Showing papers on "Inconel published in 2008"

Effect of machining parameters and cutting edge geometry on surface integrity of high-speed turned Inconel 718

Abstract: Stringent control on the quality of machined surface and sub-surface during high-speed machining of Inconel 718 is necessary so as to achieve components with greater reliability and longevity. This paper extends the present trend prevailing in the literature on surface integrity analysis of superalloys by performing a comprehensive investigation to analyze the nature of deformation beneath the machined surface and arrive at the thickness of machining affected zone (MAZ). The residual stress analysis, microhardness measurements and degree of work hardening in the machined sub-surfaces were used as criteria to obtain the optimum machining conditions that give machined surfaces with high integrity. It is observed that the highest cutting speed, the lowest feedrate, and the moderate depth of cut coupled with the use of honed cutting edge can ensure induction of compressive residual stresses in the machined surfaces, which in turn were found to be free of smeared areas and adhered chip particles.

Investigations of MX and γ′/γ″ precipitates in the nickel-based superalloy 718 produced by electron beam melting

Abstract: Samples with a composition similar to the nickel-based superalloy Inconel alloy 718 were produced by electron beam melting of prealloyed powder and investigated with respect to type and composition of the strengthening precipitates. The matrix consists of γ grains orientated in nearly the same direction, almost like a single crystal. Coarse precipitates (

Effect of microstructure on properties of friction stir welded Inconel Alloy 600

Abstract: Friction stir welding (FSW) has been widely used to metals with moderate melting temperatures, primarily Al alloys. Recently, tool materials that withstand high stresses and temperatures necessary for FSW of materials with high melting temperatures have been developed. In the present study, polycrystalline cubic boron nitride (PCBN) tool was used for partially penetrated FSW of Inconel Alloy 600, and a defect-free weld was successfully produced. Microstructural characteristics, mechanical and corrosion properties in the weld were examined. The weld had better mechanical properties than the base material due to formation of fine grain structure in the stir zone, but exhibited slightly the lower corrosion resistance in a part of the stir zone and heat-affected zone (HAZ).

Surface integrity and tool life when turning Inconel 718 using ultra-high pressure and flood coolant systems

Abstract: The use of high-pressure cutting fluids has been shown to increase tool life or enable higher cutting speeds to be used when machining advanced aerospace materials such as Inconel 718. Cutting flui...

Laser-Assisted Milling of Silicon Nitride Ceramics and Inconel 718

Abstract: Laser-assisted machining (LAM) has shown its potential to significantly reduce fabrication costs and improve product quality for advanced materials. While extensive studies have been conducted on laser-assisted turning of various ceramics and high temperature alloys, few attempts have been made to extend LAM to milling operations. In this paper, a transient, three-dimensional thermal model developed for laser-assisted milling (LAML) is presented and its accuracy is verified by surface temperature measurements with an infrared camera. LAML experiments designed by the model are successfully conducted on silicon nitride ceramics using TiAIN coated carbide end mills and Inconel 718 using SiC reinforced alumina cutting tools. The promising experimental results, including good surface roughness and acceptable tool wear, show the validation of applying the thermal model to design LAML processes and the feasibility of employing LAML for difficult-to-machine materials such as advanced ceramics and superalloys.

Numerical and experimental investigation of laser-assisted machining of inconel 718

Abstract: A numerical investigation of laser-assisted machining for Inconel 718 is presented. This study is based on a three-dimensional finite element model, which takes into account a new constitutive law of Inconel 718 as well as friction and heat transfer models at the tool-chip interface that are developed at the Aerospace Manufacturing Technology Centre (AMTC), of the National Research Council of Canada (NRC), Canada. The material flow stress is described as a function of the strain, the strain rate, and the temperature. The friction model accounts for the sticking and the sliding regions observed experimentally. The formulation of the heat transfer model is based on combining contact mechanics analysis with the solution of the thermal contact problem. The laser beam is modeled as a moving heat source, which is experimentally calibrated. To validate the three-dimensional finite element model, laser-assisted machining experiments were designed and carried out under different cutting conditions. The predicted c...

Laser-assisted machining of Inconel 718 with carbide and ceramic inserts

Abstract: Laser assisted machining (LAM) can improve the machinability of materials by locally heating the material prior to its removal. The work presented here is a study of the laser assisted machining of Inconel 718 (NiCr19FeNb at 46 HRc) with carbide and ceramic insert. The tests have shown a reduction in the cutting force, and have highlighted the impact of laser assistance on the integrity surface (roughness, appearance, residual stress) and the tool life.

