Showing papers on "Inconel published in 2009"

Studies of Standard Heat Treatment Effects on Microstructure and Mechanical Properties of Laser Net Shape Manufactured INCONEL 718

Abstract: Laser net shape manufacturing (LNSM) is a laser cladding/deposition based technology, which can fabricate and repair near-net-shape high-performance components directly from metal powders. Characterizing mechanical properties of the laser net shape manufactured components is prerequisite to the applications of LNSM in aircraft engine industrial productions. Nickel-based superalloys such as INCONEL 718 are the most commonly used metal materials in aircraft engine high-performance components. In this study, the laser deposition process is optimized through a set of designed experiments to reduce the porosity to less than 0.03 pct. It is found that the use of plasma rotating electrode processed (PREP) powder and a high energy input level greater than 80 J/mm are necessary conditions to minimize the porosity. Material microstructure and tensile properties of laser-deposited INCONEL 718 are studied and compared under heat treatment conditions of as deposited, direct aged, solution treatment and aging (STA), and full homogenization followed by STA. Tensile test results showed that the direct age heat treatment produces the highest tensile strength equivalent to the wrought material, which is followed by the STA-treated and the homogenization-treated tensile strengths, while the ductility exhibits the reverse trend. Finally, failure modes of the tensile specimens were analyzed with fractography.

Aging effects on the microstructure and creep behavior of Inconel 718 superalloy

Abstract: Standard heat treatment (HT1) for Inconel 718 superalloy is solutionizing at 1095 °C, 1 h/AC, then aging at 955 °C, 1 h/AC + 720 °C, 8 h/FC 57 K/h to 620 °C, 8 h/AC. In order to study the aging effects of the δ phase, two more conditions HT2 (no aging condition 955 °C) and HT3 (955 °C, 3.5 h/AC) were studied in this research. Lever arm creep tests were performed at 650 °C under constant stress 625 MPa. Since HT2 produces no δ phase, the stress rupture life, creep elongation to failure and steady state creep rate of HT2 are largest among these three aging conditions. However, increasing the 955 °C aging time, the stress rupture life, creep elongation and steady state creep rate raise slightly as compared to HT1, because platelet δ phase is more uniformly nucleated and more direction oriented at grain boundaries. Fractographs show ductile fracture patterns mostly and, small portion of inter-granular fracture in the HT2 specimens. Generally only inter-granular fracture is observed in the other two cases of HT1 and HT3. Besides twinning and dislocation mechanisms, grain boundary sliding is also activated, so that creep elongation to failure of HT2 specimens could reach 5.6%, whereas 1% for the other two schemes.

Investigation of the effect of process parameters on the formation and characteristics of recast layer in wire-EDM of Inconel 718

Abstract: Inconel 718 is a high nickel content superalloy possessing high strength at elevated temperatures and resistance to oxidation and corrosion. The non-traditional manufacturing process of wire-electrical discharge machining (EDM) possesses many advantages over traditional machining during the manufacture of Inconel 718 parts. However, certain detrimental effects are also present and are due in large part to the formation of the recast layer. An experimental investigation was conducted to determine the main EDM parameters which contribute to recast layer formation in Inconel 718. It was found that average recast layer thickness increased primarily with energy per spark, peak discharge current, and current pulse duration. Over the range of parameters tested, the recast layer was observed to be between 5 and 9 μm in average thickness, although highly variable in nature. The recast material was found to possess in-plane tensile residual stresses, as well as lower hardness and elastic modulus than the bulk material.

Machinability investigation of Inconel 718 in high-speed turning

Abstract: Superalloy Inconel 718 is widely used for many industrial applications due to its unique properties. However, machinability of the material is considered to be poor due to its inherent characteristics. The machinability studies of Inconel 718 had been carried out by earlier researchers mostly at low or medium cutting speed. Machinability indices used in such cases have the characteristics such as cutting force, surface roughness, cutting temperature, etc. In the case of high-speed machining of Inconel 718, machinability indices such as chip compression ratio (ζ), shear angle (Ф), surface integrity, and chip analysis are of prime importance. Most of the researchers have not given due consideration to these vital machinability indices necessary for understanding of high-speed cutting of Inconel 718. In this work, an experimental investigation was carried out to understand the behavior of superalloy Inconel 718 when machined with cemented tungsten carbide (K20) insert tool. The result and analysis of this work indicated that the above-mentioned machinability indices are important and necessary to assess the machinability of Inconel 718 material effectively during high-speed machining.

