Showing papers on "Inconel published in 2005"

Residual stresses in LENS® components using neutron diffraction and contour method

Abstract: During manufacturing of components by laser engineered net shaping (LENS®), a solid freeform fabrication process, the introduction of residual stresses causes deformation or in the worst case, cracking. The origin is attributed to thermal transients encountered during solidification. In the absence of reliable predictive models for the residual stresses, measurements are necessary. Residual stresses were measured in LENS® samples of 316 stainless steel and Inconel 718 having simple geometrical shapes by both neutron diffraction and the contour methods. The results by the two methods are compared and discussed in the context of the growth direction during the LENS® process. Surprisingly, the residual stresses are practically uni-axial, with high stresses in the growth direction.

The effect of cooling rate on the solidification of INCONEL 718

Abstract: The superalloy INCONEL 718 (IN718) is a commonly used material in aerospace and turbine components. The advantage of this type of material with sluggish precipitation-hardening kinetics is that IN718 is readily weldable. Both wrought and cast parts are used and welded together. While the alloy has been studied previously, new production processes such as laser treatment demand better knowledge of the solidification process in IN718, especially at high cooling rates. In this investigation, the solidification process was studied over a wide range of cooling rates by three different experimental techniques: differential thermal analysis (DTA), mirror furnace (MF), and levitation casting. The solidification sequence and the reaction temperatures were identified. The microstructure and the change in growth morphology were also studied. Segregation measurements were performed, and the distribution of Nb was analyzed in detail for the different types of samples, because of its strong impact on the solidification sequence and microstructure. New observations are that the latent heat decreases and the effective partition coefficient increases with increasing cooling rate. The diffusion rate also seems to be enhanced in the first part of primary solidified dendrites. It is suggested that the new observations can be explained by an increased number of lattice defects formed in the solid as the cooling rate increases.

Effect of the δ phase on the hot deformation behavior of Inconel 718

Abstract: Hot compression tests at different temperatures and strain rates were performed on Inconel 718 solution treated as well as solution treated and then aged at 900 °C for 1–24 h in order to investigate the effect of the δ phase on hot deformation behavior. A hyperbolic-sine Arrhenius-type equation was used to characterize the dependence of the peak stress on deformation temperature and strain rate. In the case of Inconel 718 with a large amount of the δ phase, the apparent activation energy was determined to be 458 kJ/mol, which was slightly higher than the activation energy of 443 kJ/mol for solution treated Inconel 718. The γ″/γ′ phases present in Inconel 718 prior to hot deformation enhanced the peak stress, but did not affect the peak strain. The δ phase present in Inconel 718 not only decreased the peak strain and the peak stress, but also promoted the flow softening after the peak stress.

Development of nickel‐titanium graded composition components

Abstract: Purpose – Three layer‐additive manufacturing methods were evaluated to producing nickel‐titanium graded composition material. One potential application is fabrication of attachment clips that join thermal protection systems to launch vehicle structure. Thermal gradients during flight generate excessive bending and shear loads that limit the service lifetime of the Inconel clips currently used. It is envisioned that a graded composition component could be tailored to reduce the stress concentrations.Design/methodology/approach – Deposits with nearly continuous composition grade were built from Ti‐6‐4 and Inconel 718 powder using laser direct metal deposition. Layered deposits were produced by flat wire welding from Ti‐6‐4 and Inconel 718 wire. Ultrasonic consolidation was used to produce layered deposits from pure nickel and commercially pure titanium foils. Microstructure, bond line morphology, chemical composition, and reaction phases were characterized.Findings – All three manufacturing methods require ...

Microstructure and mechanical properties of Inconel 718 electron beam welds

Abstract: Bead on plate, full penetration electron beam welds were produced in 2 mm thickness sheets of Inconel 718 in the solution treated condition. Welds were subjected to an aging treatment with and without post-weld solution treatment. Weld microstructures, high temperature tensile properties and stress rupture properties were evaluated. The as welded fusion zone showed a considerable amount of interdendritic niobium segregation and brittle intermetallic Laves phase. The tensile and stress rupture properties of the welds after post-weld aging treatment were found to be inferior in relation to the base metal. Post-weld solution treatment at 980°C was found to result in partial dissolution of Laves phase, some reduction in niobium segregation and the formation of δ phase needles around the Laves particles. The use of 980°C solution treatment was found to improve the weld properties to some extent, although not to the level of the base metal. The reasons for this behaviour are discussed, correlating micro...

