Papers by Keyword: EPMA

Abstract: The Ultrahigh strength Q&P automotive steel, i.e. QP980, has a broad application prospect in lightweight due to its high strength and good plasticity. In this study, the range of heat input (30 ~ 40 J/mm) was selected by controlling laser power in laser welding of QP980 in order to investigate the microstructure and properties of welded joint. At the heat input of 30 ~ 40 J/mm, the joint of QP980 had acceptable penetration. The weld widths were 417.93 mm, 582.02 mm and 521.56 mm, respectively. The macroscopic morphology of the joint is hourglass type. The microhardness of the welded joint hardening zone is higher than that of the base metal, and the maximum value is 519 HV_0.5. When the heat input is 35 J/mm, the tensile strength of the welded joint is 1109 MPa. The maximum joint factor is 91.88 %. The fracture is close to the base metal. A large number of dimples are observed on the fracture surface, implying as ductile fracture. Based on the EBSD results, the proportion of low angle grain boundary was consistent with mechanical properties. A large number of deformation twins are formed in the 35 J/mm sample through deformation, which has a great contribution to the strength of the weld.

Abstract: The article presents the results of an investigation of microstructural features and mechanical characteristics of Al-5.0Cu-0.5Mg alloy containing up to 0.4 wt. % Ag and up to 0.1 wt. % Ce. The experiment was conducted using optical microscopy, Scanning Electron Microscopy as well as an electron probe micro-analyzer and Differential Scanning Calorimetry. Samples in cast condition and after heat treatment were examined. The melting temperatures of non-equilibrium eutectics (non-equilibrium solidus), equilibrium solidus and liquidus were determined. The optimal temperature of the homogenizing heat treatment was determined, which was 500°C. Using this heat treatment mode resulted in the elimination of dendritic segregation and complete dissolution of silver in aluminum. Injection of cerium into the Al-Cu-Mg-Ag system during crystallization of the melt is accompanied by the formation of a coarse four-component phase, which has the morphology of polyhedrons, is on the grain boundaries. The estimation of the relation between microstructure characteristics and mechanical properties of the alloy has been made.

Abstract: In general, a flux is used to braze a copper alloy. In many cases, when the molten brazing filler metal spreads in the set joint gap, vaporised flux and its residue are produced, and defects (mainly voids) are formed. Voids, which are formed on the brazed layer, cause deterioration in the strength and other properties. However, with conventional evaluation methods (e.g. ultrasonic or X-ray radiography tests), the behaviour of the molten brazing filler metal during the brazing process cannot be visually observed from the outside of the joint. Therefore, the void formation process cannot be clarified. To improve the quality of the brazed layer, it is necessary to elucidate the mechanism of void formation. The purpose of this study is to observe the behaviour of the molten brazing filler metal by performing an X-ray radiography test at the same time as brazing and to study how to reduce voids. In this study, a brass specimen was brazed with a Cu–P-based brazing filler metal. The specimen was brazed by heating in an electric furnace, and the specimen was irradiated with X-rays. The state where the molten brazing filler metal spread into the gap was photographed as the transmission image. Thereafter, the behaviour of the molten brazing filler metal was analysed.

Abstract: Traditional high-throughput experiments increase the test efficiency by designing component gradient tests and other methods. This article intends to improve the traditional high-throughput experiments and proposes an experimental scheme combining nanoindentation technology and electron probe microanalysis (EPMA). Based on a new Ti-Mo-Al-Zr-Cr-Sn alloy, micro-region composition and corresponding performance at multiple indentations are directly characterized, including a series of different alloy compositions composed of 8 elements such as Mo, Al and the corresponding hardness (H) and elastic modulus (E). Then the principal analysis method in statistics, the theory of molybdenum equivalent and aluminum equivalent are used to process the obtained data, and a series of atlases such as "E-H-component characteristic parameters" and "E-H-alloy equivalents" are constructed, which has achieved high-throughput characterization of the relationship between composition and performance of titanium alloy. Related work can not only quickly determine the alloy composition range corresponding to high E and high H values, but also provide guidance for further optimization of titanium alloy composition design.

Abstract: The effects of rolling deformation on the interface bonding strength and microstructure of bimetallic clad plates were simulated. The composition and sub-structure of the interface were analyzed by electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results showed that the interfacial bonding strength of clad plates was significantly depend on the deformation process, and the bonding time was also a significant factor on bonding effect apart from total strain in the two-stage rolling. Chromium, nickel and other alloying elements have a significant diffusion zone at the bonding interface with a diffusion width of about 10µm. High resolution TEM analysis confirmed that there was an sound metallurgical bonding at the interface, and the structure of martensite in transition zone and matrix approximately meet the coherent relationship of(200) Ferrite // (111) Martensite and [020] Ferrite // [211]Martensite.

