The Ti–Al–Si alloys are promising materials for high-temperature use in automotive, aerospace or cosmic industry. The main advantages of these alloys are their low density (approximately 4 g/cm3), ...good oxidation resistance, and mechanical properties at elevated temperatures. Addition of silicon into the Ti–Al alloys improves the high-temperature behaviour and improves compactness and adhesion of the oxide layer. The resistance against oxidation can be effectively improved also by an appropriate technology of preparation. In this work, the high-temperature cyclic and isothermal oxidation resistance of the Ti–Al–Si alloys are described. The effect of powder metallurgy production route (reactive sintering, mechanical alloying, Spark Plasma Sintering) on high-temperature behaviour was compared. Cyclic and isothermal oxidation tests were carried out at 800 °C and 1000 °C, well above the air-operating limit for TiAl. It was confirmed, that the Ti–Al–Si alloys are resistant at temperature 800 °C, where only very thin oxide layer was formed. Mechanical alloying followed by Spark Plasma Sintering improved the high-temperature behaviour of these alloys, the oxide layer was even thinner.
•High temperature behaviour of Ti–Al–Si alloys.•Alloys prepared by various techniques of powder metallurgy.•Cyclic and isothermal oxidation.
Two TiAlSi intermetallic compounds produced by Spark Plasma Sintering (SPS) adding different Si content were tested by nanoindentation, toughness and wear resistance. Microstructure differences ...between the two alloys were characterized by TEM and a strengthening model was proposed. The microstructure-based strengthening model well agreed with alloys stress obtained from the nanoindentation hardness. It resulted that as Si content increases, the TiAl phase started to form lamellar structure and inter-lamellar twinning. Al reduction in favour of an equal amount of Si was found to slightly promote Ti5Si3 silicide formation and eventually a TiAl phase coarsening. Ti–15Al–15Si alloy showed submicrometric equiaxed TiAl grains. On the other hand, Ti–10Al–20Si alloy was characterized by a lamellar TiAl phase which was identified as responsible for the different mechanical responses of the two alloys.
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•Nanoindentation hardness did not change with Si in SPS TiAlSi.•Fracture toughness and wear resistance improved with Si content.•Lamellae and twin formation within γ-TiAl was favoured by Si increment in Ti70(AlxSiy)30.•A microstructure strengthening model was applied to meet the alloys mechanical responses.
This work is devoted to the preparation of alloys based on intermetallic compounds in Ti-Al-Si system by powder metallurgy using Self-propagating High-temperature Synthesis (SHS). Since samples after ...SHS are very porous, in order to reduce the porosity, a combination of SHS, milling, and Spark Plasma Sintering (SPS), has been here tested as a complex production technology. Selected mechanical properties of consolidated samples (hardness, fracture toughness) and tribological properties (abrasive wear resistance) were determined. The microstructure of compacted Ti-Al-Si alloys is almost non-porous with the combination of titanium aluminides and titanium silicides. The alloys achieve good mechanical properties except for the fracture toughness.
•Ti-Al-Si alloy prepared using reactive sintering, milling and Spark Plasma Sintering.•Alloys are formed by TiAl or TiAl3 and titanium silicides.•Alloys are characterized by high hardness and abrasive wear resistance.
•Ln:Lu2O3 (Ln = Pr, Eu, Tb, Dy) were prepared by SPS using co-precipitated powders.•Only powders with high-quality crystallinity yielded partially transparent ceramics.•Luminescence of dense ceramics ...is determined by radiative transitions of dopant ions.•Additional annealing of sintered ceramics increases its integral light yield.•SPS made dense ceramics of Pr, Tb and Dy-doped Lu2O3 is reported for the first time.
Dense ceramics of Ln:Lu2O3 (Ln = Pr, Eu, Tb, Dy) were obtained using spark plasma sintering (SPS) from co-precipitated nanocrystalline powders. X-ray diffraction, scanning and transmission electron microscopies were used for the characterization of Ln:Lu2O3 powders obtained by various annealing regimes. Transparency of the sintered ceramics was achieved when powders with highly developed crystallinity were used for sintering. Sintered ceramics exhibited luminescence with a characteristic emission based on the element doped into the Lu2O3 host. The light yield of the sintered ceramics improved when the sintered ceramics was further annealed. The annealing of the sintered ceramics also improved the transmittance in the visible region; however, the transparency was lost when the annealing temperature was too high. To our best knowledge, the SPS fabrication of dense ceramics of Pr3+, Tb3+ and Dy3+-doped Lu2O3 is reported here for the first time.
