Nimonic 80A Alloy Research Articles

Trim cut machining and surface integrity analysis of Nimonic 80A alloy using wire cut EDM

This present work deals with the features of trim cut wire EDM machining of Nimonic 80A in terms of machining parameters, to predict material removal rate (MRR), surface roughness (Ra), wire wear ratio (WWR) and microstructure analysis. Trim cut is performed after rough cut to remove the rough layer deposited after machining due to melting and re-solidification of the eroded metal from workpiece as well as from wire electrode. Taguchi’s design of experiments methodology has been used for planning and designing the experiments. The relative significance of various factors has also been evaluated and analyzed using ANOVA. The results clearly indicate trim cut potential for high surface finish compared to rough cut machining.

Fracture toughness of hard ceramic phases produced on Nimonic 80A-alloy by gas boriding

A hard boride layer was produced on Nimonic 80A-alloy using gas boriding in N2–H2–BCl3 atmosphere. This process was carried out at 920°C (1193K) for 2h. Proposed gas boriding accelerated the diffusion of boron into the surface of workpiece in comparison with other acceptable methods of diffusion boriding. The comparable thickness of boride layer was obtained after considerably shorter duration and at lower temperature. The microstructure, microhardness and fracture toughness were in detail studied. The boride layer consisted of a mixture of hard ceramic phases, i.e. nickel and chromium borides. The fracture toughness of borided layer was measured by microindentation technique using a Vickers diamond indenture under loading 100gf (about 0.981N). The measurements were carried out through a cross-section of the specimen in order to determine the differences in brittleness distribution. The changeable surface percentage of hard ceramic phases (chromium and nickel borides׳ mixtures) strongly influenced the fracture toughness which obtained the values from 0.609 to 4.436MPam1/2.

Influence of laser alloying with boron and niobium on microstructure and properties of Nimonic 80A-alloy

Ni-base superalloys were widely used in aeronautics, chemical and petrochemical industries due to their high corrosion resistance, high creep and rupture strength at high temperature. However, these alloys were not considered for applications in which conditions of appreciable mechanical wear were predominant. The diffusion boriding provided suitable protection against wear. Unfortunately, this process required long duration and high temperature. In this study, instead of the diffusion process, the laser alloying with boron and niobium was used in order to produce the hard and wear resistant layer on Nimonic 80A-alloy. The laser-alloying was carried out as a two-step process. First, the external cylindrical surface of specimens was pre-placed with a paste containing boron and niobium. Then, the pre-placed coating and the thin surface layer of the substrate were re-melted by a laser beam. The high laser beam power (P=1.56kW) and high averaging irradiance (E=49.66kW/cm2) provided the thick laser re-melted zone. The laser-borided layers were significantly thicker (470µm) in comparison with the layers obtained as a consequence of the diffusion boriding. Simultaneously, the high overlapping of multiple laser tracks (86%) caused that the laser-alloyed layer was uniform in respect of the thickness. The produced layer consisted of nickel borides (Ni3B, Ni2B, Ni4B3, NiB), chromium borides (CrB, Cr2B), niobium borides (NbB2, NbB) and Ni-phase. The presence of hard borides caused the increase in microhardness up to 1000 HV in the re-melted zone. However, the measured values were lower than those-characteristic of niobium borides, chromium borides and nickel borides. The presence of the soft Ni-phase in re-melted zone was the reason for such a situation. After laser alloying, the significant increase in abrasive wear resistance was also observed. The mass wear intensity factor, as well as the relative mass loss of the laser-alloyed specimens, was over 10 times smaller in comparison with untreated Nimonic 80A-alloy.

The effects of chemical composition of Nimonic 80A-alloy on the microstructure and properties of gas-borided layer

Ni-based alloys are characterized by great resistance to corrosion and high temperature oxidation. Diffusion boriding is well-known as a process which can improve the wear protection of these alloys. In this paper, continuous gas boronizing in N2–H2–BCl3 atmosphere is proposed for the production of the boride layer on Nimonic®80A-alloy. Microstructural characterization of this layer is studied with the use of an optical microscope, scanning electron microscope, energy-dispersive X-ray microanalysis and X-ray diffraction. The diffusion zone mainly consists of a mixture of nickel and chromium borides, occurring in the compact boride zone. Beneath this zone, there are also some areas in which borides appeared at grain boundaries. However, it is an exceptional situation. In most cases this zone is invisible. The relatively high chromium content in this alloy results in diminished depth of the boride layer in comparison with Inconel®600-alloy containing less chromium. The increase in concentration of chromium causes that grain-boundary diffusion of boron more difficult. Hence, during boriding of Nimonic®80A-alloy volume diffusion plays the more important role, which requires the high activation energy. As a consequence, the zone with borides at grain boundaries can obtain a limited depth or cannot occur. Chromium content also influences some mechanical properties of the layer. Its higher content causes an increase in hardness because of the higher percentage of harder chromium borides in the compact boride zone. The limited iron concentration in this alloy improves the quality of the layer. The microstructure is free of any porosity. It improves the tribological properties of the layer in comparison with Inconel®600-alloy.

Investigation of surface integrity, material removal rate and wire wear ratio for WEDM of Nimonic 80A alloy using GRA and Taguchi method

This paper presents the investigation on surface integrity, material removal rate and wire wear ratio of Nimonic 80A using WEDM process. Taguchi's design of experiments methodology has been used for planning and designing the experiments. All of the input parameters and two factors interactions have been found to be statically significant for their effects on the response of interest. SEM was performed on the machined samples to investigate the effect and microstructure of the samples after machining. A higher pulse-on time setting leads to thicker recast layer. At lower value of pulse-on time and higher value of pulse-off time, the wire deposition on the machined surface is low.

