In the cutting process, the cutter experiences forces up to 2–3 GPa, temperatures reaching 900–1100°C, and cutting speeds ranging from tens to hundreds of meters per minute. This means the tool is subjected to high pressure, high temperature, and high speed, making friction and wear a major issue. Hard coatings are essential in improving cutting performance and extending tool life. Among these, TiN has been widely studied due to its high hardness, low friction, and good chemical stability. However, Ti(C,N) coatings offer better anti-adhesion and thermal wear resistance. In addition to low friction, wear-resistant coatings must also possess high microhardness, toughness, and strong adhesion to the substrate. Introducing intermediate transition layers parallel to the substrate can enhance both toughness and hardness, preventing crack initiation. Studies on TiN multilayer coatings have shown improved tribological properties compared to single-layer coatings. Su et al. found that multi-layered TiN/Ti(C,N) coated tools exhibit superior performance over single-layer coatings.
The mechanical properties of coatings are crucial for determining their wear resistance and reliability. However, measuring these properties is challenging due to interactions between the film, interface, and substrate. The development of nano-hardness testers has allowed researchers to study coating properties at the micro (nano) scale. In this study, a nanometer hardness tester was used to analyze deformation, failure, and wear resistance of four different coatings. The equipment included a nanometer hardness tester (NHT) and an atomic force microscope (AFM), with optical microscope attachments for sample selection and observation. The system had a vertical displacement resolution of micrometers and load resolution of 10 μN, with indentation depth resolution of 1 nm.
Four wear-resistant coatings were prepared on a cemented carbide substrate using CVD techniques: TiN, TiN/Ti(C,N)/TiC, TiN/Ti(C,N)/TiC/Ti(C,N)/TiC, and TiN/Ti(C,N)/TiC/Ti(C,N)/TiC/Ti(C,N)/TiC. The coatings had thicknesses of 4.0 μm, 1.5/1.0/1.5 μm, 1.5/1.0/1.5/1.0/1.5 μm, and 1.5/1.0/1.0/1.0/1.5/1.0/1.5 μm, respectively.
Indentation tests were conducted to determine the relationship between load and indentation depth. Elastic modulus (E) and Vickers hardness (HV) were calculated based on Oliver’s method. The results showed that multilayer coatings exhibited better load-bearing capacity than single-layer coatings. Cracking behavior during indentation revealed that as the load increased, steps appeared on the p-h curve, indicating multiple cracks forming around the indenter. These steps corresponded to critical loads for fracture failure: 11.1 mN, 16.4 mN, 35.5 mN, and 56.3 mN for the four coatings, respectively. The higher number of layers led to increased critical load, suggesting enhanced crack resistance.
Fracture toughness values were calculated using the formula involving elastic modulus, Poisson’s ratio, crack length, and strain energy. The results showed increasing fracture toughness with more layers, with values of 1.51, 2.18, 3.4, and 3.9 MPa·m¹â„². While multilayer coatings improve performance, they also increase complexity and cost. Based on the findings, TiN/Ti(C,N)/TiC/Ti(C,N)/TiC coatings were recommended for optimal balance between performance and cost.
The p-h² curve was used to analyze interfacial changes before failure. For single-phase materials, the p-h² relationship holds until the inflection point, where the substrate begins to yield. The inflection point load (pi) represents the critical load for interfacial failure. Observations showed that TiN/Ti(C,N)/TiC coatings had higher interface strength and toughness, with pi at 7.5 mN, compared to 3.13 mN for single-layer TiN.
Wear resistance was calculated using the formula WR = KICâ°Â·âµ Eâ»â°Â·â¸ HV¹·â´Â³. The results showed that TiN/Ti(C,N)/TiC/Ti(C,N)/TiC/Ti(C,N)/TiC coatings had the highest wear resistance, matching well with cutting test results. These coatings demonstrated the longest service life among the tested samples.
In conclusion, the formation of cracks in coatings corresponds closely to steps on the load-indentation depth curve. Mechanical properties can be effectively analyzed using flat force curves and load-depth curves. The step on the p-h curve indicates fracture failure, while the p-h² curve reflects interfacial changes in multilayer coatings. Critical loads pf and pi describe fracture and interfacial failure, respectively. Multilayer coatings show superior hardness, fracture toughness, and wear resistance, with performance improving as the number of layers increases. Among all tested coatings, TiN/Ti(C,N)/TiC/Ti(C,N)/TiC/Ti(C,N)/TiC demonstrated the best overall performance.
Five Valve Groups
Five Valve Groups,Five-Link Control Multi-Way Valve,Hydraulic Solenoid Five Valve Groups,High Pressure Five Valve Groups
Huai'an Sur Hydraulic Technology Co., Ltd , https://www.surpowerunit.com