Showing papers on "Inconel published in 2011"

Microstructure and residual stress of laser rapid formed Inconel 718 nickel-base superalloy

Abstract: The microstructure and residual stress of laser rapid formed (LRFed) nickel-base superalloy Inconel 718 was investigated. The as-deposited microstructure of an LRFed Inconel 718 alloy is composed of columnar dendrites growing epitaxially along the deposition direction, and the columnar dendrites transformed to unevenly distributed equiaxed grains after annealing treatment at high temperature. Residual stress evaluation in microstructure scale by Vickers micro-indentation method indicates that the residual thermal stress is unevenly distributed in the LRFed sample, and it has a significant effect on the recrystallization during solution annealing treatment. The residual stress is introduced by rapid heating and cooling during laser rapid forming. There is an alternative distribution between high residual stress regions and low residual stress regions, within a single deposited layer, resulting in a similar distribution of recrystallized grain size.

Microstructure and mechanical properties of nickel based superalloy IN718 produced by rapid prototyping with electron beam melting (EBM)

Abstract: A nickel alloy of a composition similar to that of the nickel based superalloy Inconel alloy 718 (IN718) was produced with the electron beam melting (EBM) process developed by Arcam AB. The microstructures of the as processed and heat treated material are similar to that of conventionally produced IN718, except that the EBM material showed some porosity and the δ phase did not dissolve during the solution heat treatment because the temperature of 1000°C apparently was too low. Mechanical testing of the layer structured material, parallel and perpendicular to the built layers, revealed sufficient strength in both directions. However, it showed only limited elongation when tested perpendicular to the built layers due to local agglomerations of pores. Otherwise, data for the hardness, Young’s modulus, 0·2% yield tensile strength and ultimate tensile strength match those recommended for IN718.

Effect of serrated grain boundaries on the creep property of Inconel 718 superalloy

Abstract: This article presents an investigation of the effect of serrated grain boundaries on the high temperature creep behaviour of IN718 superalloy. XRD, DSC, SEM and TEM have been conducted to study the microstructures; experimental results have shown that the morphology of grain boundaries can be a function of heat treatment conditions. In addition, creep tests have been performed on samples with and without serrated grain boundaries under 650 °C/625 MPa. In conclusions, the formation of δ phase during the heat treatment can influence the morphology of grain boundaries, and an improvement of 400 h creep rupture life has been attributed to the serrated grain boundaries.

Analysis of Machining Characteristics in Additive Mixed Electric Discharge Machining of Nickel-Based Super Alloy Inconel 718

Abstract: Additive mixed electric discharge machining (AEDM) is a recent innovation for enhancing the capabilities of electrical discharge machining process. The objective of present research work is to study the influence of operating process input parameters on machining characteristics of nickel-based super alloy (Inconel 718) in aluminium AEDM with copper electrode. The effectiveness of AEDM process on Inconel is evaluated in terms of material removal rate (MRR), surface roughness (SR), and wear ratio (WR) using one variable at a time (OVAT) approach. It is found experimentally that particle concentration and size significantly affect machining efficiency. Aluminium powder (325 mesh size) particles of concentration 6 g/l in AEDM produce maximum machining rate, minimum SR, and 4 g/l produces minimum WR within experimental conditions.

Laser Direct Metal Deposition Technology and Microstructure and Composition Segregation of Inconel 718 Superalloy

Abstract: Multilayer of laser direct metal deposition (DMD) was prepared by depositing a gas atomized pre-alloyed powder with a composition close to Inconel 718 alloy on Inconel 718 high temperature alloy substrate. The effects of the DMD parameters on the build-up rate and the structure of the deposited layer were studied. The laser DMD sample was further processed by a solution treatment. The microstructure and property of the laser DMD zone before and after heat treatment were investigated as well. The results show that the laser parameters of actual laser power of 650 W, scanning speed of 5. 8 mm/s, beam diameter of 1 mm, powder feed rate of 6. 45 g/min, with a corresponding specific energy of 90–130 J/mm2, can be recommended as optimum parameters for high build-up rate of Inconel 718 alloy. Under the condition of optimized parameters, a directional solidification microstructure was obtained and the average distance between the columnar crystals was 5–10 μm. The microcomposition segregation was found between the columnar crystal trunk and columnar crystal. The elements of Nb, Mo, Ti concentrated in the columnar crystal trunk. After the heat treatment, the segregation was greatly minimized, and the segregation ratios were close to 1. The hardness of the laser deposited layer did not show obvious difference along the height of the layer either for the as-deposited layer or for the heat treated layer. However, the microhardness of the laser DMD zone after heat treatment was obviously higher than that after the as-deposited treatment. During the heat treatment process, some Nb- and Mo-rich phases precipitated and strengthened DMD layer.

