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XRD investigations of electrodeposited Ni and Ni/Al2O3 coatings

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Recently, metal matrix composite (MMC) coatings containing ceramic particles have been widely investigated due to their enhanced material properties (i.e. higher hardness, wear and corrosion resistance) compared to the pure metal or alloy [1÷4]. The MMC properties depend mainly on the type, structure, shape, size, morphology and content of the inert ceramic particles as well as on their distribution in the metal matrix. Several metals, e.g. nickel, copper, gold, chromium have been mainly used as a metal matrix, whereas metal oxides, carbides, borides and polymers were the co-depositing particles [5]. Electrolytic nickel coatings exhibit specific properties as hardness, durability, good corrosion resistance and catalytic activity in many electrochemical processes [6]. The addition of hard ceramic particles into Ni matrix can improve its hardness and wear resistance. These phenomena are mainly attributed to the hardening of the metal matrix by finely dispersed ceramic particles [7]. Al2O3 particle has many superior properties, such as low price, good chemical stability, high microhardness wear resistance at high temperature [8]. Insoluble particles are suspended in a conventional electrolytic bath and embedded in the growing metal during co-deposition process. The Ni/Al2O3 nanocomposites are one of the most promising materials, that can find wide engineering application as coatings of engine cylinders, high-pressure valves, car accessories, aircraft microelectronics etc. [9÷10]. Functional properties of electrodeposited composites are mainly controlled by their composition and structure. Among others, they depend strongly on their microstructure, residual stresses and due to the anisotropic properties on the distribution of crystallographic orientation. It is widely accepted that the state of residual stress on the coating surface and in the near surface area is one of the most important parameters of surface deposit quality. Mac[...]

Influence of surfactants on microstructure and corrosion resistance of Ni/Al2O3 coatings

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Composite coatings are one possibility to increase the durability and performance of materials for different applications and protect them from detrimental effect of the environment. Metal matrix composite reinforced with ceramic particles generally find wide range of engineering applications due to their enhanced hardness, better wear and corrosion resistance when compared to pure metals or alloys [1, 2]. The most sought after method of producing these kinds of composites is electrodeposition, owing to its advantages like low cost and the operating temperature. Electrodeposition of metals reinforced with dispersoids (mainly oxides or carbides) is an important technique for production of functional coatings. Such coatings are required in different fields of industry including: machinery and various device construction, machining tools, automotive and aircraft parts etc. Nickel composite coatings containing ceramic particles are used as protective coatings [3]. The plating bath for electrodeposition of Ni/Al2O3 composite coatings is frequently used a standard Watts solution with addition of alumina powder. The amount of ceramic particles incorporated into nickel affects the microstructure and properties of electrodeposited nickel composite coatings. The structure and properties of composite coatings depend not only on the concentration, size, distribution, and nature of the reinforced particles, but also on the type of used solution and electroplating parameters (current density, temperature, pH value etc.) [1, 4]. Although the Ni/Al2O3 composite coatings have been improved significantly, certain problems persist with respect to their preparation. The volume content of alumina particles in Ni/Al2O3 coating cannot be controlled quantitatively and the particles are frequently agglomerated in the composite [5]. The small inert particles like nanoalumina are difficult to embed into deposited layer because of their dispersion difficu[...]

Ball milling of Al-based alloys to obtain amorphous-nanocrystalline structure

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Considering a high strength to weight ratio of Al-based alloys as well as outstanding properties of metallic materials in a glassy state, amorphous aluminum alloys have attracted considerable attention due to their potential in structural applications for transportation and aviation industry[1÷8]. Metastable phases in amorphous or quasicrystalline state can induce two to three times higher strength as compared with those processed through precipitation/age-hardening in crystalline Al‑alloys [1, 2]. The first formation of amorphous single phase in Al‑based alloys containing more than 50 at. % Al was found in 1981 for Al-Fe-B and Al-Co-B ternary alloys [1], but they were very brittle and hence have not attracted much attention. Since then, glass forming ability has been determined in a number of Al-based alloys consisting of Al + transition metal + rare-earth elements, processed mainly by rapid solidification or gas atomization methods [8]. It has been also found that ductility in aluminum alloys can be improved when a few nanometer size crystals are embedded in the amorphous matrix [7]. Choi et al. [9] reported tensile fracture strength as large as 1980 MPa for an amorphous alloy containing about 18% Al nanocrystals - this strength was nearly 1.6 times higher than for the fully amorphous alloy. Later, Kawamura et al. [3] attained a bulk compressive strength of 1420 MPa by hot compaction of gas-atomized amorphous Al85Ni5Y8Co2 powder with nanocrystalline dispersed amorphous matrix. Among many techniques of synthesizing novel materials including nanocrystalline or amorphous products there are melt spinning, gas atomization and similar rapid quenching methods [2] but mechanical alloying (MA) by high-energy ball milling is a convenient solid state synthesis alternative for them. It gives the opportunity of obtaining various phases in the material without need to melt pure elements of the alloy. Furthermore, in the one pro[...]

