Ni-base Superalloy IN100 Research Articles

Hot Deformation Behavior and Microstructure of Cast Ni-Based Superalloy IN-100 Based on the Processing Map

Hot Deformation Behavior and Microstructure of Cast Ni-Based Superalloy IN-100 Based on the Processing Map

Simulating the effect of grain boundaries on microstructurally small fatigue crack growth from a focused ion beam notch through a three-dimensional array of grains

Microstructurally small crack (MSC) growth strongly depends on local microstructure and often displays oscillatory character in terms of crack growth rate (da/dN) as a function of the conventional stress intensity range due to crack tip/grain boundary interactions of MSCs. A fatigue indicator parameter (FIP)-based MSC growth model is presented for high temperature MSC growth in polycrystalline Ni-base superalloy IN100 that takes into account crack tip/grain boundary interaction. An expression for FIP evolution is evoked based on a sequence of finite element simulations for stationary cracks. The MSC growth model was fit to experiments within the context of a simple 1D crack growth model and then applied to model 3D crack growth from a simulated focused ion beam (FIB) notch. Simulations showed that the MSC growth rate became less oscillatory as the MSC front sampled more grains, and eventually converged to the LEFM response with further crack extension.

Investigation of Oxide Bifilms in Investment Cast Superalloy IN100: Part II. Characterization

Oxide bifilms are a proposed casting inclusion reported to have been observed in vacuum investment cast polycrystalline Ni-based superalloys. Ongoing research seeks to determine if current superalloy casting practices can result in the formation of oxide bifilms, and subsequently if it is possible to observe and characterize this phenomenon. The effect of casting atmosphere, turbulence, filtering, hot isostatic pressing, and heat treatment has been investigated to identify the critical parameters that have been reported to result in bifilm formation in Ni-based superalloy IN100. Scanning Auger microscopy (SAM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were utilized to characterize samples from each casting condition. In situ ultrahigh vacuum Auger fractography did not indicate the presence of bifilms on the fracture behavior of IN100 in any processing condition. SAM analysis identified a sulfur-enriched monolayer on the surface of dendritic casting porosity, and identified heterogeneous Ti oxycarbide inclusions in air cast IN100. SEM analysis also indicated the presence of Ti oxycarbide inclusions in air cast IN100, and determined that these inclusion structures consist of fine blocky external M(Ti, Mo)C carbide enveloping an internal core of alumina. HR-TEM analysis indicated that none of the oxycarbide inclusion interfaces exist as discontinuous unbound interfaces, and that the internal alumina core is an ultra-fine polycrystalline structure.

The Portevin-Le Chatelier Effect in the Ni-Based Superalloy IN100

The Portevin-Le Chatelier (PLC) effect has been studied in the Ni-based superalloy IN100 which is currently used as a disk material in jet engines. A series of tensile tests was carried out at 588 K, 755 K, and 922 K (315 °C, 482 °C, and 649 °C) at plastic strain rates ranging from a low of 6.21 × 10−6 s−1 to a high of 4.92 × 10−2 s−1. The activation energy was determined using the slope of a line on a strain rate/temperature graph which divided the area of the graph into two regions: (1) “PLC behavior observed,” and (2) “No PLC behavior observed.” A new statistical approach was developed to objectively differentiate between a true PLC effect and experimental uncertainty (i.e., “noise”). The value of the activation energy was found to be 1.14 eV/atom, which strongly suggests that the rate controlling process was bulk diffusion of C in the lattice. A qualitative model, based on the Orowan equation and slip band dislocation mechanics, was proposed, which unifies the seemingly disparate ideas of the process being controlled by a single atom/dislocation interaction while at the same time exhibiting significant strains during PLC load drops.

