Showing papers on "Inconel published in 2004"

Control of Laves phase in Inconel 718 GTA welds with current pulsing

Abstract: The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.

Workpiece Surface Integrity and Tool Life Issues When Turning Inconel 718™ Nickel Based Superalloy

Abstract: Inconel 718 is one of a family of nickel-based superalloys which are used extensively in the aerospace industry in the hot sections of gas turbine engines. The literature detailing the effects of varying operating parameters on tool life when machining nickel based superalloys is comprehensive, however, relatively little of this data refers to their effects on machined workpiece surface integrity. Greater knowledge of the effects of operating parameters on surface integrity is critical to the acceptance of new cutting tool materials, tool geometries, and strategies, especially by the aerospace industry. The article initially reviews prior work on the machinability and surface integrity achieved when turning Inconel 718. Following on from this a series of experiments evaluating the effects of varying cutting tool material, geometry, and operating parameters are detailed.

Plasma Assisted Milling of Heat-Resistant Superalloys

Abstract: The term Thermal Enhanced Machining refers to a conventional cutting process in which an external energy source is used to enhance the chip-generation mechanism. The work presented here analyzes the basic aspects and the experimental results obtained when applying an assisting plasma jet to the milling process. This process, known as PAM (Plasma Assisted Milling) has been applied to the machining of three very low machinability materials: a Ni-base alloy (Inconel 718), a Co-base alloy (Haynes 25), (both belonging to the group of the heat-resistant alloys) and the Ti-base alloy Ti6Al4V. The study focuses on two major topics. First, the efficiency of the milling operation in terms of cutting speed, feed, axial and radial depths of cut and the plasma operating parameters has been addressed. Second, a study on the alterations of the metallurgical structure and the properties of materials after the PAM has also been performed. The process conditions for the above-mentioned Ni-base and Co-base alloys are detailed. The study under these conditions has shown an excellent performance of the whisker reinforced ceramic tools. In fact, cutting speeds as high as 970 m/min and large radial and axial depths of cuts are possible, driving to a cost-effective machining process. The absence of changes in the metallurgical structure of the alloys after applying the PAM process is also addressed. Therefore, it can be stated that this is a feasible approach to the optimization of the machining process of heat-resistant alloys. Finally, the results obtained in the PAM of Ti6Al4V are detailed. In this experimentation, a certain level of degradation was observed in the microstructure of the alloy when undergoing the PAM process, therefore the use of this technique is not recommended for this material.

Effect of gap size and process parameters on diffusion brazing of Inconel 738

Abstract: The influence of gap size and brazing parameters (temperature and time), on the microstructure and properties of diffusion-brazed Inconel 738 (IN-738) superalloy, was investigated using two commercial brazing alloys, Amdry 'DF3' and Nicrobraz 150. The residual liquid present at brazing temperature was observed to transform on cooling into centreline eutectic constituents in 'NB 150' brazement while three different dispersed intermetallic phases were observed in the 'DF3' joint. The volume fraction of the second phases increased with gap size in both 'NB 150' and 'DF3' brazements. In addition to the centreline eutectic constituents, nickel and chromium rich borides were observed at the melt back zone in samples brazed below the Ni3B eutectic temperature of 1093°C, and above this temperature only chromium rich borides were observed. Joints containing the second phase intermetallics in 'NB 150' and 'DF3' brazed materials were found to exhibit tensile properties inferior to that of the base alloy.

Short term precipitation kinetics of delta phase in strain free Inconel* 718 alloy

Abstract: Understanding and control of short term precipitation of delta phase in Inconel 718 alloy is of importance as it is used to control grain growth during forging. This precipitation has been ...

