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The effect of high temperature on corrosion behavior and passive film composition of Ni-based alloy 825 in H2S-containing environment was investigated by Confocal Laser Microscope (CLM), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), and X-ray Photoelectron Spectroscopy (XPS). The experiment was carried out at 150 and 230°C in NaCl solution. The partial pressure of H2S was set to 1.2 MPa and CO2 was set to 3.2 MPa. The results showed that Ni-based alloy 825 presented good general corrosion resistance. Pitting corrosion was likely to occur at 230°C because of Cr depleted in the passive film. NiS appeared at high temperature and is damaging to protectiveness of passive film.

One of the most curious phenomena observed in metal melts is the temperature-induced liquid-liquid structural changes. As a result of the thermal treatment lead to LLT, a more equilibrium and micro-uniform melt consisting of atomic associations is formed. In nickel alloy melts, the changes that have occurred are irreversible and have a significant effect on the formation of the final structure and the mechanical properties of the metal in the solid state after its crystallization. In addition, they are the starting point for the scientific substantiation of new technological modes of smelting and heat treatment of alloys, which further improve their operational properties, as well as reduce metallurgical defects and production waste, and rational use of expensive ligands. All this in general will lead to a significant increase in the performance of melts and metal products. Our work is devoted to the experimental confirmation of the LLT transition in two common nickel-based alloys by a non-invasive electromagnetic method.

Besides welding, high temperature vacuum repair-brazing is already established for nickel-based alloy turbine blades in the aerospace and power plant industries. After the worn turbine blade has been decoated to its substrate material, the filler metal is deposited as a paste, (melt-spin) foil or tape which also consists of a nickel-based alloy. Following this, the hot-gas corrosion protective coating (e.g. NiCoCrAlY) is applied using thermal spraying. The brazed turbine blade is ground or milled to size and subsequently aluminized to further increase its corrosion resistance. Using the current state of technology, a turbine blade can undergo approximately 3 to 4 repair cycles. In the present study, the development of a two-stage hybrid technology for repairing turbine blades is considered which incorporates, on the one hand, a process technology and manufacturing aspects and, on the other hand, considers material-technological mechanisms. During the first stage of this hybrid technology, the filler metal together with the hot-gas corrosion protective coating is applied using thermal spraying. The subsequent second stage combines the brazing and aluminizing processes. The technology developed here brings technical and economic advantages whilst enabling the current state-of-the-art's corresponding process chain for repairing turbine blades to be shortened. DFG/SFB/871

An experimental study is reported on the grinding of a nickel-based alloy using vitrified CBN wheels. This work was motivated by switching the grinding of fir-tree root forms of jet engine blades from creep-feed grinding with conventional abrasive wheels to vitrified CBN wheels. The objective is to explore process limits and practical grinding parameters for judging the switch in terms of overall costs and productivity. Straight surface grinding experiments were conducted with water-based fluid on rectangular blocks at a fixed wheel speed v s = 45 m/s, various depths of cut a = 0.05 - 1.0 mm, and workspeeds v w = 2 - 40 mm/s. Grinding power, forces, surface roughness, and radial wheel wear were measured. Specific material removal rate of 8 mm 3/(mm.s) was reached in rough grinding using a wheel dressed for achieving surface roughness R a = 0.8 μm in finish grinding. It was found that shallow depths of cut combined with fast workspeeds, or less creep-feed modes, are more suitable for achieving high material removal rates with vitrified CBN grinding. Rough grinding is restricted by high grinding temperatures with newly dressed wheels and by chatters with worn wheels. © (2011) Trans Tech Publications, Switzerland., 14th International Symposium on Advances in Abrasive Technology, ISAAT 2011, 18 September 2011 through 21 September 2011, Stuttgart

The behavior of a Ni-based superalloy, Haynes 230, was investigated at macro and micro scale level by means of a Crystal Plasticity (CP) model implemented in an open source Finite Element code, Warp3D. Single Crystal and polycrystalline specimens have been experimentally characterized with Digital Image Correlation (DIC) to identify the local strain field evolution. The results of single crystal’s tensile tests were used to obtain an estimation of the constitutive model parameters. Then a polycrystalline model, reproducing a tensile test with loading/unloading steps, was created starting from the microstructural data obtained with EBSD (electron back-scatter diffraction), which allowed the identification of grains geometry and orientations. The polycrystalline simulations were used to verify the prediction of the CP model over the experiment. The results of this study show that the comparison between experiments and numerical analysis is in good agreement on both global and local scale levels.

