Pavol Hvizdoš

SiC/Si3N4 nano/micro-composite — processing, RT and HT mechanical properties

Two SiC/Si3N4 nano/micro composites were prepared from a starting mixture of crystalline α-Si3N4, amorphous SiNC, Y2O3 and/or Al2O3. The composite material for room temperature (RT) application has high strength of 1200 MPa, Weibull modulus of 19 and moderate fracture toughness of 7 MPa m1/2. The composite for high temperature (HT) application, without Al2O3 has RT strength of 710 MPa and is able to keep 60% of its RT strength up to 1300°C. The creep resistance of composite material is approx. 1 order higher compared to relative monolith up to 1400°C.

Bending creep behaviour of pressureless sintered MoSi2

Creep behavior in bending of the hot pressed MoSi{sub 2} was studied in the temperature and stress intervals from 1,100 C--1,200 C and from 20 to 100 MPa, respectively. In spite of the fact that the MoSi{sub 2} was not reinforced with a second particle/whisker phase the creep resistance of the material was comparably high because of the clean character of the MoSi{sub 2}/MoSi{sub 2} grain boundaries. The resulting data, the creep exponent from n = 1.3 to 2.4 and the apparent activation energy from Q = 159 to 634 kJ mol{sup {minus}1} are comparable with the data achieved in compressive creep tests for similar materials and together with TEM results they prove that the principal creep mechanism at 1,200 C is probably dislocation climbing. The bending creep test seems to be a good technique for the characterization of the high temperature mechanical properties of MoSi{sub 2} based materials, but similarly as in the case of structural ceramics it is limited to the low-deformation regimes.

Creep behaviour of MoSi2–SiC and MoSi2–HfO2

Abstract Creep resistance of two MoSi 2 -based materials containing SiC and HfO 2 particles, respectively, in ambient atmosphere was studied in the temperature range 1100–1400°C under a load of 100 MPa. The microstructure and its response to high-temperature load were investigated by TEM using the thin foil technique. Comparison of the creep resistance of both materials at each particular testing temperature shows that the performance of MoSi 2 –HfO 2 is about one order of magnitude better than the other one.

Experimental in-vitro bone cements disintegration with ultrasonic pulsating water jet for revision arthroplasty

The paper deals with the study of using the selective property of ultrasonic pulsating water jet for the disintegration of the interface created by bone cement between cemented femoral stem and trabecular bone tissue as a potential technique for revision arthroplasty. Six types of commercial bone cements based on Polymethyl Methacrylate were used for investigation. The cements were mixed using the DePuy - SmartMix® CTS / vacuum mixing bowl. Mechanical properties of hardened bone cements were determined by nanoindentation. The bone cement samples were disintegrated using the pulsating water jet technology. The water pressure varied between 8÷20 MPa. A circular nozzle with an orifice diameter of 0, 7 mm was used for water jetting. The stand-off distance from the target material was 2 mm and the traverse speed 1 mm/s. The volume of material removal and depth of created traces were measured by MicroProf FRT optical profilometer. The results positively support an assumption that pulsating water jet has a potential to be a suitable technique for the quick and safe disintegration of bone cement during revision arthroplasty.

Carbon Nanofibers Reinforced Ceramic Matrix Composites

Modern ceramic materials have, thanks to their crystallographic structure and strong atomic bonds, many excellent properties, such as extremely high hardness, strength, high thermal and chemical stability, high corrosion resistance, and wear resistance. Their weakness is low fracture toughness and crack growth resistance and hence high brittleness and lower reliability. One of the ways how to overcome these drawbacks is preparation of composite materials, where the base ceramic matrix is reinforced by secondary phases in forms of particles/whiskers and in recent years increasingly in a form of fibrous structures. In advanced fine grained ceramics these usually take form of nanofibers and/or nanotubes. Among the most promising candidates are carbon-based filamentous nanomaterials such as carbon nanotubes (CNTs) and also carbon nanofibers (CNFs), which attracted a lot of attention due to their outstanding mechanical properties, excellent thermal performance and useful electrical characteristics (high electrical conductivity). Nowadays, new ceramic/carbon nanotube composites are being developed mostly with two aims: to improve the mechanical properties of the ceramic materials by reinforcing with carbon nanofibers and to develop functionalized ceramics with improved magnetic and electric properties. Studies show that CNTs (both single-wall and multi-wall) should be ideal reinforcing/functionalizing elements for composites due to their small size, low density and good electrical and thermal conductivity. This work focuses on investigations of ceramic matrix composites based on alumina, zirconia and silicon nitride reinforced by carbon nanofibers and nanotubes. The basic characteristics of commercially available nanofibers/nanotubes are studied by various techniques. The chapter then focuses on mechanical properties of reference monolithic and experimental composite materials. The effect of volume fraction of carbon nanofibers on hardness and fracture toughness is illustrated. Further, the possibilities of improving the tribological and wear properties are discussed. The chapter concludes with the section that explores important aspect of functionalization of ceramics composites by improving their electrical properties, namely electrical conductivity.

