Inconel 738LC Research Articles

Comparative Study of Microstructure and High Temperature Low Cycle Fatigue Behaviour of Nickel Base Superalloys Inconel 713LC and MAR-M247

The present work is focused on the study of microstructure and low cycle fatigue behavior of the first generation nickel-base superalloy IN 713LC (low carbon) and its promising second generation successor MAR-M247 HIP (hot isostatic pressing) at 900 °C. Microstructure of both alloys was studied by means of scanning electron microscopy (SEM). The microstructure of both materials is characterized by dendritic grains, carbides and casting defects. Size and morphology of precipitates and casting defects were evaluated. Fractographic observations have been made with the aim to reveal the fatigue crack initiation place and relation to the casting defects and material microstructure. Low cycle fatigue tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of both materials were obtained. Cyclic stress-strain curve of MAR M247 is shifted approximately to 120 MPa higher stress amplitudes in comparison with IN 713LC. Significantly higher fatigue life of MAR-M247 has been observed in Basquin representation. On the other hand IN 713LC shows prolonged lifetime compared with MAR-M247 in the Coffin-Manson representation. Results obtained from high temperature low cycle fatigue tests are discussed.

Influence of Cutting Conditions on Profile Milling of INCONEL 738LC Alloy

This article presents particular results from a long term research focused on machining of INCONEL alloys. As a representative of this group of material INCONEL 738LC is selected and the article presents results of different experiments conducted. The behavior of material under different conditions was evaluated with focus to define cutting condition that can be recommended as suitable cutting conditions for profile milling of material. Basic problems of profile milling are exposed with focus to the respective material. Several machining experiments are explained and archived results are discussed. Effect of tool geometry and geometrical constraints and relations during profile milling is defined. Tool wear and cutting forces were measured and evaluated. The final conclusion is a recommendation for successful machining of given material.

Material Analysis of Nickel Superalloy for Military Technology

In the aerospace industry, the nickel-based superalloys are often used due to their ability to withstand extreme conditions. They find their use particularly as turbine blades in jet engines. An important example of this type of superalloy is INCONEL. This construction material must meet a wide range of complex requirements with regard to its properties and technological and operational characteristics that are required by the heavy duty in extreme conditions.The INCONEL Superalloys represent multicomponent and multiphase materials with their complex alloying base and structure with distinct dendritic segregations. Their long life and reliability in operation are directly related to the microstructure, or to its stability in a long-term operational application, respectively.The presented work deals with the evaluation of microstructural parameters at two variants of cast superalloy INCONEL 713LC, applying the light microscopy and electron microscopy, including the fractographic analysis.

Thermal fatigue behaviour of Al–Si coated Inconel 713 LC

The effect of single and two-stage Si modified aluminide coatings on thermal fatigue behaviour of nickel based superalloy Inconel 713LC was examined. Specimens were loaded under test condition of heating to 1100°C followed by cooling to25°C. The experimental results showed that the coatings increased thermal fatigue resistance in both crack initiation and propagation stages. The comparison of the crack growth rates indicated that both coatings imparted resistance to the crack lengthening. However, the effect of single stage coating on the fatigue resistance was superior compared with that of two-stage coating. Through scanning electron microscopy observation, it was found that the width of γ′ denuded zone was the main reason in the control of crack growth in all specimens.

Degradation of Aluminide Coatings Deposited on Nickel Superalloys

Cyclic oxidation and hot corrosion behaviours of aluminide and Si modified aluminide diffusion coatings deposited on two superalloys are compared in the paper. Samples based on cast nickel superalloys with and without protective coatings were studied under cyclic oxidation and hot corrosion conditions. The main goal of the paper was to compare the cyclic oxidation and hot corrosion resistance of protective aluminide coatings deposited on two types of nickel superalloys, Inconel 713LC and MAR-M247. All samples were exposed to cyclic oxidation and hot corrosion environment at Silesian University of Technology in Katowice, Poland. Hitachi SEM with EDS microanalysis was used for analysis of surfaces and cross-sections of the samples. Experimental cyclic oxidation test was carried out in inductive furnace at 1100°C and samples were exposed to 24 cycles. Heating time took 23h. After each oxidation cycle, the samples were taken out of furnace and cooled in the air. Mass changes of the samples were written down during each second cycle to observe the progress of cyclic oxidation. The resulting graph of the sample masses revealed that resistance to cyclic oxidation of IN713 LC samples without protective coating exposed to 24 cycles was very good and without any noticeable damage. The oxidation of the superalloy surface of MAR-M247 without the protective coating was very fast. Hot corrosion is the accelerated oxidation of a material at elevated temperature induced by a thin film of fused salt deposit. Superalloys samples were coated by help of the method out-of-pack. Corrosive environment was created using tablets of Na2SO4 at temperature 920°C. Results of tested samples revealed that the samples with Si modified aluminide coating had the highest life-time.

