OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 2 5 toughness, chemical stability and impact fatique strength, as well as increased material removal rates at high temperatures in dry machining [19]. When analyzing the published papers, the lack of information on the cutting properties of Y-TZP/Al2O3 ceramic composites containing from 5 to 40 wt. % Al2O3 draws attention. At the same time, it is known that in comparison with Y-TZP such composites have higher bending strength at room temperature (up to 1,400 MPa), and also retain increased strength at high temperature [4]. The presence of a second phase in the form of Al2O3 in Y-TZP/Al2O3 composites is responsible for an additional strengthening mechanism associated with thermal residual stresses generated by the difference in the thermal expansion coefficient between the two phases [20‑22]. The dispersed Al2O3 inclusions in the Y-TZP matrix lead to increased hardness, elastic modulus and improved high-temperature mechanical properties, including a high value of fracture toughness [4]. These composites are promising materials for blade machining under extreme conditions [23‑25]. The purpose of the present work is to study the behavior of replaceable cutting inserts made of Y-TZP-A12O3 ceramics under conditions of dry high-speed (200 m/min) cutting of AISI 5135 steel (HRC 43‑48). In order to achieve the above purpose, the following tasks were solved: The aim of the present work was to study the behaviour of replaceable cutting inserts made of Y-TZP-A12O3 ceramics under conditions of dry high-speed (200 m/min) cutting of AISI 5135 steel (HRC 43-48). In order to achieve the above aim, the following tasks were solved: – testing of the hypothesis about the possibility of using Y-TZP-Al2O3 ceramics as a tool material for machining thermally hardened low-alloyed AISI 5135 steel; – fabrication and investigation of samples in the form of round ceramic cutting inserts by powder metallurgy methods from commercial powder of TZ-3Y20AB grade; – performance tests in a wide range of cutting modes (speed, feed rate) under conditions of dry high-speed longitudinal turning without impacts; – establishment of technological limitations on cutting modes when using ceramic cutting inserts, as well as the study of the peculiarities of destruction and wear of contact areas. Designations HV, HRC – Vickers and Rockwell hardness, respectively; ρ – density, g/cm3; dgrain – grain diameter, μm; σb – bending strength, MPa; K1c – fracture toughness, MPa·m1/2; V – cutting speed, m/min; S – feed rate, mm/rev; t – cutting depth, mm; L – cutting path, mm. Research methodology The AISI 5135 steel blank for testing was made from a round bar with a diameter of 130 mm. The steel blank had a total length of 350 mm. Heat treatment (volume hardening) was performed on conventional modes, taking into account the long holding time in order to uniformly heat the entire blank across the crosssection from the periphery to the future axis of rotation. Heat-treated AISI 5135 steel was adopted in connection with the set production task on intensification of machining of necks of cutting tool bodies in conditions of LLC “PK MION” (Tomsk). It is also known from the literature that ceramics based on oxide compounds are widely used in cutting of thermally hardened and wear-resistant iron-based alloys [8, 9, 14, 26]. As a raw material for the production of blanks of prototypes of ceramic cutting inserts a commercial powder with the designation TZ-3Y20AB, produced by Tosoh (Japan) was used. The technological process
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