Papers by Keyword: Nickel Aluminide

Abstract: A high entropy Ni-Al-Ti-Mn-Co-Fe-Cr alloy (HEA) system was fabricated using spark plasma sintering (SPS). The alloys at different elemental compositions were developed at a sintering temperature of 850 °C, a heating rate of 90 °C/min, a pressure of 50 MPa, and a dwelling time of 5 min. The sintered alloys' mechanical characteristics, microstructure, phase evolution, and density were assessed. The evolved microstructure of the sintered HEAs shows a homogenous dispersion of the alloying metals. The sintered microstructures showed a mixture of simple and complex phases. The phase refinement shows that the sintered HEAs exhibited a lower and the least grain size of 2.28 µm compared to the Ni₅₀Al₅₀ alloy having 8.26 µm. Likewise, a higher micro-strain value of 1.25E-1 was attained by the non-equal atomic HEA, while the unalloyed has 1.87E-3. The microhardness value of the sintered alloys varied from 103.5 HV to 139.2 HV, while their measured density varied from 5.23 g/cm³ to 6.44 g/cm³.

Abstract: Owing to its fairly higher melting point (2468°C) and superior thermal conductivity, Niobium alloys are rendered as candidate material for high temperature applications, where state of the art Nickel base super alloys cannot be used. Its applications possess wide range of aerospace components mainly encompassing aircraft exhaust chambers, thrust augmenters, rocket engines and other industries such as chemical and petrochemical. The only limitation with niobium alloys is their inferior oxidation resistance, which can be tackled by developing a high temperature oxidation resistant coating. In this regard, Nickel Aluminide (NiAl) having a melting point of 1638°C embraces a paramount importance amongst the coating categories. In this study, NiAl was synthesized using vacuum melting and strip casting followed by ball milling. The powder was coated on C-103 Niobium alloy specimens using air plasma technique and evaluated for high temperature stability. It was deduced that the coating was exceptionally stable up to 1234 °C in ambient conditions.

Abstract: In the recent search nickel superalloy Inconel 600 was coated with Zr-modified aluminide diffusion coating using pack cementation technique. Diffusion coating was done in a single step utilizing a conversion reaction of 10% Al, 2% ZrO₂, 4% NaCl, and 84 percent Al₂O₃ (wt. percent ) and a simultaneous aluminizing-zirconizing process. The diffusion coating operations were performed in an argon environment at 1050 °C for 10 hours. The test of the isothermal oxidation in dry air was performed on the Inconel Alloy 600 (IA600) without and with Zr-modified aluminide coating for 800-1000 °C. The oxidation kinetic of IA600 and its coated system was found to follow the parabolic law. The activation energy is 243 kJ/mol. for the coated system and 457 kJ/mol. for the uncoated system. XRD analysis show that oxide phases are formed on an uncoated IA600 surface during most of the oxidation exposure conditions are NiO, Cr₂O₃, Fe₂O_3, NiCr₂O₄ and NiFe₂O_4, , whereas alumina scale is the major oxide that is obtained on the surface of coated samples.

Abstract: Coatings were obtained by the method of electrospark deposition (ESD), using Ni-Al intermetallic alloys, steel having been used as cathodes. The structure of samples preliminarily, coated with nickel aluminides of various phase compositions (NiAl, Ni₃Al), was investigated. In addition to the indicated anode materials, a complex alloyed metal matrix alloy obtained by the method of self-propagating high-temperature synthesis, was used. It was established that the coating microstructure consisted of columnar crystallites, vertically oriented to the cathode surface. X-ray microanalysis of the transverse sections showed a change in the composition of crystallites along their height. It was found that the content of the cathode components decreased from the surface of the sample to the upper part of its coating, however, the content of the anode components increased. The revealed regularities indicate the fact that the coating structure obtained at ESD, was formed through the stage of liquid-phase mixing, which explained high coating adheasion. The mechanisms of structure formation of both single-layer and two-layer coatings proved to be identical.

Abstract: Nickel aluminide (βNiAl) is a bond coat material used in thermal barrier coating (TBC) system of aeroengines. The performance of TBC is significantly influenced by the thermal response of bond coat (BC) material. Usually, the most failures of the TBCs are attributed to poor performance of a BC. There are several factors that affects the performance, such as; oxidation, mechanical damages, manufacturing oriented problems (thermal residual stresses) etc. In this study, βNiAl was deposited onto CMSX-4 superalloy substrates using in-situ chemical vapour deposition (CVD) method. Zirconium was also incorporated as a dopant into βNiAl coating. Residual stresses were measured using X-ray diffraction (XRD) method. In particular, the comparison was made between the doped and undoped coating samples. Results demonstrated minimum thermal stresses in the zirconium doped coating in comparison to its undoped counterpart. Possible mechanism of stress removal is discussed.