Stress rupture characteristics of Inconel 718 alloy for ramjet combustor

Abstract: To evaluate the accelerated creep phenomena for ramjet combustor, the stress rupture tests for Inconel 718 alloy were performed at a temperature range of 649–760 °C and a stress range of 381–1093 MPa. The stress exponent, n , under the given conditions was obtained. Also, the activation energy, Δ H , was calculated from the experimental results. An empirical formula of accelerated creep rate for Inconel 718 alloy was calculated by computer simulation. The accelerated creep life of Inconel 718 alloy was evaluated by using Larson–Miller parameter.

Residual Stresses Distribution through Thick HVOF Sprayed Inconel 718 Coatings

Abstract: Residual stress buildup in thick thermal spray coatings is a property of concern. The adhesion of these coatings to the substrate is influenced by residual stresses that are generated during the coating deposition process. In the HVOF spray process, significant peening stresses are generated during the impact of semimolten particles on the substrate. The combination of these peening stresses together with quenching and thermal mismatch stresses that arise after deposition can be of significant importance. Both numerical method, i.e., Finite Element Method (FEM), and experimental methods, i.e., the Modified Layer Removal Method (MLRM) and Neutron Diffraction, to calculate peening and quenching stresses have been utilized in this work. The investigation was performed on thick Inconel 718 coatings on Inconel 718 substrates. Combined, these numerical and experimental techniques yield a deeper understanding of residual stress formation in the HVOF process and thus a tool for process optimization. The relationship between the stress state and deposit/substrate thickness ratio is given particular interest.

Mathematical modelling of Inconel 718 particles in HVOF thermal spraying

Abstract: High velocity oxygen fuel (HVOF) thermal spray technology is able to produce very dense coating without over-heating powder particles. The quality of coating is directly related to the particle parameters such as velocity, temperature and state of melting or solidification. In order to obtain this particle data, mathematical models are developed to predict particle dynamic behaviour in a liquid fuelled high velocity oxy-fuel thermal spray gun. The particle transport equations are solved in a Lagrangian manner and coupled with the three-dimensional, chemically reacting, turbulent gas flow. The melting and solidification within particles as a result of heat exchange with the surrounding gas flow is solved numerically. The in-flight particle characteristics of Inconel 718 are studied and the effects of injection parameters on particle behavior are examined. The computational results show that the particles smaller than 10 μm undergo melting and solidification prior to impact while the particle larger than 20 μm never reach liquid state during the process.

Microstructures of thin and thick slurry aluminide coatings on Inconel 690

Abstract: Two slurry aluminide coatings are produced on the Ni-base super alloy Inconel 690 by applying two different thicknesses of the same slurry on to the 690 substrate, followed by a two-step heat-treatment. The resulting thin aluminide coating consists of a single layer of Ni-rich β-NiAl matrix containing few large Cr precipitates with a high P content. The thick aluminide coating has a precipitate free inner layer of Ni-rich β-NiAl. An outer layer of Al-rich β-NiAl with many α-Cr precipitates has formed as well. The present metallurgical characterization shows a significant influence of slurry thickness on the morphology and composition of the coatings formed during heat treatment.

Microstructure transformations and cracking in the matrix of γ–γ′ superalloy Inconel 713C melted with electron beam

Abstract: The paper presents the results of metallographic examination of microstructural changes in the matrix of γ–γ′ superalloy Inconel 713C, subject to electron beam fusion. The obtained fusions simulate the phenomena that occur in the weld and the heat-affected zone during welding. Changes of γ′ phase morphology in the fusion zone, in HAZ and in the areas adjacent to grain boundaries that can affect crack initiation were determined. Changed morphology in the recrystallized γ′ zone can result from its reduced melting point due to impoverishment in niobium and titanium as well as to changed aluminium concentration or accelerated diffusion of alloying elements. The cracks found in HAZ propagate mainly through grain boundaries in the microporosity areas or, possibly, the areas left by molten carbide phases. However, no secondary phases with lower melting point or eutectics like (γ–γ′) (MxCy + Zr + Si) were found in the neighbourhood of cracks. The cracks present in the fusion zone were initiated at high temperature and propagate in the areas of interdendritic voids. The cracks were caused by the high solidification rate in the fusion zone and low thermal conductivity of the alloy.