Magnesium alloys are, due to high specific strength and stiffness, materials suitable for lightweight applications in automotive and aeronautical industries. Very poor corrosion resistance of ...magnesium and magnesium alloys significantly limits their wide utilization. Magnesium alloys are very susceptible to galvanic corrosion that can result in serious pitting corrosion, particularly in wet and salty environment. Magnesium and its alloys can be protected by formation of protective surface layers which can be achieved by plasma spraying capable of preparing metal and/or ceramic coatings. In this work, plasma coatings of NiAl10 and NiAl40 on AZ91 magnesium alloy substrate were prepared by the hybrid plasma spraying system WSP®-H 500. Present results show a significant effect of the preheat temperature of the AZ91 substrate during plasma spraying on development of a diffusion bonding due to the formation of sub-layer composed of Mg3AlNi2, Al12Mg17 phases and of Mg and Al solid solutions. The plasma sprayed coatings were observed by scanning electron microscope with elements point analysis and by X-ray phase analysis. The mechanical properties of prepared coatings were evaluated by adhesion tests. The corrosion resistance of prepared coatings was evaluated using the method of potentiodynamic measurements performed in the 0.5mol·l−1 NaCl solution while the long-term corrosion resistance was assessed in condensation chamber in wet air atmosphere at the temperature of 35°C. Both the tests showed significant effect of present sub-layers on resulting corrosion resistance.
•Coatings NiAl10 and NiAl40, prepared by WSP-H 500, had diffusion bond to AZ91.•Adhesive strength of NiAl10 and NiAl40 coatings was 25MPa and 12MPa, respectively.•Diffusion bond of NiAl40 coating had significant influence on corrosion resistance.•NiAl10 coatings showed up to twelve times higher polarization resistance values (Rp) compared to uncoated AZ91.
The aim of the present paper was to compare the evolution of Ni-Ti intermetallics in two non-conventional production techniques for the synthesis of NiTi shape memory alloy. Short term ultrahigh ...energy mechanical alloying is proposed to be able to describe the early stages of the milling process, which was not described in the literature previously, and to obtain intermetallics in shorter process durations. The reactive sintering using high heating rate (>300°C min
− 1
) is a process designed to suppress the formation of secondary intermetallics and to reduce the porosity of the product. The same phases' formation sequence was determined for both processes. The detrimental Ti
2
Ni phase forms preferentially, and therefore, its presence cannot be avoided in any of the investigated techniques.
An Al95Cr3.1Fe1.1Ti0.8 (in at.%) alloy was made into rapidly solidified powder by melt atomization. The powder was compacted by two processes: 1) uni-axial cold compression at an ultra-high pressure ...of 6GPa and 2) hot extrusion at 480°C. The structures, mechanical properties and thermal stability of both materials were compared with the commercial AlSi12Cu1Mg1Ni1 (in wt.%) casting alloy, which is generally considered to be thermally stable. It was found that cold compression at ultra-high pressure created a compact and porosity-free material, which was similar to the material that was prepared with the commonly used hot extrusion method. The Vickers hardness, compressive strength and compressive yield strength of the cold-compressed alloy were 161 HV, 680MPa and 547MPa, respectively, which were higher than the values obtained for the hot-extruded and casting alloys. The thermal stability of the hot-extruded Al95Cr3.1Fe1.1Ti0.8 alloy was excellent because its mechanical properties did not change significantly, even after 100h of annealing at 500°C. The mechanical properties and thermal stability of the investigated materials were discussed in relation to their structures and diffusivities of the alloying elements.
► The Al95Cr3.1Fe1.1Ti0.8 alloy was prepared by compression at an ultra-high pressure of 6GPa. ► The resulting material was dense and porosity-free. ► The material had high hardness of 161 HV and a compressive strength of 680MPa. ► The material had excellent thermal stability at 500°C.
Al–23Si–8Fe–1Cr and Al–23Si–8Fe–5Mn (in wt%) alloys were prepared via melt centrifugal atomization following powder compaction by uni-axial pressing at 6GPa and 450°C for 60min. The obtained ...materials were porosity-free with good particle-to-particle contact. The “composite-like” microstructures were very fine, showing silicon particles distributed in an α-Al matrix and displaying nearly equiaxed intermetallic phases. The intermetallic phases were identified as β-Al5FeSi and α-Al9.3FeMn1.4Si1.8 in the Al–23Si–8Fe–1Cr and Al–23Si–8Fe–5Mn alloys, respectively. The Vickers hardness and compressive yield strength were 182HV5 and 540MPa, respectively, for the Al–23Si–8Fe–1Cr alloy and 197HV5 and 650MPa, respectively, for the Al–23Si–8Fe–5Mn alloy. The thermal stability of the alloys was studied by mechanical testing after long-term annealing at 300–400°C, by compressive testing at 200–300°C and by creep testing at 300°C and 250MPa. The thermal stability of both alloys was significantly better when compared to the “thermally stable” casting Al–12Si–1Cu–1Mg–1Ni alloy that is commonly utilized in the automotive industry for thermally loaded components such as pistons for combustion or diesel engines.
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