Institute of Fundamental Technological Research

The aim of this research was to investigate an effect of low temperature on the mechanical properties and mi-crostructure of 6061-T6 aluminium alloy (AA6061-T6) subjected to dynamic loading. The specimens were subjected to dynamic compression at a low temperature of −80°C in a range of strain rates from 1.25 × 10 3 1/s to 3.4 × 10 3 1/s to compare their mechanical responses. The deformation mechanisms were analysed through EBSD observations during which dynamic recovery, was found as the dominant one. Furthermore, microstruc-tural analysis indicated that deformation under high strain rate conditions and temperature of-80°C enables to keep the constant initial grain size of the material after the loading applied. The material behaviour was modelled using mechanism-based viscoplastic constitutive equations. Furthermore, an accuracy of the developed model was validated by comparing it to experimental data. The set of constitutive equations proposed has been successful in modelling the stress-strain behaviour of the material for the range of strain rates and temperatures encountered in aluminium-forming processes under low-temperature conditions.

Split Hopkinson pressure bar (SHPB),Low temperature,AA6061-T6,Microstructure

Direct Metal Laser Sintered Haynes 282 specimens as well as wrought ones were subjected to high-temperature exposure at 1000 °C for 100h in air to compare their oxidation behaviour. The specimens were removed from the furnace after 1h, 5h, 25h, 50h and 100h to reveal and study oxidation mechanisms through morphological and cross-sectional examination by using scanning electron microscopy with energy dispersive spectroscopy attachment and X-ray diffraction. Microstructural studies revealed that the oxidation kinetics, determined by changes in thickness scale and depth of aluminium diffusion zone, were mainly driven by the formation of Cr2O3 for the wrought material, and TiO2 for DMLS one. The wrought material was characterized by the oxidation rate equal to 0.96 and followed the logarithmic law. On the other hand, DMLS-manufactured Haynes 282 exhibited oxidation rate of 0.90 and follows the linear law for the thickness scale considerations. However, when the depth of aluminium diffusion was investigated, it had an oxidation rate of 0.87 and followed cubic law.

In this research, an effect of low temperature on the mechanical properties and microstructure of 6061-T6 aluminium alloy (AA6061-T6) subjected to static and dynamic loading was investigated systematically. The specimens were subjected to compression at the temperature of − 80°C in a range of strain rates from 0.001 to 0.1 1/s under static conditions, and from 1250 to 3400 1/s under dynamic conditions to compare their mechanical responses. The deformation mechanisms were discussed based on EBSD analysis. It was found, that under both testing conditions, dynamic recovery was the dominant mechanism responsible for material deformation.

The paper presents a comparison of microhardness, fatigue and high temperature corrosion of Inconel 740H nickel alloy in its as-received state and the same material with nitrided surface layers. The nitrided layers were produced using traditional glow discharge nitriding (specimens nitriding on the cathode potential) and an active screen (specimens nitriding at the plasma potential). A microstructure of the layers was characterized through the scanning electron microscopy, X-ray energy dispersive spectroscopy and X-ray diffraction analysis. Mechanical properties of the nitrided Inconel 740H alloy were examined using microhardness measurements and standard fatigue tests. It was found that Inconel 740H with a nitrided surface exhibited an improved fatigue response of 50 MPa in the whole range of stress amplitudes from 350 to 650 MPa and almost 325% increase of hardness for plasma modified surface and 250% for cathode modified surface. Additionally, the application of cathode nitriding enhanced the corrosion resistance of the alloy in question and effectively protected it against a high temperature oxidation.

nitriding, nickel alloys, coatings, fatigue, corrosion

High-entropy alloys (HEA) are a group of modern, perspective materials that have been intensively developed in recent years due to their superior properties and potential applications in many fields. The complexity of their chemical composition and the further interactions of main elements significantly inhibit the prediction of phases that may form during material processing. Thus, at the design stage of HEA fabrication, the molecular orbitals theory was proposed. In this method, the connection of the average strength of covalent bonding between the alloying elements (Bo parameter) and the average energy level of the d-orbital (parameter Md) enables for a preliminary assessment of the phase structure and the type of lattice for individual components in the formed alloy. The designed TiCoCrFeMn alloy was produced by the powder metallurgy method, preceded by mechanical alloying of the initial elementary powders and at the temperature of 1050 °C for 60 s. An ultra-fine-grained structured alloy was homogenized at 1000 °C for 1000 h. The X-ray diffraction and scanning electron microscopy analysis confirmed the correctness of the methodology proposed as the assumed phase structure consisted of the body-centered cubic (BCC) solid solution and the C14 Laves phase was obtained.

HEA, solid solution, laves phase, U-FAST sintering

The aim of this research was to investigate an effect of low temperature on the mechanical properties and microstructure of 6061-T6 aluminium alloy (AA6061-T6) subjected to dynamic loading. The specimens were subjected to dynamic compression at a low temperature of -80°C in a range of strain rates from 1.25×103 1/s to 3.4 ×103 1/s to compare their mechanical responses. The deformation mechanisms were analysed through EBSD observations during which dynamic recovery, was found as the dominant one. Furthermore, microstructural analysis indicated that deformation under high strain rate conditions and temperature of -80°C enables to keep the constant initial grain size of the material after the loading applied.

Split Hopkinson Pressure Bar (SHPB), low temperature, AA6061, microstructure, EBSD