Showing papers on "Inconel published in 1994"

Oxidation of high-temperature alloys (superalloys) at elevated temperatures in air: I

Abstract: In continuation of previous work, the oxidation behavior of three more alloys, namely UHBA 25L, Sanicro 28, and Inconel 690, was studied at high temperatures (600 to 1200°C). The oxidation kinetics of UHBA 25L and Sanicro 28 followed the parabolic-rate law at 800 and 1000°C. At 600°C oxidation rates were very low, while at 1200° C the parabolic-rate law was initially observed, followed by “breakaway.” Both alloys suffered extensive spalling at all temperatures, despite their high Cr contents of about 25% and 27%, respectively. This is atrributed to significant amounts of Mn present. Sanicro 28, with higher Cr, suffered an early breakaway at 1200°C because of the presence of Mo, which forms a low-melting oxide. Inconel 690 showed mixed behavior at 600 and 800°C, parabolic at 1000°C and cubic at 1200°C. Inconel 690 and Incoloy 800H gave the best overall performance for the range of temperature and exposure time under study. This may be ascribed to the absence of Mo, the presence of small amounts of Ti and Al, and relatively small amount of Mn in these alloys.

Delta Phase in INCONEL 718: Mechanical Properties and Forging Process Requirements

Abstract: To fullfill the Inconel 718 requirements, it is necessary to understand the influence of delta phase on microstructure evolution and on mechanical resistance. Therefore three comprehensive studies have been carried out: a validated delta phase characterization methodology, of the ' effects of (con~entr/emvology) on mecmhaa?cal properties: delta phase delta content affects yield strength and both content and morphology affect creep rupture properties, a validated delta solutionning model predicting content evolution and a study pointing out the parameters of delta particles pinning the grain boundary. Superalloys 718,625,706 and Various Derivatives Edited by B.A. Loria The Minerals, Metals&Materials Society, 1994

Environmental enhancement of creep crack growth in Inconel 718 by oxygen and water vapor

Abstract: Inconel 718 alloy is widely used in high temperature applications. Because of its sensitivity to environmentally enhanced crack growth at high temperatures, its use has been limited to modest temperatures (i.e., below 973 K). To improve its performance and to better predict its service life, it is important to develop a better understanding of the processes of crack growth at high temperatures in this alloy. It has been shown that the creep crack growth rates (CCGR) in air are at least two orders of magnitude faster than those in vacuum or inert environments. CCGR were also found to depend strongly on temperature. Fractographic studies showed that crack growth was intergranular in air and in vacuum with brittle appearing grain boundary separation in air and extensive cavity formation in vacuum. The increased CCGR in air has been attributed to the enhancement by oxygen; principally through enhanced cavity nucleation and growth by high-pressure carbon monoxide/dioxide formed by the reactions of oxygen that diffused into the material with the grain boundary carbides. The appropriateness of this mechanism, however, may be questioned by the absence of cavitation on the crack surfaces produced in air. As such the mechanism for crack growth needs to bemore » re-examined. Because of the presence of moisture in air, the possible influence of hydrogen needs to be considered as well. In this study, preliminary experiments were conducted to examine the process of environmentally enhanced creep crack growth in Inconel 718 alloy in terms of possible mechanisms and rate controlling processes. Creep crack growth experiments were carried out in air, oxygen (from 2.67 to 100 kPa), moist argon (water vapor) and pure argon at temperatures from 873 to 973 K.« less

The effect of grain boundary precipitates on the creep behavior of Inconel 718

Abstract: Inconel 718 has been heat treated to produce materials with microstructures that have the same distribution of γ″-strengthening precipitates within the grains but with grain boundaries that are either clean or have a nearly uniform distribution of 5 μ δ-Ni3Nb precipitates Creep tests on specimens with these two types of microstructures have been conducted in the temperature range of 600–650 °C at constant applied stresses in the range of 745–820 MPa It is observed that the presence of precipitates at grain boundaries increases the creep rate and its stress exponent It is suggested that the presence of precipitates on grain boundaries changes the creep mechanism from volume-diffusion controlled to grain-boundary controlled It is likely that the “constant structure” creep model proposed by Robinsonet al is applicable to the material with precipitates on the grain boundaries