Microstructure-sensitive weighted probability approach for modeling surface to bulk transition of high cycle fatigue failures dominated by primary inclusions

A simulation-based probabilistic strategy is developed to characterize the surface to bulk transition of high cycle fatigue failures dominated by primary inclusions. The probability of fatigue crack initiation in the surface region is calculated by computing the expected number of critical fatigue hot spots in this region. This is done by considering the probability of inclusion-matrix debonding and the fatigue crack initiation potency of partially-debonded inclusions for a given load ratio and stress amplitude.A case study is presented whereby the surface initiation probability is studied in uniaxial strain-controlled cyclic loading simulations of round smooth specimens of the fine grained powder metallurgy (PM) processed Ni-base superalloy IN100. The fatigue crack initiation potency of partially-debonded nonmetallic inclusions is assessed by calculating the Fatemi–Socie (FS) critical plane parameter from generalized plain strain crystal plasticity finite element simulations. Idealized spherical ceramic inclusions with homogeneous linear elastic isotropic material properties are considered to isolate the FS parameter sensitivity to inclusions’ size, stress amplitude, and polycrystalline microstructure realization around the inclusion.

On “macroscopic” characterization of mixed grain boundaries

Grain boundaries having no special geometric features are referred to as mixed. Mixed boundaries constitute a large class, and the need for a finer differentiation arises. A mixed boundary can be characterized by linking it to the nearest boundaries with special geometric attributes, in particular, by its decomposition into twist and tilt components. We investigate and compare the quantitative methods and parameters used for description of mixed boundaries. The considered methods are based either on decomposition or on some other measures of deviations from pure-twist or pure-tilt boundaries. Furthermore, the methods are either limited to boundary representations with the smallest misorientation angles or take into account all symmetrically equivalent boundary representations, and these two approaches differ in their meaning, physical significance and conclusions. The relationships between the methods of mixed boundary characterization are clarified and the suitability of particular parameters for analysis of experimental data is assessed. These issues are important for a thorough understanding of grain boundary distributions in the space of macroscopic boundary parameters. The considered techniques and parameters are used to examine mixed boundaries in the Ni-based superalloy IN100.

Investigation of failure mechanism of thermal barrier coatings (TBCs) deposited by EB-PVD technique

Failure mechanism of thermal barrier coatings (TBCs) prepared by electron beam physical vapor deposition (EB-PVD) technique owing to formation of micro cracks was investigated. The TBCs were deposited on the Ni-based super alloy IN-100 and the micro cracks were observed within the top ceramic coat of thermally cycled TBCs at 1050°C. It was observed that these cracks propagate in the ceramic coat in the direction normal to interface while no cracks were observed in the bond coat. SEM/EDS studies revealed that some non-uniform oxides were formed on the interface between ceramic top and metallic bond coat just below the cracks. Study proposed that the cracks were initiated due to stress owing to big difference in Pilling-Bed worth ratio of non-uniform oxides as well as thermal stress, which caused the formation of cracks in top ceramic coat leading to failure of TBCs

Creep properties of different γ′-strengthened Co-base superalloys

Abstract The influence of various alloying elements on the creep properties of polycrystalline Co-base superalloys hardened by a ternary L1 2 compound, Co 3 (Al,W) (γ′-phase), was investigated. A Ti containing quaternary alloy shows creep strength similar to Ni-base superalloys IN100 and IN713C at 850 °C and strongly superior to conventional Co-base superalloys as Haynes188. The activation energy for creep between 850 and 950 °C is similar to the polycrystalline Ni-base superalloy IN100 in the same temperature range. Strengthening of the grain boundaries by third phase precipitates was found to be crucial for the mechanical properties. This can be achieved either by precipitation of borides or by additional intermetallic phases which precipitate due to oversaturation. During compressive creep at 850 °C only a slight tendency for directional coarsening occurs, while at 950 °C distinct γ/γ′-rafts perpendicular to the external compressive stress axis are formed which indicate a positive lattice misfit even at 950 °C.

Microstructure-sensitive probabilistic modeling of HCF crack initiation and early crack growth in Ni-base superalloy IN100 notched components

Microstructure-sensitive simulation-based strategies for modeling fatigue life reduction in cyclically loaded notched components offer a means to augment costly experiments and to project performance of microstructures not yet processed. To advance design tools for notch fatigue resistance in aircraft gas turbine engine components, we present a formulation that links microstructure heterogeneity (grain size distribution) to size effects and fatigue scatter in notched polycrystalline Ni-base superalloy IN100 specimens. Simulated double-edged notched specimens with various notch radii are subjected to completely-reversed, quasistatic, isothermal (650 °C), strain-controlled loading at three different strain amplitudes. Polycrystal plasticity and experimentally-calibrated crack formation/growth laws are used to correlate cyclic plastic slip to the probability of forming and propagating a crack from grain scale to a transition crack length at which LEFM is applicable. Probabilistic strain-life and cumulative distribution function (CDF) plots show that larger notch sizes display a larger notch size effect and fatigue knock-down effect. The proposed CDF can be determined for any failure probability and number of cycles, which has implications for minimum fatigue life design of aircraft gas turbine engine components.

