Showing papers on "Inconel published in 2014"

Thermal effects on microstructural heterogeneity of Inconel 718 materials fabricated by electron beam melting

Abstract: Additive manufacturing technologies, also known as 3D printing, have demonstrated the potential to fabricate complex geometrical components, but the resulting microstructures and mechanical properties of these materials are not well understood due to unique and complex thermal cycles observed during processing. The electron beam melting (EBM) process is unique because the powder bed temperature can be elevated and maintained at temperatures over 1000 °C for the duration of the process. This results in three specific stages of microstructural phase evolution: (a) rapid cool down from the melting temperature to the process temperature, (b) extended hold at the process temperature, and (c) slow cool down to the room temperature. In this work, the mechanisms for reported microstructural differences in EBM are rationalized for Inconel 718 based on measured thermal cycles, preliminary thermal modeling, and computational thermodynamics models. The relationship between processing parameters, solidification microstructure, interdendritic segregation, and phase precipitation (δ, γ′, and γ″) are discussed.

Selective laser melting additive manufactured Inconel 718 superalloy parts: High-temperature oxidation property and its mechanisms

Abstract: This work presented a comprehensive study of high-temperature oxidation behaviors and mechanisms of Selective laser melting (SLM) processed Inconel 718 superalloy parts using different methods including isothermal oxidation testing, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The experimental results revealed that the oxidation process of the tested parts processed at a lower volumetric laser energy density experienced the severe spallation. On reasonably increasing the applied volumetric laser energy density, the oxidation kinetics of the as-produced parts obeyed a parabolic law, exhibiting the significantly improved oxidation resistance performance. The constitutional phases within the oxidation film were identified and the corresponding formation mechanisms were elucidated in detail according to the thermodynamic principles. The cross-sectional morphologies of oxidized Inconel 718 parts indicated that the oxidation microstructure mainly consisted of an external oxidation layer and an internal oxidation zone. The oxidation process was controlled by the outward diffusion of oxide forming elements and inward penetration of oxygen, by which the interaction mechanisms between the microstructures and internal oxidation zones were clarified. On the basis of the experimental results and theoretical analyses, the physical oxidation mechanisms were accordingly established to illustrate the oxidation behaviors of SLM-processed Inconel 718 parts at elevated operative temperatures.

Additive manufacturing of nickel-based superalloy Inconel 718 by selective electron beam melting: Processing window and microstructure

Abstract: Cube-shaped IN718 samples were produced by selective electron beam melting (SEBM) with varying beam power, deflection speed, and beam spot size. Process parameter windows were identified where fully dense samples are obtained with no surface unevenness. High deflection speeds were demonstrated to result in smaller demand of area energy. This result is explained by the reduced time for heat dissipation into the substrate during hatching. The grain structure was strongly affected by SEBM process parameters. Under certain conditions, epitaxial growth over many layers and well-developed columnar grain structures were obtained with a polycrystalline substrate plate. A more defocused beam led to a lower melt pool temperature and shallower melt pool geometry where maximum temperature gradients and solidification rates were more or less in parallel with the building direction and primary dendrite arm orientation. These conditions help to suppress grain nucleation ahead of the nucleation front as vigorous melt movement, fragmentation of dendrites, and tertiary arm growth are suppressed.

Experimental Investigation and Analysis of EDM Characteristics of Inconel 825

Abstract: Recently, electro-discharge machining (EDM) has become one of the preferred machining techniques for Ni-based super alloys. Although extensive research has been reported on EDM characteristics of Inconel 718, not much information is available on Inconel 825. Owing to the excellent resistance to corrosion, Inconel 825 finds particular application in highly corrosive environment. Therefore, the current investigation aims at studying the influence of different EDM process variable peak current (I p ), duty factor (T au), and pulse-on duration (T on) on various performance characteristics such as material removal rate (MRR), surface roughness (SR), radial overcut (ROC), and surface crack density (SCD). Experiments were designed and carried out using L9 orthogonal array. The most influencing factor for responses MRR, SR, and ROC was found to be I p with percentage contribution of 51.22%, 81.08%, and 54.78%, respectively, while it was T on for SCD with 39.54% contribution. Since EDM involves multiple performanc...

Analysis of Form Tolerances in Electrical Discharge Machining Process for Inconel 718 and 625

Abstract: This article presents an experimental work and investigation on electrical discharge machining (EDM) of Inconel 718 and 625 superalloys. These superalloys are used for making parts like turbine blades, marine components, and nuclear reactor components. The precise components made up of superalloys which have cylindrical, square, and hexagonal machined features are required regular estimations of cylindricity, circularity, perpendicularity, and parallelism. In this work, EDM of the above said superalloys was carried out and form tolerances were analyzed. The significance of input parameters namely peak current, pulse-on time (T on), and pulse-off time (T off) on the form tolerances were investigated. In addition to these, the influence of individual parameters were also analyzed by analysis of variance (ANOVA) technique.