Abstract: Powder metallurgy method was used to consolidate nickel aluminide reinforced multi-walled carbon nanotubes through planetary ball mill in order to facilitate the effective dispersion of carbon nanotubes (CNTs). In this investigation, 0.5 wt% of CNTs was added to the powder mixture of nickel and aluminum through two ball milling processes: low energy ball mill (LEBM) and high energy ball mill (HEBM). The bulk composites were synthesized by spark plasma sintering (SPS) at constant temperature, holding time, pressure of 32 MPa, 800 °C and 5 min respectively. The heating rate was varied between 50 and 150 °C/min. Microstructural evolutions of the composites were studied and densification of the composites was improved with increase in heating rate but depreciated as the heating rate was further increased. Vickers microhardness values of the fabricated composites were enhanced with increase in heating rate.

Abstract: This research aims to study the simultaneous silicon-modified pack aluminizing method using silica (SiO₂) from Rice Husk Ash (RHA) which contains 99.45% SiO₂ in comparison with commercial SiO₂ in the form of quartz. Samples can thus be categorized into two groups: quartz-doped and RHA-doped. Simultaneous silicon-modified pack aluminizing of pure nickel was performed at 1000°C for 4 hours under an argon atmosphere. The pack used in this research was prepared from aluminum (Al), ammonium chloride (NH₄Cl), alumina (Al₂O₃) and silica (SiO₂, i.e. quartz and RHA) powder at ratios of 29:2:60:9 by weight, respectively. Post aluminized samples were characterized by glancing incident-angle X-ray diffractometer (GIXD). Quantitative analysis of the layer was performed using energy dispersive spectroscopy (EDS). A scanning electron microscope (SEM) was employed to observe the resulting microstructure. It was found that simultaneous silicon-modified pack aluminizing can be successfully performed by doping RHA and quartz into the pack. The aluminized layer consists of Ni₂Al₃ and NiAl₃ with a small amount of silicon. RHA was found to be more effective than quartz as a silicon source providing a higher amount of silicon in the aluminized layer. Moreover, using RHA successfully forms a silicon-rich interdiffusion layer beneath the typical aluminized layer.

Abstract: In the present study, a mixture of powders (87.9 at.% Ni, 12 at.% Al, 0.1 at.% B) was used as the initial material to produce sintered Ni₃Al + B alloy. Spark Plasma Sintering (SPS) method was used to compact the powder. The powder mixtures were previously prepared in two ways: mixing the initial powders in a mortar (М1) and mechanical activation (М2). The microstructure was observed using optical microscope (OM). The addition of small amount of boron to the initial mixture of nickel and aluminum improves the density of the sintered Ni₃Al intermetallic compound (98.8%). The results of density, bending and microhardness tests showed, that the provisional three-minute mechanical activation improves almost all properties of the sintered material. The compact obtained by SPS by M2 contributes to the formation of a homogeneous fine-grained structure of the material. It leads to further increase in flexural bending strength up to 2200 MPa. This value is almost 8 times the strength of the intermetallic Ni₃Al stoichiometric composition obtained by SPS.

Abstract: Structure and mechanical properties of the PN85YU15 - Ni composite materials obtained by spark plasma sintering were investigated. Two types of powder mixtures, namely, nickel mixed with coarse-grained nickel aluminide and nickel mixed with fine-grained nickel aluminide were used to obtain the composites. Nickel aluminide and nickel powders were taken in the ratio 7:3 respectively. The effect of the initial nickel aluminide particle sizes and plastic deformation due to the ball milling on the structure and mechanical properties of materials sintered at 1100 °C and pressure of 40 MPa was determined. Plastic deformation and refining the initial intermetallic powder particle sizes leads to increasing the sintered material relative density to 95%. The tensile strength of the PN85YU15-Ni composite material obtained by sintering of the milled PN85YU15 powder and nickel in the ratio 7:3 was 1060 MPa. This value is almost twice as high as the tensile strength of the composite containing a no significant plastic deformed coarse-grained intermetallic compound powder (590 MPa), and three times higher than the tensile strength of the sintered nickel aluminide powder (380 MPa).

Abstract: PN85U15 - Ni composites were obtained by spark plasma sintering (SPS) of the powder mixture consisted of nickel and nickel aluminide. Particular attention in this study was focused on the discussion of the problem concerning the influence of the nickel content on mechanical properties of the sintered composites. The microstructure of the sintered materials consisted of spherical intermetallic particles homogeneously distributed in the nickel matrix. The relative density of all sintered materials was higher than 90 %. The hardness of the fabricated composites decreased from 3100 MPa (PN85U15 sintered powder) to 2500 MPa (70 % PN85U15 with 30 % Ni). It was found that the PN85U15 – Ni composite containing approximately 30 wt. % of Ni possessed the highest bending strength (1900 MPa).