Marcin Rosiński

Nanocrystalline NiAl-TiC Composites Sintered by the Pulse Plasma Method

The paper presents the results of the examination of nanocrystalline NiAl-TiC composites with 25 wt.% and 40 wt.% of TiC. The starting materials were coarse-grained powders which were subjected to mechanical refining to obtain a nano-crystalline grain size. These powders were then sintered using the pulse plasma method. After sintering the NiAl-TiC composites have a density of 99.9% of the theoretical value. The grain size, determined by X-ray diffraction using the Hall-Williamson method; density; hardness and fracture toughness of the composites were investigated. The results obtained showed that the pulse plasma sintered NiAl-TiC have a density very close to the theoretical value and that the nano-crystalline microstructure was maintained. The NiAl-TiC composites containing 25wt.% of TiC have a hardness of 750 HV1 and a stress intensity factor KIC of 7 MPa⋅m1/2, whereas those containing 40 wt.% of TiC have a hardness of 1070 HV1 and KIC of 11.8 MPa⋅m1/2.

Heat Sink Materials Processing by Pulse Plasma Sintering

A Pulse Plasma Sintering (PPS) process was employed to manufacture Cu-diamond composites with a 50% volume fraction of each constituent. Pure and Cr (0.8wt.%) alloyed copper matrices were used and commercial diamond powders. The composites were sintered at temperature of 900°C for 20 min and under pressure of 60 MPa. In these sintering conditions diamond becomes thermodynamically unstable. Cu0.8Cr-diamond and Cu-diamond composites with relative densities of 99,7% and 96% respectively were obtained. The thermal conductivity of Cu0.8Cr-diamond composite is equal to 640 W(mK)-1 whereas that of Cu-diamond is 200 W(mK)-1. The high thermal conductivity and relative density of Cu0.8Cr-diamond composite is due to the formation of a thin chromium carbide layer at the Cu-diamond interface.

Nanocrystalline Cu-Al2O3 Composites Sintered by the Pulse Plasma Technique

The paper presents the results of examination of the structure and properties of nanocrystalline Cu-Al2O3 composites with the two different Al2O3 contents: 10 and 20 vol.%. The composites were produced using a mixture of copper and Al2O3 powders with an average crystallite size of about 60nm for Cu and about 40nm for Al2O3. The powders were consolidated by pulse plasma sintering (PPS) for 5 minutes at a temperature of 650oC under a load of 60 MPa. Irrespective of the volumetric content of Al2O3, the relative density of the composites was about 92%, and the average Cu crystallite size was about 80nm. The hardness of the composites varied with the volumetric content of Al2O3, and was equal to 270 HV0.1 for 20 and to 240 HV0.1 for 10% of Al2O3. The Cu-20%Al2O3 composite had a resistivity of 0.386 while that with 10% of Al2O3 was 0.149 56m.

Pulse Plasma Sintering of Nano-Crystalline Cu Powder

Nanocrystalline copper powders, produced by the reduction of the CuO with hydrogen, were consolidated using the pulse plasma sintering (PPS) method. The sintering process was carried out at temperatures between 500 and 900 oC under a load of 60 MPa for 5 min. The average crystallite size of the sintered component obtained at 500 oC was about 80nm and at 900 oC 1880 nm. The components produced at 500 oC had a relative density of 90 %, and those sintered at 900 oC 92 %; their hardness was 215 and 140 HV0.1, respectively.

