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

Sulima I., Figiel P., Jaworska L., Hyjek P.

Inżynieria Materiałowa

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2011

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Vol. 32, nr 1

40-43

EN

Powder metallurgy (P/M) is an ideal technique for producing the dispersion- strengthened materials as it produces a homogeneous distribution of dispersoids in the matrix. Dispersion strengthening by addition of the ceramic particles improves the mechanical properties of the sintered stainless steels. In this work, the AISI 316L stainless steel was chosen as a matrix alloy and was reinforced with TiB2 particles. The titanium diboride (TiB2) was selected as reinforcement because it exhibits a very high hardness, high strength at elevated temperature and good thermal stability. The influence of TiB2 ceramics on the properties and microstructure of the AISI 316L stainless steel was investigated. In the present study, the high temperature-high pressure (HT-HP) method to prepare the austenitic AISI 316L stainless steel reinforced with 2 vol. % TiB2 ceramics was used. Materials were sintered at pressure of 5 Pa and 7.5 GPa and at temperature of 900÷1300°C. The duration of sintering was 60 seconds. Mechanical properties were determined by Vickers hardness test and the compression test. Young's modulus measurements were carried out using ultrasonic method. The microstructure features of the sintered materials were revealed by means of the light microscope and scanning electron microscope. The results show that the properties of the sintered materials depends on the applied conditions of the sintering. The hardness and the compression strength decrease with increasing temperature, while the Young's modulus increases. The materials sintered at pressure of 7.5 GPa exhibit better properties compared to the samples sintered at 5 GPa. The microstructural investigations indicated that the TiB2 ceramics was distributed not evenly along the grain boundaries of steel.

PL

Metalurgia proszków jest efektywną technologią wytwarzania materiałów umacnianych dyspersyjnie, gwarantującą jednorodne rozmieszczenie fazy umacniającej w osnowie. Umocnienie dyspersyjne cząstkami ceramicznymi pozwala poprawić właściwości mechaniczne spiekanych stali. W pracy zastosowano stal austenityczną AISI 316L jako osnowę oraz ceramikę TiB2 jako fazę umacniającą. Diborek tytanu (TiB2) został wybrany jako umocnienie, ponieważ charakteryzuje się bardzo wysoką twardością, wysoką wytrzymałością w podwyższonej temperaturze oraz dobrą stabilnością cieplną. Głównym celem pracy było zbadanie wpływu ceramiki TiB2 na właściwości i mikrostrukturę stali austenitycznej AISI 316L. Spiekanie przeprowadzono metodą wysokociśnieniowego-wysokotemperaturowego spiekania (HP-HT). Spiekanie materiałów przeprowadzono pod ciśnieniem 5 GPa i 7,5 GPa oraz w temperaturze 900÷1300°C. Czas spiekania wynosił 60 s. Badania właściwości mechanicznych obejmowały próbę mikrotwardości sposobem Vickersa oraz wytrzymałość na ściskanie. Pomiar modułu Younga przeprowadzono metodą ultradźwiękową. Mikrostrukturę umacnianej stali autentycznej AISI 316L obserwowano za pomocą mikroskopu świetlnego oraz skaningowego mikroskopu elektronowego (SEM). Wykazano, że właściwości spiekanej stali AISI 316L umacnianej TiB2 zależą od zastosowanych parametrów spiekania. Wraz ze wzrostem temperatury zaobserwowano zmniejszenie się twardości i wytrzymałości na ściskanie oraz zwiększenie wartości modułu Younga. Stal austenityczna spiekana pod ciśnieniem 7,5 GPa uzyskała lepsze właściwości w porównaniu z materiałami spiekanymi pod ciśnieniem 5 GPa. Badania mikrostruktury wykazały niejednorodne rozmieszczenie ceramiki TiB2 wzdłuż granic ziaren stali austenitycznej.

2

The influence of the sintering conditions on the properties of the stainless steel reinforced with TiB2 ceramics

Sulima I., Klimczyk P., Hyjek P.

Archives of Materials Science and Engineering

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2009

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Vol. 39, nr 2

103-106

EN

Purpose: The paper analyzes the influence of the temperature and pressure on the properties and structure of the austenitic AISI 316L stainless steel reinforced with 1% vol.TiB2 ceramics. Design/methodology/approach: The sintered austenitic AISI 316L stainless steel reinforced with 1% vol.TiB2 were obtained using the high temperature-high pressure (HT-HP) method at pressure of 5.0 and 7.5 š 0.2 GPa and temperatures 900°C, 1150°C and 1300°C. The duration of sintering was 60 seconds. Young's modulus measurements were carried out using ultrasonic method. Mechanical properties were determined by Vickers hardness test. For microstructure observation scanning electron microscope JEOL JSM-6460LV was used. Findings: The decrease of the hardness of the sintered austenitic AISI 316L stainless steel with the increasing temperature of sintering was observed. However, the Young's modulus increases with the growth of the temperature of sintering. The results showed that the hardness increased with increasing pressure. The microstructural investigations indicated that the TiB2 ceramics were distributed along grain boundaries. Practical implications: The obtained results show that the temperature and pressure have influence on the mechanical and physical properties of the investigated steel reinforced with 1% vol.TiB2. These results may be used to design new materials i.e. austenitic stainless steel reinforced with TiB2 ceramics. Originality/value: The results from this work can be useful in determining conditions for sintering the austenitic AISI 316L stainless steel reinforced with various volume fractions of TiB2 ceramics.

3

Sintering of TiB2 ceramics

Sulima I., Figiel P., Suśniak M., Świątek M.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 11

687-690

EN

Purpose: Titanium diborides (TiB2) ceramic is particularly interesting because it exhibits high elastic modulus and hardness as well as high thermal conductivity. The interest in TiB2 ceramic increased enormously due to these properties but applications seem to be limited due to difficulties during densification process. In the experiment the TiB2 compacts was obtained using HP-HT method. The aim of this study is to work out and optimize the sintering densification process of TiB2 ceramics. Design/methodology/approach: The high temperature-high pressure (HT-HP) Bridgman type apparatus was used for densification method of TiB2 powder. Ceramics were sintered at pressure of 7.2 ± 0.2 GPa and temperature at 1500-2300*C ± 50*C. The duration of sintering was 60 seconds. In order to investigate the structure changes, the optical and scanning electron microscope was used. Mechanical properties were determined by Vickers hardness. Young modulus measurements were carried out using ultrasonic method. Findings: The TiB2 ceramics was obtained without using sintering agents. The properties and structure of TiB2 ceramics strongly depend on conditions of sintering process. The application of the temperature of 1500*C ± 50*C and pressure of 7.2 ± 0.2 GPa and time of 60 seconds permits to obtain the TiB2 ceramics without cracks. Practical implications: The TiB2 ceramic might be used for production of composites. From a practical position it is important to optimize the sintering densification of TiB2 ceramic. Originality/value: The TiB2 ceramics were formed using HP-HT technique without the use of additives. This method of sintering for TiB2 ceramics is original one.