In this work, combined gradient ZrC/Ni-nanodiamond ultradispersed diamonds (UDD) coatings were synthesized on the surface of knife blades made of hard alloy WC-2 wt.% Co by electroplating and cathode arc evaporation PVD techniques to increase the durability period of a wood-cutting milling tool. The microstructure, phase and elemental composition, microhardness, and adhesion strength of the coatings were investigated. Ni-UDD layer is not mixed with the ZrC coating and hard alloy substrate. Cobalt is present in Ni-UDD layer after deposition of ZrC. The ZrC/Ni-nanodiamond coating consists of separate phases of zirconium carbide (ZrC), a-Ni, and Ni-UDD. The maximum value of microhardness of the Ninanodiamond coating is 5.9 GPa. The microhardness value of the ZrC/Ni-nanodiamond coatings is 25 ± 6 GPa, which corresponds to the microhardness of the hard alloy substrate and ZrC coating. The obtained high values of the critical loads on the scratch track of the ZrC/Ni-nanodiamond coating in 24 N prove a sufficiently high value of the adhesion strength of the bottom Ni-UDD layer with WC-Co substrate. Pilot testing of ZrC/Ni-nanodiamond-coated cutting tools proved their increasing durability period to be 1.5-1.6 times higher than that of bare tools, when milling laminated chipboard.
The laser welding of copper‐niobium microcomposite wires was investigated. It was determined that the joint structure does not have welding defects, while microscopic examination of the joint cross‐section showed that the microstructure of the autogenous weld consists mainly of a copper‐based solid solution strengthened by niobium‐rich precipitations. The weld obtained with use of filler material consists of two distinct zones, which are formed due to melting of filler wire and microcomposite wire. This structure of the joint provides an insignificant increase in electrical resistance and sufficient ultimate strength and plasticity of the joint. The tensile strength of the sample welded without filler material reaches 335 MPa, but such welded joints are very brittle due to very low ductility. However, an autogenous laser welding joint has about 1.6 times better ductility, and the tensile strength of the joint depends on the applied filler material and is equal to the tensile strength of this material.
Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.
Mokslinis vadovas doc. dr. Nikolaj VIŠNIAKOV (Vilniaus Gedimino technikos universitetas, medžiagų inžinerija-T 008). Vilniaus Gedimino technikos universiteto Medžiagų inžinerijos mokslo krypties disertacijos gynimo taryba: Pirmininkas doc. dr. Justinas GARGASAS (Vilniaus Gedimino technikos universitetas, medžiagų inžinerija-T 008). Nariai: prof. dr. Oleg DEVOINO (Baltarusijos nacionalinis technikos universitetas, medžiagų inžinerija-T 008), doc. dr. Irmantas GEDZEVIČIUS (Vilniaus Gedimino technikos universitetas, medžiagų inžinerija-T 008), dr. Rasa KANDROTAITĖ JANUTIENĖ (Kauno technologijos universitetas, medžiagų inžinerija-T 008), prof. dr. Voitech STANKEVIČ (Vilniaus Gedimino technikos universitetas, fizika-N 002). Disertacija bus ginama viešame Medžiagų inžinerijos mokslo krypties disertacijos gynimo tarybos posėdyje 2020 m. rugpjūčio 24 d. 14 val. Vilniaus Gedimino technikos universiteto Senato posėdžių salėje.
The repair of chemical industry equipments often requires to replace long time operated pipes or welded inserts with the simi-lar chemical composition. During the study the joints from corro-sion resistant steel X6CrNiTi18-10 were welded by manual metal arc welding with covered electrodes (MMA process 111) and tungsten inert gas welding (TIG process 141) at different welding parameters. The visual, radiographic, penetrant control and ferrite content analysis were carried out. The transverse tensile and bending samples were produced from welded samples; also the macroscopic and microscopic analyse were carried out. Atliekant chemijos pramonės įrenginių remontą, dažnai tenka pakeisti ilgą laiką eksploatuotus vamzdžius ar įvirinti analogiškos cheminės sudėties intarpus. Tyrimo metu suvirintų jungčių bandomieji pavyzdžiai iš korozijai atsparaus plieno X6CrNiTi18-10 buvo suvirinti rankiniu lankiniu būdu glaistytaisiais elektrodais (111 MMA procesas) ir lankiniu suvirinimu volframo elektrodu inertinėse dujose (141 TIG procesas), esant skirtingiems suvirinimo režimų parametrams. Suvirintiems bandiniams buvo atlikta vizualinė, radiografinė, spalvinė kontrolė, nustatytas išsiskyrusio ferito kiekis. Iš suvirintų ruošinių buvo pagaminti skersinio tempimo, lenkimo bandiniai, taip pat atlikti virintinių jungčių makroskopinis ir mikroskopinis tyrimai.
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