Investigation of electron-beam welding in wrought Inconel 706—experimental and numerical analysis

Abstract: Electron-beam welding (EBW) is commonly employed in the aeroengine industry for the welding of high integrity components, fabricated from high-strength superalloys. For such applications, it is important to predict distortions and residual stresses induced by the process. Melt run trials have been carried out on nickel-base superalloy Inconel 706 plates using the EBW technique in order to analyse the effects of welding parameters on geometrical characteristics and microstructure of the bead. Butt-welded plates have been then investigated by means of tensile tests, microstructural analysis, and X-ray diffraction measurements. A finite element model of the process has been set up using an uncoupled thermal–mechanical analysis. The heat source was modelled using a superimposition of a spherical and a conical shape heat source with Gaussian power density distribution in order to reproduce the nail shape of the fusion zone (FZ). The parameters of the source were chosen so that the model would match with experimentally determined weld pool shape and temperatures, measured with thermocouples. Subsequently, the thermal analysis was used to drive the non-linear mechanical analysis. The predicted residual stresses were then compared with X-ray diffraction measurements. It was found that the correct thermal and residual stresses prediction is influenced by the shape of the fusion zone, the highest thermal tensile stress arising under the nailhead of the fusion zone where microfissuring can be observed.

Finish Machining of Nickel-Base Inconel 718 Alloy with Coated Carbide Tool under Conventional and High-Pressure Coolant Supplies

Abstract: Single-point turning of Inconel 718 alloy with commercially available Physical Vapour Deposition (PVD)-coated carbide tools under conventional and high-pressure coolant supplies up to 20.3 MPa was carried out. Tool life, surface roughness (Ra), tool wear, and component forces were recorded and analyzed. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. The highest improvement in tool life (349%) was achieved when machining with 11 MPa coolant supply pressure at higher speed conditions of 60 m · min−1. Machining with coolant pressures in excess of 11 MPa at cutting speeds up to 40 m · min−1 lowered tool life more than when machining under conventional coolant flow at a feed rate of 0.1 mm · rev−1. This suggests that there is a critical coolant pressure under which the cutting tools performed better under high-pressure coolant supplies. Cutting forces increased with increasing cutting speed due probably to reac...

Alloys 625 and 725: trends in properties and applications

Abstract: INCONEL® alloy 625 (UNS N06625) has been widely used for over 50 years in the marine and petroleum industries for applications requiring high strength, fracture toughness, fabricability and resistance to corrosion. By increasing the titanium content of the alloy in the presence of its content of niobium, an alloy that can be significantly strengthened by heat treatment is created. By the precipitation of various secondary phases in an austenitic matrix, INCONEL alloy 725 (UNS N07725) offers the high strength of alloy 718 along with the corrosion resistance of alloy 625. The metallurgy of alloy 725 is discussed along with information about its properties, fabrication, and applications.

A study of the heat-affected zone (HAZ) of an Inconel 718 sheet welded with electron-beam welding (EBW)

Abstract: In this paper the heat-affected zones (HAZs) of the Inconel 718 sheets welded with electron-beam welding (EBW) were studied by using hardness measurement, metallographic etch and electrochemically potentiostatic etch methods. Before EBW, the Inconel 718 sheets were pretreated in three different conditions: as-received, solution- and precipitation-treatments. The results show that there is an obvious difference in the dimension of the widths of HAZs evaluated by the methods. The width, ca. 1.5 mm, of the HAZ in solution-pretreated weld can be estimated based on the variation of its hardness distribution curve. But the HAZs in as-received and precipitation-pretreated welds were difficult to detect from their hardness distribution curves. After metallographic etching, the HAZs in the welds were very hard to observe with optical microscope, but those with a width within 100 μm in solution- and precipitation-pretreated welds, except in as-received weld, can be observed with scanning electron microscope (SEM). The HAZ with a width ca. 300 μm of each weld can be revealed by using anodically potentiostatic etching in 3.5 wt.% NaCl solution due to different corrosion rates among the HAZ, fusion zone and base metal in the weld. The above-mentioned behavior of HAZs evaluated by different methods was discussed in detail in this work.

Porosity reduction in Nd–YAG laser welding of stainless steel and inconel alloy by using a pulsed wave

Abstract: This study investigates the influence of the Nd?YAG laser power wave mode on the porosity and mechanical properties of SUS 304L and inconel 690 weldments. Initially, a rectangular laser power waveform is specified. The output is then progressively changed from a pulsed wave mode to a continuous wave mode by reducing the value of ?P (?P = Pp?Pb, where Pp is the peak power and Pb is the base power) to zero. Bead-on-plate (BOP) and butt welding are performed at a constant mean output power (1.7?kW). The BOP results demonstrate that the depth/width (D/W) ratio of both materials increases with ?P and attains a maximum value when full penetration just occurs. The D/W ratio and the travel speed for full penetration are higher for SUS 304L than for inconel 690. In butt-welds of inconel 690 and SUS 304L, the porosity ratio decreases from 7.1% to 0.5% and from 2.1% to 0.5%, respectively, as ?P increases from 0 to 2780?W. Therefore, the tensile strength and percentage elongation are enhanced significantly in inconel 690. The degree of porosity reduction in inconel 690 exceeds that of SUS 304L. This suggests that the viscosity of the molten inconel 690 metal is higher than that of SUS 304L. Consequently, the effect of porosity reduction due to the increase in molten metal fluidity caused by increasing ?P is greater for inconel 690 than for SUS 304L.