Application of powder suspended in dielectric fluid for fine finish micro-EDM of Inconel 718

Abstract: Inconel 718 is an extremely hard and difficult-to-cut material used extensively in manufacturing because of its superior wear and corrosion resistance. Microelectrical discharge machining (micro-EDM) is one of the effective methods of machining this extremely hard material. However, due to short circuiting and arcing, the surface of microholes produced by micro-EDM has black traces and cones. This study investigates the influence of molybdenum disulfide (MoS2) powder suspended in dielectric fluid on the performance of micro-EDM of Inconel 718 with focus in obtaining quality microholes. It was observed that MoS2 powder suspension with 50 nm of size and 5 g/l of concentration can produce better quality microholes in Inconel 718. Moreover, it was also found that 50 nm MoS2 powder was the best powder size to achieve the highest material removal rate.

On the precipitation of delta phase in ALLVAC® 718Plus

Abstract: ALLVAC 718Plus is a new commercial superalloy derived from Inconel 718, but possessing a higher temperature capability whilst employing the same philosophy regarding the microstructure. Many articl...

Enhanced Field Emission Properties from CNT Arrays Synthesized on Inconel Superalloy

Abstract: One of the most promising materials for fabricating cold cathodes for next generation high-performance flat panel devices is carbon nanotubes (CNTs). For this purpose, CNTs grown on metallic substrates are used to minimize contact resistance. In this report, we compare properties and field emission performance of CNTs grown via water assisted chemical vapor deposition using Inconel vs silicon (Si) substrates. Carbon nanotube forests grown on Inconel substrates are superior to the ones grown on silicon; low turn-on fields (∼1.5 V/μm), high current operation (∼100 mA/cm2) and very high local field amplification factors (up to ∼7300) were demonstrated, and these parameters are most beneficial for use in vacuum microelectronic applications.

Characterisation of microstructure and creep properties of alloy 617 for high-temperature applications

Abstract: Current energy drivers are pushing research in power generation materials towards improved efficiency and improved environmental impact. In the context of new generation ultra-supercritical (USC) power plant, this is represented by increased efficiency, service temperature reaching 750 °C, pressures in the range of 35–37.5 MPa and associated carbon capture technology. Ni base alloys are primary candidate materials for long term high temperature applications such as boilers. The transition from their current applications, which have required lower exposure times and milder corrosive environments, requires the investigation of their microstructural evolution as a function of thermo-mechanical treatment and simulated service conditions, coupled with modelling activities that are able to forecast such microstructural changes. The lack of widespread microstructural data in this context for most nickel base alloys makes this type of investigation necessary and novel. Alloy INCONEL 617 is one of the Ni-base candidate materials. The microstructures of four specimens of this material crept at temperatures in the 650–750 °C range for up to 20,000 h have been characterised and quantified. Grain structure, precipitate type and location, precipitate volume fraction, size and inter-particle spacing have been determined. The data obtained are used both as input for and validation of a microstructurally-based CDM model for forecasting creep properties.

Fabrication of nano-TiCp reinforced Inconel 625 composite coatings by partial dissolution of micro-TiCp through laser cladding energy input control

Abstract: Nano-particulate reinforced metal matrix composites (nPRMMCs) exhibit excellent comprehensive properties unmatched by conventional micro-particulate reinforced metal matrix composites (μPRMMCs). However, current techniques for fabricating nPRMMCs usually use nano-powders as raw materials, which are not preferred due to their agglomeration trend and harmful size. In this paper, we developed a technique to fabricate nano-TiC p reinforced Inconel 625 composite coatings by laser cladding of an Inconel 625 + 5 wt.% TiC powder mixture, particle size of the raw powders both in micrometer range. By controlling the specific energy input, the micro-TiC p partially dissolved into nanometer scale. The influence of specific energy input on particle size, morphology and the microstructure, phase constitution and mechanical properties of the composite coatings were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and nano-indentation test. Nano-TiC p reinforced Inconel 625 composite coatings were achieved at the specific energy input of 25.3 kJ/g. The hardness and modulus of the nPRMMCs are 3.36 GPa and 190.91 GPa, increased by 10.33% and 12.39% respectively compared to laser cladded Inconel 625 substrate. The nPRMMCs show potential in applications such as the fabrication of turbine blades and engine components with improved performance.

Selective laser melting additive manufacturing of TiC/Inconel 718 bulk-form nanocomposites: Densification, microstructure, and performance

Abstract: Selective laser melting (SLM) process was used to prepare the nanocrystalline titanium carbide (TiC)-reinforced Inconel 718 matrix bulk-form nanocomposites in the present study. An in-depth relationship between SLM process, microstructures, properties, and metallurgical mechanisms was established. The insufficient laser energy density (η) input limited the densification response of shaped parts due to the formation of either larger-sized pore chains or interlayer micropores. The densification of SLM-processed part increased to a near-full level as the applied η was properly settled. The TiC reinforcements generally experienced successive changes from severely agglomerated in a polygon shape to the uniformly distributed with smoothened and refined structures on increasing the applied η, while the columnar dendrite matrix exhibited strong epitaxial growth characteristic concurrently. The optimally prepared fully dense part achieved a high microhardness with a mean value of 419 HV0.2, a considerably low friction coefficient of 0.29, and attendant reduced wear rate of 2.69 × 10−4 mm3/N m in dry sliding wear tests. The improved densification response, SLM-inherent nonequilibrium metallurgical mechanisms with resultant uniformly dispersed reinforcement microstructures, and elevated microhardness were believed to be responsible for the enhancement of wear performance.