Durability of polymer-ceramics composite implants determined in creep tests

The polymer base composites are considered as one of the most promising groups of materials in medicine. Implants made of these materials have mechanical properties similar to natural tissues, show good biological compatibility, and also can be formed into various shapes. In living organism longterm working implants are subjected to mechanical stresses as well as aggressive body liquids. While aging, they can change their mechanical and biological properties. Investigations presented in this study show the influence of conditions simulating human body on the mechanical properties of two types of polymer composites such as: polysulphone–hydroxyapatite (PSU + HAP) and poly(lactide-co-glicolide)–hydroxyapatite (PGLA + HAP). Durability of investigated materials was estimated on the basis creep tests. The analysis of biological durability has been also performed, including the effects of modifying additives on the performance of examined composites. The biostable materials may be used as long-term implants with the stress level between 10% and 20% of initial strength. For resorbable polymers and their composites the time of resorption is a very important factor, and it depends on polymer’s microstructure and the presence of modifying phases.     

Fabrication and technological properties of nanoporous spinel/forsterite/zirconia ceramic composites

In this work, nanoporous spinel/forsterite/zirconia ceramic composites were fabricated at 1600 °C for 2 h. The influence of zirconia content (up to 10 mass%) on the technological properties, nanopores formation, phase compositions, microstructure and thermal diffusivity of nanoporous ceramic composites was investigated. Nanospinel and nanoforsterite powders were synthesized via a modified co-precipitation and sol–gel techniques, respectively. Results indicated that apparent porosity of the fired nanoporous ceramic composites is mostly in the range 14.26–56.14% with the average pores diameter 35.8 nm. Using of nanopowders (spinel and forsterite) as the staring materials were achieved high mechanical (cold crushing strength ∼ 235–164 MPa) and elastic (Young’s modulus ∼ 123.6–4.5 GPa) properties of the prepared nanoporous ceramic composites. Microstructure analysis exhibited all of the crystalline phases and pores of the nanoporous ceramic composites are in the nanosize (35–40 nm). These nanoporous ceramic composites are promising porous ceramic materials for using in advanced applications due to their excellent combination properties.     

Sol–gel derived nanoscale bioactive glass (NBG) particles reinforced poly(ε-caprolactone) composites for bone tissue engineering

This study investigated the effect of the addition of sol–gel derived nanoscale bioactive glass (NBG) particles on the mechanical properties and biological performances of PCL polymer, in order to evaluate the potential applications of PCL/NBG composites for bone tissue regeneration. Regardless of the NBG contents (10, 20, and 30 wt.%), the NBG particles, which were synthesized through the sol–gel process using polyethylene glycol (PEG) polymer as a template, could be uniformly dispersed in the PCL matrix, while generating pores in the PCL/NBG composites. The elastic modulus of the PCL/NBG composites increased remarkably from 89 ± 11 MPa to 383 ± 50 MPa with increasing NBG content from 0 to 30 wt.%, while still showing good ultimate tensile strength in the range of 15–19 MPa. The hydrophilicity, water absorption and degradation behavior of the PCL/NBG composites were also enhanced by the addition of the NBG particles. Furthermore, the PCL/NBG composite with a NBG content of 30 wt.% showed significantly enhanced in vitro bioactivity and cellular response compared to those of the pure PCL.     

Improvement of the bonding interface of a sintered Al 2014–(Ti5Si3)p composite by the copper coating of the reinforcement

AA 2014 aluminium-based composites reinforced with (5–20 wt.%) Ti₅Si₃ intermetallic particles, with and without Cu coating, were obtained in a Turbula powder mixer from commercially-available prealloyed powders. Mechanical alloying was used for the deposition of Cu on the surface of the Ti₅Si₃ particles. Compaction of the specimens was performed using a hydraulic press and a floating die. The results show that the liquid formation and phase distribution are modified by the copper coating of the ceramic reinforcement, resulting in changes in the materials microstructure and the mechanical properties. The presence of the reinforcement particles improves densification of the composites. Improved densification was found for the 2014 + Ti₅Si₃ composites. 2014 + Ti₅Si₃–Cu composites exhibit superior mechanical properties compared to the 2014 + Ti₅Si₃ composites.     

Mechanical properties of a degradable phosphate glass fibre reinforced polymer composite for internal fracture fixation

This paper reports on the mechanical properties and pH upon degradation of phosphate glass fibre reinforced methacrylate-modified oligolactide. Phosphate glass fibres of the composition 51.04 P₂O₅–21.42 CaO–25.51 Na₂O–2.03 SiO₂ (mol%) were produced by a crucible spinning technique. Fibres were embedded into a matrix of a degradable organic polymer network based on methacrylate-modified oligolactide; samples with and without addition of CaCO₃ for pH control were produced. pH during degradation in physiological NaCl solution could be increased to up to 6.5 by addition of 20 wt.% calcium carbonate to the fibre composites. pH in Tris buffer solution was about 7.11. Mechanical properties of dry specimens were investigated during 3-point bending tests and gave elastic moduli in the range of cortical bone (15 to 20 GPa). However, addition of calcium carbonate decreased tensile strength of the fibre composites and resulted in brittle fracture behaviour, while CaCO₃-free composites showed a fibrous fracture mode. Control of pH and degradation is a requirement for obtaining a fracture fixation device with degradation properties matching in vivo requirements. Results show that addition of CaCO₃ is suitable for controlling the pH during degradation of metaphosphate glass polymer composites.     

