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Wear resistance of dental burs with a diamond coating


  The scientific work on extending the operational life of dental instruments - primarily dental drills - has been ongoing for many years. The expected characteristics distinguishing dental instruments in terms of their design and operation include: - high reliability, - safety of use for operators and patients, -ease of operation, - specific set of mechanical properties as well as geometry useful to perform a specific procedure, - corrosion resistance in operating conditions, - design enabling full sterilisation of the instrument or device, - ergonomic nature and aesthetics of the design and manufacture. Specific conditions existing in the human body create very strict criteria both for metallic materials used for implants and dental instruments as well as for the layers on their surfaces. Good biocompatibility, high adhesion to the basic metal, and corrosion resistance are only some of the requirements to be met when applying specific material in medicine [1÷13]. MATERIAL AND METHODS OF TESTS The studies were carried out on commercial dental drills with a diamond coat. Drills made of a corrosion resistant steel were covered with a nickel-diamond composite of varying diamond grain size. Drills of various shapes of the working part and also of varying grain size of the coat were used, inter alia drills designed to remove old fillings and crowns (the flame-shaped drills) as well as drills intended to prepare tooth tissue by grinding (round and flame-shaped drills). Long-term operational tests of dental drills were performed in a dentist's surgery. The operation consisted of a d[...]

Microstructure and high-temperature strength characteristics of boiler tubes produced by foreign companies in accordance with Ukrainian standard DOI:10.15199/24.2015.11.3


  Features of microstructure and high-temperature strength characteristics (creep rupture strength and plasticity) of boiler tubes produced of steel grades 20 and 12Cr1МoV by Z-Group Steel Holding Divize Válcovny Trub Chomutov (Czech Republic), Tubos Reunidos Industrial, S.L.U. (Spain), Benteler Steel/Tube GmbH (Germany) and Shanghai Rongfa Enterprise Development LTD (China) in accordance with Ukrai- nian standard (TU 14-3-460) were analyzed. Availability of utilization in Ukrainian heat and power engineering of boiler tubes produced by above-mentioned companies on conditions that their production process is enhanced to ensure quality indicators of boiler tube material (including operating characteristics) in accordance with Ukrainian normative documents. Dokonano analizy cech mikrostruktury i charakterystyki wysokotemperaturowej wytrzymałości (wytrzymałość na pęknięcia pełzaniowe i plastyczność) rur kotłowych produkowanych ze stali gatunków 20 i 12CrMoV przez Z-Group Steel Holding Divize Válcovny Trub Chomutov (Czechy), Tubos Reunidos Industrial, S.L.U. (Hiszpania), Benteler Steel/Tube GmbH (Niemcy) and Shanghai Rongfa Enterprise Development LTD (Chiny) w zakresie ich zgodności z normami ukraińskimi (TU 14-3-460). Mo􀄪liwość wykorzystania w ukraińskim przemyśle energetycz- energetycznym rur kotłowych wyprodukowanych przez wy􀄪ej wymienione zakłady uwarunkowana jest zapewnieniem wskaźników jakości materiału rur kotłowych (łącznie z charakterystykami pracy) w zgodności z ukraińskimi dokumentami normatywnymi. Key words: boiler tubes, rolling, heat treatment, microstructure, high-temperature strength Słowa kluczowe: rury kotłowe, walcowanie, obróbka cieplna, mikrostruktura, wytrzymałość w podwy􀄪szonej temperaturze.Introduction. Tubes produced in accordance with Ukrainian Standard U 14-3-460 titled Seamless Steel Tubes for Steam Boilers and Piping are operated in boiler units of thermal power stations for long perio[...]

Vacuum-arc chromium coatings for the protection of gun barrels


  Chromium coatings applied on the internal surface of tubular samples of (0.3÷0.4%C, 1.2-1.5 %Cr, 3÷3.5%Ni, 0.35÷0.45% Mo, 0.1÷018% V ) steel by the vacuum-arc deposition method are discussed in the paper. The results of metallographic examination of the structure and properties of the coatings are given. It has been shown that under the conditions of dynamic loadings, high temperature influence and frequent heat changes, no thermal fatigue cracks are present on samples with a vacuum-arc plasma coating, whereas parts with an electrolytic coating have by 1.8÷2.2 times more cracks compared to samples in the initial condition. The results of the research show the potential of the method for producing coatings by vacuum-arc evaporation of refractory metals with the subsequent condensation of ionized vapors on the internal barrel surface to protect the gun barrels against propellant-induced erosion and wear. W pracy omówiono kwestię nanoszenia chromowych powłok ochronnych na wewnętrzne części próbek rurowych ze stali (0,3÷0,4%C, 1,2÷1,5 %Cr, 3÷3,5%Ni, 0,35÷0,45% Mo, 0,1÷018% V ) z wykorzystaniem metody próżniowo-łukowej. Przestawione zostały wyniki badań metalograficznych oraz własności badanych struktur powłok. Udowodniono, że w warunkach dynamicznego obciążenia, wysokich temperatur oraz ich częstych zmian, nie występują pęknięcia zmęczeniowe w próbkach pokrywanych w technologii plazmowo-próżniowo-łukowej, natomiast w próbkach pokrywanych elektrolitycznie występowało o 1,8÷2,2 więcej pęknięć niż w próbkach wyjściowych. Wyniki badań wskazują na znaczny potencjał omawianej metody produkcji powłok za pomocą odparowywania metali reaktywnych z jednoczesnym osadzaniem zjonizowanej pary na wewnętrznych ściankach lufy, podnosząc w ten sposób odporność korozyjno-erozyjną. Key words: vacuum coatings, refractory metals, erosion protection, gun barrel Słowa kluczowe: próżniowe nanoszenie powłok, metale reaktywne, ochrona przed erozją, lufa armatnia.Introduct[...]

The influence of deformation scheme on grain boundaries structure of carbon steel boiler tubes


  The structure of grain boundaries was investigated in ferritic boiler tubes made of steel 20, manufactured by hot extruding and hot rolling. It has been observed that in the metallic matrix structure of hot extruded tubes the amount of special boundaries Σ = 3n (acc. to the concept of coincidence-sites) is significantly higher (up to 26.5%) than in hot rolled tubes (up to 12.5%), which has a positive impact on the ultimate strength. Wykonano badania struktury granic ziarn, ferrytycznych rur kotłowych ze stali 20, wytworzonej poprzez wyciskanie na gorąco i walcowanie na gorąco. Zaobserwowano, że w strukturze metalicznej osnowy rur wyciskanych na gorąco ilość granic specjalnych Σ = 3n (według koncepcji gęstości węzłów koincydentnych) jest istotnie większa (do 26,5%), niż w walcowanych na gorąco (do 12,5%), co ma pozytywny wpływ na wytrzymałoś doraźną. Key words: materials for power industry, grain boundary engineering, rolling, extruding Słowa kluczowe: materiały dla przemysłu energetycznego, inżynieria granicy ziarna, walcowanie, wytłaczanie.Introduction. In the structure of generating ca- pacities of developed countries industry the share of electricity generated by thermal power stations (TPS) is around 50%. The main elements of TPS equipment consist of seamless tubes, operating long time (100 and more thousand hours) under conditions of high pres- sures and elevated temperatures, under influence of water, steam, flue gases, and ash. The tubes destruction can have disastrous effects and the length of reliable failure-free operation has a significant impact on eco- nomic indicators of TPS operation. The reliability of tubes operation under high-tem- perature creep conditions depends primarily on their heat resistance, determined by the chemical compo- sition and structure, which develops during the pro- duction process. Therefore the improvement to tubes structure is one of effective methods to increase the op- erational[...]

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