The oxidation behavior of the new nickel-based superalloy Inconel 740 with and without Na2SO4 deposit

Abstract: The new nickel-based superalloy, Inconel 740, with and without Na2SO4 deposit were oxidized in still air between 850 and 1000 °C to investigate the oxidation and hot corrosion behavior by means of XRD, SEM and EDS. The kinetic curves of the alloy oxidized at 950 °C without Na2SO4 deposit and at 850 °C with Na2SO4 deposit obeyed the parabolic law, whereas, the uniform parabolic growth behavior of oxide was not followed at 1000 °C without Na2SO4 deposit and at 950 °C with Na2SO4 deposit due to oxide spallation at 1000 °C and the evaporation of Na2CrO4 melt at 950 °C, respectively. The oxide scales consisted of Cr2O3, (Ni,Co)Cr2O4, TiO2, Al2O3 and internal oxides at all temperatures. The internal sulfidation took place due to the existence of Na2SO4 deposit. The complex layered structure of oxide scales was in favor of the resistance to oxidation. The deposition of Na2SO4 accelerated the oxidation of the alloy and the degradation of corrosion resistance of alloy with Na2SO4 deposit was attributed to the dissolution of Cr2O3 induced by basic fluxing in molten Na2SO4.

Effect of solution treatment temperature on microstructure and mechanical properties of hot isostatically pressed superalloy Inconel* 718

Abstract: Hot isostatically pressed superalloy Inconel 718 heat treated as per the standard schedule of aerospace material specification (AMS) 5662 (solution treatment at 980°C/1 h/water quenching followed by two step aging at 720°C/8 h/ furnace cooling to 620°C/8 h/air cooling to room temperature) has shown yield strength (YS) and ultimate tensile strength (UTS) comparable to that of wrought heat treated alloy, but it had poor ductility and inferior stress rupture properties To find an appropriate heat treatment to improve these properties, the influence of solution treatment temperature on the structure and properties of the alloy has been studied The results show that although YS and UTS decrease with increasing solution treatment temperature, considerable improvement occurs in the ductility of the unaged alloy For the aged alloy, an increase in solution treatment temperature resulted in only a marginal improvement in strength, but the 650°C ductility and stress rupture life were improved significantl

Development of Protective Coatings for High-Temperature Metallic Materials

Abstract: Metallic material systems with potential for high-temperature operations are critical for many land-based and space-based systems. Advanced alloys with improved elevated temperature properties and/or reduced densities offer improved structural ef"icieney and longer service life compared to more conventional alloys. However, in extreme operating environments, these alloys require coatings for environmental protection and thermal control. We discuss some results from a program to develop ultrathin, lightweight, protective coatings applied via sol-gel techniques for some emerging high-temperature alloys. The coatings were designed to reduce oxidation, increase emittance, and reduce the catalytic efficiency for recombination of dissociated hot-gas species for the candidate materials. The alloys considered in this study include PM1000 (an oxide dispersion strengthened Ni-based alloy), 602CA Ni-based alloy, and a gamma titanium aluminide alloy. Inconel 617, a Ni-based alloy, was included as a reference. Microstructural analysis and oxidation weight gain results indicated that the coatings significantly reduced oxidation damage during extended high-temperature exposures for these alloys. In addition, one coating system was shown to improve the emittance of Inconel 617. A substantial reduction in the recombination of atomic nitrogen and oxygen at the surface of Inconel 617 substrates in a hot flowing airstream was also observed.

Liquation of various phases in HAZ during welding of cast Inconel* 738LC

Abstract: The weld heat affected zone (HAZ) of tungsten inert gas (TIG) welded cast IN 738 superalloy has been examined HAZ microfissuring was observed in alloy welded in solution treated and overaged conditions Closer and careful microstructural examination by analytical scanning electron microscopy revealed the liquation of boride, sulphocarbide, MC type carbides, γ′ precipitate particles and γ-γ′ eutectic, which were present in the preweld alloy, and the formation of resolidified constituents along the microfissured HAZ grain boundaries, thereby indicating that HAZ cracking in this alloy involves liquation cracking Liquation of these phases, as well as characteristics of the intergranular liquid film contributing to the low resistance to HAZ cracking of the alloy have been examined and are discussed

Laser powder fusion repair of Z-notches with inconel 713 powder

Abstract: A method is provided for repairing Z-notch wear surfaces on low pressure gas turbine engine turbine blades. The method is directed to turbine blades made of superalloy Inconel 713. Powdered Inconel 713 is welded to the Z-notch wear surface by directing an Nd:YAG laser beam upon the material. The laser beam is focused and traverses the wear surface in a stich-like pattern. The method allows Inconel 713 turbine blades to be repaired with the same material in a manner that does not generate cracking in the matrix material.

