Micropowders of oxide-dispersion-strengthened (ODS) steel have been synthesized using the ultrasonic irradiation method with variations in amplitude. The ultrasonic irradiation process is performed for 50 h at a frequency of 20 kHz with 40%, 50%, and 60% amplitudes in toluene solution. The formation of Fe-Cr microalloys in the preparation of Fe-15Cr-0.5Y 2 O 3 powder was analyzed using SEM-EDS, X-ray diffraction (XRD), and TEM-EDS. The percentage of Fe-Cr phase mass fraction of ODS steel micropowder formed during ultrasonic irradiation with 40%:50%:60% amplitude was 12.2%:34.1%:22.1%, with 25.67:77.02:38.51 nm crystallite size. The crystallite size at 50% amplitude was the largest, and the diffusion process of Fe-Cr-Y 2 O 3 microparticles was most dominant at 50% amplitude. The Fe and Cr phases are still present when the ODS particles successfully dispersed in the main particle. AbstrakSintesis Baru Paduan Mikro Baja ODS dengan Irradiasi Ultrasonik Amplitudo Tinggi. Serbuk mikro dari baja yang diperkuat dengan dispersi oksida (ODS) telah disintesis menggunakan metode iradiasi ultrasonik dengan variasi amplitudo. Proses iradiasi ultrasonik dilakukan selama 50 jam pada frekuensi 20 kHz dengan amplitudo 40%, 50%, dan 60% dalam larutan toluena. Pembentukan paduan mikro Fe-Cr dalam preparasi serbuk Fe-15Cr-0.5Y2O3 dianalisis menggunakan SEM-EDS (scanning electron microscopy-energy-dispersive spectroscopy), difraksi sinar-X (XRD), dan TEM-EDS (transmission electron microscopy-energy-dispersive spectroscopy).

The 56Fe16.6Cr25Ni0.9Si0.5Mn austenitic superalloy has been produced in an induction furnace; it was made from granular ferro-scrap, ferrochrome, ferrosilicon, and ferromanganese materials. Originally, this alloy had been proposed for use in high mechanical loads and high temperature conditions (such as in nuclear and fossil fuel power plant facilities). Tensile strength tests showed that the alloy has an average yield strength of about 430.56 MPa, which is higher than Incoloy A-286 (a commercially available alloy). A combination of microscopy techniques by means of an optical microscope, X-ray diffraction [XRD], scanning electron microscopy [SEM], and transmission electron microscopy [TEM] techniques were applied in order to get detailed information about the fine structure of the alloy. XRD confirmed that the alloy matrix exhibits an FCC crystal structure with a lattice parameter of about 3.60 Å and grain sizes ranging from 50 to 100 µm. The results of the TEM analysis revealed the new type of precipitations that formed at the grain boundaries. These needle-like precipitations, probably Fe/Cr-rich precipitations of the (Fe,Cr)xCy type, acted as the source of intergranular corrosion (IGC). Small coherent plate-like and much smaller granular precipitations were found distributed homogenously along grain boundaries and inside the grains. Combining the tensile strength test and microstructure analysis suggested that these precipitations play significant roles in the hardness of the investigated sample.

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The present contribution summarises first results that have been achieved with the new brazing material Sn75Cu20Ge5 (wt-%) for transient liquid phase (TLP) bonding of aluminium cast alloy AlSi7Mg0.3 (wt-%). The microstructure of the braze ribbons and the obtained joints have been thoroughly investigated on different lengthscales using scanning and transmission electron microscopy as well. Whereas the braze ribbon material is only composed of beta-tin, h-phase (Cu 6 Sn 5 ) and some germanium rich precipitates, the transient liquid phase joint displays a much more complex microstructure that consist mainly of beta-tin and different aluminium-copper and aluminium-germanium phases. In addition small silicon oxide rods and a hitherto unreported hexagonal aluminium-copper-magnesium-germanium phase with approximated lattice parameters a = 0.7123 nm, c = 2.40 nm have been found in the seam of the joint.Keywords: Transient liquid phase / copper / tin / germanium / aluminium / electron microscopy / electron backscatter diffraction / energy dispersive X-ray spectroscopy / electron diffraction / hexagonal crystal structure Der vorliegende Beitrag fasst erste Ergebnisse fü r das neuentwickelte Lö tmaterial Sn75Cu20Ge5 (wt-%) fü r die transient liquid phase (TLP)-Bindung der Aluminium-Gusslegierung AlSi7Mg0.3 (wt-%) zusammen. Die Mikrostruktur der Lö tbä nder und die dadurch bedingten Lö tstellen wurden auf verschiedenen Lä ngenskalen mittels Raster-und Transmissionselektronenmikroskopie untersucht. Wä hrend das Lö tbandmaterial lediglich aus Beta-Zinn, h-phase (Cu6Sn5) und einigen germaniumreichen Ausfä llungen besteht, zeigen die Transient-liquid-phase-Lö tstellen sehr viel komplexere Mikrostrukturen, die hauptsä chlich aus Beta-Zinn und anderen Aluminium-Kupfer-und Aluminium-Germanium-Phasen aufgebaut sind. Zusä tzlich wurden kleine Siliziumoxid-Stä bchen und bisher nicht beschriebene hexagonale Alumi-Corresponding author: R. Iskandar, nium-Kupfer-Magnesium-Germanium-Phasen mit den ungefä hren Gitterparametern a = 0,7123 nm und c = 2,40 nm in den Nä hten gefunden.Schlü sselwö rter: Flü ssigphasenü bergang / Kupfer / Zinn / Germanium / Aluminium / Elektronenmikroskopie / Elektronenrü ckstreubeugung / energiedispersive Rö ntgenspektroskopie / Elektronenbeugung / hexagonale Kristallstruktur

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