Tensile deformation and fracture characteristics of delta-processed Inconel 718 alloy at elevated temperature

Abstract: Three specimens with different initial δ phase contents have been used to study the tensile deformation and fracture characteristics of the delta-processed Inconel 718 alloy at elevated temperatures by tensile tests at 950 °C. The results indicated that the tensile stress–strain curves of the three specimens were the elastic-uniform plastic curves, and there were two deformation processes during the uniform plastic deformation stage of the delta-processed specimens. The strain hardening exponent in the first deformation process was higher than that in the second process, and the value of the strain hardening exponent increased as the content of δ phase increased. In addition, the plasticity of the specimen at elevated temperatures decreased as the content of δ phase increased. However, the fracture mechanisms for all the specimens were all microvoid coalescence ductile fracture, and the δ phase and carbide were the nucleuses for the formation of micropores. The elongation for the specimen with 8.21% pre-precipitated δ phase was still as high as 80%. Thus, delta-processed Inconel 718 alloy presented excellent high-temperature plasticity.

Quantifying the vibrothermographic effect

Abstract: Vibrothermography, also known as Sonic IR and thermosonics, is a method for finding cracks through thermal imaging of vibration-induced crack heating. Due to large experimental variability and equipment which has, up to now, yielded mostly qualitative results, little data has been available to help quantify the vibrothermographic effect. This paper quantitatively evaluates the relationship between vibrothermographic crack heating, crack size, and vibrational stress in a series of tests on 63 specimens each of Ti-6-4 titanium and Inconel 718 at three different sites with different equipments. Test specimens are excited in a resonant mode. Infrared cameras record the crack heating, and vibrational stress is evaluated from the known vibrational mode shape combined with vibrational velocities measured using a laser vibrometer. Crack heating increases both with crack length and dynamic vibrational stress level. Data from all three sites gives similar probability of detection (POD) curves. The relationship of crack heating to crack size and vibrational stress will provide a means in the future to predict crack detectability based on vibration measurements.

Dynamic mechanical behaviour and dislocation substructure evolution of Inconel 718 over wide temperature range

Abstract: A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behaviour and microstructural evolution of Inconel 718 at strain rates ranging from 1000 to 5000 s −1 and temperatures between −150 and 550 °C. The results show that the flow stress increases with an increasing strain rate or a reducing temperature. The strain rate effect is particularly pronounced at strain rates greater than 3000 s −1 and a deformation temperature of −150 °C. A significant thermal softening effect occurs at temperatures between −150 and 25 °C. The microstructural observations reveal that the strengthening effect in deformed Inconel 718 alloy is a result primarily of dislocation multiplication. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. By contrast, the dislocation cell size decreases with increasing strain rate, but increases with increasing temperature. It is shown that the correlation between the flow stress, the dislocation density and the dislocation cell size is well described by the Bailey–Hirsch constitutive equations.

Hold-time effect on the thermo-mechanical fatigue crack growth behaviour of Inconel 718

Abstract: In-phase TMF crack growth testing with different lengths of the hold time at the maximum temperature of 550 °C has been conducted on Inconel 718 specimens Focus has been on establishing a method f

Variations in overall- and phase-hardness of a new Ni-based superalloy during isothermal aging

Abstract: Influence of isothermal aging on the microstructures and hardness in Inconel 740, a relatively new Ni-based superalloy, was explored using the specimens aged at 810 °C for different times. As aging time increased, the size of gamma prime precipitates continuously increased while their fraction remained almost constant. Nanoindentation experiments revealed that the overall hardness increased till the aging time of 100 h and then decreased with the aging time. Estimation of phase hardness by applying a simple rule-of-mixture showed that, with aging time, the hardness of gamma matrix decreased whereas that of gamma prime precipitates increased. The aging-induced strength change is discussed in terms of the possible contributions of precipitation strengthening and solid solution strengthening.