An Overview of Long Duration Sodium Heat Pipe Tests

Abstract: High temperature heat pipes are being evaluated for use in energy conversion applications such as fuel cells, gas turbine re-combustors, and Stirling cycle heat sources; with the resurgence of space nuclear power, additional applications include reactor heat removal elements and radiator elements Long operating life and reliable performance are critical requirements for these applications Accordingly long-term materials compatibility is being evaluated through the use of high temperature life test heat pipes Thermacore International, Inc, has carried out several sodium heat pipe life tests to establish long term operating reliability Four sodium heat pipes have recently demonstrated favorable materials compatibility and heat transport characteristics at high operating temperatures in air over long time periods A 3l6L stainless steel heat pipe with a sintered porous nickel wick structure and an integral brazed cartridge heater has successfully operated at 650 to 700 C for over 115,000 hours without signs of failure A second 3l6L stainless steel heat pipe with a specially-designed Inconel 60 I rupture disk and a sintered nickel powder wick has demonstrated over 83,000 hours at 600 to 650 C with similar success A representative one-tenth segment Stirling Space Power Converter heat pipe with an Inconel 718 envelope and a stainless steel screen wick has operated for over 41 ,000 hours at nearly 700 0c A hybrid (ie gas-fired and solar) heat pipe with a Haynes 230 envelope and a sintered porous nickel wick structure was operated for about 20,000 hours at nearly 700 C without signs of degradation These life test results collectively have demonstrated the potential for high temperature heat pipes to serve as reliable energy conversion system components for power applications that require long operating lifetime with high reliability, Detailed design specifications, operating hi story, and test results are described for each of these sodium heat pipes Lessons learned and future life test plans are also discussed

Effect of process parameters on grain structure formation during VAR of INCONEL alloy 718

Abstract: The development of grain structure during Vacuum Arc Remelting (VAR) of INCONEL1 alloy 718, a nickel-based superalloy, is complex depending both on compositional variations and a range of process parameters. A multiscale model is presented which combines a macroscopic solution of the heat transfer, fluid flow and electromagnetism with a mesoscopic model of grain nucleation and growth. The model was used to investigate the influence of variations in process control parameters upon the macroscopic molten pool size and shape, together with the predicted grain structure. Simulations of structures produced for variations in melt rate, arc power and arc focus (both thermal and electrical) were compared with observations from instrumented and characterized plant-trials for steady state melting conditions; good agreement was achieved.

Investigation of the crack growth behavior of Inconel 718 by high temperature Moiré interferometry

Abstract: The effect of environment on creep crack growth behaviors of many nickel-base superalloys is a well-documented and serious problem. Stress accelerated grain boundary oxidation (SAGBO) is accepted as the prior mechanism of the environment effect. In this paper, the crack growth behavior of Inconel 718 was investigated by high temperature moire interferometry (HTMI), coupled with SEM/EDAX. Based on the results obtained from this research, the mechanism is proposed to be caused by the segregated Nb, which couples with the oxygen diffusing into the grain boundaries in front of the crack tip and forms an NbO layer on the grain boundaries, thereby causing the brittle elastic cracking behavior.

