Bożena Bierska-Piech

Influence of thermal treatment on the corrosion resistance of electrolytic Zn–Ni+Ni composite coatings

This study was undertaken in order to obtain and characterize the corrosion resistance of Zn–Ni+Ni composite coatings. The influence of thermal treatment on surface morphology, phase composition, and corrosion resistance of Zn–Ni+Ni coating was investigated. The Zn–Ni+Ni coating was deposited under galvanostatic conditions (j = 40 mA cm−2). Thermal treatment was carried out in argon atmosphere. The surface morphology of Zn–Ni+Ni coatings was carried using a scanning electron microscope (JEOL JSM-6480) and the surface chemical composition was determined by the EDS method. Structural investigations were conducted by X-ray diffraction method. The studies of electrochemical corrosion resistance were carried out in a 5% NaCl solution, using potentiodynamic and scanning vibrating electrode (SVET) methods. On the grounds of corrosion investigations, it was stated that thermal treatment improves both total and localized corrosion resistance of Zn–Ni+Ni coating in a 5% NaCl water solution. The higher corrosion resistance of the thermally treated Zn–Ni+Ni coating could be attributed to the increase in the amount of zinc bonded to nickel in the form of Ni2Zn11 and Ni5Zn21 intermetallic phases. The SVET analysis indicated that thermal treatment of Zn–Ni+Ni coating causes a decrease in the number of corrosion centers on their surface area.

Mechanical Synthesis and Heat Treatment of Ni75Ti25 Alloy

The investigations of the microstructure changes of Ni75Ti25 powder prepared by mechanical alloying in as-milled state and after annealing treatment were performed. The X-ray diffraction (XRD) method was used to investigate a mechanically induced solid state reaction between nickel and titanium powders. The crystallite sizes and lattice strains were analyzed by using Williamson-Hall method. The compacted powder morphology was analyzed by SEM method. The Ni(Ti) solid solution was formed as a result of the milling process. The crystallite sizes of all alloys are below 100 nm. The annealing treatment, in the temperature range of 773 K to 1173 K leads to reduction of the breadth of Ni(Ti) diffraction lines, which indicates at the increase in size of crystallites. However, the phase composition of annealed Ti75Ni25 powder does not change, so the presence of any Ni-Ti intermetallic phases is not stated.

Influence of thermal treatment on the corrosion resistance of electrolytic Zn-Ni coatings

This study was undertaken in order to obtain and characterize the corrosion resistance of Zn-Ni coating. The process was carried out under galvanostatic conditions (j = 50 mA·cm−2) chosen on the ground of an analysis of the deposition process in the Hull’s cell. The Zn-Ni coatings were deposited on austenitic (OH18N9) steel substrate from the ammonia bath. Thermal treatment of Zn-Ni coating was carried out in argon atmosphere. Structural investigations were conducted by X-ray diffraction method. Surface morphology of the obtained coatings was determined using a scanning electron microscope (JEOL JSM-6480) with EDS attachment. The electrochemical corrosion resistance of the prepared Zn-Ni coatings, austenitic (OH18N9) and (St3S) steels, was defined. The studies of electrochemical corrosion resistance were carried out in 5 % NaCl, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. Examinations of localized corrosion resistance were conducted using scanning vibrating electrode technique (SVET). On the grounds of these investigations it was found that Zn-Ni coating after thermal treatment was more corrosion resistant than the Zn-Ni coating before thermal treatment. The relatively good corrosion resistance of Zn-Ni coatings is not as high as the resistance of (OH18N9) steel substrate, but higher compared to (St3S) steel. Therefore, the Zn-Ni coatings may be regarded as a protective coating for St3S steel.

The Characteristic of the Multilayer Thin Films by X-Ray Reflectometry Method

The X-ray reflectometry (XR), as a non-destructive method, is a powerful tool in obtaining information about parameters of thin films such as thickness, average density and interface roughness. In this paper Cu/Au, Au/Cu and Cu/Ag multilayer thin films (where the total thickness is less then 1000Å) are presented. The multilayer films are obtained by thermal evaporation in a UHV system, on the silicon substrate. The experimental XR curves contained critical angle and classical Kiessig’s fringes. For these materials the density (), the thickness () and interface roughness () information for every layer separately were calculated. The experimental reflectometry curves were analyzed using the WinGixa programme X’Pert software. The values of layer density show that they are reached in neighbor density and it is connected with the creation of the Cu-Au or Ag-Cu interlayer reached into Cu, Au or Ag, respectively. The analysis of roughness show that there are comparable to roughness of substrate only for 2-3 first layers. Further the roughness of Cu, Au, Ag layers are increasing. The comparison of results show that increasing of Ag an Au roughness is bigger than Cu.