Microstructural change and impact toughness property of Inconel 738LC after 12years of service

The Domestic and Foreign Object Damage (DOD & FOD) are knownas serious problems for many heavy duty (or high temperature) device such as compressor, different turbine sections of jet engines and gas turbine, therefore the impact resistance study plays an important role to prevent any catastrophic failures. In this study a V94.2 Siemens gas turbine blade was used, which has been exposed to hot gases, heating the material to a temperature of 800–900°C in 105,120 operating hours. Initial metallographic investigation confirmed microstructural damage in the airfoil compared with the root of turbine blade.Charpy V-Notch tests were made according to the specification ASTM-E23 in ambient and service temperature (900°C). The fracture surfaces of the Charpy specimens were analyzed with the scanning electron microscopy,in order to identify the fracture mechanisms. The results showed that, with increasing the test temperature from 25 to 900°C, the impact energy of the root in both temperatures were relatively equal and far from airfoil. The microstructural investigation confirmed that the microstructure of airfoil was damaged due to the long operation at high temperature. Also, rafting behavior is observed in airfoil section.Fractographic investigations showed fracture mechanism of transgranular cleavage and dimples in the airfoil and root specimens in both temperatures.

The effect of substrate's heat treatment on microstructural and mechanical evolution of transient liquid phase bonded IN-738 LC

Transient liquid phase (TLP) bonding of Inconel-738 LC superalloy was investigated using AMS 4777 filler alloy. The bonding was performed at 40 and 80μm gap sizes at sufficient time in order to achieve complete isothermal solidification. Solution treatment (1120°C/2h) was carried out in two different sequences, one before and the other after TLP bonding of the base metal accompanying subsequent aging treatment (845°C/24h) which are called HT-A and HT-B, respectively. In both cases, no morphological changes in diffusion affected zone (DAZ) precipitates were observed. However, line scan analysis indicates enrichment of base metal alloying elements (Ti, Al) at isothermal solidification zone (ISZ) of heat treated samples, particularly HT-A joints resulted in increased hardness of the centerline. In addition, improved shear strength was seen in heat treated joints conforming to the ductile fracture surfaces. The maximum hardness of 759Hv and the highest shear strength of 565MPa in the joint area, were found in HT-A condition with 40 gap size. Enhanced mechanical properties were mainly controlled by solid solution strengthening mechanism.

High Temperature Low Cycle Fatigue Characteristics of Grit Blasted Polycrystalline Ni-Base Superalloy

The present work is focused on the study of low cycle fatigue behavior of grit blasted nickel-base superalloy Inconel 713LC (IN 713LC). Grit blasting parameters are obtained. Button end specimens of IN 713LC in as-received condition and with grit blasted surface were fatigued under strain control with constant total strain amplitude in symmetrical cycle at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of both materials were obtained. Both materials exhibit the same stress-strain response. It has not been observed any improvement or reduction of low cycle fatigue life in representation of total strain amplitude versus number of cycles to failure of grit blasted material in comparison with as-received material. Surface relief and fracture surface were observed in SEM. The little effect of surface treatment on fatigue characteristics is discussed.

An optimization technique on ultrasonic and cutting parameters for drilling and deep drilling of nickel-based high-strength Inconel 738LC superalloy with deeper and higher hole quality

In this research work, an ultrasonic assisted drilling system is employed to apply both rotation and vibration to drill bits. The transducer horn transfers power very efficiently and changes tools effortlessly. The setup used to conduct drilling tests is Inconel 738LC with depth-to-diameter ratios from 2 to 10 by conventional drilling (CD), ultrasonic assisted drilling (UAD), and electro discharge drilling (EDD). The effects of ultrasonic vibration amplitude, spindle speed, and number of steps to drill each hole on machining force and surface roughness in UAD are investigated. The results demonstrate not only a significant improvement in tool life (by applying ultrasonic vibration to the drilling process) but also a 40 % reduction in thrust force compared to CD. The UAD technique seems more appropriate than the EDD method due to the ability to reduce machining process time by up to 90 %, improve cylindricity by roughly 50 %, increase hole dimension accuracy by up to 80 %, and reduce surface roughness by 52 %.