Interfacial reactions between lithium silicate glass-ceramics and Ni-based superalloys and the effect of heat treatment at elevated temperatures

Abstract: Two lithium silicate glasses (S- and BPS-glass) were sealed to four different Ni-based superalloys (Inconel 600, Inconel 718, Haynes 230, and Hastelloy C-276) and the effects of long-term heating at 700–900°C on the chemical, microstructural, and mechanical properties of sealed interfaces were studied. The presence of a small amount of ZnO in the BPS-glass leads to the formation of a thin interfacial second phase layer and a less rough alloy interface compared to the ZnO-free S-glass. Inconel 718 was found to be the most reactive of the alloys, with Cr and Nb diffusing into the glass and forming a coarse glass-ceramic microstructure at the interface. Heat treatment of all the reaction assemblies at 900°C for 100 h in air resulted in degradation of the seals and their spontaneous failure. Heat treatments at 700 or 800°C did not cause any interfacial coarsening in BPS sealed to Inconel 600, Haynes 230, and Hastelloy C-276 alloys and did not alter the bond strength of Haynes 230 bars, sealed with a thin layer of BPS-glass, demonstrating the potential of these material combinations for applications up to 800°C.

Evaluation of the performance of different nano-ceramic tool grades when machining nickel-base, inconel 718, alloy

Abstract: High-speed machining of aerospace alloys can be enhanced by the use of advanced cutting tool materials such as nano-grain size ceramics that exhibit improved physical and mechanical properties than their micron grain counterparts. The performance of recently developed nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions. The tools were rejected mainly due to wear on the tool nose. It is also evident that chemical compositions of the tool materials played significant role in their failure. The alumina base ceramics performed better than the silicon nitride base ceramics. Severe abrasion wear was observed on both rake and flank faces of the cutting tools while cutting forces increased with increasing cutting speed when machining with the silicon nitride base nano-ceramic tools. This is probably due to the lower superplastic flow temperature of the nitride base nano-ceramics. The alumina base ceramics are more susceptible to chipping at the cutting edge than the silicon nitride base ceramics despite their higher edge toughness.

Fabrication and characterisation of silicon carbide/superalloy interfaces

Abstract: Both silicon carbide ceramic (sintered SiC or reaction-bonded Si-SiC) and Inconel 600 superalloy (Ni 72 Cr 16 Fe 8 in wt.%) are promising structural materials for high temperature application because of their excellent mechanical properties and good high temperature corrosion resistance. In this study, the reaction-bond silicon carbide (RBSC) was joined to an Inconel 600 (Ni 72 Cr 16 Fe 8 in wt.%) superalloy using the diffusion bonding method at temperatures from 900 to 1080 °C. The interfacial reaction between the RBSC and superalloy was investigated using optical and scanning electron microscopy (SEM), coupled with energy dispersive X-ray analysis (EDX) and wavelength dispersive spectroscopy (WDS). The reaction products were also studied using X-ray diffraction technique. The mechanical properties of the joints were examined using shear testing. Experimental results showed that the interfacial reaction products at 900 and 950 °C were various silicides with some voids formed in the RBSC. As the bonding temperature increased to 1000 °C, the superalloy/RBSC reactions become more intensive, although some pores in the RBSC were filled by the reaction products. With the bonding temperature increasing to 1080 °C, a thin layer of CrSi 2 was formed at superalloy/SiC interface without formation of any pores in the RBSC. The shear strength of this joint was measured as 126 MPa.

Corrosion Behavior of Candidate Alloys for Supercritical Water Reactors

Abstract: The corrosion and stress corrosion cracking behavior of metallic cladding and other core internal structures is critical to the success of the Generation IV Supercritical Water-cooled Reactors (SCWR). The eventual materials selected will be chosen based on the combined corrosion, stress-corrosion, mechanical performance, and radiation stability properties. Among the materials being considered are austenitic stainless steels, ferritic/martensitic steels, and nickel-base alloys. This paper reports initial studies on the corrosion performance of the candidate alloys 316 austenitic stainless steel, Inconel 718, and Zircaloy-2, all exposed to supercritical water at 300-500 deg. C in a corrosion loop at the University of Wisconsin. Long-term corrosion performance of AISI 347, also a candidate austenitic steel, has also been examined by sectioning samples from a component that was exposed for a period of about 30 years in supercritical water at the Genoa 3 Supercritical Water fossil power plant located in Genoa, Wisconsin. (authors)