Behavior of Branch Cracking and the Microstructural Strengthening Mechanism of Polycrystalline Ni-Base Superalloy, IN100 under Creep Condition

Recently, the development of the high-efficiency technology for gas turbine and jet engine is required to minimize carbon dioxide and nitrogen oxide emission. It is effective way to increase the operational temperature to develop the high-efficiency technology for high temperature instruments. To increase the operating temperature, advanced Ni-base superalloys have been developed as a turbine blade material.Even though a Ni-base superalloy is used for a structural component, creep damages and creep cracks may be caused due to the external tensile load under high temperature conditions. Therefore, a predictive law of creep crack growth life is necessary to maintain operational safety.This study is aimed to clarify the branch cracking behavior due to the microstructural strengthening mechanism of polycrystalline Ni-base superalloy IN100 under the creep condition. The creep crack growth tests were conducted at a temperature of 900°C. The creep crack growth behavior and creep damage formulation were observed by in-situ observational system and FE-SEM/EBSD. Additionally, two-dimensional elastic-plastic creep finite element analyses were conducted for the model which describes the experimental results. The creep crack growth behavior and the creep damage progression were found to be affected by the distribution behaviors of grains and grain boundaries around the notch tip. By comparison of experimental results with mechanical analysis using FEM analyses, mechanisms of the creep crack growth and the creep damage formulation were clarified.

Extraction replication studies of near-surface microstructures in laser-drilled samples of the powder metallurgy Ni-based superalloy IN100

Hybrid extraction replication has been used to prepare TEM samples from laser-drilled coupons of the Ni-based superalloy IN100. In addition to extracting the inert carbide and boride particles, these carbon replicas reveal the microstructure of the surrounding metallic phases allowing the particle distribution to be studied. It is shown that the IN100 base metal contains large (> 100 nm) MC, M 23C 6 and M 3B 2 particles, consistent with previous TEM studies on this alloy. In the recast layers on the interior surfaces of the laser-drilled holes, however, dendritic micro-segregation in the supersaturated γ phase gives a cellular sub-structure, and the inert particles observed are nano-scale Ti-rich MC-type carbides at the cell boundaries. The replicas also reveal that the base metal/recast interface is abrupt. These observations illustrate the power of the hybrid replication technique for revealing variations in nano-scale features over much larger length scales (≫ 10 μm).

Simulation-based extreme value marked correlations in fatigue of advanced engineering alloys

The objective of this research is to estimate the microstructure dependence of the extreme value probabilities of fatigue crack formation at the scale of the grains in polycrystalline and polyphase microstructures to facilitate preliminary parametric design exploration and property assessment. A simulation-based methodology is introduced for computing correlation functions of microstructure attributes marked by the extreme value microstructure-scale fatigue indicator parameters. Multiple statistically representative microstructure volumes simulated using a crystal plasticity constitutive model coupled with the FEM are used to characterize these extreme value marked correlation functions. By comparing these marked correlation functions to traditional correlation functions sampled from the bulk material, the interacting microstructure attributes important to the extreme value response are identified. This methodology is applied to identify dominant crystallographic relationships relative to fatigue crack formation in the polycrystalline P/M Ni-base superalloy IN100 and duplex Ti-6Al-4V. It is demonstrated that certain high contrast orientation relationships in both IN100 and Ti-6Al-4V (where grains oriented for hard slip are near grains oriented for easier slip) can significantly increase the driving forces for fatigue crack formation.

