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The properties and microstructure of austenitic stainless steels reinforced with Al2O3 particles

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Iron base alloys or steels have been used as matrix materials for metal matrix composites, owing to their lower cost, versatility and adequate mechanical and wear properties. The austenitic stainless steels grades have superior corrosion resistance and tensile ductility. However, they have relatively poor wear resistance, the cause of their low hardness. The addition of hard ceramic particles into stainless steels provides a more practical way of increasing the mechanical properties of steels [1÷3]. The hard compounds play a very important role in determining the corresponding mechanical properties of composites such as hardness. Ceramic particles which have been proposed for use as reinforcement in iron-based composites include carbides (TiC, WC, Cr3C2 etc.), oxides (ZrO2, Al2O3, Y2O3), nitrides (TiN, Si3N4) and borides (TiB2, ZrB2) [4÷7]. One of these, Al2O3 is the most commonly used reinforcement because has low density, the high hardness and Young’s modulus, and the high melting point. This ceramic exhibits the high chemical stability, good wear resistance, excellent oxidation resistance and outstanding mechanical properties at high-temperature [8]. In recent years, the research concerning the influence of the Al2O3 and Y2O3 ceramics on the properties of the stainless steels was realized. These tests were carried out using the high temperature sintering techniques. Vardavoulias et al. [9] investigated the dry sliding wear behaviour of two P/M austenitic stainless steels (AISl 304L and 316L) and their composites containing two different types of ceramic particles (Al2O3 and Y2O3) using different sintering activators (BN and B2Cr). To obtain the highest values of density for austenitic stainless steels reinforced with the ceramic particles Y2O3 ceramic and B2Cr sintering activator are used. The addition of ceramic particles positively effected on the wear behaviour of both types of stainless steels. In the case of AISI [...]


  The influence of the titanium addition into aluminium on the bond strength properties and structure of interface of the AlTi6/Al2O3 joints was investigated. The bond strength of the metal/Al2O3 joints was determined by the push-off test. Addition of 5.9 wt.%. Ti to Al caused the reduction of shear strength of the AlTi6/Al2O3 joints. The investigations by mean of electron microscopy equipped with a spectrometric system for microanalysis of the chemical composition revealed TiAl3 phases formed at the AlTi6/Al2O3 interface. Oxygen was detected in some areas of TiAl3 phases. Finally, this structure of the AlTi6/Al2O3 interface was responsible for lower bond strength comparing to properties of the Al/Al2O3 joints. Keywords: AlTi6/Al2O3 joint; shear strength, interface WŁAŚCIWOŚCI I MIKROSTRUKTURA POŁĄCZENIA AlTi6/Al2O3 W pracy przedstawiono badania dotyczące wpływu dodatku tytanu do aluminium na wytrzymałość na ścinanie oraz mikrostrukturę połączenia AlTi6/Al2O3. Wyniki wykazały, że dodanie tytanu do aluminium wpływa na obniżenie wytrzymałość na ścinanie badanego połączenia. Badania mikrostrukturalne (SEM oraz TEM) połączone z analizą składu chemicznego wykazały powstanie wydzieleń fazy TiAl3 na granicy rozdziału połączenia. W obszarach fazy TiAl3 obserwowano obecność tlenu. Tworzenie nowych faz na granicy rozdziału połączenie AlTi6/Al2O3 odpowiada za obniżenie wytrzymałości w porównaniu z połączeniem Al/Al2O3. Słowa kluczowe: połączenie AlTi6/Al2O3 joint; wytrzymałość na ścinanie, granica rozdziału Introduction The basis of the technological processes such as soldering, brazing and production of metal matrix composite materials is the assurance of the appropriate wettability of ceramic by liquid metals and receiving the stable joint between the metal and ceramic. Therefore, the wetting of the Al2O3 by liquid aluminium has been investigated by several authors using the sessile drop method [1÷5]. These studies concentrated mainly on the in[...]


  Mechanical properties of Ni-Al-Ti-B alloys are discussed in the paper. The samples were tested by compression in a wide range of temperatures and strain rates. The Ni-Al-Ti-B alloy is characterized by high hardness and addition of Ti does not show any significantly negative effect on brittleness. The conducted compression tests demonstrated decrease of yield point and increase of ductility with increase of temperature. The evolution of structure at various strain levels is also reported, especially in the aspect of application of the alloy for working at higher temperatures. Additionally, observations of samples’ surface from the onset of cracking until failure of the sample were performed. Keywords: NiAl-based alloys, mechanical properties, microstructure MIKROSTRUKTURA I WŁAŚCIWOŚCI MECHANICZNE STOPU Ni-Al-Ti-B W artykule przedstawiono wyniki badań dotyczące właściwości mechanicznych stopu Ni-Al-Ti-B. Otrzymano je z testów ściskania prowadzonych w szerokim zakresie temperatur i prędkości odkształcenia. Stop Ni-Al-Ti-B charakteryzuje wysoka twardość, a dodatek tytanu nie wpływa w sposób istotny na wzrost kruchości. Wykonane próby ściskania wykazały obniżenie granicy plastyczności i podwyższenie ciągliwości ze wzrostem temperatury. Przedstawiono także obserwacje zmian strukturalnych przy różnych poziomach odkształcenia, szczególnie w aspekcie przydatności tego stopu do pracy w podwyższonych temperaturach. Dokonano także obserwacji powierzchni próbek od stadium inicjacji pękania aż do zniszczenia. Słowa kluczowe: stopy na osnowie NiAl, właściwości mechaniczne, mikrostruktura.Introduction Studies in the field of new materials for high temperature applications have stimulated interest in alloys based on intermetallic phases, mainly from equilibrium systems of NiAl, FeAl and TiAl. These alloys are characterised by unusual mechanical and physicochemical properties as well as corrosion resistance, making them eligible for operation at [...]

The properties of AISI 316L stainless steel reinforced with TiB2 ceramics sintered by the HT-HP process

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Austenitic steel is a material characterized by high and stable mechanical properties at high temperature as well as high resistance to the aggressive environments. However, TiB2 ceramics is characterized by a unique combination of the properties (high melting point 3127°C, high hardness 33 GPa, high modulus 570 GPa and low density 4.451 g/cm3), which provide opportunities to apply it in a high temperature and corrosive environment. The TiB2 ceramics has a very good resistance to the oxidation, chemical and structural stability at high temperatures, resistance to the thermal shocks and abrasion resistance [1÷5]. Therefore, titanium diboride is the good reinforcing material for composites than for example carbides, which are less stable at high temperature. For several years research on a group of iron-base oxide dispersion strengthened (ODS) alloys were conducted. ODS alloys have been considered as the material of choice for many high temperature applications for a long time, because of their attractive mechanical properties such as outstanding creep and fatigue strengths at temperatures exciding 1000°C. The oxide dispersoids such as Al2O3 i Y2O3 are much more stable even up to temperature of 1200°C than precipitates such as carbides or intermetallic phases [5÷9]. However, Vardavoulias et al. [10] were studied the influence of Al2O3 and Y2O3 (5 wt. %) ceramics and two different sintering activators BN and B2Cr (1 or 2 wt. %) on the tribological properties the AISI 304L and ALSI 316L stainless steel. The materials were received by the free sintering process in vacuum at temperature of 1250°C, where the duration of the process was 30 min. Wear tests were carried out using pin-on-disc apparatus. The application of Y2O3 ceramic and B2Cr sintering activator gave the highest density of the composites. However, the presence of ceramic particles (Al2O3 and Y2O3) and sintering activators improved significantly t[...]

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