Chemical and Microstructural Aspects of Creep Crack Growth in Inconel 718 Alloy

Abstract: Coordinated surface chemistry and microstructural studies were carried out, in conjunction with crack growth measurements, to better understand environmentally enhanced creep crack growth in Inconel 718 alloy. Creep crack growth response was determined as a function of stress intensity factor (K) and temperature in air, pure oxygen, moist and dry argon. Crack growth was found to be thermally activated, with apparent activation energies of about 287 f 46 kJ/mol in pure oxygen and 19 1 f 77 kJ/mol in moist argon. The growth rates were independent of oxygen pressure from 2.67 to 100 kPa at 973 K, and were about four orders of magnitude faster than those in high purity argon. Fractographic examinations showed predominantly intergranular cracking and the presence of copious amounts of niobium carbides. X-ray photoelectron spectroscopic (XPS) examinations showed that the oxides on the fracture surfaces were enriched in niobium oxide near the crack tip, and with iron and molybdenum away from the tip. Parallel XPS studies showed considerable segregation of niobium at the grain boundaries of polycrystals, and significant enrichment of single crystal alloy surfaces with niobium after heating for 1 h at temperatures above 775 K (with surface concentration in excess of 25 at% at 975 K). These results and observations suggest that niobium has a strong surface affinity in IN718 alloy and may be responsible for the environmental enhancement of creep crack growth at high temperatures. The oxidation and decomposition of niobium carbides as a source for segregated niobium and as the rate controlling process for crack growth are discussed. Niobium as a source for embrittment of other nickel-base superalloys is considered. Acknowledgement: Work supported by the Materials Research Group (MRG) Program of the Division of Materials Research, National Science Foundation, under Grant No. DMR-9102093. Material provided by General Electric Aircraft Engines (GEAE), Evendale, OH. Superalloys 718, 625,706 and Various Dcrivntivcs Edited by E.A. Loria The Minerals, Metals & Materials Society, 1994

Chip formation analysis in high speed machining of a nickel base superalloy with silicon carbide whisker-reinforced alumina

Abstract: High speed turning tests were performed on a heat resistant alloy (Inconel 718), using SiC (20%) whiskers reinforced ceramic tools. The main aims of these tests were the following: (1) mapping cutting speed-feed and machined volume in order to find a region free from tool breakage; (2) analysing tool wear and chip formation mechanisms; and (3) from the experimental results modelling analytically both chip formation processes and tool wear mechanism. Tool and chip were observed at the SEM and EDAX semiquantitative analyses were carried out to evaluate micro-welds on the chip and areas of welded or scattered material over the tool. Micro-hardness mapping was carried out on the longitudinal cross-section of the chips to monitor its dependence by process parameters. Variable wear mechanisms along the tool-chip contact length that were attributed to variations in plastic deformation energy were observed. There variations were analytically modelled in orthogonal cutting conditions. Longitudinal and tranverse shear planes into the chip were also observed. The causes and the mechanisms of wear, chip formation and the hardening of work material were deduced. The presence of whiskers pull out mechanisms due to temperature effects in the tool-chip interface were also observed.

HVOF particle flow field characteristics

Abstract: The effect of varying fuel/oxygen mixture ratio and combustion chamber pressure on the sprayed particle temperature and velocity in the supersonic, high pressure HVOF process is examined. Particle temperature is shown to correlate to the fuel/oxygen mixture and particle velocity is a function of combustion chamber pressure. inconel 718 coatings were fabricated at the same conditions as the particle measurements. High particle velocities resulted in high micro hardness. Deposition efficiency is a function of both particle temperature and velocity. The optimal deposition efficiency occurs at an average particle temperature which is below the melting point of Inconel 718 and the lowest velocity investigated. Oxide content is a function of substrate temperature and not entrained air or excess combustion oxygen.