Characterisation of β phase in WE54 magnesium alloy

Precipitation hardened magnesium-rare earth alloys offer attractive properties for the aerospace and racing automotive industries. The most successful magnesium alloys developed to date have been those based on the Mg-Y-Nd system identified as WE54 (Mg-5.0wt%Y-4.1wt%RE-0.5wt%Zr) and WE43 (Mg-4.0wt%Y-3.3wt%RE-0.5wt%Zr), where RE represents neodymium-rich rare earth elements. Precipitations sequence in WE-system alloys involved the formation of phases designated β”, β’, β1 and β depending on the ageing temperature. WE54 alloy with the equilibrium β-phase exhibits good ductility and medium tensile strength. The β phase precipitated in Mg-Y-Nd alloy during ageing at 300 °C was studied using X-ray diffraction analysis and transmission electron microscopy. Precipitation at 300 °C for one hour causes formation of the equilibrium β phase. This phase has an f.c.c. structure (a = 2.2 nm), which makes it isomorphous with Mg5Gd. With the prolonged ageing time at 300 °C, the volume fraction of the β phase increases and lattice parameter of the solid solution of α-magnesium decreases.

Characterization of Ni75Mo25 Alloy Prepared by Mechanical Alloying and Heat Treatment

The process of Ni75Mo25 powder synthesis via mechanical alloying (MA) was studied. Process was carried out from pure elements: Ni and Mo with a particle size under 150 μm. A ball-to-powder weight ratio and the rotational speed were 5:1 and 500 rpm, respectively. Oxidation was reduced by milling under an argon atmosphere. The milling process was performed during up to 60 hours. X-ray diffraction (XRD) and scanning electron microscopy techniques have been used to investigate resulting products. It was found that the particle sizes decrease with the increase in milling time. The resulting powder consists of metastable Ni(Mo) and Mo(Ni) solid solutions. Milled Ni75Mo25 powder was subjected to heat treatment at temperature of 773K, 973K and 1173K. As a result of annealing the formation of Ni4Mo and NiMo intermetallic phases was observed.

Structure and Properties of Electrolytic Zn-Mn Coatings Deposited by the Galvanostatic Method

The Zn-Mn coatings were deposited under galvanostatic conditions from a sulfate galvanic bath. The influence of thiocarbamide additions in the bath on surface morphology, chemical and phase composition and corrosion resistance of the electrolytic Zn-Mn coatings was investigated. On the basis of these investigations it was found that Zn-Mn coatings can be obtained by the galvanostatic method. Morphology and chemical composition of the electrolytic Zn-Mn coatings depend on the thiocarbamide concentration in the galvanic bath. XRD investigations of obtained coatings showed a single phase structure (α-Mn1.08Zn2.92). The additions of thiocarbamide improve the protective properties of the Zn-Mn coatings.

The Study of Zink-Nickel Composite Coatings after Annealing

The Zinc composite coatings containing Ni powder were obtained by the electrodeposition and electroless methods. Electrodeposited Zn+Ni coatings were plated with the current density jk = 150 mA/cm2 from the zinc chloride bath containing the suspension of nickel powder. Electroless (Zn-Ni)+Ni coatings were obtained by chemical reduction of Ni2+ and Zn2+ ions from the sulphate bath containing sodium hypophosphite as a reducing agent and mechanically dispersed Ni powder suspension. The thickness of (Zn-Ni)+Ni layer was ~8 m. In order to enhance the Zn content the obtained coatings were covered with the electrolytic Zn layers of different thickness (5 m, 8 m and 14 m) – (Zn-Ni)+Ni/Zn. The thermal treatment of the obtained composites was carried out at a temperature of 320oC, during 2h in argon atmosphere. The electrodeposited coatings show the presence of Zn, Ni(Zn) and ZnO phases. The electroless coatings show the presence of Zn, Ni(Zn) and ZnO phases. The additional electrodeposition of Zn leads to the creation of dilayer coatings (Zn-Ni)+Ni/Zn. The annealing of such obtained coatings leads to the creation of Ni2Zn11 intermetalic phase. The average Ni(Zn) and Ni crystallite size before annealing is in a range of 200 Å and after annealing the size is increasing to values of 600-800 Å.

The Reflectometry Studies on SiC and SiN Thin Layers

The X-ray reflectivity measurements were used for the analyses of the SiC and SiN thin layers. Density, roughness and the thickness were determined for searching materials. The calculations and simulations were carried out using the WinGixa software. The obtained results show that the studied layers are non-homogenous and there are consist of “sub-layers” rich in Si-C, Si-N, SI-O phases. Moreover, the presence of the main amorphous phase was observed in all searching samples.