Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"MACIEJ SZCZERBA"

Ni-Mo alloys electrodeposited under direct current from citrate-ammonia plating bath

Czytaj za darmo! »

Ni-Mo alloys are characterized by high hardness, wear, thermal and corrosion resistance [1, 2]. Due to this reason they could offer an important alternative to hard chromium coatings, which according to EU directives (2000/53/WE, 2011/37/UE) have to be eliminated from manufacturing processes [3]. However, these alloys are difficult to obtain by conventional thermal methods, what is caused by the large difference in metals melting points (Ni . 1455 C, Mo . 2620C) and the limited mutual solubility. Convenient way to produce these type of coatings, which overcomes above mentioned problems, is a low-temperature and relatively simple electrodeposition technique. It enables uniform surface covering with simultaneous control of thickness and microstructure and thus allow to influence the properties of the layer. The mechanism of Ni-Mo alloys electrodeposition is still not clearly understood, although a few hypotheses are presented in the literature [4?€7]. Nevertheless, it is known that molybdenum (as well as another reluctant elements, such as W, Ge) cannot be deposited alone from aqueous solution of their salts. However, it could be readily co-deposited with iron-group metals (such as Ni, which acts as a catalyst) with an alloy formation. This phenomenon was called induced co-deposition by Brenner [8]. However, Ni-Mo coatings deposited from solution containing only molybdenum and nickel ions are of poor quality and contain high amount of molybdenum oxides. This effect is probably related to the formation of multimolecular heteropolymolybdates, which are difficult to electroreduce. Addition of an appropriate complexing agent, such as sodium citrate (characterized also by buffering, leveling and brightening properties), causes decomposition of heteropolymolybdates and the formation of the electroactive molybdenum [MoO4(Cit)H]4. and then nickel [NiCit]. citrate complexes (Cit = C6H5O7 3.) [9]. It results in an im[...]

Optimization of Ti - Cr - N multilayer wear resistance coatings through microstructure control

Czytaj za darmo! »

In the current work, multilayer coatings on Cr/CrN and TiN/CrN basis were deposited by the Pulsed Laser Deposition (PLD) technique at room temperature using an industrially designed 4-beam multi-spot PLD evaporator. Coatings were built of 2, 8, 32 and 64 layers with the total thickness of 1 ￿m . In the case of Cr/CrN, metallic layers are tough but soft and nitride layers are hard but [...]

Directionally solidified CMSX-4 nickel based superalloys; microstructure, orientation, residual stress, microanalysis

Czytaj za darmo! »

Single crystal nickel based superalloys still belong to the most widely used and reliable materials for the most exposed parts of gas turbine [1÷5]. Directional solidification (DS) is a technology, which enables to produce gas turbine blades and vanes with columnar crystal or single crystal structures. High temperature mechanical properties of single crystal nickel base superalloy castings are better than castings with polycrystalline structures [1]. The aims of producing of the blades as single crystals are to eliminate grain boundaries which favour creep and ensuring of [001] crystal orientation with minimum of Young’s modulus that is suitable for thermal fatigue resistance. The final structure of the castings prepared by DS is influenced by the parameters of the process, therefore it is inevitable to map and control them [5]. A large number of the alloys used rely on carefully tailored compositions and heat treatment schedules that result principally in a microstructure consisting of gamma (γ) matrix (FCC crystal structure) and ordered gammaprime (γʹ) (L12) phases [4]. The aim of investigations was to study microstructure in respect to its inhomogeneity in different scale, defect of microstructure in nanoscale, crystallographic orientation measured using X-ray texture technique as well as residual stress by application of X-ray method in directionally solidified CMSX-4 nickel-based superalloys produced using the facilities working at the Rzeszow University of Technology. mATERIAL AND METH ODS OF EXAMINATI ONS Materials for examination were fabricated at the vacuum metallurgy laboratory of the Faculty of Materials Science and Technology at the Rzeszow University of Technology by application of the single crystal casting system. A nickel based superalloy CMSX-4 was produced with the nominal chemical composition as follows: Cr-5.7; Co-11; Mo-0.42; W-5.2; Ta-5.6; Al-5.2; Ti-0.74; Re-3; Hf- 0.1; Ni-balance.[...]

 Strona 1