Evaluation of Cutting Edges Made of Nanocrystalline Cemented Carbides Sintered by the Pulse Plasma Method

In our investigations, nanocrystalline WC-5 wt % Co was consolidated by the pulse plasma sintering method at various temperatures between 1320 and 1560 K under a pressure of 60 MPa for 300 s. The cemented carbides sintered at 1520 K have a relative density of 100 %, hardness of 2100 HV30, and tungsten carbides WC crystallite size of about 150-300 nm. An increase of the sintering temperature to 1560 K results in the increase of the WC crystallite size to about 300-500 nm and the hardness being decreased to 1980 HV30. The tool life of the cutting edges made of nanocrystalline cemented carbides sintered by the pulse plasma method is increased about two times in comparison with cutting edges made of standard and fine-grained cemented carbides during the turning of EN1.45.40 1H18N9T austenitic steel. On the basis of the literature data 1-4 and our own investigations 5-8, a decrease reduction of the tungsten carbides WC grain size in WC-Co cemented carbides increases the fracture toughness, bending strength, and hardness. WC-Co cemented carbides are most often produced by sintering with the partici- pation of a liquid cobalt phase. The presence of a liquid cobalt phase during the WC-Co sintering causes the growth of the WC grains. The growth of the WC grains is due to the high rate of diffusion of WC through the liquid cobalt phase. In the newest sintering methods; for example, spark plasma sintering SPS, field assisted sintering FAST, and plasma assisted sintering PAS9-11, the sintering process is very short and carried out at a lower temperature than in the conventional methods. A characteristic feature of the SPS, FAST, and PAS methods is a current pulse for heating the powders during sintering. Spark discharges during a current pulse are ignited in the pores. The discharges formed in the pores remove absorbed gases and oxides from the surface of powder particles, thereby facilitating the formation of active contact between them. The present investigation was concerned with sintering nanocrystalline WC-5 wt % Co powders using a new pulse plasma sintering PPS method 12. As in the SPS, PAS, and FAST methods, in the PPS method the spark discharges during a current pulse are ignited in the pores. The phenomena occurring in the PPS process are shown in Fig. 1. In this article, the results of a comparative investigation of the durability of cutting edges made of nanocrystalline WC-5 wt % Co cemented carbides sintered by the pulse plasma method and cutting edges made of standard and fine-grained cemented carbides 1.5 m of the same chemical composition during the turning of EN1.45.40 1H18N9T austenitic steel are presented. Austenitic steel, widely applied in the food and chemical industry, belongs to hard machinable materials 13. The hard machinability of auste- nitic steel comes from a surface hardening phenomenon during machining. Therefore, the machining is carried out with very low cutting parameters. For this reason, the investigations of nanocrystalline ce- mented carbides were taken into consideration. The nanocrystalline cemented carbides are significantly harder and more wear resistant then the standard or fine-grained cemented carbides 4-6.

Synthesis and characterization of cBN/WCCo composites obtained by the pulse plasma sintering (PPS) method

The cBN/cemented carbide containing 30vol% of cBN particles was produced using a mixture of a 6wt% Co added-WC powder, with a WC grain size of 0.4 μm and a cBN powder with a grain size ranging from 4 to 40 μm. The mixture was sintered to produce a plate, 20 mm in diameter, 3 mm thick. The sintering processes were conducted at temperature of 1100°C under a load of 100 MPa. The phase composition, density, hardness and micro structure of the sintered parts thus obtained were examined. The fractures through the WCCo/cBN composite showed the cBN particles torn out from the cemented carbide matrix were only few, whereas most of them have cleaved along the fracture plane. This gives evidence that the bond at the WCCo/cBN interface is mechanically strong.

WC/Ti Composite Material Enriched with CBN Particles Produced by Pulse Plasma Sintering (PPS)

Tungsten carbide (WC) and WCCo powders added with 30 vol.% cubic boron nitride (cBN) and 5 and 12 wt% of Ti were sintered by the pulse plasma sintering (PPS) technique. The sintering process was conducted under a load of 75 MPa at a pressure of 5.10- 5 mbar and a temperature of 1100-1500°C for 5min. The phase composition, density, hardness and microstructure of the sintered material thus obtained were examined. In the cBN-WCTi5wt% composite with an addition of 6wt% Co, the cBN particles are well bound with the matrix. The transcrystalline fractures of the cBN particles also indicate that the binding forces between these particles and the WCCoTi matrix exceed the matrix cohesion. The interfaces between the cBN grains and the surrounding matrix are almost straight lines, and no reactions between the cBN grains and the matrix were revealed in SEM observations.