Evaluation of an Inconel 738LC Surface by Using the Minimum Reflection

Evaluation of an Inconel 738LC Surface by Using the Minimum Reflection

The Research of the Surface Profile after Profiling of Superalloys

Production of so-called superalloys is increasing in the present. This paper is about milling of Inconel 738 LC and Inconel 718. There are main mechanical properties as well as chemical composition of Inconel 738 LC and Inconel 718 in this paper. Special properties of superalloys cause, that they are very hard machining materials, mainly thanks to their high thermal stability during machining. For this reason it was necessary to measure the surface roughness after machining turbine blades made of Inconel 738LC and Inconel 718 depending on profiling. For roughing and finishing of Inconel 738 LC and Inconel 718 were used the best cutting parameters from previous research. After machining of turbine blades were measured parameters of the surface roughness and wear of the cutting tools.

Thermal fatigue behavior of cast superalloy Inconel 713LC

Abstract The thermal fatigue behavior of superalloy Inconel 713LC was investigated at peak temperatures of 900, 1 000 and 1 100 °C. Thermal fatigue tests were performed on self-constraint single-edge V-type notch specimens. The effect of the maximum temperature, T max in the thermal cycles on the crack characteristics was studied. Under identical test conditions a comparable crack propagation rate was observed for all three peak temperatures. The results showed that cycle numbers for crack initiation decreased while crack propagation rate increased with the increase in peak temperature. Therefore, it was concluded that in the current experimental conditions, thermal fatigue resistance reduced dramatically with the rise of upper temperature. Through optical microscopy and scanning electron microscopy observation, it was found that the primary cracks generally propagated along a preferential direction. Microstructure changes after thermal fatigue are also discussed on the basis of scanning electron microscopy observation.

Evaluation of hot corrosion behavior of plasma sprayed scandia and yttria co-stabilized nanostructured thermal barrier coatings in the presence of molten sulfate and vanadate salt

In this study, the substrates of Inconel 738-LC superalloy were first sprayed with an NiCrAlY bondcoat and then with a nanostructured scandia (3.6mol%) and yttria (0.4mol%) co-stabilized zirconia (4SYSZ) topcoat by air plasma spraying (APS). Hot corrosion studies of plasma sprayed thermal barrier coatings (TBCs) were conducted in 45wt% Na2SO4+55wt% V2O5 molten salt at 910°C for 300h. The results show that the failure of this TBC occurred in bondcoating layer due to the formation of mixed oxide (NiO, NiAl2O4 and NiCr2O4) in this layer.

Application of Acoustic Emission for Identification of Differences in Fatigue Damage of Selected Materials for Power Plants

An acoustic emission is remarkable source of information about the fatigue process and its intensity under cyclic loading. Specimens made of reactor steel and INCONEL 713LC were subjected to bending fatigue loading in the high-cycle range. This study presents results of acoustic emission signal analysis. The main aim of this study is to propose a methodology for evaluation of the early manifestations of fatigue damage and to identify material changes in both materials by AE parameters. Signal comparison material indicates differences of damage mechanism in observed. An examination of crack initiation sites and microstructure has been also performed.Experiments were realized in cooperation between laboratories of Brno University of Technology and University of West Bohemia in Pilsen and its related to solving of project of the Czech Ministry of Industry and Commerce: “A diagnostic complex for the detection of pressure media and material defects in pressure components of nuclear and classic power plants“ and project New Technologies for Mechanical Engineering (NETME +).

Real Structure of Milled Inconel 738LC Turbine Blades

Machining of nickel super-alloys is difficult since mechanical hardening and, consequently, extreme tool wear occur. In the case of turbine blades, castings can no longer meet stringent requirements for precision; hence, they are being ground or milled in order to comply with the demanded dimensions. In this contribution, castings made of Inconel 738LC were machined by four axis milling. The resulting surface of gas turbine blades are characterized by several surface integrity parameters with respect to the structural inhomogeneities caused by mutual effect of plastic deformations and thermal fields during the cutting process. Moreover, the impact of effective contact area of the cutter was considered as well. It will be shown that ideal machining parameters viewed from the standpoint of surface roughness and economy of the whole machining process can lead to appreciable tensile normal stresses.