Abstract: Microstructure evolution during the homogenization heat treatment of an Al-Zn-Cu-Mg (AA7475, which is typically used for the manufacture of aircraft design) alloy, was investigated using a combination of light microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ingots after different types (one-or two-steps treatments) of temperatures (from 380 to 510 °C) of homogenization and cooling conditions (cooling with an air or quenching to water) were investigated. The results show that the microstructure of ingot presents a typical microstructure with some isolated Al₇Cu₂Fe particles, which after homogenization almost remains in both the size and morphology. The structure ingot after homogenization below 400 °C contains secondary phases, based on η (MgZn₂), S (Al₂CuMg) and T (Al₂Mg₃Zn₃) are distributed along the grain boundary. In the T (Al₂Mg₃Zn₃) phase copper dissolves up to 30 wt.%. Then the increase in temperature and the complication of heat treatment of homogenization, which led to the complication of the kinetics of the evolution of inter-dendritic phases, were found. The two-steps homogenization has a better effect than a single homogenization, as its completely dissolution of non-equilibrium phases was established.

Abstract: High-strength wrought magnesium alloys are one of the sought-after materials in the automotive sector owing to the demands for weight reduction in the automobiles due to fuel economy and CO₂ emission. However, because of low room temperature strength and formability of Mg alloys, only a few applications in wrought form have been explored with these materials. In the present investigation, a high strength, good ductility and low cost wrought magnesium alloy with Mg-Sn-Zn composition have been developed and subjected to conventional wrought processing. Hot rolling was carried out at 350°C without homogenization and after homogenization at 300°C and 330°C. The phase stability, microstructure and texture of the alloy has been investigated for as-cast, homogenized and hot rolled conditions. The compositional and microstructural characterization was carried out by Electron Probe Micro-analysis (EPMA) and optical microscopy respectively. Texture evolution was investigated by X-ray diffraction method. A strong (0002) basal texture develops after hot rolling without homogenization. The (0002) basal texture has been weekend by splitting of poles and double peak distribution when hot rolling was carried out after homogenization.

Abstract: Microsegregation is intimately coupled with solidification, the development of microstructure, and involved in the formation of various casting defects. This paper demonstrates how the local composition of the metal matrix of graphitic cast irons, measured using quantitative electron microprobe analysis, can be used to determine its solidification chronology. The method is applied in combination with Fourier thermal analysis to investigate the formation of micropores in cast irons with varying proportions of compacted and spheroidal graphite produced by remelting. The results indicate that micropores formed at mass fractions of solid between 0.77 and 0.91, which corresponded to a stage of solidification when the temperature decline of the castings was large and increasing. In 4 out of the 5 castings, pores appear to have formed soon after the rate of solidification and heat dissipation had reached their maximum and were decreasing. While the freezing point depression due to build-up of microsegregation and the transition from compacted to spheroidal type growth of the eutectic both influencing solidification kinetics and the temperature evolution of the casting, the results did not indicate a clear relation to the observed late deceleration of solidification.

Abstract: In material science, there is an increased demand for mapping of microstructural components and their composition. EPMA (Electron Probe Micro Analysis) with WDS (Wavelength Dispersive Spectrometry) is known as having high spectral resolution and sensitivity, but in practice considered to be slow in mapping applications. The present work describes a development of EPMA including design of both instrumental hardware and software related to electronics and calibration.

Abstract: A common and straightforward method for the standardisation in electron-probe microanalysis (EPMA) is the use of homogeneous reference materials prepared by various techniques such as by melting, sintering, high-temperature annealing and hot-pressing. The reference materials have to be analysed by independent methods accurately in order to define their “true” composition. For some compounds the preparation techniques are difficult because of their specific thermo-chemical properties (e.g. low diffusivities, high equilibrium nitrogen pressure, incongruent melting). In addition, many compounds show large homogeneity ranges with an a priori existing uncertainty in composition, contrary to what is generally preferred: to use compounds with a narrow homogeneity range (“line compounds”). For the latter, diffusional preparation techniques can be applied to yield diffusion layers instead of massive samples for standardisation. However, also single-phase samples with narrow homogeneity ranges can be prepared by diffusion, depending on the phase equilibria in the corresponding system. The presentation summarises efforts that have been made in order to prepare various reference materials for carbon and nitrogen standardisation of EPMA by various techniques. The boundary conditions such as phase stabilities, phase compositions and diffusion kinetics, which are important for their preparation to obtain well-defined reference samples are discussed. These samples were applied to various WDS/EPMA-based studies of phase diagrams and diffusion kinetics by means of Cameca SX 50 and SX 100 microprobes.