An experimental study was undertaken to explore the conditions and performance on rough and finish grinding fir-tree root forms of turbine blades made of a nickel-based alloy using vitrified CBN wheels and water-based grinding fluid. This work was motivated by switching the grinding of fir-tree root forms from grinding with conventional abrasive wheels to vitrified CBN wheels for reducing overall production cost and enhancing productivity. Grinding experiments were conducted to measure grinding forces, power, surface roughness, and stress near the blade roots under various dressing and grinding conditions. Wheel re-dressing life in terms of the total number of good parts ground between dressing was tested with the condition producing the maximum material removal rate while satisfying preset part quality and process requirements. It was found that the maximum material removal rate achievable in rough grinding was restricted by the stress limit and the wheel re-dressing life was dominated by the radial wheel wear limit. The targeting part quality and process requirements were achieved. It was proved that vitrified CBN grinding process is feasible and very promising to machine fir-tree root forms., 17th International Symposium on Advances in Abrasive Technology, ISAAT 2014, 22 September 2014 through 25 September 2014

An experimental study is reported on the grinding of a nickel-based alloy using vitrified CBN wheels. This work was motivated by switching the grinding of fir-tree root forms of jet engine blades from creep-feed grinding with conventional abrasive wheels to vitrified CBN wheels. The objective is to explore process limits and practical grinding parameters for judging the switch in terms of overall costs and productivity. Straight surface grinding experiments were conducted with water-based fluid on rectangular blocks at a fixed wheel speed ν s = 45 m/s, various depths of cut a = 0.05-1.0 mm, and workspeeds ν w = 2-40 mm/s. Grinding and dressing power, forces, surface roughness, and radial wheel wear were measured. Specific material removal rate of 8 mm 3/(mm.s) was reached in rough grinding using a wheel dressed for achieving surface roughness R a = 0.8 μm in finish grinding. It was found that shallow depths of cut combined with fast workspeeds, or less creep-feed modes, are more suitable for achieving high material removal rates with vitrified CBN grinding. Rough grinding is restricted by high grinding temperatures with newly dressed wheels and by chatters with worn wheels. Copyright © 2012 Inderscience Enterprises Ltd.

The alloy 22 (UNS N06022) is one of the candidates for the manufacture of containers of radioactive waste high level. These containers provide services in natural environments characterized by multi-ionic solutions, it is estimated they could suffer three types of deterioration: general corrosion, localized corrosion (specifically crevice) and stress corrosion cracking (SCC). It has been confirmed to produce cracking, requires the presence of bicarbonate and chloride ions. It has also determined that susceptibility to SCC could be related to the occurrence of an anodic peak in the polarization curves in these media to at potentials previous transpassive zone. The aim of this work is to study the anodic behavior of alloy 22 and its alloying effect in different media containing bicarbonate and chloride ions in different concentrations and temperatures. Polarization curves were made of alloy 22 (Ni-22% Cr-13% Mo), Ni-Mo (Ni-28, 5% Mo) and Ni-Cr (Ni-20% Cr) under the following conditions: 1 mol/L NaCl at 90 °C, and 1.148 mol/L NaHCO3, 1.148 mol/L NaHCO3 + 1 mol/L NaCl, 1.148 mol/L NaHCO3 + 0.1 mol/L NaCl at 90 °C, 75 °C, 60 °C and 25 °C. It was found that the alloy 22 has a current peak in the anodic at potential previous to transpassive zone, only when the medium has bicarbonate ions. Curves performed in 1 mol/L NaCl did not show any anodic peak, in any of the alloys tested. The curves made to alloys Ni-Mo and Ni-Cr in the media with bicarbonate ions, allowed to determine that Cr, is responsible for the appearance of the anodic peak in the Alloy 22. The curves of alloy B-3 showed no current peak in the conditions studied. The potential, at which the peak appears in the Alloy 22 and Ni-Cr alloy, increases with decreasing temperature. It also presents a variation of the peak with the composition of the solution. When the chloride ion is added to bicarbonate solution, the peak is shifted potential and higher current densities, depending on the concentration of added chloride ions. Fil: Zadorozne, Natalia Silvina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; Argentina. Universidad Nacional de San Martin. Instituto Sabato; Argentina Fil: Giordano, Mabel Cristina. Universidad Nacional de San Martin. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigaciones y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina Fil: Rebak, Raúl B.. GE Global Research; Estados Unidos Fil: Ares, Alicia Esther. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; Argentina Fil: Carranza, Ricardo M.. Comision Nacional de Energia Atomica. Centro Atomico Bariloche; Argentina. Universidad Nacional de San Martin. Instituto Sabato; Argentina