Agnieszka Szczotok

Effect of Heat Treatment on Chemical Segregation in CMSX-4 Nickel-Base Superalloy

Superalloys display a strong tendency toward chemical segregation during solidification. Therefore, it is of great importance to develop appropriate techniques for the melting and casting of superalloys. Elements partitioning between the γ and γ′ phases in single crystal superalloys have been investigated by several authors using electron probe microanalysis (Hemmersmeier and Feller-Kniepmeier Mater Sci Eng A 248:87-97, 1998; Kearsey et al. Intermetallics 12:903-910, 2004; Kearsey et al. Superalloys 2004, pp 801-810, 2004; D’Souza et al. Mater Sci Eng A 490:258-265, 2008). We examined the effect of the particular stages of standard heat treatment (solution treatment and ageing) applied to CMSX-4 single crystal superalloy on chemical segregation that occurs between dendrites and interdendritic areas. Dendritic structures were observed using a scanning electron microscope. Analyses of the chemical composition were performed using energy dispersive x-ray spectroscopy. The obtained qualitative and quantitative results for the concentrations of elements enabled us to confirm the dendritic segregation in as-cast CMSX-4 superalloy. The concentrations of some refractory elements (tungsten, rhenium) were much greater in dendrites than in interdendritic areas. However, these differences in chemical composition gradually decreased during heat treatment. The results obtained in this study warrant further examination of the diffusion processes of elements during heat treatment of the investigated superalloy, and of the kinetics of diffusion.

Electrospark Alloying of Carbon Steel with WC-Co-Al2O3: Deposition Technique and Coating Properties

The paper is concerned with the performance properties of electrospark deposited coatings. The properties were assessed by analyzing the coating microstructure, X-ray diffraction, microhardness, roughness and bonding strength.The studies were conducted using WC-Co-Al2O3 electrodes produced by sintering nanostructural powders. The anti-wear coatings were electro-spark deposited over C45 carbon steel by means of an EIL-8A. These coatings are likely to be applied to increase the abrasive wear resistance of tools and machine parts.

Microstructural studies of carbides in MAR-M247 nickel-based superalloy

Carbides play an important role in the strengthening of microstructures of nickel-based superalloys. Grain boundary carbides prevent or retard grain-boundary sliding and make the grain boundary stronger. Carbides can also tie up certain elements that would otherwise promote phase instability during service. Various types of carbides are possible in the microstructure of nickel-based superalloys, depending on the superalloy composition and processing. In this paper, scanning electron and scanning transmission electron microscopy studies of carbides occurring in the microstructure of polycrystalline MAR-M247 nickel-based superalloy were carried out. In the present work, MC and M23C6 carbides in the MAR-M247 microstructure were examined.

Quantitative evaluation of carbides in nickel-base superalloy MAR-M247

It has been established that carbides in superalloys serve three functions. Fine carbides precipitated in the matrix give strengthening results. Carbides also can tie up certain elements that would otherwise promote phase instability during service. Grain boundary carbides prevent or retard grain-boundary sliding and strengthen the grain boundary, which depends significantly on carbide shape, size and distribution. Various types of carbides are possible, depending on superalloy composition and processing. In the paper optical and scanning electron microscopy investigations of carbides occurring in specimens of the polycrystalline nickel-base superalloy MAR-M247 were carried out. Conditions of carbides revealing and microstructure images acquisition have been described. Taking into consideration distribution and morphology of the carbides in matrix a method of quantitative description of Chinese script-like and blocky primary carbides on the basis of image analysis was proposed.

The bootstrap analysis of one-way ANOVA stability in the case of the ceramic shell mould of airfoil blade casting

The analysis of variance (ANOVA) is a classic tool for an identification of discreet factors impact on the measurable output by a specific decomposition on a total variance according to the scheme proposed by R.A Fisher in the 1920s. There are many explicit and implicit assumptions required as a preliminary of ANOVA computations. The ANOVA computations scheme is well known and implemented in many types of software but all estimations are provided with the assumption of a normal and homoscedasticity distribution of the noise disturbing the output. Computation procedures produce a single number output (e.g. F statistics, p-Value) without any analysis of their own dispersion. This paper analyzes the ANOVA output using the bootstrap approach. It seems to be the most convenient as a data-driven procedure. The source raw data are taken from the image analysis conducted during the investigation of the impact of the ceramic layer thickness on the wax pattern assembly of a turbine blade on the (γ+γ’) eutectic in the IN713C superalloy.

