Research On Friction, Wear Characteristics And Coated Tool, Gear Performances Of TiN And TiAlN

As a kind of high hardness materials, ceramic coatings can be deposited on the surface of substrate in some ways to improve the abrasion resistance, mechanical property and service life of the substrate without changing its shape and size. With the rapid development of surface engineering technique, preparative technique and application domain of the high-performance ceramic coatings are becoming richer and enlargement gradually. TiN and TiAIN ceramic coatings are featured by low friction coefficient, high melting point and hardness, and excellent wear-resistance against to metals, making them have been widely used in industrial such as machinery and microelectronics, especially cutting tools and becoming a research focus of hard coating materials both in China and abroad.In this paper, TiN and TiAIN coatings were deposited on the specimens’surfaces of40Cr steels, cemented carbide cutting tools, and gears by PVD technology, respectively. And the following experiments have been carried out in current work:(1) The reciprocating sliding tests of TiN and TiAIN coatings on the surfaces of40Cr steels have been performed to investigate the friction coefficients of coatings affected by various normal loads with a friction pair of304stainless steel ball. The wear morphologies and mechanisms have been also analyzed under corresponding tests conditions.(2) The dry turning tests of40Cr steel were conducted with uncoated, TiN and TiAIN coated tools. The cutting forces and surface roughness were measured in the different cutting parameters.(3) The turning experimental model was presented with the cutting speed, feed rate and depth of cut as design variables, and the surface roughness as performance characteristics based on Taguchi method. Orthogonal dry turning tests were carried out on40Cr steel with coated tools and optimal cutting parameters of TiN and TiAIN coated tools for surface roughness were obtained.(4) The dry turning process of coated tools was simulated using Deform3D software. The distribution and changing of the stress filed, temperature field and cutting forces at various cutting speeds were obtained and compared with the experiment results.(5) Micro-morphologies in the worn zone of TiN and TiAIN coated tools after cutting tests were observed using scanning electron microscope (SEM). The wear form and mechanism of coated cutting tools were explored in this study.(6) The bench tests of the TiN and TiAIN coated gears were performed on the test rig. The influence of coatings on the gear transmission efficiency and wear resistance were analyzed. Based on the theoretical and experimental analysis, main conclusions are drawn as follows: (1) The friction coefficient of the TiN coatings decreases with the increase of the normal loads and the changing curve is smooth. However, the friction coefficient of the TiAlN coatings first increases and then decreases with the increase of the normal loads and the changing curve fluctuates greatly. The wear mechanism of TiN and TiAlN coatings is mainly abrasive wear on the low normal loads and the oxidation wear, abrasive wear and adhesion wear coexist when the normal loads is high.(2) According to the size of the cutting forces and the machined surface roughness, they can be arranged in the order of TiAlN coated tool<TiN coated tool<YT15tool under the same cutting parameters.(3) When the surface roughness is the optimal objective, the Taguchi method analysis shows that cutting speed of120m/min, feed rate of0.1mm/r and depth of cut of0.8mm are the optimal cutting parameters of TiN coated tools. Meanwhile, the most optimal performance characteristic for surface roughness is1.85μm. Cutting speed of190m/min, feed rate of0.1mm/r and depth of cut of0.8mm are the optimal cutting parameters of TiAlN coated tools. Meanwhile, the most optimal performance characteristic for surface roughness is1.27μm.(4) The simulation results show stress on deformation zone in front of tool nose is most concentrated and complicated, and the stress increases with the increase of cutting speeds, which means the tool nose is the most easy to wear. The distribution of cutting temperature field and the forming process of the chip during the simulation is consistent with the metal cutting theories. Main cutting forces predictions showed a maximum error of8.3%and minimum error of5.1%.(5) After cutting tests, rake face and flank of TiN and TiAlNcoated tools appears different degree of wear. The wear form and mechanism of TiN coated tool is mainly crater wear on the rake face and adhesion wear and abrasive wear on the flank. Crater wear on the rake face is serious and have an obvious breaking off of coatings in this area. The deeper abrasive scratches can be observed on the flank and the tool nose is not tipping, but worn dull seriously. The wear form and mechanism of TiAlN coated tool is mainly the breakage of cutting edge and the damage of tip, accompanied with diffusion and oxidation wear.(6) The transmission efficiency of coated gears is earlier turning into steady stage than that of uncoated. Coated gears increase the transfer gearbox’s efficiency by1.1%-4.2%%and the TiAlN coated gear shows better wear-resistance than TiN coated gear.