Microstructural mapping in closed die forging process of superalloy Nimonic 80a valve head

Optical microscopy, XRD, TEM and FEM were used to study the microstructral map in the alloy in the upsetting and closed die forging processes. The maps of hardness, grain size, dislocation and the secondary phase γ′ in the upset and closed die forged nimonic 80a alloy valve head were investigated. It is found that the metals flowed from the asymmetric central axis outwards in the upsetting and forging process. The flowing model of metals together with the thermal field led to a heterogeneous distribution of grain size, dislocation configuration and the secondary phase γ′. It is also necessary to mention that the largest grain size, the lowest density of dislocation and secondary γ′ phase only occurred in the transitional region between the valve head and valve stem, which may weaken the strength in this region.

Optimal closed die finish forgings for nimonic80-A alloy using FEM method

Conventional closed die forging, is widely used for manufacture of superalloy parts. Despite recent technological advancements in the area of forging design, empirical and trial-and-error methods are still widely used in forging super alloy materials. This paper investigates the effect of flash thickness and various geometrical forging design parameters including internal and external drafts and internal and external corner radii, on the die cavity filling, forging load and raw material cost when forging Nimonic80-A a superalloy material. A new design methodology based on DOE-designated fractional factorial and FE simulations is proposed to establish optimal closed die finish forging and to find the optimum values of the design parameters. Also a response-surface-methodology (RSM) based method for forging load prediction is presented.

Properties of Nimonic 80A alloy with change in the chemical compositions and Heat Treatment Paths

Properties of Ni-base superalloys of Nimonic 80A alloy system were investigated by the observation of microstructures, precipitates ana hardness as a function of the chemical compositions ana the paths of heat treatment. The higher hardness values showed, the higher Ti/Al ratio among high compositions of Cr and Co element. The lower (Ti+Al) and Fe contents decreased in the same Ti/Al ratio, the higher hardness values showed. This results are considered that coherent deformation was increased with increasing Ti/Al ratio. Hardness showed higher value when Cr contents was <TEX>$18 wt\%$</TEX> less than <TEX>$21wt\%Cr$</TEX>. In <TEX>$3.15 wt\%$</TEX>Co alloy, <TEX>$\gamma'$</TEX> phase was very fine as around 50nm and, its volume fraction and hardness showed the highest value by 2step-aging treatment.

Effect of some sodium salts coatings on the high-temperature oxidation of Nimonic-80A alloy at 1173 K

The effects of some sodium salts, namely Na 2SO 4, NaCl, NaNO 3 and Na 2CO 3 coatings, on the high-temperature oxidation behaviour of Nimonic-80A (N-80A) alloy at 1173 K in a slow current of air are presented. The oxidation kinetics and effects of salt deposition on the N-80A alloy were investigated. The alloy is more severely attacked by NaCl than by Na 2SO 4, due to the formation of volatile chlorides. NaNO 3- and Na 2CO 3-induced alloy seem to be more aggressive than Na 2SO 4 and NaCl due to the evolution of nitrogeneous and CO/CO 2 gases respectively. The scale morphologies were determined on the basis of X-ray diffraction analysis and scanning electron microscopic techniques.

Novel instabilities in the oxidation of a Nimonic alloy when YBaCuO is deposited upon it

When an YBaCuO film is deposited onto a Nimonic 80A alloy substrate using a plasma technique there is extensive inter-reaction. The microstructural and compositional relationships between the layered products in this interfacial scaling process are described using data obtained by conventional edge-on TEM techniques. Our results demonstrate the way in which the segregation of chromium to the YBaCuO overlayer dominates the scaling behaviour that is seen, despite the formation of intermediate layers which would normally have been expected to act as diffusion barriers, and highlight the potential difficulties in making well behaved electrical contacts for this superconductor.

The application of DTA to hot corrosion studies of chromium and nickel powders and nimonic 80A

DTA has been successfully employed to study the hot corrosion behaviour of chromium and nickel powders and Nimonic 80A alloy samples in the presence of corrodants such as NaCl and Na2SO4.

The interaction of dislocation loop and γ' precipitate in nickel based alloys

Abstract The nucleation and growth of interstitial loops during irradiation has a : ontrolling effect on the subsequent swelling behaviour of metals. In nickel based alloys containing ordered γ' precipitate (Ni3Al, Ti), interactions occur between the nucleated loops and γ' particles. This effect has been studied in two nickel based alloys using a High Voltage Electron Microscope. For the case of Nimonic 80A alloy containing 18% volume fraction : gamma;' precipitate, dislocation loop-particle interactions obeyed the developed isotropic elasticity theory.2'3'12 Consequently, rather low dislocation densities were developed and the swelling resistance was high during electron irradiation. In Nimonic 115A alloy, loop nucleation and growth was dependent on the availability of interfacial dislocation surrounding the γ' particles. With regard to the swelling behaviour of γ' hardened alloys, it : s concluded that several mechanisms contribute to make these materials resistant. Coherency strains at the γ' particles reduce the density of : limbing dislocations. The γ' precipitate affects the climb efficiency of the : ucleated dislocations by: pinning the dislocation line, thus introducing a line tension force : hich opposes dislocation climb and reduces swelling; reducing the available volume of material in which dislocation loops : an nucleate and grow.