Control and Monitoring System for Composite Materials Fabrication Based on PPS Method

Cubic boron nitride (cBN) is commonly used as a cutting tools material for the sake of its high hardness and wear-resistance. But on the other hand cBN, it requires application of an expensive HPHT (High Pressure High Temperature) to avoid the transformation of cBN into low-hardness h-BN, they must be sintered under a pressure of 5 to 6 GPa which substantially increases their production costs. An alternative method, called PPS (Pulse Plasma Sintering), was proposed to decrease the production costs. The PPS significantly decreases the costs of production and therefore it is very attractive for industry. However, automation and dedicated control system for PPS is required to carefully control parameters and hamper the transformation of cBN into hBN. Only the application of automated production line guarantee high-quality of cubic boron nitride samples. The paper discusses the requirements and presents the architecture of the control system dedicated for pulse plasma sintering system.

Unlimited possibilities of sintering by SPS

O ile w przypadku materiałów o małej rezystancji wzrost temperatury następuje poprzez wydzielanie się ciepła Joule’a w wyniku przepływu impulsów prądu elektrycznego przez spiekany proszek (grzanie bezpośrednie), to dla materiałów o dużej rezystancji stosowane wartości napięcia – od kilku do kilkunastu woltów – okazują się zawodne ze względu na przepływ prądu elektrycznego jedynie przez formę grafitową, w której prowadzony jest proces spiekania (grzanie pośrednie). W rezultacie spiekany materiał nagrzewany jest od powierzchni spieku do rdzenia tak, że szybkość i efektywność nagrzewania są małe. Zgodnie z ideą metod spiekania aktywowanych polem elektrycznym energia cieplna jest wydzielana bezpośrednio w całej objętości spiekanego materiału, co stanowi o dużej energooszczędności tych metod (małe straty energii cieplnej wypromieniowanej do otoczenia). Grzanie pośrednie ogranicza efektywne wykorzystanie techniki SPS w procesach spiekania. Podstawową wadą tego typu procesów jest konieczność stosowania wyższej temperatury i dłuższego czasu dla uzyskania spieku o dużej gęstości. Warunki te wpływają na rozrost ziarna * Dr inż. Joanna Wachowicz (joanna.wachowicz@genicore.pl), dr. inż. Marcin Rosiński (marcin.rosinski@genicore.pl), mgr inż. Damian Mątewski (damian.matewski@genicore.pl) – Centrum Produkcji i R&D, GeniCore Sp. z o.o. Dzisiejszy świat techniki i medycyny poszukuje nowych materiałów o unikalnych właściwościach. Zwykle jedyną technologią wytwarzania takich zaawansowanych materiałów jest spiekanie. W ostatnich latach nastąpił szybki rozwój nowoczesnych metod spiekania, wykorzystujących do nagrzewania impulsy prądu elektrycznego. Jedną z technik spiekania aktywowanych prądem elektrycznym jest metoda SPS (spark plasma sintering). SŁOWA KLUCZOWE: spiekanie, SPS (spark plasma sintering)

Control and monitoring system prototype for pulse plasma sintering process

Cubic boron nitride is commonly used as a cutting tools material for the sake of its high hardness and wear-resistance. Pulse Plasma Sintering was proposed to decrease the production costs. This method is very attractive for industry, because it significantly decreases the costs of production. The goal of this paper is to present the control system prototype for Pulse Plasma Sintering processes based on programmable logic controller. Only sintering process with carefully controlled parameters allows to restrict the transformation of cBN into hBN and guarantee production of high-quality cubic boron nitride samples. Thus a dedicated control system was developed to control parameters and therefore to improve the production process. This paper presents also a visualisation system which allows the operator to control, monitor and analyze the production process. Prepared application consists of manual and auto operating mode.