Solidification Structures of Inconel 718 with Microalloying Elements

Abstract: The microalloying effects on the solidification structure of Inconel 7 18 were examined by means of differential thermal analysis, optical microscopy and scanning electron microscopy, in order to elucidate the mechanism of the macrosegregation in the alloy. The solidification and precipitation sequence of Inconel 718 was found to be characterized by the following five reactions; (1) the proeutectic y reaction at about 1360°C (2) the y+MC eutectic reaction at about 1290°C (3) the y+Laves phase eutectic reaction at about 1160°C (4) the 6 phase precipitation reaction in the y phase at about 1145”C, and (5) the y ’ and y ” precipitation reaction in the y phase at about 1000°C. By combining this result with the analysis of the solute distributions in the ESR ingots, the mechanism for the occurrence of the freckles was proposed in Inconel7 18. Superalloys 718,625,706 and Various Derivatives Edited by E.A. Loria The Minerals, Metals & Materials Society, 1994

Deformation and Damage Mechanisms in Inconel 718 Superalloy

Abstract: The deformation and damage mechanisms in wrought, double-aged, Inconel718 superalloy (AMS 5663D) tested under monotonic tensile strains of 2% and lo%, fully-reversed fatigue, and tensile strain (2% or 10%) followed by fully-reversed fatigue conditions were investigated by examining the microstructures of representative specimens. All tests were conducted in air at room temperature. The specimens were sectioned and examined by transmission electron microscopy to reveal typical microstructures as well as the active deformation and damage mechanisms. Specific mechanistic features addressed include the type of slip, interaction of dislocations with y”, y’ and the carbides (precipitated during solidification and the subsequent heat treatment received by the superalloy), twinning, and microcracking. In all cases the microstructure of the as-received superalloy is employed as the reference to establish the nature and distribution of the secondary phases before the superalloy is subjected to different types of mechanical loading. Results of the investigation and comparisons of the mechanisms of deformation and damage observed under monotonic tensile strain, fully-reversed fatigue, and tensile strain followed by fully-reversed fatigue in Inconel 718 superalloy are reported. Superalloys 718,625,706 and Various Der~at~ves Edited by EA. Loria The Minerals, Metals & Materials Society, 1994

Metallurgical Factors Influencing the Machinability of Inconel 718

Abstract: Because of the large volume of Inconel 718 used by the aerospace and power generation industries and the high percentage of metal removed to machine complex component geometries; understanding and improving the machining characteristics of Inconel 718 would result in substantial cost savings. While progress has been made in developing improved tool materials and machining processes, a detailed understanding of the metallurgical factors influencing the machinability of Inconel 718 has not been generated. This paper presents work conducted by United Technologies Research Center and Pratt & Whitney Division establishing the relationship between the metallurgy and machinability of Inconel7 18. Factors such as fabrication technique (investment cast, cast + HIP and wrought), hardness, grain size and carbon content were all found to influence machinability. In addition to presenting the relationship between metallurgy and machinability of Inconel 718, suggestions are made in order to improve Inconel 718 machining characteristics and reduce fabrication costs. Superalloys 718,625,706 and Various Derivatives Edited by E.A. Loria The Minerals, Metals &Materials Society, 1994

The Time-Temperature-Transformation Behavior of Alloy 706

Abstract: The isothermal time-temperature-transformation behavior of wrought, triple melted (VIM-ESR-VAR) and homogenized INCONEL@ alloy 706 was characterized by X-ray diffraction, SEM/EDX, and optical metallographic techniques. Microstructural features, including phase compositions, morphologies, and crystal structures are discussed. Alloy 706 is an agehardenable superalloy strengthened by 7’ and y U precipitation at lower temperatures. The propensityfor the alloyto form q at higher temperatures distinguishes alloy 706T-T-T behavior from that of the well documented INCONEL@ alloy 718. The effect of differing Nb-Ti-Al ratios and Fe content on the physical metallurgy of Nb-Containing superalloys is discussed.

INVESTIGATION ON HIGH THERMAL STABILITY AND CREEP RESISTANT MODIFIED INCONEL-718 WITH COMBINED PRECIPITATION OF gamma'' AND gamma'

