Porosity and Microstructure Iron-Based Graded Materials Sintered by Spark Plasma Sintering and the Conventional Method

Using PNC-60 powder with the addition of graphite, cylindrical products characterized by different compositions of core and outer layers were made. Some compacts were sintered via the conventional process, while others were subjected to the spark plasma sintering method (SPS) at different times and temperatures. The gradient microstructure was obtained in the transition zone by mixing powders during die filling, followed by pressing and diffusion during sintering. The effect of sintering parameters on the nature of the gradient zone and the morphology of the pores was shown. After conventional sintering, the gradient zone was wider than it was after SPS. Via SPS, the short sintering time confined the diffusion to a local range, making its influence on the gradient structure negligible. Differences in the microstructure were confirmed by functional description

Ceramic, metallic and composite materials sintered by SPS method

W pracy przedstawiono wyniki badań właściwości fizycznych i mechanicznych materiałów ceramicznych, metalicznych i kompozytowych wytwarzanych metodą SPS. Materiały wytwarzane tą metodą znalazły zastosowanie między innymi jako narzędzia skrawające oraz elementy zawierające ziarna diamentu do szlifowania i wygładzania. Zaprezentowano krzywe spiekania materiałów o osnowie Al2O3 wytwarzanych metodą SPS. Określono wpływ nagrzewania prądem impulsowym na czas trwania procesu spiekania materiałów tlenkowych i kompozytowych o osnowie Ab03 w porównaniu do spiekania swobodnego i mikrofalowego. Przedstawiono krzywe spiekania oraz wybrane właściwości materiałów o osnowie Al2O3 z dodatkiem stałych faz smarujących (WS2) oraz z dodatkiem dwuborku tytanu. W przypadku zastosowania spiekania SPS możliwe jest otrzymywanie materiałów przy niższych parametrach (temperatura i czas wygrzewania) odznaczających się dobrymi właściwościami fizycznymi i mechanicznymi. Wprowadzenie faz WS2 oraz TiB2 do osnowy materiałów kompozytowych AbOrTi(C,N) umożliwiło znaczące obniżenie współczynnika tarcia. W pracy przed stawiono również właściwości materiałów o osnowie azotku krzemu. Materiały o osnowie Si3N4 z dodatkiem faz o dobrej przewodności elektrycznej (np. TiN, TiB 2) spiekane metodą SPS odznaczały się wysoką twardością, modułem Younga oraz niską opornością elektryczną. Poprawa przewodności elektrycznej tworzyw ceramicznych o osnowie Si,N4 umożliwiła zastosowanie obróbki elektroerozyjnej do formowania gotowych wyrobów. Zaprezentowano materiały ceramiczne (TaB2) wytwarzane w wyniku reakcji syntezy tantalu i boru podczas nagrzewania. Porównano właściwości fizyczne i wytrzymałościowe materiałów borkowych wytwarzanych metodą spiekania reakcyjnego SPS oraz materiałów barkowych spiekanych z komercyjnych proszków TaB2. Przedstawiono także właściwości materiałów supertwardych o osnowie metalicznej konsolidowanych przy zastosowaniu techniki spiekania reakcyjnego FAST/SPS. Egzotermiczna reakcja syntezy proszków w trakcie procesu spiekania SPS umożliwia zwiększenie kinetyki nagrzewania i konsolidacji kompozytowych materiałów z dodatkiem proszków diamentowych w zakresie niższych temperatur bez grafityzacji fazy supertwardej.The paper presents the results of physical and mechanical properties of ceramic, metallic and composite materials obtained using the SPS method. Materials sintered by this method have been used, among others, as cutting tools and grinding and polishing elements containing diamond grains. The sintering curves of Al203 matrix materials produced by SPS are presented. The influence of pulse current heating on the duration of the sintering process of oxide and composite materials with the Al203 matrix was determined. The properties of SPS sintering materials were compared with the properties of materials after conventional and microwave sintering processes. The sintering curves and selected properties of Al203 based materials with the addition of solid lubricating phases (WS2) and the addition of titanium diboride are presented. In the case of using SPS sintering it is possible to obtain materials characterized by high physical and mechanical properties at lower parameters (temperature and duration).The additive ofWS2 and TiB2 phases to the matrix of AI203-Ti(C,N) composite materials made it possible to significantly reduce the friction coefficient. The paper also presents the properties of materials based on silicon nitride sintered by SPS method. Si.ifV1 based materials with the addition of phases with good electrical conductivity (eg TiN, TiB2) sintered with SPS method were characterized by high hardness, Young's modulus and low electrical resistance. The improvement of electrical conductivity of Si3N4 ceramic materials enabled the use of electro discharge machining process to form finished products. The ceramic materials (TaB2) produced as a result of the synthesis reaction of tantalum and boron during heating were presented. The physical and mechanical properties of boride materials produced by the reaction sintering SPS and boride materials sintered of commercial TaB2 powders were compared. It also presents the properties of super-hard materials with a metallic matrix consolidated using the FAST/SPS reaction sintering technique. The exothermic reaction of powder synthesis during the SPS sintering process allows to increase the kinetics of heating and consolidation of composite materials with the addition of diamond powders in the range of lower temperatures without graphitization of the super-hard phase