Effect of pre- and post-weld heat treatment on metallurgical and tensile properties of Inconel 718 alloy butt joints welded using 4 kW Nd:YAG laser

Abstract: The effects of pre- and post-weld heat treatments on the butt joint quality of 3.18-mm thick Inconel 718 alloy were studied using a 4 kW continuous wave Nd:YAG laser system and 0.89-mm filler wire with the composition of the parent metal. Two pre-weld conditions, i.e., solution treated, or solution treated and aged, were investigated. The welds were then characterized in the as-welded condition and after two post-weld heat treatments: (i) aged, or (ii) solution treated and aged. The welding quality was evaluated in terms of joint geometries, defects, microstructure, hardness, and tensile properties. HAZ liquation cracking is frequently observed in the laser welded Inconel 718 alloy. Inconel 718 alloy can be welded in pre-weld solution treated, or solution treated and aged conditions using high power Nd:YAG laser. Post-weld aging treatment is enough to strengthen the welds and thus post-weld solution treatment is not necessary for strength recovery.

Improvement of mechanical properties of Inconel 718 electron beam welds—influence of welding techniques and postweld heat treatment

Abstract: Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle, and elliptical) in controlling Nb segregation, Laves formation, and tensile behavior of Inconel 718 electron beam welds were studied. Effects of various postweld heat treatments on tensile behavior were compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous finer Laves in the interdendritic regions compared to that of unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited better mechanical properties than unoscillated beam welds in both solution-treated and aged and directly aged conditions.

Mechanical properties of thermal barrier coatings after isothermal oxidation. Depth sensing indentation analysis

Abstract: Thermal barrier coatings (TBC) are extensively used to protect metallic components in applications where the operating conditions include aggressive environment at high temperatures. Isothermal oxidation degrades the performance of these coatings, so this work analyses the mechanical properties (Young's modulus, E, and hardness, H) of TBC and its evolution after thermal exposure in air. ZrO2(Y2O3) top coat and NiCrAlY bond coating were air plasma sprayed onto an Inconel 600 Ni base alloy. The TBC were isothermally oxidized in air at 950 °C and 1050 °C for 72, 144 and 336 h. Depth sensing indentation tests were carried out on the ceramic coating to evaluate E and H in the as-sprayed materials and after isothermal oxidation. An approach based on multiple tests at different loads was used to determine size independent apparent E an H. These mechanical properties, measured perpendicular to the surface, clearly decreased after isothermal oxidation as a consequence of microcracking within the ceramic coating.

Development of Microstructure and Mechanical Properties in Laser-FSW Hybrid Welded Inconel 600

Abstract: The present study was carried out to evaluate the microstructure and mechanical properties of Inconel 600 subjected to laser-assisted hybrid friction-stir welding (HFSW). In this process, friction-stir welding (FSW) was performed at a constant speed (400 rpm) while a 2-kW YAG laser preheated the material just in front of the rotating tool. We found that HFSW was 1.5 times faster than conventional FSW. In addition, analysis of the grain boundary character distribution by electron back scattered diffraction (EBSD) showed that the increased welding speed and dynamic grain recrystallization caused the average grain size to decrease from 5.5 μm (in the base material) to 3.2 μm (in the stir zone of the welded specimen). This grain refinement led to 30% and 10% improvements in microhardness and tensile strength, respectively.

Effect of Machining Parameters and Cutting Edge Geometry on Surface Integrity when Drilling and Hole Making in Inconel 718

Abstract: Superalloys such as Inconel 718 have high strength at elevated temperatures, which make them attractive towards various applications in aerospace industry. However, these materials are considered difficult to machine materials. The state of a workpiece surface after machining is definitely affected by cutting parameters, such as cutting speed, feed rates, drill types and drill geometries. Drilling tests, at different spindle-speed, feed rates, drills and point angles of drill, were conducted in order to investigate the effect of the above parameters on the quality of machined holes and surface integrity of Inconel 718. The quality of machined holes was evaluated in terms of the geometrical accuracy and burr formation. Surface integrity involved the aspect of surface roughness, metallurgical alterations and microhardness of the substrate of the hole surface. High hole quality was observed even at holes produced using worn tools, in relation to dimensions, surface roughness and burr height. However, microhardness measurements and microstructural analysis of work-piece showed significant microstructural changes related with a loss of mechanical properties. In general the cutting parameters have significant effects on the surface quality and surface integrity when drilling Inconel 718 using uncoated carbide drill.

