Mechnik V. Formation regularities and technological principles of controlling structures of composite materials of the diamond–Fe–Cu–Ni–Sn system with improved operation characteristics

The dissertation is concerned with the development of physico-mechanical principles of wear resistance of composite diamond-containing materials due to the improvement of adhesion strength of the diamond–metal binder contact, which provides a high degree of the diamond retention by the binder. It has been found that the metal binder structure of the diamond–51%Fe-32%Cu-9%Ni-8%Sn composites produced by sintering in a furnace at a temperature of 800C for an hour using a mold, regardless of technological parameters of the hot second compaction, consists of solid solutions based on iron and copper of the variable compositions and Cu9NiSn3 and Ni3Sn compounds. In this case the diamond–metal binder transition zone is of a purely hierarchic structure and depends essentially on the pressure and process duration. The transition zone of diamond-containing composites produced at the insufficient pressure (below 200 MPa) and duration of hot second compaction (lower than 3 min) consists of combinations of the -Cu, and Ni3Sn phases with graphite inclusions, which is the reason for the zone fracture by the mechanism of intensive cracking, premature falling-out of diamonds from the matrix, and material wear. The transition zone of diamond-containing composites produced at a pressure of no less than 200 MPa and a time for the second pressing of no less than 3 min consists of -Fe phases and Fe3C carbide interlayers of 5–40 nm in thickness, which increases wear resistance and operation properties of such composites. The mechanism of the nanostructure formation in the transition zone consists in the diffusion of carbon released due to the diamond graphitization at a stage of the composition sintering in the furnace into the -Fe crystal structure. The prospects are analyzed and the advantages showed of the use of CrB2 and NbN in composite materials of the diamond–Fe-Cu-Ni-Sn system, which made it possible to reveal additional sources to produce composite materials with new useful properties. High operation characteristics of such composites are achieved by the formation of a diamond–metal binder of the nanostructure with Cr3C2, Cr7C3, Fe3C and Cr1.65Fe0.35B0.96 5–40 nm thick as a result of the interaction of carbon released due to diamond graphitization at a stage of sintering compositions with CrB2, NbN and -Fe hard phases in the course of hot second pressing of them at a certain pressure and time of sintering. Based on the above scientific principles of controlling structure formation processes in the diamondFe-Cu-Ni-Sn-CrB2 heterophase composition, the system parameters and technological conditions of the hot second pressing were defined, which made it possible to develop a diamond-containing composites with the wear resistance exceeding that of materials produced according to existing industrial technologies by a factor of 2–5.