Microstructure-sensitive extreme value probabilities for high cycle fatigue of Ni-base superalloy IN100

To quantify the effects of interactions between various microstructure attributes on fatigue life in the high cycle fatigue (HCF) regime, we have proposed a new microstructure-sensitive extreme value statistical framework. This framework couples the extreme value distributions of certain fatigue indicator parameters (FIPs) or response functions to the correlated microstructure attributes that exist at the extreme value locations of these FIPs. We demonstrate the application of this statistical framework to investigate the microstructure-sensitive fatigue response of the PM Ni-base superalloy IN100 at 650 °C. To accomplish this task, we construct statistical volume elements (SVEs) used to compute the local response for 200 instantiations of IN100. These SVEs are constructed and simulated via the finite element method with crystal plasticity constitutive relations. The results of the simulations are used to explore extreme value statistics of the FIPs for these microstructures. The extreme value distributions of the Fatemi–Socie FIP are fit with high confidence by the Gumbel distribution and are defined in a representative nature with as few as 25 simulated microstructure instantiations (i.e., SVEs). The extreme value marked correlation functions of the apparent Schmid factor based on the geometry of the slip systems relative to the loading direction indicate that cube slip may be important to fatigue crack formation in this material system. This supports previous experimental observations of fatigue crack formation and microstructurally small fatigue crack growth along cube planes in IN100 in grains that are unfavorably oriented for octahedral slip at elevated temperatures.

A hybrid replication technique for the analysis of precipitate-boundary interactions in Ni-based superalloys

A hybrid replication technique is described for complex alloy systems whereby the surface is etched to reveal the microstructure of the metallic phases prior to producing an extraction replica. By applying this approach to the Ni-based superalloy IN100, it has been shown that the inert carbide and boride particles can be extracted for analysis in the TEM whilst retaining information about their location with respect to the metallic phases in the alloy. This approach is particularly useful for studying the effects of inert particles on microstructural evolution, such as pinning effects during grain growth.

Extraction Replication of Carbides and Borides in the Ni-base Superalloy IN100

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Characterization of the microstructure and phase equilibria calculations for the powder metallurgy superalloy IN100

The microstructure of the Ni-based superalloy IN100 processed by a powder metallurgy route was evaluated to reveal the structures, volume fractions, distributions, and chemistries of the various phases present. These data were compared with those predicted by computational thermodynamics. It is shown that the microstructural parameters expected on the basis of global equilibrium conditions differ significantly from those measured experimentally. However, modification of these calculations by use of constrained and successive equilibria compensated for kinetic effects and led to accurate (or better) predictions of phase volume fractions and chemistries in this alloy. This demonstrated that such modified phase equilibria calculations could be powerful tools for modeling microstructures, even in complex multicomponent alloys processed under nonequilibrium conditions.

Evolution of dislocation structures and cyclic behaviour of a 316L-type austenitic strainless cycled in vicuo at room temperature : Gerland, M., Mendez, J., Violan, P. and Saadi, B.A. Mater. Sci. Eng. A Oct. 1989 A118, (1–2), 83–95

To quantify the effects of interactions between various microstructure attributes on fatigue life in the high cycle fatigue (HCF) regime, we have proposed a new microstructure-sensitive extreme value statistical framework. This framework couples the extreme value distributions of certain fatigue indicator parameters (FIPs) or response functions to the correlated microstructure attributes that exist at the extreme value locations of these FIPs. We demonstrate the application of this statistical framework to investigate the microstructure-sensitive fatigue response of the PM Ni-base superalloy IN100 at 650 °C. To accomplish this task, we construct statistical volume elements (SVEs) used to compute the local response for 200 instantiations of IN100. These SVEs are constructed and simulated via the finite element method with crystal plasticity constitutive relations. The results of the simulations are used to explore extreme value statistics of the FIPs for these microstructures. The extreme value distributions of the Fatemi–Socie FIP are fit with high confidence by the Gumbel distribution and are defined in a representative nature with as few as 25 simulated microstructure instantiations (i.e., SVEs). The extreme value marked correlation functions of the apparent Schmid factor based on the geometry of the slip systems relative to the loading direction indicate that cube slip may be important to fatigue crack formation in this material system. This supports previous experimental observations of fatigue crack formation and microstructurally small fatigue crack growth along cube planes in IN100 in grains that are unfavorably oriented for octahedral slip at elevated temperatures.