The influence of SPS heating rates on the synthesis reaction of tantalum diboride

TaB2 is a material from the Ultra High Temperature Ceramics group and is rather unexplored because it is difficult to procure the raw materials and to densify TaB2. Using SPS technique to realize reactive sintering processes of powders mixture according to the reaction Ta + 2B → TaB2 makes it possible to achieve TaB2 in one technological step. The aim of the study was to determine the influence of heating rates on the synthesis reaction and on the multistage densification mechanisms during SPS processes. The mixture was sintered at constant parameters of 2200 °C, 48 MPa for 5 min with the usage of heating rates from 50 °C/min up to 400 °C/min. The densification processes were studied through analyzing the shrinkage of powder compacts during SPS (Spark Plasma Sintering) processes. The comparison of the densification curves indicates that the reactions do not proceed completely at slow heating rates. Namely, too low heating rates contribute to the sintering of tantalum before the synthesis reaction and demonstrate the presence of boron in liquid state. The best material obtained in this study has Young's modulus 571 GPa, Vickers hardness 20.7 GPa (HV1) and indentation fracture toughness KIC 4.7 MPa m1/2

Enhancing NiZn ferrite properties through microwave sintering: A comparative studyMejora de las propiedades de la ferrita de NiZn mediante sinterización por microondas: un estudio comparativo

The structural, microstructural, morphological, and electromagnetic properties of a micro- and nanostructured nickel–zinc ferrite ((Cu0.12Ni0.23Zn0.65)Fe2O4) were studied after sintering between 900 and 1100 °C. The microparticulated ferrite (MICRO) was a commercial material, while the nanoparticulated ferrite (NANO) was obtained through high energy milling of the former. The effect of microwave heating (MW), compared to traditional infrared sintering (IR), was investigated. Microwave sintering successfully controlled the grain growth of both granulometries and produced sintered bodies with high relative densities (low porosity), small average grain size, narrow grain size distribution, and a high value of the complex magnetic permeability-imaginary part (μ″) for the MICRO ferrite. In the case of the NANO ferrite, microwave sintering yielded values similar to those obtained by conventional IR. Microwave sintering significantly affected the densification and grain growth processes for both granulometries studied. Additionally, reducing the granulometry of the starting ferrite powder had a noticeable impact on the microstructure and electromagnetic properties of the sintered ferrites, regardless of whether microwave or infrared radiation was used. However, the magnetic property (μ″) decreased when the particle size of the starting powder was reduced from micro to nanometric scale, irrespective of the sintering source. This observation is supported by our previously published mathematical models that establish relationships between the complex magnetic permeability, magnetization mechanisms, angular frequency, and ferrite microstructure.Se estudiaron las propiedades estructurales, microestructurales, morfológicas y electromagnéticas de una ferrita de níquel-zinc micro y nanoestructurada ([Cu0.12Ni0.23Zn0.65]Fe2O4) tras su sinterización en el intervalo 900-1100°C. La ferrita microparticulada (MICRO) era un material comercial, mientras que la nanoparticulada (NANO) se obtuvo por molienda de alta energía de la primera. Se investigó el efecto del calentamiento por microondas (MW), en comparación con la sinterización tradicional por infrarrojos (IR). La sinterización por MW controló eficazmente el crecimiento de grano de ambas granulometrías y produjo piezas sinterizadas de alta densidad relativa (baja porosidad), un tamaño medio de grano pequeño, una distribución de tamaños de grano estrecha y un alto valor de la parte imaginaria de la permeabilidad magnética compleja (μ″), para la ferrita MICRO. En el caso de la NANO, la sinterización por MW condujo a valores similares a los obtenidos por la sinterización convencional por IR. La sinterización por MW afectó significativamente los procesos de densificación y crecimiento de grano para ambas granulometrías estudiadas. Además, reducir la granulometría del polvo de ferrita de partida tuvo un impacto notable en la microestructura y propiedades electromagnéticas de las ferritas sinterizadas, independientemente de si se utilizó radiación por MW o IR. Sin embargo, la propiedad magnética (μ″) disminuyó cuando el tamaño de partícula del polvo de partida se redujo de escala micro a nanométrica, independientemente de la fuente de sinterización. Esta observación está respaldada por nuestros modelos matemáticos previamente publicados que establecen relaciones entre la permeabilidad magnética compleja, los mecanismos de magnetización, la frecuencia angular y la microestructura de la ferrita