetheless, the presentation of machining, such as progression solidity, tool wear and live performance, and surface finish quality, is significantly affected by differences in high-performance machining, which commonly requires a high material removal rate (MMR) [38, 39]. However, CBN coatings' application speeds and tool life are still lower than those of some other tools. Certain adjustments and upgrades are required, including raising the coating thickness and a rotational mechanism during the coating process. Hard coatings are typically more fragile and less lasting, whereas reinforced coatings lack strength. For real-world industrial operations, it is more critical to have coatings with a high hardness without sacrificing too much toughness.

Milling is the most common method of cutting metal. There are a variety of milling operations, but the ultimate shape and condition of the raw material dictate which ones are used. Adding features like slots or threaded holes necessitates using a milling machine. The cutting tool quality is directly proportional to the cutting process performance. In order to cut a tough workpiece materials, a harder cutting materials are needed [5]. Due to high process forces and temperatures, the first tool wear occurs in complex machining. The initial tool wear occurs in complex machining due to the high process of forces and temperatures. The machining market offers a wide variety of cutting tools, classified as coated or uncoated. Coated cutting tools typically perform better than uncoated cutting tools. Commercially available coated cutting tools include aluminium nitride (AlN), titanium nitride (TiN), titanium aluminium nitride (TiAlN), and others [28].

Due to the availability of suitable coating materials for cutting tools, this ferrous cutting material is indispensable in various industry disciplines. Certain heat-resistant CBN cutting tools are typically used on difficult-to-machine materials, such as aerospace, die steel, or hardened steel [34, 35]. CBN cutting tools have remarkable mechanical and thermal properties, including high-temperature strength, abrasion resistance, and hardness comparable to diamond. Thus, it has been demonstrated recently that CBN instruments produce excellent results in various sorts of research [37, 38]. The use of CBN as a cutting substance is a beneficial strategy that may significantly impact productivity.

CBN-based materials with bonding capabilities are frequently used to improve the machining process, which pushes researchers to continue improving coatings by utilising appropriate materials and procedures. For example, Ni-reinforced vitrified bonds are created in a high magnetic field for CBN grinding wheels. The addition of Ni does not affect the vitrified bond's refractoriness but enhances its fluidity and bending strength [40].

Additionally, CBN composites have poor machinability characteristics, such as brittleness. One way to mitigate this difficulty is to combine CBN and graphene oxide (GO) composites with the inclusion of Al-SiC at elevated temperatures and a high-pressure sintering procedure, which results in a 27.5% increase in fracture toughness compared to monolithic CBN composites. Besides this, the composites' bending strength increased from 564.2 MPa to 696.9 MPa [41]. Other studies discovered the use of ultrasonic probe sonication and spark plasma sintering (SPS) to investigate the microstructural, thermomechanical. Tribological properties of low-temperature sintered CBN and Ni-coated CBN reinforced bearing steel composites. It showed that these newly developed CBN and Ni-coated CBN-reinforced conducting steel composites sintered at a temperature of 1000 C resulted in increased wear resistance with high wear and fatigue resistance [42].

This study [28] found that an electroless nickel co-deposition technique successfully coated the HSS cutting tool with Ni/YSZ composite. In another study, TiN coated surfaces with mean thickness of 59 μm shows smooth and uniform surface demonstrating consistent surface roughness measurements. For Al/SiC metal matrix composites cutting tool, the surface roughness decreased from 1.3 μm to 0.6 μm m over time when the cutting speed is increased from 300 to 450 mm/min [43].

This study was conducted to investigate the effects of a new electroless Ni-CBN composite evenly coated onto an HSS and carbide substrate. This ceramic-metal surface coating is well-known for its superior resistance to thermal wear [44]. Additionally, the layer was produced using electroless nickel co-deposition, which is more straightforward, requires less energy, and is less expensive than typical thermal spraying procedures [45].