Abstract: One of the recent advances in INCONEL 718 development is intended to find a modified Alloy 718 with high thermal structure stability and creep resistance to be used beyond the ceiling temperature of 650°C. Twelve heats of modified Alloy 718 with chemical composition variation were designed to study the effect of Al, Ti, Nb and MO on yN and y’ precipitation morphology and on microstructure stability and high temperature mechanical properties above 650°C. Detail TEM and high resolution electron microscopy (HREM) study has shown that associated precipitation and compact morphology of yU and y’ in modified 718 Alloys characterize with higher thermal stability than separate precipitation of yN and y’ in conventional INCONEL 718. Creep rupture life depends not only on Nb f Al -jTi content but also on coefficient k = 2/(Al +Ti/Nb)‘+ (Al/Ti)* l Nb. Long time aging stability study at 650, 700 and 750°C for 5000 hrs has shown that the modified Alloy 718 with associated precipitation and compact morphology of y” and y’ expresses excellent thermal structural stability. * This research project in supported by China National Natural Science Foundation under the contract NO: 58971944 Superalloys 718,625,706 and Various Derivatives Edited by E.A. Loria The Minerals, Metals&Materials Society, 1994

Effect of P, S, B and Si on the Solidification Segregation of Inconel 718 Alloy

Abstract: The effect of P,S,B and Si on the solidification process of Inconel 718 has been studied in laboratory tests. It essentialy revealed the tendency of P,S,B and Si to greatly aggravate the solidification of Inconel 718 . A low segregation Inconel 718 ingot developed based on the laboratory study and a conventional Inconel 718 ingot were parrallel melted in industrial scale for segregation comparison, which confirmed the laboratory results. Superalloys 718,625,706 and Various Derivatives Edited by E.A. Loria The Minerals, Metals &Materials Society, 1994

77 to 1200 K tensile properties of several wrought superalloys after long-term 1093 K heat treatment in air and vacuum

Abstract: The 77 to 1200 K tensile properties of approximately 1.3 mm thick wrought sheet Co-base Haynes alloy 188 and Ni-base Haynes alloy 230 and Inconel 617 have been measured after heat treatment in air and vacuum for periods up to 22,500 h at 1093 K. Significant changes in structure were produced by prior exposures, including precipitation of second phases and, in the case of heat treatment in air, oxide scale and surface-connected grain boundary pits/oxides, as deep as 50 to 70 µm, in all three superalloys. Due to the geometry of the experiment, the vacuum-exposed samples were protected from loss of volatile elements by evaporation; hence, such specimens were simply given 1093 K anneals in an innocuous environment, which produced very little surface attack. Compared to the properties of as-received alloys, prior exposure tended to reduce both the yield strength and ultimate tensile strength, with the greatest reductions at 77 and 298 K. The most dramatic effect of heat treatment was found in the low-temperature residual tensile elongation, where decreases from 40 to 5% at 77 K were found. Ductility is the only property that was found to have a consistent dependency on environment, with air exposure always yielding less tensile elongation than vacuum exposure.

High Temperature Deformation of INCONEL 718 Castings

Abstract: Computational models of solidification have proven to be very valuable to foundrymen in optimizing their casting processes. Current computer models can predict feeding characteristics, macroporosity formation, and even the development of grain structure in some alloys. However, stress related defects like hot tearing continue to plague foundries. Present research is attempting to incorporate stress analysis into the computational framework to better understand hot-tearing and related defects during casting. Proper mechanical constitutive relationships for the alloys of interest must be determined for the very high temperature deformation adjacent to and including the mushy zone of the casting. This paper presents the effects of temperature and strain rate on the compression response of Inconel7 18 castings. The experimental data is compared with other investigations and potential constitutive relationships are reviewed. The observed mechanical behavior is discussed with respect to the underlying microstructural features and appropriate deformation mechanisms.

AES and SAM studies of oxide formation on Inconel 600 at high temperatures

Abstract: Characterization of the oxide formed on a Ni-based alloy (Inconel 600) at high temperatures has been carried out using AES and SAM combined with ion-etched depth profiling. The oxidation experiment was done at 1000 o C, in atmospheric air and under mild (H 2 /H 2 O) oxidation conditions. In air, the resulting surface is highly inhomogeneous, featuring large Ni-rich islands on top of a continuous Cr-rich oxide layer. When the oxygen partial pressure (H 2 /H 2 O) was lowered, the Ni-rich layer was not formed

Microfractographic aspects of stress corrosion cracking of Inconel 600 in a pressurized water reactor environment

Abstract: Stress corrosion cracking (SCC) tests are performed on Inconel 600 in a pressurized water reactor environment in order to obtain a better knowledge of the damage mechanisms. Particular attention is paid to the analysis of the fracture surface which is known to be generally integranular. A pseudointergranular microcracking is, however, reported for the first time. It is interpreted as a signature of a possible SCC mechanism and related to a recent model of interaction between corrosion and plasticity.