Structural investigation of Mg-3Ca, Mg-3Zn-1Ca and Mg-3Zn-3Ca as cast alloys

  Magnesium alloys made of Mg-Zn-Ca system are interesting, because of possible application as bioresorbable cardiovascular stents or orthopaedic implants [1÷3]. During the last ten years, rapid growth of research in the application of magnesium and its alloys as biomaterials has been observed [4÷6]. Usage of magnesium based bone implants instead of those made of titanium or steel allows to avoid the removal surgery. Mg is the lightest of all structural metals with density close to those typical for cortical bone (1.75÷2.1 g/cm3). Other material parameters, like Young’s modulus (~45 GPa) are also similar [3]. Moreover, Mg is considered as biocompatible and non-toxic material and has been shown to increase the rate of new bone formation - it is an important ion in the formation of the biological apatites [3]. It was reported that the adult person normally consumes about 300÷400 mg of magnesium every day and an excess of Mg2+ is excreted through the urine [7, 8]. Magnesium is a cofactor for many enzymes and stabilized the structures of DNA and RNA [7, 8]. It is worth noticing that calcium and zinc are also recognized as biocompatible elements [1, 9]. A lot of studies have been performed on rare elements or/and Al containing alloys [10, 11], but these additions increase the cost of possible implant, and biocompatibility of RE is doubtful. An addition of Al can influence human nerves and induces Alzheimer disease [12]. From the metallurgical point of view, alloys made of Mg-Zn-Ca system can undergo solid-solution hardening and Ca is believed to be an effective grain refiner [13÷15]. In spite of possible benefits from magnesium based bone implants, there are a few important questions, which remain open up to date. There are problems with precise control of corrosion rate, which is usually very rapid and connected with hydrogen evolution. Rapid release of H2 in a high amount may cause inflammation process or even death [16]. Thu[...]

Ball milling amorphization and consolidation of NiTiZrNb and NiNbTiZrCoCu alloys

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Amorphous nickel rich alloys have been obtained in recent years by rapid quenching from the liquid state or by mechanical alloying in a planetary mill [1÷9]. One advantage of the latter method is that it makes it possible to obtain new materials from powders of different elements, which are immiscible in the liquid state. Binary NiTi alloys subjected to ball milling or severe plastic deformation can be obtained amorphous [1÷3]. The tendency to form an amorphous structure depends on the relative values of the deformation temperature and martensite start (Ms) temperature. Lowering of the deformation temperature in the range below the martensite finish temperature facilitates amorphization [3]. Mechanical alloying of Ni60Nb20Zr20 alloy [4] involves two consecutive amorphization reactions, leading first to the amorphization reaction between Ni and Zr layers and on further milling consequently a Ni-Nb amorphous phase forms. The resulting two amorphous phases homogenize at longer milling times. Multicomponent nickel base alloys can be obtained as bulk glass at composition of Ni50Co10Nb20Ti10Zr10 (at. %) alloys with reported large supercooled liquid region of more than 40 K formed by copper-mold casting. The alloys with 5 and 10 at. % cobalt possess the highest glass-forming ability [5]. Mechanically alloyed Ni57Zr20Ti18Al5 alloy powders synthesized by high-energy ball milling have shown a complete amorphization after 5 h of milling, even broader supercooled region of 56°C and crystallization temperature above 500°C [6]. Substitution of aluminum by silicon [7] also allowed to obtain amorphous Ni57Zr20Ti20Si3 powders by mechanical alloying of pure Ni, Zr, Ti, Si, and ceramic powder mixture; the metallic alloy amorphized after 5 hours milling indicating a good glass forming ability. In [8] Amorphous Ni59Zr20Ti16Sn5 alloys were fabricated by melt spinning and by mechanical alloying (MA) techniques. Differences in crystallization temperat[...]

Microstructure and properties of ball milled and hot compacted powder of 7055 aluminium alloy

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7xxx series (Al-Zn-Mg-Cu) aluminum alloys are widely used in the aircraft industry due to their low density, high strength and good workability [1, 2]. Their strengthening increases with the concentration of Zn and is associated with higher density of very fine precipitates of metastable η′-phase enriched with Zn and Mg. The high solute (about 8 wt. % of Zn) alloy designated AA 7055 (ALCOA) evokes the highest strength aluminium alloys produced by ingot metallurgy and is applied as upper wing skin materials in commercial aircraft [3]. The 7055 composition processed using the T77 temper provides a microstructure at and near grain boundaries that is resistant to both intergranular fracture and interglanular corrosion. Aluminium based materials produced by powder metallurgy (PM) processing offer a number of interesting opportunities for high strength applications. Powder metallurgy enables to fabricate high quality parts close to final dimensions with refined microstructure as compared with these produced by the conventional ingot metallurgy [4, 5]. The ball milling applied before the compaction allows obtaining a very fine microstructure and the extension of the solid solubility limits of the elements added to the alloy [6]. It results in improved mechanical and corrosion properties of the compacted products. PM technology provides more homogenous distribution of the precipitates and reduces the particle size that makes corrosion more uniform [7]. The aim of the present investigation was to study the effect of ball milling and hot pressing on the microstructure and properties of milled and compacted 7055 aluminium alloy powder. Exp erimental details The mixtures of elemental powders of aluminum, zinc, magnesium, copper and zirconium were used as starting materials to yield (wt. %) Al - 8% Zn - 2% - Mg - 2.3% Cu - 0.2% Zr compositions corresponding to 7055 commercial aluminium alloy. The ball milling of the powder was [...]

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

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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.[...]

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