The Microstructural Evolution of Inconel Alloy 740 During Solution Treatment, Aging, and Exposure at 760 C

Abstract: In this study, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy. During double solution heat treatment, carbon is liberated from the dissolution of MC carbides during the first solution treatment at 1150 °C, and fine MC carbides are precipitated on gamma grain boundaries during the second solution treatment at 1120 °C. Due to the concurrent decrease in carbon solubility and the increase in the contribution of grain boundary diffusion at lower temperatures, the MC carbides on the gamma grain boundaries provide a localized carbon reservoir that aids in M23C6 carbide precipitation on gamma grain boundaries during exposure at 760 °C. The γ′ phase, which is the key strengthening phase in alloy 740, is incorporated into the alloy microstructure during aging at 850 °C. The main source of microstructural instability observed during exposure at 760 °C was the coarsening of the γ′ phase.

Study of Inconel 718 weldability using MIG CMT process

Abstract: This work investigates the weldability of Inconel 718 using the metal inert gas (MIG) welding process called ‘cold metal transfer’. This arc welding process is reported for working with a lower heat input compared to other arc processes. The consequences are less base metal impaired, low deformation and low residual stress level in assembly. In order to check these abilities, metallographic, texture, chemical and residual stress analyses have been carried out. Results show that MIG cold metal transfer has good properties for the welding of Inconel 718 inasmuch as no defect has been detected and a lower level of residual stresses has been introduced in metal compared to classic MIG.

Combined Butt Joint Welding and Post Weld Heat Treatment Simulation Using SYSWELD and ABAQUS

Abstract: Due to increases in computational power, the finite-element (FE) method is now widely used to predict the thermal, material, and mechanical effects of welding. Welding simulations can provide important information about component distortions and residual stresses. This facilitates a reduction in lead-time and cost associated with the process planning. Moreover, welding is generally performed in combination with other manufacturing processes such as stress relief heat treatment. This article presents a simple method where welding and post weld heat treatment operations are combined using an uncoupled plasticity—creep model. Two FE codes, welding-function-specific SYSWELD and the general-purpose FE package, ABAQUS, were used to perform butt joint welding and post weld heat treatment simulations of two Inconel 718 plates. The predicted results obtained from the two FE codes, such as thermal histories, residual stresses, nodal displacements, and stress relaxation, are compared. Based on the results presented,...

Microstructural and Mechanical Evaluation of a Cu-Based Active Braze Alloy to Join Silicon Nitride Ceramics

Abstract: Self-joining of St. Gobain Si3N4 (NT-154) using a ductile Cu-Al-Si-Ti active braze (Cu-ABA) was demonstrated. A reaction zone approx.2.5-3.5 microns thick) developed at the interface after 30 min brazing at 1317 K. The interface was enriched in Ti and Si. The room temperature compressive shear strengths of Si3N4/Si3N4 and Inconel/Inconel joints (the latter created to access baseline data for use with the proposed Si3N4/Inconel joints) were 140+/-49MPa and 207+/-12MPa, respectively. High-temperature shear tests were performed at 1023K and 1073 K, and the strength of the Si3N4/Si3N4 and Inconel/Inconel joints were determined. The joints were metallurgically well-bonded for temperatures above 2/3 of the braze solidus. Scanning and transmission electron microscopy studies revealed a fine grain microstructure in the reaction layer, and large grains in the inner part of the joint with interfaces being crack-free. The observed formation of Ti5Si3 and AlN at the joint interface during brazing is discussed.

Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures

Abstract: Turbine disks are of large importance to turbine designers as theyare exposed to hot environment and subjected to high loads. Inorder to analyze such components with respect to fatigue crackinitiat ...

Electrochemical Impedance Spectroscopy Investigation of Alloy Inconel 718 in Molten Salts at High Temperature

Abstract: and natural ash (collected in a power plant). Different experimental runs were made attempting to establish the material behavior. The results showed that the corrosion process was controlled by activation and in some cases by diffusion. The aggressiveness of the salts increased with temperature, as indicated for the corrosion rates values derived. On the whole, the corrosion rates were somewhat similar at the lowest test temperatures. However at 588°C the 80V

Performance of PVD-Coated Carbide Tools When Turning Inconel 718 in Dry Machining

Abstract: Inconel 718 has found its niche in many industries, owing to its unique properties such as high oxidation resistance and corrosion resistance even at very high temperatures. Coated carbide tool wit...