Papers by Keyword: Superalloy

Abstract: In this work, nanocomposites Alloy 625-xTiB₂ (x=1.25; 2.5; 3.75; 5.0 wt%) were processed through suction casting. The microstructure and selected properties were analyzed using light microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. It has been observed that introducing TiB₂ particles into Alloy 625 strongly influences the as-cast microstructure. A dendritic microstructure with irregular distribution of the strengthening precipitates has been revealed. In reference Alloy 625, the Nb-rich carbides and Laves phase precipitates exist in the interdendritic spaces. The TiB₂ interacted with the liquid Alloy 625 during suction casting, leading to microstructural changes like more precipitates in interdendritic spaces including newly formed B-rich phases.

Abstract: The manufacturing industry has a significant impact on the economy of a country. Therefore, carrying out necessary developments and modifications in manufacturing machine components is essential. Some materials, called superalloys, are challenging to machine, and they have a wide application in the turbine components of aerospace, submarines, oil, nuclear, steam, and other power generation industries. Due to the exceptional properties of these superalloys their machining becomes very difficult and time-consuming; They damage the cutting tool, and excessive use of lubricants eventually affect the material handling and cost. These problems lower down the sustainability and therefore an attempt has been made in the current research work to eliminate the use of cutting fluid by impinging solid lubricant on AlTiN coated tungsten carbide cutting tool by using pulsed direct current magnetron sputtering and cathodic arc physical vapour deposition techniques. The micro-texturing is first done on rake face of the milling insert such that graphite, which acts as a solid lubricant, can be then deposited in those micro-textures. The end milling of Nimonic 90, a superalloy, is done using the solid lubricant filled microtextured insert under compressed air environment, and the cutting forces, cutting temperature, tool wear, and surface roughness are analysed. It is found that there is a substantial decrease in the cutting forces and tool wear when compared with non-textured tool due to less friction and temperature at the machining zone. Sustainability of such solid lubricant based textured cutting tool has shown improvement when compared with non-textured cutting tool. The machinability of Nimonic 90 is increased by implementing the solid lubricant-based cutting tool, and therefore, it can be effectively utilised for the machining of superalloys soon.

Abstract: Hastelloy is a nickel-chromium-molybdenum-iron-based alloy and a member of the ‘superalloy’ family. Hastelloy has exceptional properties like high strength, wear resistance and high-temperature stress-corrosion resistance. Therefore, Hastelloy is used in gas turbines, power plants, metal injection molding, etc. Many industrial applications are related to the properties of the surface. Wettability is a key surface property that affects applications like lubrication, adhesion, coating, heat conduction, etc. Laser Texturing is an excellent method to modify the surface properties of materials like metal, polymers and ceramic. In the present study, a carbon dioxide laser created unidirectional textures on Hastelloy (C22, C276, X). Different sets of unidirectional textures were formed by changing the laser power and frequency. Various roughness parameters were compared for every laser parameter. In this paper, the effective change in wettability properties of Hastelloy (C22, C276, X) after the Laser texturing process for a range of power and frequency were studied under DI water and glycerol as test fluids. Results show that the contact angle of the test fluid increases as the laser power increases, and the contact angle decreases as the laser frequency increases for all three superalloys. The surface energy of a given set of samples was also measured using the recorded contact angle of DI water and Glycerol by the OWRK equation. Similar trends were found in surface energy for all three Hastelloy.

Abstract: An isothermal aging study was carried out on direct aging GH4169G alloy forging disk for up to 10000 hours at 650°C. The evolution of microstructure and mechanical properties of the alloy were systematically studied via scanning electron microscope (SEM), transmission electron microscope (TEM) and physicochemical phase analysis. The results show that the size of main strengthening phases γ′′ and γ′ in GH4169G alloy direct aging disk increases gradually, while their quantity decreases with prolonging aging time. The total amount of γ′′ and γ′ is 14.1% at as-heat treated condition, which decreases by 3.1% at 10000h. The amount of δ phase increases gradually, and the content of δ phase reaches 5.4% at 10000h, which increases nearly twice. The α-Cr phase adjacent to the δ phase on the grain boundaries shows a parabolic increase in its content, and reaches 2.231% at 10000h. The yield strength, stress rupture life shows varying degrees of reductions as prolonging thermal aging time.

