Ni−W/ZrO2Ni-W/ZrO_2 nanocomposites obtained by ultrasonic DC electrodeposition

Composite coatings consisting of a nanocrystalline Ni–W alloy matrix reinforced with ZrO2 particles (average size of 50 nm) were synthesized by electrochemical deposition assisted by an external ultrasonic field. The Ni–W/ZrO2 coatings were deposited from aqueous sulphate–citrate electrolytes containing zirconia nanopowder in suspension on steel substrates in a system with a rotating disk electrode (RDE). The influence of relevant processing parameters (i.e., concentration of zirconia powder in plating bath, current density, hydrodynamic conditions, ultrasonic field frequency) on the composite characteristics was discussed. Based on micromechanical (microhardness, Young’s modulus) and microstructural (morphology, phase composition, crystallite size) properties of the coatings, the conditions for electrodeposition of crack-free, homogeneous Ni–W/ZrO2 nanocomposites with enhanced functional properties have been developed

Elektroosadzanie i właściwości nanokrystalicznych stopów na osnowie niklu z trudnotopliwym metalem z kąpieli cytrynianowych

Głównym celem pracy było ustalenie optymalnych warunków procesu elektroosadzania metalicznych powłok Ni-Mo o podwyższonych właściwościach mikromechanicznych. Charakteryzowane stopy zostały osadzone na podłożu ze stali ferrytycznej, w warunkach galwanostatycznych, w modelowym układzie z wirujaca elektroda dyskowa (WED), z wodnych kompleksowych roztworów cytrynianowych zawierających sole niklu i molibdenu. Określono wpływ pH elektrolitu (regulowanego przez dodatek kwasu siarkowego lub amoniaku) na zawartość molibdenu w stopie, jakość osadów, jak również wydajnosc pradowa procesu elektroosadzania. Stwierdzono, że wzrost pH jest związany ze stopniowym zwiększaniem zawartości molibdenu w powłokach. Maksymalna zawartość molibdenu uzyskano w stopach wydzielonych z kąpieli galwanicznej o pH 7, gdzie jednocześnie zaobserwowano najwyższe stężenie cytrynianowych, elektroaktywnych kompleksów molibdenu typu [MoO4(Cit)H]4?-(Cit=C6H5O3-7 ). Dla wybranej kąpieli galwanicznej o optymalnym pH badano wpływ gęstości prądu katodowego (kluczowego parametru operacyjnego, kontrolującego między innymi skład chemiczny oraz mikrostrukturę, w tym skład fazowy i rozmiar krystalitów) na właściwości mechaniczne i tribologiczne wytworzonych powłok. Wykazano, że w całym analizowanym zakresie gęstości prądu, otrzymano powłoki Ni-Mo bez siatki mikropęknięć, o dobrej adhezji do stalowego podłoża, charakteryzujące się podwyższoną twardością w zakresie 6.5 do 7.8 GPa. Ponadto, powłoki osadzane przy wyższych gęstościach prądu (powyżej 3.5 A/dm2) odznaczają się zwartą i jednorodną mikrostrukturą, a tym samym najwyższą odpornością na zużycie przez tarcie.The main aim of the present work was to determine the optimal conditions for electrodeposition of metallic Ni-Mo coatings of enhanced micromechanical properties. These alloys were electrodeposited on the ferritic steel substrate, under galvanostatic regime in a system with a rotating disk electrode (RDE), from an aqueous citrate complex solution containing nickel and molybdenum salts. The effect of the electrolyte solution pH (adjusted by sulphuric acid or ammonia) on the molybdenum content and on deposit quality as well as on the current efficiency of the electrodeposition process, has been studied. It was established that increase of bath pH is correlated with gradual increase of molybdenum content in deposits up to pH 7, where the maximum concentration of Mo(VI) electroactive citrate complex ions [MoO4(Cit)H]4- (Cit= C6H5O7-3 ) in plating bath was observed. In the selected bath of the optimum pH value, the effect of cathodic current density, as a crucial operating parameter which strongly controls the chemical composition and microstructure parameters (e.g. phase compositions, crystallite size), on the mechanical and tribological properties of the resulting coatings has been determined. It has been shown that - under all investigated current density range - crack-free, well adherent Ni-Mo coatings, characterized by microhardness of 6.5-7.8 GPa, were obtained. Alloys deposited at higher tested current densities (above 3.5 A/dm2) were characterized by compact and uniform microstructure, and thus had the highest wear and friction resistance

X-ray diffraction grazing-incidence methods applied for gradient-free residual stress profile measurements in electrodeposited Ni coatings

The present work investigates the possibility of bias introduced in grazing- incidence-angle X-ray diffraction techniques applied to residual stress measurements. In these studies, monotextured nanocrystalline nickel coatings obtained by electrodeposition were examined as the model reference samples. Selected Ni coatings exhibited well developed and simple gradient-free residual stress states that were visible using conventional sin 2 measurements with varying X-ray penetration depths. These results were verified against the stress state picture obtained by two variants of grazing-incidence X-ray methods: multi-reflection (different hkl ) and constant angle of incidence (single hkl ). The outcome of both grazing techniques consistently excluded stress gradients in the samples, which agreed with conventional sin 2 measurement results. However, only the results of the constant angle of incidence technique agreed with those obtained by the sin 2 method in terms of calculated residual stress level, suggesting this approach could be applied in further studies of graded material coatings. All analysed coatings yielded uniformly distributed tensile residual stress related to gradual structure development in electrodeposited Ni coatings studied by electron microscopy technique