Vysokoteplotní tribologická ochrana laserově navařovaných materiálů pro komponenty energetických zařízení

Článek je zaměřen na analýzu a porovnání vlastností laserových návarů typu „Stellit 6“ a „Stellit 21“ na základní materiál 1.4923 + QT používaný pro komponenty energetických zařízení. V toto článku je řešeno porovnání vlastností návarů navařených na hřídel o průměru 63 mm navařených bez předehřevu i s předehřevem dvěma odlišnými šířkami návarových housenek, které jsou navařeny laserovou svařovací hlavou s šířkou návarové housenky 1 mm a 3 mm. Dále je zde vyhodnoceno pomocí EDX analýzy chemické promíšení návarových housenek se základním materiálem. V článku je popsáno podrobně metalografické zhodnocení návarů vrstev a zhodnocení tepelně ovlivněné oblasti v závislosti na změně tvrdosti včetně tribologická analýzy navařené vrstvy za provozních podmínek 550 °C.The paper examines and compares the properties of laser clad deposits of Stellite 6 and Stellite 21 on 1.4923 + QT base material which is often used for power generation components. Cladding was performed using two different bead widths on a 63 mm diameter shaft with and without pre-heating. The widths of the beads deposited by a laser welding head were 1 millimetre and 3 millimetres. Using EDX, chemical dilution between the clad beads and the base material was examined. The paper gives a detailed description of metallographic observation of the claddings and the heat-affected zone and correlates the findings with hardness values. It also presents results of wear analysis conducted at simulated service conditions at 550°C

Vysokoteplotní tribologická ochrana laserově navařovaných materiálů pro komponenty energetických zařízení

Článek je zaměřen na analýzu a porovnání vlastností laserových návarů typu „Stellit 6“ a „Stellit 21“ na základní materiál 1.4923 + QT používaný pro komponenty energetických zařízení. V toto článku je řešeno porovnání vlastností návarů navařených na hřídel o průměru 63 mm navařených bez předehřevu i s předehřevem dvěma odlišnými šířkami návarových housenek, které jsou navařeny laserovou svařovací hlavou s šířkou návarové housenky 1 mm a 3 mm. Dále je zde vyhodnoceno pomocí EDX analýzy chemické promíšení návarových housenek se základním materiálem. V článku je popsáno podrobně metalografické zhodnocení návarů vrstev a zhodnocení tepelně ovlivněné oblasti v závislosti na změně tvrdosti včetně tribologická analýzy navařené vrstvy za provozních podmínek 550 °C.The paper examines and compares the properties of laser clad deposits of Stellite 6 and Stellite 21 on 1.4923 + QT base material which is often used for power generation components. Cladding was performed using two different bead widths on a 63 mm diameter shaft with and without pre-heating. The widths of the beads deposited by a laser welding head were 1 millimetre and 3 millimetres. Using EDX, chemical dilution between the clad beads and the base material was examined. The paper gives a detailed description of metallographic observation of the claddings and the heat-affected zone and correlates the findings with hardness values. It also presents results of wear analysis conducted at simulated service conditions at 550°C

Low-pressure turbine blade leading edge protection using robotic laser cladding technology

Low pressure turbine blades are the most erosion-exposed moving parts of the steam turbine. This article brings a detailed overview of an innovative system applying a stellite coating to the leading edge of the steam turbine blades using the robotic laser cladding technology. The system is based on a software that gathers measured data of the shape-specific workpiece from a laser profile scanner, creates a 3D model of the workpiece and generates a set of laser cladding trajectories that are used for the task of robot navigation during the laser cladding process. The navigation algorithm takes the workpiece-specific requirements of the laser cladding process as well as collision avoidance necessities into account. The shape and thickness of the resulting layer of the laser cladded coating alloy is verified by an external 3D scanning system showing the compliance of the system with the requirements as well as a space for future development. The feasibility of the developed method is also verified by multiple material and metallographic tests

Low-pressure turbine blade leading edge protection using robotic laser cladding technology

Low pressure turbine blades are the most erosion-exposed moving parts of the steam turbine. This article brings a detailed overview of an innovative system applying a stellite coating to the leading edge of the steam turbine blades using the robotic laser cladding technology. The system is based on a software that gathers measured data of the shape-specific workpiece from a laser profile scanner, creates a 3D model of the workpiece and generates a set of laser cladding trajectories that are used for the task of robot navigation during the laser cladding process. The navigation algorithm takes the workpiece-specific requirements of the laser cladding process as well as collision avoidance necessities into account. The shape and thickness of the resulting layer of the laser cladded coating alloy is verified by an external 3D scanning system showing the compliance of the system with the requirements as well as a space for future development. The feasibility of the developed method is also verified by multiple material and metallographic tests

Search for Pair Production of Second-Generation Scalar Leptoquarks in pp Collisions at sqrt(s) = 7 TeV

A search for pair production of second-generation scalar leptoquarks in the final state with two muons and two jets is performed using proton-proton collision data at sqrt(s) = 7 TeV collected by the CMS detector at the LHC. The data sample used corresponds to an integrated luminosity of 34 inverse picobarns. The number of observed events is in good agreement with the predictions from the standard model processes. An upper limit is set on the second-generation leptoquark cross section times beta^2 as a function of the leptoquark mass, and leptoquarks with masses below 394 GeV are excluded at a 95% confidence level for beta = 1, where beta is the leptoquark branching fraction into a muon and a quark. These limits are the most stringent to date

Measurement of Dijet Angular Distributions and Search for Quark Compositeness in pp Collisions at sqrts=7sqrt{s} = 7 TeV

Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at sqrt(s) = 7 TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36 inverse picobarns. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Lambda = 5.6 TeV is obtained at the 95% confidence level