Joanna Panek

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.

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.

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.

ELECTROLYTIC Ni-BASED COMPOSITE COATINGS CONTAINING MOLYBDENUM AND SILICON FOR HYDROGEN EVOLUTION REACTION

Ni + Mo + SiNi composite coatings were prepared by codeposition of Ni with powders of molybdenum and silicon (covered with the electroless plated nickel — SiNi) on a steel substrate from the nickel bath in which Mo and SiNi particles were suspended by stirring. Deposition was conducted under galvanostatic conditions. Deposits were characterized by the presence of Mo and Si phases embedded into the nickel matrix. For comparison Ni + Mo composite coatings without silicon were obtained under comparable conditions. Incorporation of Mo and SiNi powders into electrolytic nickel matrix causes an increase in the real surface area of the deposits.