Effect of substrate on phase formation and surface morphology of sol-gel lead-free KNbO3, NaNbO3, and K0.5Na0.5NbO3 thin films

Environmentally acceptable lead-free ferroelectric KNbO3 (KN) or NaNbO3 (NN) and K0.5Na0.5NbO3 (KNN) thin films were prepared using a modified sol-gel method by mixing potassium acetate or sodium acetate or both with the Nb-tartrate complex, deposited on the Pt/Al2O3 and Pt/SiO2/Si substrates by a spin-coating method and sintered at 650°C. X-ray diffraction (XRD) analysis indicated that the NN and KNN films on the Pt/SiO2/Si substrate possessed a single perovskite phase, while NN and KNN films on the Pt/Al2O3 substrate contained a small amount of secondary pyrochlore phase, as did KN films on both substrates. Scanning electron microscopic (SEM) and atomic force microscopic (AFM) analyses confirmed that roughness Rq of the thin KNN/Pt/SiO2/Si film (≈ 7.4 nm) was significantly lower than that of the KNN/Pt/Al2O3 film (≈ 15 nm). The heterogeneous microstructure composed of small spherical and larger needle-like or cuboidal particles were observed in the KN and NN films on both substrates. The homogeneous microstructure of the KNN thin film on the Pt/SiO2/Si substrate was smoother and contained finer spherical particles (≈ 50 nm) than on Pt/Al2O3 substrates (≈ 100 nm). The effect of different substrates on the surface morphology of thin films was confirmed.

Wear Behavior of ZrO2-CNF and Si3N4-CNT Nanocomposites

Tribological behavior of ZrO2 and Si3N4 based nanocomposites with addition of carbon nanofibres and nanotubes has been studied by the pin-on-disc technique. Friction coefficients were measured and recorded, wear rates were calculated in terms of material volume loss per load and sliding distance. The wear damage was studied using optical and electron microscopy and its mechanisms were identified. In monolithic materials the dominant wear mechanism was abrasion, in composites with CNF and with higher volume fraction of CNTs (5 and 10%) fiber pull-out and lubricating by the carbon phases occurred.

Surface integrity of Mg-based nanocomposite produced by Abrasive Water Jet Machining (AWJM)

ABSTRACT This paper investigates the influence of jet traverse speed on the surface integrity of 0.66 wt% Al2O3 nanoparticle reinforced metal matrix composite (MMC) generated by Abrasive Water Jet Machining (AWJM). Surface morphology, surface topography, and surface roughness (SR) of the AWJ surface were analyzed. The machined surfaces of the nanocomposites were examined by laser confocal microscope and field emission scanning electron microscope (FESEM). Microhardness and elasticity modulus measurement by nanoindentation testing were also performed across thickness of the samples to see depth of the zone, affected by AWJ cutting. The result reveals that extent of grooving by abrasive particle and irregularity in AWJ machined surface increases as the traverse speed increased. Similarly, the rise in value of surface roughness parameters with traverse speed was also seen. In addition, nanoindentation testing represents the lower hardness and elastic modulus due to softening occurs in AWJ surface.

Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films

Double-scale composite lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from both the pure sol and the composite suspension on Pt/Al2O3 substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL−1. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction (XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and ≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films deposited on Pt/Al2O3 substrates was evaluated.

Fracture Characterization of Silicon Nitride Based Layered Composites

Silicon nitride based structural ceramics are a family of advanced materials that exhibit a combination of high hardness, high strength, good corrosion and erosion behaviour, high elastic modulus and dimensional stability. Major application of these ceramics includes wear components, cutting tools and parts of engines (turbochargers, bearings, etc.). Their wide application is, however, still limited mainly due to their brittleness, low flaw tolerance and low reliability1,2. In recent years nitride based ceramics have been very intensively investigated all over the world with the aim to improve their mechanical properties and make them suitable for structural applications. The main ways of improving the room temperature mechanical properties of silicon nitride based ceramics can be summarized as follows: improving the strength level and reducing the strength values scatter, i.e., enhancing the reliability by reduction of the critical defect size (improved properties of powders, clean room manufacturing, etc.) — the flaw diminution approach3,4; promoting the localized bridging behind the crack tip (in the form of frictional and mechanical interlocking, or pull out) by which the flaw tolerance of the material can be improved — the flaw tolerance approach5−7; improving the strength values by incorporating into the matrix the nano-sized, second-phase particles with different expansion coefficients — the nano-particle dispersion strengthening8; improving the structural reliability by designing novel laminar composites with a promoted crack deflection at the interlayer boundaries and utilizing the compressive residual stresses arisen during cooling down from the sintering temperature because of the differences in the thermal expansions between the layers which have different compositions — the laminar structure approach9−12.