Papers by Keyword: Metallography

Abstract: The preparation of metallographic samples remains a crucial aspect of microstructural analysis, especially with the continuous development of advanced materials and imaging techniques. Despite its significance, sample preparation is often underestimated, yet achieving a surface with minimal structural distortion is essential for accurate microstructure evaluation and data interpretation. This study aimed to optimize steel sample preparation methods to obtain surfaces suitable for correlative imaging using multiple microscopic techniques, including modern scanning electron microscopy (SEM) with sample bias and electron backscatter diffraction (EBSD). The results demonstrate that specific contrast features observed in SEM can, in some cases, be qualitatively verified using EBSD. Furthermore, variations in SEM settings, such as lower landing energy, influence information depth, which in turn affects the accuracy of phase quantification, particularly when utilizing artificial intelligence-based methods.

Abstract: The advent of innovative, reasonably priced additive manufacturing techniques has been facilitated by the industry 4.0 era. This study aims to characterize the ER70S-6 wire arc additive manufacturing (WAAM) layer in metal inert gas (MIG) as a result of controlled process speed, electrode type, voltage, and weld current using a three-axis automated motion framework. The study approach begins with the design and building of an automated MIG welding motion system, which includes component manufacture, assembly, calibration, and motion path testing. The specified settings modify the speed of the weld probe motion in response to manual welding parameter adjustments. The investigation continues with the characterization of single to four-layers of WAAM to know the corrosion rate, microstructure, and the Vickers hardness. Corrosion testing results showed that the single-layer of WAAM had the lowest corrosion rate, as well as the highest hardness. Whereas the four-layer had the highest corrosion rate and the lowest hardness.

Abstract: Chemical etching is an integral part of metallographic sample preparation. Maintaining precise etch times can be difficult and therefore repeatability is limited. The aim of this work is to improve the repeatability of sample preparation using robotization. Prior to etching, metallographic samples of S355J2 (1.0577) structural steel were finely mechanically polished. For verification, 15 specimens were prepared using an in-house designed automated etching machine with a built-in 5-axis robotic arm and 15 specimens prepared manually by an expert metallographer. The samples were etched with Kourbatoff no. 4 reagent for 8 seconds in a beaker placed in an ultrasonic cleaner at 80 kHz. The samples were then cleaned in 7 beakers of cleaning fluid also placed in the ultrasonic cleaner. The robotic etching and cleaning process was optimized and the quality of the resulting surface is at least as good as that of the samples prepared by an expert metallographer. The surfaces were compared using a light optical microscope (LOM) and a confocal laser scanning microscope (CLSM). The repeatability of the preparation process is a key aspect for obtaining a large dataset of steel microphotographs for training a deep neural network that will be used in future research.

Abstract: Austempered Ductile Irons is a promising material with a favorable combination of low price and good mechanical properties. It is produced by isothermal hardening of cast iron with nodular graphite. The heat treatment parameters directly influence the structure of the matrix. The structure consists of an ausferrite matrix - a mixture of epitaxial ferrite + residual austenite and graphite. The resulting mechanical properties depend on the proportion and morphology of the individual phases. Therefore, a thorough structural characterisation is needed to describe the influence of the heat treatment parameters. However, conventional methods such as optical microscopy do not provide sufficient accuracy. Therefore, this work used a very accurate EBSD method to evaluate the structure in the as-received state and after heat treatment.

Abstract: Aircraft components have different functions and characteristics, for example, the bolt and nut pressure switch of Cessna Grand Caravan 208B, which functions to determine the pressure of oil and fuel flowing. At the end of the bolt and nut, there is a small hole to press the sensor in the component, then the result of the pressure will be converted to the system and sent to the indicator located in the cockpit, so the pilot sees the actual in the cockpit. The purpose in this research was to determine the characteristics of the bolt and nut pressure switch. This study used chemical composition, Vickers hardness, and metallographic testing methods. The test results of the chemical composition of bolt and nut on the pressure switch of Cessna Grand Caravan 208B, show that the elements, iron (Fe) = 67.58% and chromium (Cr) = 17.04%, are the dominant elements, therefore it is included as an alloying element of Fe-Cr. The test an average hardness value of 254.64 VHN. These values were obtained from the total percentage of iron 67.58% and chromium 17.04%. Chromium (Cr) is an element that can increase the hardness of carbon steel and increase corrosion resistance. Therefore, the hardness of the bolt and nut pressure switch of Cessna Grand Caravan 208B is high due to the addition of Cr which help the main element, Fe, properties. The novelty of this study is the dominant presence of chromium, so the properties of this material are hard, heat resistant, and corrosion resistant