Abstract: The effect of high temperature annealing on microstructure evolution of Ni-24Fe-14Cr-8Mo alloy was investigated through Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Rockwell Hardness Testing Machine. Three kinds of grain growth patterns were found at different annealing temperatures due to carbides precipitation and dissolution. After a combination of high temperature annealing and aging treatment, the hardness versus time curves performed a parabolic pattern. The highest hardness was achieved under 1070°C/60 minutes treatment, and the desirable annealing time should be 60 minutes to 90 minutes.

Abstract: In this paper, the contact interface between FGH96 superalloy melts and refractory slurry with corundum powder and silica sol at 1600°C with different soaking time in 10-240 min range was investigated. The morphology and composition of the contact interface were studied by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the reaction layer formed on the contact interface between the melting superalloy and the refractory slurry, and is mainly consist of Alumina and contains a small amount of other metal elements such as Ti and Cr. The reaction layer was not smooth on the micro level, and there was a peninsula-like structure protruding into the internal part of the melting superalloy on the reaction zone, and even started to fall off at some places to form islands. With the increase of soaking time, the reaction between melt of superalloy and refractory slurry increased gradually and the reaction layer began to combine with the refractory slurry substrate and form obvious interaction layered structure, resulting in the corrosion of refractory slurry substrate. With the soaking time over 120 min, the stable contact interface was destroyed. Thermodynamic calculation shows that the substitution reaction between Al in superalloy and SiO₂ in refractory slurry meets the thermodynamic conditions, and the reaction can proceed forward.

Abstract: Spinning forming is an effective method for processing thin-walled rotating body parts. The influence of process parameters on the spinning forming limit of materials was studied for the four high-temperature alloys of GH3044, GH3625, GH3536 and GH4169 used in aero-engines. The results can be used as aero-engine high-temperature alloy parts spinning process and provides experimental basis and process guidance. The research results showed that the forming temperature had a significant effect on the spinning forming performance of superalloy materials. When the temperature increased to 800°C and above, the ultimate thinning rate raised 70%. The ultimate thinning rate of GH4169 was higher than the other three materials and GH3044 and GH3536 was at the middle level, GH3625 was relatively low. At the same time, the feed ratio and the corner radius of the rotary wheel had a certain influence on the ultimate thinning rate of different superalloys. The spinning process needs to select reasonable process parameters according to the actual situation when the spinning is applied to manufacture parts.

Abstract: The effects of cast and heat treatment processes on microstructure and mechanical property of K4169 alloy have been investigated. The results show that low shell and pouring temperature can significantly improve the room temperature tensile and elevated temperature stress-rupture properties of the alloy; The joint function of hot isostatic pressing (HIP) and homogenization+solution+aging (HSA)standard heat treatment can effectively close casting defects such as micro-looseness, significantly improve the segregation of the alloy structure, basically eliminate the Laves phase, only a small amount of MC carbide dispersed in the grain boundary and short rod-shaped δ-phase. What is the most significant is that a large number of lenticular γ'' phases are uniformly precipitated, Which enhance the microstructural stability, and significantly improve the room temperature tensile properties and high temperature endurance properties of K4169 alloy.

Abstract: This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

Abstract: Effects of different loading and uninstalling and safe loading time on the low-cycle fatigue-creep interaction behavior of GH4169 superalloy at 650°C/850MPa have been investigated. The study found that under the safe loading time, with the longer the loading and unistalling time, the fatigue-creep property and life of this alloy were gradually improved. However, under the same loading and uninstalling time, with the extension of the loading time, property of the fatigue-Creep of the alloy was gradually reduced, and its life was gradually shortened. In addition, The fracture failure behavior of the alloy under different conditions was studied in detail. Interestingly, With the extension of the holding time, the fracture failure of the alloy was changed from fatigue damage to creep damage, which makes its fracture mode transition the transgranular fracture into intergranular fracture extension.