Mechanical properties and wear resistance of multi

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Mechanical properties and wear resistance of multi-layer coating of cutting tools

in the cutting process, the cutting force borne by the tool is up to 2 ~ 3GPa, the cutting temperature is up to 900 ~ 1100 ℃, and the cutting speed is usually in the order of tens of meters to hundreds of meters per minute, so under high pressure The friction and wear of cutting tools working at high temperature and speed. The challenges faced by the current personal hygiene products market and the high level of consumer demand have prompted all partners in the value chain of hygiene products to accelerate the research and development process and launch more innovative product solutions. Hard coating plays an important role in improving cutting performance and prolonging tool life. So far, tin coating has been studied most, which has high hardness, low friction and good chemical stability. Compared with tin coating, Ti (C, n) coating has better adhesion resistance and thermal wear resistance. In addition to the low friction coefficient, the wear-resistant coating must also have high microhardness, high toughness and adhesion to the matrix. By introducing a certain number of intermediate transition layers parallel to the matrix, the toughness and hardness of coated tools can be improved and crack initiation can be prevented. The study of tin multilayer coating shows that it has better tribological properties than a single coating. Su et al. Studied the wear resistance and cutting performance of multi-layer tin/ti (C, n) coated tools, which showed that its performance was better than that of single-layer coating. The wear resistance and reliability of coatings are often subject to their mechanical properties. Due to the interaction between film, interface and matrix, it is difficult to evaluate the mechanical properties of the coating The appearance of nano hardness tester enables people to deeply understand the mechanical properties of coatings from the history of micro scale (nano scale) In this paper, the deformation, failure and wear resistance of four kinds of coatings were analyzed and compared by using nano hardness tester

1Test method

test device

the test device is produced by CSEM instruments, Switzerland. The system is composed of nano hardness tester (NHT) and atomic force microscope (AFM), and is equipped with optical microscope accessories. The indenter and the optical microscope for selecting the position of the sample and observing the indentation are controlled by the electromechanical positioning system, and the displacement resolution in the vertical force direction is m. The pressure bar is loaded by the electromagnetic force generated by the electromagnetic coil installed on the pressure bar supported by the guide spring, and the pressure head is a standard Vickers diamond pressure head. Use capacitance sensor to measure the displacement of pressure bar. The load and indentation depth resolutions of the whole system are 10 N and 1nm respectively. In the process of loading and unloading, the sapphire ring that always keeps in contact with the surface of the sample to be tested enables the indenter to accurately locate the vertical force direction with the surface of the sample

four kinds of wear-resistant coatings, 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/ti (C, n)/tic, were prepared on the cemented carbide substrate by CVD technology Using 99.50% H2, 99.99% N2, 99.99% CH4, 99.50% CO2, chemically pure TiCl4 and AlCl3 and other raw materials, the cemented carbide matrix is passivated, cleaned, fired and heated, and then CVD coating is deposited and cooled, which is the coating sample to be tested. The thickness of the four coatings are 4.0 m, 1.5 m/1.0 m/1.5 m, 1.5 m/1.0 m/1.5 m/1.0 m/1.5 m and 1.5 m/1.0 m/1.0 m/1.5 M/1.0 m/1.0 m/1.0 m/1.5 m/1.5 m respectively. 2 test results and discussion

mechanical properties

indentation tests were carried out on four kinds of coatings with nano hardness tester, and the relationship curve between load and indentation depth was obtained during loading and unloading. E is the elastic modulus, HV is the Vickers hardness value of the coating, which is determined according to Oliver et al. In addition to the unloading curve, the shape of the indenter and the indentation depth are also considered to calculate the contact area under load. The hardness is regarded as the average pressure borne by the material during unloading. The bearing capacity of multi-layer coating is better than that of single-layer coating. Li et al. Analyzed various crack processes on the coating surface during the pressing process with a nano hardness tester and found that the high stress in the contact area caused the first approximately annular crack penetrating the film around the indenter; High lateral pressure makes the coating/substrate interface peel and break in the contact area; A second approximately annular crack or crack fragment penetrating the film appears at the edge of the bent film due to the action of bending stress. In the first stage, if there is an approximately annular crack penetrating the film layer in the coating, a step will appear on the P-H curve, otherwise there will be no step. We studied the failure characteristics of four coatings. It can be seen that with the increase of the pressing load, steps appear on the P-H curve, indicating that several approximately annular cracks penetrating the film have sprouted in the coating. Each step corresponds to an approximately annular crack penetrating the film layer in the coating, so the load pf at the step is defined as the critical load of coating fracture failure. Thus, from the indentation curve, the fracture failure critical loads of the four coatings are 11.1mn, 16.4mn, 35.5mn and 56.3mn respectively. It can be seen that the fracture failure load of multilayer coating is significantly higher than that of single-layer tin coating; The critical load PSub F value increases with the increase of the number of coating layers. This is because the intermediate layer in the multilayer coating can prevent crack initiation and propagation (the ability of the intermediate layer to prevent crack initiation and propagation is related to its thickness and number of layers). According to a document, the fracture toughness ksub IC of the coating can be calculated by the following formula:

e and V are the elastic modulus and Poisson's ratio of the coating; 2prc is the length of cracks in the coating; T is the coating thickness; U is the change of strain energy before and after the crack appears. The area on the P-H curve reflects the elastic-plastic deformation energy of the coating/substrate system. The strain energy u released when the first approximately annular crack penetrating the film layer is generated can be calculated from the product at the step on the curve. Kazmanli et al. Also described the relationship between steps on the P-H curve and crack formation. According to formula (1), the fracture toughness of the four coatings are 1.51mpa m, 2.18mpa m, 3.4mpa m and 3.9Mpa m respectively. It can be seen that the fracture toughness increases with the increase of the number of coating layers. However, the use of multi-layer coating increases the complexity and cost of the process, so the appropriate number of layers should be selected. Therefore, we recommend tin/ti (C, n)/tic/ti (C, n)/tic coating

p-h curve describes the fracture failure of the coating; The p-H2 curve can reflect the change of coating/substrate boundary before the fracture failure of antifriction and wear-resistant coating, especially the change of interface between multilayer coatings. For single-phase materials, if the plastic deformation component in the indentation depth is HP and the elastic deformation component is he, then the total indentation depth h:f and y are parameters related to the geometry of the indenter; P is the load; HV is hardness; E is the modulus of elasticity

therefore, p=kh2 can be obtained, and K is the loubet elastoplastic parameter For the press in process of mono phase material, P H2. When studying the coating/substrate system, it is found that the straight line segment from the origin to the inflection point on the typical p-H2 relationship curve conforms to the p-H2 relationship, which reflects the elastic-plastic deformation of the coating. According to the Hertz contact theory analysis, it is found that the maximum shear stress is still located in the pressed coating. Its development can widely drive the technological progress and innovation of coatings in many fields such as energy conservation and environmental protection, new energy, electric vehicles, information and communication, and can not make the substrate yield. Therefore, the straight-line segment only reflects the deformation of the coating After crossing the inflection point, the high shear stress makes the matrix yield, so that the coating bends and the interface changes. During the unloading process, part of the interface desorbs, and there is material accumulation around the contact area under the action of tensile stress, until cracks appear at the steps. Therefore, the load PI at the inflection point is used to represent the critical load changing at the coating boundary. The p-H2 and P-H curves completely reflect the whole process of coating interface change and fracture failure For the p-H2 curves of the four coatings, the dotted line is a straight line in line with P H2, the solid line is a p-H2 curve in the process of pressing, and the inflection point is located at the separation point of the solid line and the dotted line Any line segment from the origin to the inflection point reflects the deformation of the coating itself, and the load value at the inflection point is lower than that at the step Through SFM observation, it can be found that cracks appear on the coating surface under the corresponding step load with economic warming. According to the indentation test data, the interface change of single-layer tin coating occurs at pi=3.13 Mn, indicating that the interface bonding of single-layer coating is weak, and the toughness of the coating is also poor The interface of tin/ti (C, n)/tic coating changes when pi=7.5 Mn. From the origin to the step, it is a straight line segment (the real and dotted lines coincide), indicating that the two coatings have no obvious interface changes before fracture failure. Therefore, tin/ti (C, n)/tic/ti (C, n)/tic and tin/ti (C, n)/tic/ti (C, n)/tic/ti (C, n)/tic multilayer coatings have higher interfacial strength and better toughness

wear resistance

the surface of brittle coating material breaks, peels and breaks during the friction process. At this time, the wear resistance of the coating mainly depends on the brittle fracture resistance of the material. Therefore, increasing the strength and fracture toughness of the material can improve its wear resistance. Considering the quality factors of the material (the influence of temperature and chemical wear in the friction zone is not considered here, and it needs to be corrected if the influence of temperature is considered), the wear resistance WR of the coating material can be expressed as:

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