Continuous drive friction welding of Inconel 718 and EN24 dissimilar metal combination

Abstract: Nickel based superalloy Inconel 718 and low alloy steel EN24 are welded by continuous drive friction welding in annealed condition and then post-weld heat treated (PWHT). The welds exhibit low strength and high toughness in the as welded condition. Post-weld heat treatment applicable to either Inconel 718 or EN24, led to reduction in toughness and increase in strength. Toughness degradation after PWHT as per Inconel 718 was predominant. The observed trends in mechanical properties are explained on the basis of observed microstructure, fracture behaviour, electron probe microanalysis and X-ray diffraction.

Experimental Investigations Into the Carbide Cracking Phenomenon on Inconel 718 Superalloy Material

Abstract: Inconel 718 (IN718) presents significant challenges in machining due to its high strength properties at high temperature, attributable to the hard niobium and titanium carbide phases. Machined surfaces (oblique turning) at conventional conditions of speeds and feeds, typically show a tendency of those carbides to crack, drag and smear under the machining stresses and deformation. Such behavior can severely debilitate the fatigue strength of the material, and cause accelerated damage. This paper describes the experimental investigations as well as the qualitative and quantitative studies undertaken to study and mitigate the impact of process variables and tool geometry parameters on the carbide surface cracking phenomenon. SEM observations showed the feed rate (or chip thickness), nose radius, and insert grade-edge geometry to have significant influences on the behavior of these surface carbides.Copyright © 2009 by ASME

Inhibition of the corrosion of nickel and its alloys by natural clove oil

Abstract: The corrosion behavior of nickel, Inconel 600, and Inconel 690 in different concentrations of HCl solutions and its inhibition by clove oil was studied using potentiostatic polarization measurements. As the acid concentration increases, the rate of corrosion increases, indicating that HCl accelerates the dissolution of nickel and its alloys. The inhibition efficiency of the clove oil was found to increase with increase of its concentration. The inhibitive action of this oil was discussed in view of adsorption onto the metal surface. The adsorbed layer acts as a barrier between the metal surface and aggressive solution, leading to a decrease in corrosion rate. The adsorption process follows Langmuir adsorption isotherms. It was found that the clove oil provides good protection to nickel and its alloys against pitting corrosion in chloride-containing solution using potentiodynamic anodic polarization techniques.

Residual stresses on inconel 718 turbine shaft samples after turning

Abstract: Results of X-ray residual stress measurements on Inconel 718 turbine shaft samples are here proposed. The paper presents part of the EU STREP project VERDI activity, where the aim was to supply those who numerically simulate machining process with an experimental database of proved reliability. Measurements were planned on a set of samples machined with different levels of cutting speed and feed rate. Due attention was given to the assessment of the uncertainty of experimental results. A database of surface residual stress values and depth profiles is presented with the estimated uncertainty both on stress and depth values. The stress proved to be always tensile at the surface and compressive below the surface. Higher cutting speed and feed rates produce higher surface tensile stresses but the trends are different for the two measurement directions.

Ni-based superalloy as a potential tool material for thixoforming of steels

Abstract: Semisolid processing, already a well established manufacturing route for the production of intricate, thin walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand complex load profiles and relatively higher forming temperatures for thousands of forming cycles for this near-net shape process to be attractive for steels on an industrial scale. The potential of a Ni-based superalloy, Inconel 617, reported to exhibit superior thermal fatigue resistance in demanding tooling applications, was investigated. The response to thermal cycling of this alloy at high temperatures was compared with that of X38CrMoV5 hot work tool steel widely used in the manufacture of conventional forging dies. The favourable thermophysical properties of the latter were completely negated by its limited temper resistance, while the Inconel 617 alloy responded to thermal cycling by the usual heat cracking mechanism.

Optimization of high speed turning parameters of superalloy Inconel 718 material using Taguchi technique

Abstract: Superalloy, Inconel 718 is widely used in sophisticated applications due to its unique properties desired for the engineering applications. Due to its peculiar characteristics machining of Superalloy Inconel 718 is difficult and costly. The present work is an attempt to make use of Taguchi optimization technique to optimize cutting parameters during high speed turning of Inconel 718 using tungsten carbide cutting tool. Taguchi method is a powerful design of experiments (DOE) tool for engineering optimization of a process. It is an important tool to identify the critical parameters and predict optimal settings for each process parameter. Analysis of variance (ANOVA) is used to study the effect of process parameters and establish correlation among the cutting speed, feed and depth of cut with respect to the major machinability factor, cutting forces such as cutting force and feed force. Validations of the modeled equations are proved to be well within the agreement with the experimental data.