Thermal degradation behavior of inconel 617 alloy

Abstract: Inconel 617 alloy is a candidate material for potential use as an intermediate heat exchanger (IHX) and as a hot gas duct (HGD) in high-temperature gas-cooled reactors (HTGRs) for H2 production. This alloy supports severe operating conditions of a pressure over 8 MPa and temperature that exceed 950 °C in He gas with some impurities. In this work, the oxidation behavior of Inconel 617 alloy was studied after exposure at 1050 °C for 2000 h in both air and He atmospheres. The external oxide scale was mainly composed of Cr2O3 and small amount of TiO2. The internal oxide was observed just below the external oxide scale and was distributed on the grain boundaries. The internal oxide was confimed as Al2O3. The Cr-depleted zone and internal oxide in both environments became thicker as the exposure time increased. The Cr2O3 in air at 2000 h was thinned in terms of its scale by CrO3 evaporation and delamination. The Cr2O3 in He was constantly maintained.

Joining of Superalloys to Intermetallics Using Nanolayers

Abstract: Joining nickel based superalloys to gamma-TiAl intermetallic alloys will contribute to a more efficient application of these advanced materials, particularly in extreme environments. In this study, Inconel alloy and gamma-TiAl are joined using as filler alternated nanolayer thin films deposited onto each base material. The nanolayers consisted in Ni/Al exothermic reactive multilayer thin films with periods of 5 and 14 nm deposited by d.c. magnetron sputtering in order to improve the adhesion to the substrates and to avoid the reaction between Ni and Al. Diffusion bonding experiments with multilayer coated alloys were performed under vacuum at 800°C by applying 50 MPa during 1h. Bonding was achieved in large areas of the centre of the joints where regions without cracks or pores were produced, especially when using multilayer thin films with a 14 nm modulation period.

Weld Solidification Cracking in Solid-Solution Strengthened Ni-Base Filler Metals

Abstract: The weld solidification cracking susceptibility of several solid-solution strengthened Ni-base filler metals was evaluated using the transverse Varestraint test. The alloys tested included Inconel 617, Inconel 625, Hastelloy X, Hastelloy W, and Haynes 230W.* Susceptibility was quantified by determining the solidification cracking temperature range (SCTR) which is a direct measurement of the range over which cracking occurs. This temperature range was then compared to the equilibrium solidification temperature range derived from Calphad-based ThermoCalc™ calculations, Scheil-Gulliver solidification simulations, and in-situ measurements using the single sensor differential thermal analysis (SS-DTA) technique.

Effect of filler alloy composition on post-weld heat treatment cracking in GTA welded cast Inconel 738LC superalloy

Abstract: The effect of filler alloy composition on post-weld heat treatment (PWHT) cracking in Inconel (trade name of the Special Metals group of companies) 738LC (IN-738LC) superalloy was investigated. Five filler alloys (IN-625, IN-718, FM-92, C-263 and Rene-41), containing varying concentrations of Al and Ti, were used to gas tungsten arc (GTA) weld IN-738LC superalloy specimens which were given two different preweld heat treatments. Additionally, autogenous (without filler) welds were also made on the same two preweld heat treated materials. The preweld heat treatments consisted of the standard industrial solution heat treatment (SHT) at 1120°C for 2 h in vacuum followed by argon quenching and a new heat treatment (UMT), developed by the authors to improve the heat affected zone (HAZ) cracking resistance of IN-738LC. The latter heat treatment comprised of solution treatment at 1120°C for 2 h followed by aging at 1025°C for 16 h and then water quenching. The welded specimens were given a PWHT consisting...

Influence of Artificial Aging on Microstructure and Mechanical Properties of Dissimilar Welds between 310 Stainless Steel and INCONEL 657

Abstract: This investigation is carried out to characterize welding of AISI 310 austenitic stainless steel (SS) to INCONEL 657 nickel-chromium superalloy. The welds were produced using four types of filler materials: the nickel-based corresponding to INCONEL 82, INCONEL A, INCONEL 617, and 310 austenitic SS. This article describes the effects of aging treatment on the joints. A comparative evaluation based on microstructural features and estimation of mechanical properties was performed. INCONEL A and INCONEL 82 exhibited the highest thermal stability and mechanical properties, while INCONEL 617 and 310 SS filler materials showed weak mechanical properties and thermal stability. It is therefore concluded that for the joints between INCONEL 657 and 310 SS, INCONEL A and INCONEL 82 filler materials offer the best compromises.