Исследовано влияние вакуумно-плазменной поверхностной обработки, сочетающей ионное азотирование в газовой плазме и нанесение износостойкого покрытия TiAlN в металло-газовой плазме вакуумно-дугового разряда на стойкость торцевых фрез из быстрорежущей стали Р6М5.bVacuum-plasma wear-resistant coatings have received wide application recently for increasing durability of highspeed steel (HSS) cutting tools. High hardness and oxidation resistant coatings, such as TiAIN, ensure high wear resistance of the cutting tools under high cutting speed. However, owing to a difference between the properties of HSS and the coating (mainly, modulus of elasticity and coefficient of thermal expansion) it is very difficult to achieve a good adhesion, which is one of principal quality characteristics of the cutting tool with vacuum-plasma coatings. Therefore, it was proposed to produce an intermediate layer by means of ion nitriding before TiAIN coating deposition. Automated multifunctional vacuum-plasma equipment for the production of the nitrided layer and coating deposition was developed (Fig. 1). This equipment allows to generate the gas plasma (for ion nitriding) and the metal-gas plasma (for coating deposition) in a vacuum-arc discharge. Fig. 2a shows the microstructure of HSS sample after nitriding in the pure nitrogen atmosphere and TiAIN deposition. In this case the nitrided layer consists of the nitrided zone (e+r'-phase) and the diffusion zone (6-phase). Formation of a brittle nitrided zone under TiAINcoating is the cause of flaking of the cutting edges of HSS face-milling cutters. Argon addition to the gas mixture prevents the formation of a brittle nitrided zone (Fig. 2b) and increases cutters durability. Fig. 3 shows a comparison of crack pattern of a sample with TiAIN coating (Fig. 3 a) and of a sample with the diffusion nitrided layer and TiAIN coating (Fig. 3b). Obviously, peeling of TiAIN coating takes place in the first case. The formation of the intermediate nitrided layer allows to achieve a good adhesion. Efficiency of HSS face-milling cutters depends on the properties of the nitrided layer and TiAIN coating, which are determined by variations in the vacuum-plasma process conditions. The dependences of the wear of HSS face-milling cutters at the cutting edge (hз) from nitriding temperature (И_A), nitriding time (Ф_A), volumetric percent of nitrogen in the gas mixture N,+Ar (KN2) and TiAIN deposition time (Ф_(TiAlN)) were obtained (Fig, 4). These relationships in all cases have a local extremum. Fig. 5 shows the dependence of the wear of HSS face-milling cutters at the cutting edge from cutting time. Obviously, cutters durability with the nitrided layer and TiAIN coating is increased 2,9 times as compared with only TiAIN coating under optimum conditions of vacuum-plasma process.
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