Inhomogeneous dislocation structure in fatigued INCONEL 713 LC superalloy at room and elevated temperatures

Abstract: The dislocations arrangement was studied using transmission electron microscopy in specimens of polycrystalline INCONEL 713 LC superalloy cyclically strained up to failure with constant total strain amplitudes at temperatures 300, 773, 973 and 1073 K. Planar dislocation arrangements in the form of bands parallel to the {1 1 1} planes were observed in specimens cycled at all the temperatures. The bands showed up as thin slabs of high dislocation density cutting both the γ channels and γ′ precipitates. Ladder-like bands were observed at room temperature.

Validation of three-dimensional finite element model for electron beam welding of Inconel 718

Abstract: A three-dimensional finite element model for the prediction of the distortion and residual stresses induced during electron beam welding is described. The model is validated by butt welding experiments on two Inconel 718 plates. A particular effort is made to determine a good model for the heat input. A combined conical and double ellipsoid heat source is used to model the deep penetration characteristic of the electron beam and this source is calibrated using the results from a separate thermodynamic simulation, using the ELSIM finite difference code. Parallel computation is used to reduce the overall simulation time in the coupled thermomechanical simulation of welding. The agreement between calculations and experiments is good with respect to the residual stresses. Measured and computed deformations agree qualitatively although they differ in magnitude.

Influence of high-temperature exposure on the microstructure and mechanical properties of dissimilar metal welds between modified 9Cr-1Mo steel and alloy 800

Abstract: Transition joints between ferritic steel and austenitic stainless steel are commonly encountered in high-temperature components of power plants. Service failures in these are known to occur as a result, mainly, of thermal stresses due to expansion coefficient differentials. In order to mitigate the problem, a trimetallic configuration involving an intermediate piece of a material such as Alloy 800 between the ferritic and austenitic steels has been suggested. In our work, modified 9Cr-1Mo steel and 316LN stainless steel are used as the ferritic and austenitic components and the thermal behavior of the joints between modified 9Cr-1Mo steel and Alloy 800 is described in this article. The joints, made using the nickel-base filler material INCONEL 82/182 (INCONEL 82 for the root pass by gas-tungsten arc welding and INCONEL 182 for the filler passes by shielded-metal arc welding), were aged at 625 °C for periods up to 5000 hours. The microstructural changes occurring in the weld metal as well as at the interfaces with the two parent materials are characterized in detail. Results of across-the-weld hardness surveys and cross-weld tension tests and weld metal Charpy impact tests are correlated with the structural changes observed. Principally, the results show that (1) the tendency for carbon to diffuse from the ferritic steel into the weld metal is much less pronounced than when 2.25Cr-1Mo steel is used as the ferritic part; and (2) intermetallic precipitation occurs in the weld metal for aging durations longer than 2000 hours, but the weld metal toughness still remains adequate in terms of the relevant specification.

The effect of nb, ti, al on precipitation and strengthening behavior of 718 type superalloys

Abstract: Inconel 718 characterizes with unique mechanical properties and has wild application in different high temperature industries. However, the ceiling temperature for Alloy 718 is 650 because of ℃ the instability of main strengthening phase γ″-Ni3(Nb,Ti,Al). At high temperatures the metastable γ″ changes for stable phase δ-Ni3Nb with large size and plate- like morphology. In result of that Alloy 718 looses structure stability and strengthening effect. Recently, many researchers have studied the stability of Alloy 718 and try to develop modified 718 Alloys to be used beyond 650 . The basic idea of this paper is to raise the stability of ℃ γ″ and γ′ strengthening phases in the following ways: raising the solution temperature of γ″ and γ′, retarding the γ″ phase change for δ-Ni3Nb and changing the precipitation behavior of γ″/γ′ phase. The experimental heats were prepared for this study in variation of Nb, Ti, Al and the atomic ratio among them on the base chemical composition of Alloy 718. The precipitated phase γ″ and γ′ behavior was studied in detail by means of SEM and TEM and the weight fraction of γ″+γ′ phases was exactly determined by electrolytic isolation and followed by micro-chemical analyses. The mechanical properties including hardness, tensile properties and stress rupture for several heats were also tested. － The structure of a new developed 718 type Alloy Allvac ® 718 Plus TM has been also adopted for comparison. A detail discussion has been conducted for 718 type superalloys in structure stability and strengthening effect both.

Method to restore an airfoil leading edge

Abstract: The present invention provides methods and apparatus to restore a blade leading edge (17) on a gas turbine engine component such as an airfoil (10) of a turbine blisk. The method utilizes welding image technology and power control systems in order to provide effective welding with superalloy materials such as Inconel 713 and Inconel 625. The method includes machining away a damaged leading edge (17) and providing a repaired region through successive depositions of superalloy powder filler through laser fusion welding. Deposition material is added until the repaired region exceeds the original dimensions of the airfoil (10). The airfoil is then machined and finished to return it to original airfoil dimensions.