Performance enhancement of Inconel alloy X-750 during creep via optimal solution treatment and control of morphology of grain boundary carbide

Abstract: The effect of solution treatment temperature on both the morphology of grain boundary carbides and the creep rupture behaviour of Inconel alloy X-750 has been investigated. Solution treatment at 1050°C led to precipitation of Ti/Nb carbide along grain boundaries, and as a result the formation of chromium carbide during subsequent aging treatment was considerably affected. This led to changes in the morphology of the grain boundary carbide and reduction in the width of ‘clear’ zone. This modification in the morphology of grain boundary carbide reduced the creep resistance of the alloy, leading to a reduction in rupture lifetimes, whereas strains tofracture were unaffected.MST/1981

Prediction of rupture lifetime in thin sections of a nickel base superalloy

Abstract: The prediction of rupture lifetime of a component can be based on the data generated from round, flat and tubular specimens. An investigation on the influence of specimen geometry on the creep behavior of Inconel alloy X-750 showed that the tubular specimen exhibited better creep performance when rupture lifetime data were compared on the basis of section size. However, the time to rupture data of all three specimen geometries merged together when compared on the basis of the volume to surface area ratio (V/S) indicating that there is a definite relationship between V/S and the rupture lifetime. This analysis is now extended in another gamma prime strengthened nickel base superalloy. The chemical composition of the alloy in wt%, is as follows: 0.07C-0.66Si-0.07Cu-0.79Fe-19.1Cr-2.35Ti-1.52Al and remainder nickel. Analysis of the rupture lifetime data of a gamma prime strengthened nickel base superalloy shows that time-to-rupture is controlled by the volume to surface area ratio. Furthermore, the normalization of the volume to surface area ratio with the grain size shows that the time-to-rupture data of two grain sizes, 55 and 250 [mu]m, can be represented by a single curve.

Clad steel plate excellent in corrosion resistance and toughness at low temperature

Abstract: PURPOSE:To simultaneously secure the corrosion resistance of a high alloy and the strength, toughness, and adhesion of a base material by providing a cast clad steel plate where both sides of surface layer are composed of stainless steel or Ni alloy and an inner layer is composed of low alloy steel. CONSTITUTION:Both sides of surface layer are composed of a high alloy excellent in corrosion resistance, that is, austenitic, ferritic, martensitic, or dual phase stainless steel or nickel alloy, such as 'Incoloy(R)' 825 and 'Inconel(R)' 625. As a low alloy steel used as inner layer, a material with high strength and high toughness as to have a strength of >=X52 (APT Standard) and a toughness at low temp. of 2vE-30>=10kgf-m and vTrs<=-60 deg.C is used. Transition layers having thickness 2 to 10% of steel plate thickness exist in the boundaries of the multilayer structure in the order of A, B, A, by which the occurrence of peeling and crack in the boundaries can be prevented. Further, the components of the material used as inner layer are regulated to respectively specified values.

Tensile properties of Haynes alloy 230 and Inconel 617 after long exposures to LiF-22CaF2 and vacuum at 1093 K

Abstract: As a part of a study of a space-based thermal energy storage system utilizing the latent heat of fusion of the eutectic salt LiF-20CaF2 (mole%), the two wrought Ni-base superalloys Haynes alloy 230 and Inconel 617 were subjected to molten salt, its vapor, and vacuum for periods as long as 10,000 h at 1093 K. Following exposure, the microstructures were characterized, and samples from each superalloy were tensile tested between 77 and 1200 K. Neither the structure nor mechanical properties revealed evidence for additional degradation due to exposures to the salt. Although some loss in tensile properties was noted, particularly at 77 K, this reduction could be ascribed to the influence of simple aging at 1093 K.

The Vacuum Arc Remelting of Large Diameter Alloy 706

Abstract: INCONEL alloy 706@ is a precipitation hardenable alloy that provides high mechanical strength in combination with good fabricability. It was developed more than 20 years ago from INCONEL alloy 718. The chemistry of this alloy allows the production of large, triple melted, high quality ingots. This paper describes the effects of VAR melt rate and electrode-to-crucible fill ratio on INCONEL alloy 706 ingot quality.