Abstract: The combination of the conventional forming processes rolling and extruding enables the continuous production of cross-sectional aluminum long products. Regarding power consumption and resulting material specifications, the combined process offers various advantages in comparison to its conventional alternatives [1, 2]. The combined rolling and extrusion process is in an early stage of maturity. The production of pure aluminum wire is state of the art. The material flow within the process can partially reproduced by the use of numerical simulations [3]. Some process specific characteristics need to be understood and controlled to obtain a better process design and to enable the future production of complex cross-sectional products. This paper describes the results of experimental and numerical investigations regarding the combined rolling and extrusion process. The test specimen of a visioplastic examination on an industrial scale plant [3] was examined by the use of metallography. Those results where compared to a numerical simulation of the industrial experiment. The comparison of these results where then linked to some specific characteristics of the process. The existence of a dead zone with a shape comparable to the conventional indirect extrusion process was proved. The deformation zone of the combined process was divided into four zones which can be differentiated in the experimental as well as the numerical results. General design rules were derived from this differentiation. These design rules were used to optimize the forming geometry of an industrial scale plant. Critical process forces where reduces and resulting scrap material was minimized.

Abstract: The most common titanium alloy used in combination with additive manufacturing is Ti-6Al-4V ELI. On the other hand, the 3D printing of β-Ti alloys is still in the stage of development of both materials and their treatment. The newly developed biomedical Ti alloys are often containing Nb, Ta, Zr. These alloys are showing very good values in terms of biocompatibility and corrosion resistance while their elastic modulus may be in the range of 30-70 GPa. The printing of these alloys is however limited by their relative novelty. Powders are not yet available through traditional commercial ways. In this work, Ti–24Nb–8Ta–4Sn specimens prepared by the selective laser melting (SLM) method were used. The porosity was evaluated by two methods: area porosity evaluated by image analysis on metallographic specimens and volume porosity evaluated by micro-computed tomography (μCT). The microstructure was observed using both light and scanning electron microscopy (SEM). The SEM was as well used for energy dispersive spectroscopy (EDS) for chemical analysis and the analysis of crystallographic orientation was conducted using the method of electron backscattered diffraction (EBSD).

Abstract: With high operating parameters of the medium in medium-pressure and high-pressure steam pipelines of fossil power plants, creep damage occurs, especially in welded joints leading to complete rupture of the pipe wall in the last phase. Detection of creep damage at an early stage before major cracks may occur can prevent these accidents. For these purposes, phased array ultrasonic testing was performed using a high frequency probe. This testing was performed on real welded joints cut from the power plant. To verify the possibility of detection, metallographic analysis on the tested locations was performed. When comparing the results, it is possible to refine the interpretation of the ultrasonic data and the metallographic results can also be used in the eventual qualification of non-destructive testing.

Abstract: Directed energy deposition (DED) is an Additive Manufacturing process deposing fused metal powder on a preexisting substrate. This document shows the influence of heat treatment on P295GH deposit made by DED, for hybridization process. The heat treatment must reduce the macroscopic differences between the rolled substrate and the deposited DED material. The experimental plan has been defined around AC₃ temperature, according to P295GH existing literature. XRD analysis, hardness measurements and metallographic inspections have been performed on samples before and after heat treatment. XRD analysis and hardness measurements have shown an isotropic material. The as-built microstructure is ferritic and acicular, but coarsens after the heat treatment. The study promotes a heat treatment at 800°C during 3 hours to obtain the best compromise between properties, impact on the substrate and differences with the rolled substrate.

Abstract: For the corrosion resistance analysis of the heat exchanger plates (made of AISI 316L steel) the samples with visible damage was delivered. The major part of the surface damages was located at the place of "close proximity" (or surface contact) of individual plates. Some of delivered samples showed an unequal layers of sediments, which indicating a different flow velocities of operating fluid through the plates. At locations of the upper part of the plates with no sedimentation (high velocity flow), the most surface damage was detected in "near contact" areas as well as outside. On the other hand, the area of the lower part of the plates, where the sediment deposition was massive (lowest velocity flow), was observed the smallest surface damage. The results of the chemical composition analyses showed a lower amount of molybdenum and a higher amount of phosphorus in case of all samples. The contents of the key elements necessary for the corrosion resistance (chromium and nickel) were only just above the lower limit of the prescribed chemical composition interval. For detailed study of surface damage, selected defects were observed and documented using scanning electron microscopy. Localized damage showed intercrystalline failure of material with typical surface morphology degraded as a result of cavitation damage under hydrodynamic stress.