Factorial Approach to Assessment of GPU Computational Efficiency in Surrogate Models

Surrogate models are very useful to replace very accurate but time-consuming huge data numerical models. The process of construction and optimization of surrogate models may require large computational power. It may be delivered by multi-core CPU or by massively multi-core GPGPU. This paper presents a consistent approach to make quantitative assessment of the computational efficiency with different hardware configurations: with one and multi-core CPU and with GPGPU card. The design of experiments factorial approach is used to analysis of the obtained data. The linear main effects model with two-way interaction is identified. The results show that the investment to multi-core CPU and GPGPU cards simultaneously is impractical due to negligible effects of CPU efficiency which is masked by dominated GPGPU performance.

Phase transformations in CMSX-4 nickel-base superalloy

Thermophysical properties (including transformation temperatures) are the critical input parameters in mathematical models of solidification and casting of metallic materials. The technique of Differential Scanning Calorimetry (DSC) was selected for the study of precipitation and phase changes in CMSX-4 alloy system. The results of the calorimetric measurements together with phase transformation temperatures determined from DSC heating and cooling curves was described. In the present paper, DSC results accompanied by scanning electron microscope characterization of CMSX-4 superalloy is applied to understand significance of precipitation or phase changes in alloy system for design heat treatment for the nickel based superalloy.

Production and properties of electro-spark deposited coatings modified via LBM

The paper is concerned with determining the influence of laser treatment process on the properties of electro spark coatings. The properties were assessed after a laser treatment by analysing microstructure and X-ray diffraction and measuring surface geometric structure and microhardness. The studies were conducted using WC-Cu electrodes produced by powder metallurgy of nanostructural powders. The coatings were deposited by means of the EIL-8A model and they were laser-treated with the Nd:YAG, BLS 720 model.

Laser treatment of heterogeneous surfaces formed by electro-spark deposition

This study is an investigation of the effect of laser treatment on the properties of surface coatings produced by a conventional electro-spark deposition (ESD) process. A combination of ESD process and laser treatment has been developed, and tested, and improvement of certain surface properties has been demonstrated. These coatings are heterogeneous surfaces, which mean that there are variable characteristics along the depth of the thin coating. The study is carried out on a conventional C45 steel as substrate, coated by Cu–Mo electrode by electro-spark deposition. The coating showed an improved metallurgical bond to the substrate material, and desirable surface topography, microstructure and micro-hardness distribution along the depth of the coating. The developed process has a minimal thermal effect on the bulk material, below the coating. This is combined with an exceptionally homogeneous hard outer surface. This combination demonstrated also improvements of certain tribological properties, such as a rise of seizure resistance of the rubbing surfaces. The properties of heterogeneous surfaces, based on laser treated ESD, are largely dependent upon material combination systems, manipulating methods, ESD and laser parameters as well as process control.

The Fuzzy Approach to Assessment of ANOVA Results

Typically, the analysis of variance (ANOVA) is used to compare means in the subsets obtained through the division of a large numerical dataset by assigning a categorical variable labels to dataset’s values. The test criterion for the decision on ‘all equal’ vs. ‘not all equal’ is a comparison of the significance level described by a well-known p-value and the a priori assigned critical significance level, α, usually 0.05. This comparison is treated very strictly basing on the crisp value; however, it should not be so, especially if p-value is near α, because the certainty of the decision varies rather smoothly from ‘strongly not’ to ‘no opinion’ to ‘strongly yes’. It is very interesting to analyze such results on the basis of the fuzzy arithmetic theory, using the modified Buckley’s fuzzy approach to the statistics combined with the bootstrap approach, because it may be adopted to the cases where subjective assessments are introduced as quasi-measurements.