Ellina Lunarska

Wear and corrosion properties of TiN layers deposited on nitrided high speed steel

The susceptibility of high alloyed tool steel, prenitrided under glow discharge conditions and then covered with plasma-assisted chemical-vapour deposited TiN formed at different gas flow rates, to wear and corrosion has been found to depend on both the structure and properties of the surface TiN layer and the chemical composition and properties of the substrate. Nitrogen from the steel surface assists in the TiN formation and this process affects the structure and hardness of the nitrided layer and the structure of the TiN deposit. Depletion of the steel surface in nitrogen during TiN formation may improve the wear resistance but deteriorates the corrosion resistance. By appropriate combination of nitriding and TiN deposition parameters, the optimum combination of wear and corrosion properties could be achieved.

Correlation between critical hydrogen concentration and hydrogen damage of pipeline steel

Abstract The critical hydrogen concentration for the low sulfide pipeline steel was determined in the electrochemical permeation tests. To correlate this value with the state of metal degradation, the internal friction measurements within the grain boundary relaxation, as well as tensile and permeation tests were conducted for the specimens hydrogen treated to the concentration below and above the critical one and then degassed. Hydrogen treatment below the critical content was found to modify the internal friction spectrum, the mechanical properties and hydrogen permeation parameters, revealing substantial rearrangement of dislocations and decohesion of grain boundaries. In overcritical condition, the formation of micro crevices at the grain and phase boundaries accompanied by the recovery of IF peak parameters and by the decrease in the steel plasticity has been observed.

Effect of plasma nitriding on hydrogen behavior in electroplated chromium coating

Abstract The phase composition and hydrogen behavior in coatings produced on Armco iron by electrochemical deposition of chromium (Cr) and subsequent plasma-assisted nitriding were investigated. At cathodic Cr deposition, no hydrogen charging of the iron substrate occurs. The amount of hydrogen absorption within the Cr coating (50 μm thick) was measured as high as 450 ppm. Plasma-assisted nitriding of a galvanic Cr coating caused the formation of a surface layer consisting of compact nitrides (Cr 2 N+CrN) and precipitates of nitride within the bulk of the Cr coating and a (Cr,Fe) alloy layer between the chromium coating and the steel substrate. The compact nitride layer prevented hydrogen escape from the Cr coating. The nitride precipitates served as hydrogen traps, and thus hampered hydrogen desorption. Hydrogen-assisted phase transformations in nitrided electroplated Cr coating were observed and are discussed.

The hydrogen-induced modification of the properties of the metal surface coated with oil and lubricant

The change of elastic and damping properties of the subsurface layer of iron and steel due to the coating with mineral oil and lubricants has been found in internal friction measurements. The effects were not observed for oil coated ceramics but did occur for iron and steel charged with hydrogen. In the case of coated metals, the formation of new internal friction peaks, increase in yield strain and increase in density of the slip lines of stretched foils were accompanied by the hydrogen uptake, was similar to the case of hydrogen charged metals. The origin of the phenomena is to be the hydrogen evolution from oil and lubricants at their catalytic decomposition, the hydrogen entry into the metal and the hydrogen-dislocation interaction within the subsurface layer of a metal. The hydrogen-induced modification of this layer and the possibility of hydrogen-induced softening or hardening should be taken into account in consideration of the tribological contacts.

Hydrogen effects in anodic grinding of Ti alloy

Abstract Intensification of wear and environmental degradation processes is a goal in the case of anodic grinding of hardly machined materials. To achieve the goal, the mechanical and electrochemical processes occurring at anodic grinding have been studied to select the optimum treatment parameters. The effects of cathodic prepolarization and application of different anodic polarization on the properties and quality of the surface layer of commercial Ti–Al–V–Cr–Mo alloy and on the efficiency of treatment were studied. The formation of crystallographically oriented needle precipitates of TiH 1.924 hydride, the change of the lattice parameters and increase in dislocation density in α-Ti phase, as well as the formation of the surface microcracks were observed after cathodic polarization due to the hydrogen absorption. Hydrogen induced deterioration was affected by kind of electrolyte, applied cathodic polarization and metal cold work. Cathodic prepolarization of Ti alloy affected the yield of subsequent anodic grinding. The nonmonotonical effect of increasing anodic polarization was observed on the surface roughness, the energy consumption and the wear of tool at grinding of non-prepolarized material. The optimum values of above parameters were achieved at application of anodic polarization at which the hydrogen ingress into the ground metal, affecting the microhardness and stress distribution within the subsurface layer was stated. The assistance of hydrogen induced deterioration of subsurface layer in the anodic grinding of Ti alloy has been discussed. In wear–corrosion degradation of Ti alloy exposed to different environments, the hydrogen effects should be considered.