Microstructural Characterization of Slurry Aluminide Diffusion Coatings

Commercially pure aluminium powder and a mixture of aluminium and silicon powders, both in a liquid amyl acetate-based organic binder, were sprayed onto the surface of Inconel 713LC nickel base superalloy. A two-stage heat treatment process in an argon atmosphere flow was designed and applied to produce nickel aluminide diffusion coatings. Two coating systems composed of different layers with gradual changes in chemical composition and phase quantities were formed. Scanning electron microscope, scanning electron microscope/focused ion beam, both equipped with energy dispersive microanalyzers, were utilized to characterize the microstructure and chemical composition of the coatings.

Critical Weak Points of Atmospheric Plasma Sprayed Thermal Barrier Coatings

The 8 wt. % yttria stabilized zirconia top coat (TC) and the CoNiCrAlY bond coat (BC) were sprayed onto the surface of newly developed fine-grained cast polycrystalline nickel-based superalloy Inconel 713LC by means of atmospheric plasma spraying (APS). As-prepared samples were isothermally exposed at the temperature of 1050 °C for 200 hours in an ambient atmosphere. Structural changes in the thermal barrier coatings (TBC) system after thermal exposure were studied by means of scanning electron microscope equipped with an energy dispersive microanalyzer. Critical weak points were identified on both the substrate-bond coat and bond coat-top coat interfaces.

Effect of Thermal Barrier Coating on Low Cycle Fatigue Behavior of Cast Inconel 713LC at 900 °C

The effect of thermal barrier coating (TBC) on low cycle fatigue behavior of cast superalloy Inconel 713 LC has been studied at 900 °C. The TBC consisting of a CoNiCrAlY bond coat and a zirconia (ZrO2) top coat stabilized by 8% yttria (Y2O3) was deposited on the gauge section of cylindrical specimens using the atmospheric plasma spray technique. Cylindrical specimens of Inconel 713LC in as-received condition and with surface treatment were cyclically strained under strain control with constant total strain amplitude in symmetrical cycle at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of coated and uncoated material were obtained. The stress response of the TBC coated specimens is lower in comparison with the uncoated specimens. Detrimental effect of surface treatment on the Basquin curve is documented. Specimen sectioning and fracture surface observations revealed fatigue damage mechanisms and help to discuss differences in fatigue behavior of the coated and uncoated superalloy.

<i>In Situ</i> Study of the Mechanisms of High Temperature Damage in Elastic-Plastic Cyclic Loading of Nickel Superalloy

In-situ Low Cycle Fatigue test (LCF) at temperature 635 °C have been performed in SEM on flat specimen ofcast Inconel 713LC superalloy. The aim of the investigation was to studymechanisms of the fatigue damage during elastic-plastic cycling by theobservations of the characteristic surface relief evolution and theaccompanying internal dislocation structures. The selected locations on thesurface were systematically studied in-situ and documented by SEM and usingAFM. The surface relief in the first tensile half-cycle was formed by numerousslip steps on the primary slip planes (111). In the following compressionhalf-cycle additional opposite slip were formed. The relief was modified in thenext cycles but without forming additionally new slip traces in the primarysystem. The reorientation of two grains in the gauge area was measured usingEBSD. At the end of cyclic loading the relation between surface persistent slipmarkings and persistent slip bands in the interior of the material wasdocumented by TEM on lamella prepared by FIB. The early stages of extrusion andintrusion formation were documented. The damage mechanism evolution is closelyconnected with the cyclic strain localization to the persistent slip bands thatare also places of fatigue crack initiation.

Improving the hot corrosion resistance of plasma sprayed ceria–yttria stabilized zirconia thermal barrier coatings by laser surface treatment

Ceria–yttria stabilized zirconia (CYSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying on NiCoCrAlY-coated Inconel 738LC substrates. After that, the surface of plasma sprayed CYSZ TBCs were glazed using a pulsed Nd:YAG laser. The effects of laser glazing on hot corrosion resistance of the coatings were evaluated in presence of 45wt%Na2SO4+55wt%V2O5 corrosive molten salt at 1000°C. The results revealed that the hot corrosion resistance of plasma sprayed CYSZ TBCs were enhanced more than twofold by laser surface glazing due to reducing specific reactive area of the dense glazed surface layer and consequently, decreasing the reaction between molten salt and zirconia stabilizers.