SURFACE MODIFICATION of Fe-8Si ALLOY by BORONIZING AND ITS CHARACTERIZATION

In this study Fe-Si binary alloy containing 8 at. % Si and pure iron were pack boronised at 900 degrees C, 1000 degrees C and 1100 degrees C for 3 h using Ekabor II powder. The microstructure, chemical composition, phase contents and microhardness of the formed boride coatings were characterized by means of XRD, SEM-EDS and Vickers Microhardness measurements. The saw-tooth morphology was observed on both substrates, it tended coarsen with boriding temperature and especially with the addition of Si to the substrate. Silicon did not dissolve in the boride layer but accumulated between boride layer and Fe-8Si substrate and formed a Si rich transition zone with an average hardness of 500 HV. The average hardness value of the boride layers on both substrates were approximately 2200 HV. The boride layer thickness increased near-linearly with boronizing temperature for both materials. The presence of silicon in the substrate reduced the thickness of boride layer compared to the boride layer thickness on pure iron. The amount of boron rich FeB phase compared to Fe2B phase was higher on the boride layer of Fe-Si alloy than of pure iron

Mg65Ni20Y15-xAgx (X=1, 2, 3, 5) ALLOYS PREPARED VIA ATMOSPHERE CONTROLLED INDUCTION SYSTEM

In this work, Mg65Ni20Y15–XAgX (X = 1, 2, 3, 5) alloys were manufactured by atmosphere controlled induction system. The effect of Ag ratio on the microstructural properties, micro-hardness, density, and homogeneity of the Mg–Ni–Y alloys were investigated. These alloys were characterized by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Vickers micro-hardness measurement. According to XRD results, Ni3Y and Mg6Ni phases were observed as well as AgY and Ag17Mg54 phases, which were obtained in alloys. The quantitative results of EDX analysis confirm that the chemical composition of the obtained phases is very close and their homogeneities are so high. The average micro-hardness values of the ingot alloys were measured between 208 and 266 HV for matrix. The elastic modulus and densities of the Mg65Ni20Y15–XAgX (X = 1, 2, 3, 5) alloys increased by increasing Ag in the alloys and they were determined in the range of 58.18–68.12 GPa and 3.14–3.53 g/cm3, respectively.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Powder production, FAST processing and properties of a Nb-silicide based alloy for high temperature aerospace applications

A Nb-silicide based alloy with nominal composition Nb–18Ti–22Si–6Mo-1.5Cr–2Sn-1Hf (at. %), designed for high temperature aerospace applications, was produced via a powder metallurgy (PM) route. The raw elements were arc melted, crushed, and milled to powder, then consolidated using Field Assisted Sintering Technology (FAST). The compressive creep of the alloy was evaluated using electro-thermal mechanical testing (ETMT). The study demonstrated the production of larger 60 mm diameter samples, with potential for further scale up. The microstructure of the FAST alloy, which is comprised of bcc Nbss and tetragonal αNb5Si3 was more homogenous compared with the cast alloy, with some interstitial contamination that occurred during powder production. The FAST alloy had lower density than state of the art Ni-based superalloys and refractory metal complex concentrated alloys (RCCAs) and high entropy alloys (RHEAs), and its yield strength and specific yield strength was higher than those of the latter metallic Ultra high temperature materials (UHTMs) and comparable to those of Nb-silicide based alloys with B addition. The stress exponent n in compressive creep was in the range 1.7–2.6, similar to that of binary Nb–10Si and Nb–16Si alloys and its creep rate at 1200 °C and 100 MPa was similar to that of the MASC alloy (Nb–25Ti–16Si-8Hf-2Al–2Cr (at.%)). Like the latter, the creep of the FAST alloy did not meet the creep goal