Effect of second phase particles on hydrogen embrittlement of iron alloys

Abstract The effect of hydrogen on the plasticity and fracture mode of pure iron and iron containing iron oxides, aluminum oxide and cementite particles has been studied. Cathodic hydrogen charging causes the embrittlement of Fe, FeAl2O3 and FeC alloys and little or no degradation effect on FeFeO and FeFeOAl2O3 materials, despite the high strength of those alloys and high amount of absorbed hydrogen. High hydrogen resistivity of alloys containing iron oxides accounts for the weak iron oxide/iron matrix cohesion established by the internal friction measurements. The effect of hydrogen softening and hydrogen enhanced local plasticity in the resistance of studied alloys to the hydrogen action has been discussed.

Corrosion resistance of plasma-assisted chemical vapour deposition (PACVD) TiN-coated steel in a range of aggressive environments

Abstract The protective effects of plasma-assisted chemical vapour deposition (PACVD) TiN layers deposited at 570–720 °C on the corrosion, active dissolution and passivation of high speed steel in H 2 SO 4 , H 3 PO 4 and NaOH solutions have been estimated. The effect of the deposition temperature was found to manifest itself through the quality of the TiN layer and interphase formed at the various temperatures studied. The effect of the TiN porosity varies in the different solutions and depends on the electrochemical behaviour of the substrate in those solutions. In the active (H 2 SO 4 ) or passive (NaOH) state of the substrate the effect of the layer porosity is less pronounced than in the case of a solution causing the active as well as the passive state of the substrate (H 3 PO 4 ). The effect of the TiN layer porosity can be overshadowed by the effect of the interphase quality. TiN produces different effects on the corrosion, anodic dissolution and passivation of coated steel since it has different effects on the individual cathodic and anodic processes.

Electrochemical determining of penetrating porosity and the chemical and phase composition of pulse plasma deposited Ti–Al and Ni–Al coatings

The electrochemical behavior of Ti–Al and Ni–Al coated iron was compared to that of bulk Ti–Al and Ni–Al-based alloys of defined chemical and phase composition. Bulk pure metals of Al, Ni, Ti, and Fe, intermetallic compounds of Ti3Al, TiAl, TiAl3, Ni3Al, NiAl and several Ti–Al and Ni–Al alloys, as well as pulse-plasma deposited coatings of Ti–Al and Ni–Al on iron were tested in 2 N solutions of HNO3 ,H 2SO4 ,N a 2SO4 ,H 3PO4 and NaOH. The penetrating porosity (permeability) of each coating was determined using an electrolyte in which the electrochemical behavior of Ti–Al and Ni–Al alloys differed from that of the Fe substrate. To estimate the chemical composition of deposits, a relationship between some electrochemical parameters and the Al content established for bulk alloys was used. The phase composition of deposits was estimated by comparing the shape of polarization curves recorded for material coated with aluminides with those for bulk alloys, in the chosen electrolytes. The chemical and phase composition of coatings established by electrochemical methods was in good agreement with the data obtained by EDS and XRD analyses. The electrochemical tests with application of microcell may be used to check the properties of deposited layers and thus, to optimize the process of deposition of alloys and intermetallic compounds. # 2001 Elsevier Science Ltd. All rights reserved.

Surface acoustic wave studies of hydrogen entry into a Ni‐base alloy

Rayleigh acoustic waves were propagated along the surface of a sheet sample of a Ni alloy while the alloy was undergoing electrolytic charging with hydrogen. The waves were propagated, at frequencies from 2 to 15 MHz, from a transmitting to a receiving transducer, and their attenuation and velocity were monitored. A number of experiments was conducted to ensure that Rayleigh conditions were met and that extraneous results due to such effects as passive film changes and bubble formation were minimal. During cathodic polarization, wave velocity and attenuation decreased. The attenuation decrease followed two stages: an instantaneous one, probably due to polarization effects in the electrolyte, and a gradual one associated with the entry of hydrogen into the alloy. Both the instantaneous and gradual decreases were reversible and were recovered when polarization was removed. The kinetics of the recovery of the gradual component of attenuation were described by the Granato‐Hikata‐Lucke model for unpinning of d...

Effect of Cavitation on Absorption and Transport of Hydrogen in Iron

Using the specially designed ultrasonic cavitation facility enabling to measure the hydrogen permeation, the experimental evidence have been provided for hydrogen to ingress in the metal subjected to cavitation in the 3% NaCl solution under the open circuit conditions. Increase in the vibration amplitude resulted in the increase in amplitude of the electrochemical voltage and current pulses and in the hydrogen permeation rate, as well. The cavitation induced modification of hydrogen transport through the membrane has been stated on the base of different appearance of the hydrogen permeation transients at cavitation in comparison with those recorded for the unstressed membrane. The hydrogen behavior has been affected by the cavitation induced dynamic stresses, metal hardening and stress relaxation due to microcracking of the metal.