Thermal shock behavior of nano-sized SiC particulate reinforced AlON composites

Aluminum oxynitride (AlON) has been considered as a potential ceramic material for high-performance structural and advanced refractory applications. Thermal shock resistance is a major concern and an important performance index of high-temperature ceramics. While silicon carbide (SiC) particles have been proven to improve mechanical properties of AlON ceramic, the high-temperature thermal shock behavior was unknown. The aim of this investigation was to identify the thermal shock resistance and underlying mechanisms of AlON ceramic and 8 wt% SiC–AlON composites over a temperature range between 175 °C and 275 °C. The residual strength and Young's modulus after thermal shock decreased with increasing quenching temperature and thermal shock times due to large temperature gradients and thermal stresses caused by abrupt water-quenching. A linear relationship between the residual strength and thermal shock times was observed in both pure AlON and SiC–AlON composites. The addition of nano-sized SiC particles increased both residual strength and critical temperature from 200 °C in the monolithic AlON to 225 °C in the SiC–AlON composites due to the toughening effect, the lower coefficient of thermal expansion and higher thermal conductivity of SiC. The enhancement of the thermal shock resistance in the SiC–AlON composites was directly related to the change of fracture mode from intergranular cracking along with cleavage-type fracture in the AlON to a rougher fracture surface with ridge-like characteristics, crack deflection, and crack branching in the SiC–AlON composites.     

A new hydroxyapatite-based biocomposite for bone replacement

Since the 1970s, various types of ceramic, glass and glass–ceramic materials have been proposed and used to replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining HA-based composites. Unfortunately, high temperature treatments (1200 °C ÷ 1300 °C) are usually required in order to sinter these systems, causing the bioactive glass to crystallize into a glass–ceramic and hence inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are realized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the employment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation.     

Effect of a weak fiber interface coating in ZrB2 reinforced with long SiC fibers

This study reports the microstructural analysis and mechanical properties of a ZrB₂ ceramic containing long BN-coated Hi-Nicalon SiC fibers. A composite was produced and thoroughly characterized by transmission electron microscopy to study the interfaces at the nanoscale level. Full densification was accomplished by hot pressing at 1450 °C. The fiber in the sintered material retained its pristine aspect, confirming that the coating was effective in preventing degradation due to interactions with the matrix. Pull-out was observed on fractured surfaces, but toughness values were about 4.5 MPa√m, which was comparable to those of ZrB₂ materials with SiC additions in the form of particles or short fibers. However, the composites exhibited a controlled fracture behavior, as confirmed by a notably higher work of fracture, 140 J/m², compared with 20–30 J/m² of unreinforced ZrB₂ or ZrB₂ containing chopped fibers.     

The effects of texture and grain morphology on the fracture toughness and fatigue crack growth resistance of nanocrystalline platinum films

The fracture toughness and fatigue crack growth resistance of nanocrystalline materials are significantly affected by the thickness of the specimen. In this work we relate the mechanical properties of nanocrystalline platinum films to their texture and grain morphology. Tensile, creep and fatigue testing of annealed, ∼1 μm films resulted in mechanical properties similar to the as-received films (yield strength of ∼1.2 GPa, fracture toughness ∼17.8 MPa √m, and a fatigue crack growth power law exponent of ∼4.2). However, the breakdown of the initially columnar grain morphology had a marked effect on the transition point from an intergranular to transgranular fatigue cracking mode. Finite element modeling suggests that cyclic (fatigue) grain coarsening and the transition from inter- to transgranular cracking modes are a result of the relative importance of dislocation slip accommodation on in-plane and through-thickness oriented slip directions.     

Aluminum matrix composites based on preceramic-polymer-bonded SiC preforms

Polymethylsiloxane (PMS) was used as a binder to make self-supporting SiC preforms for pressurized aluminum melt infiltration. The SiC particles were coated with preceramic polymer by spray drying; this ensured a fine and homogeneous distribution coupled with a high yield of the binder. The conditioned SiC powder mixtures were processed into preforms by warm pressing, curing and pyrolysis. A polymer content of 1.25 wt.% conferred sufficient stability to the preforms to enable composite processing. Using this procedure, SiC preforms with various SiC particle size distributions were prepared. The resulting Al/SiC composites with SiC contents of about 60 vol.% obtained by squeeze casting infiltration exhibit a 4-point bending strength of ∼500 MPa and Young’s moduli of ∼200 GPa. These values are comparable to those of compositionally identical, but binder-free composites. It is thus shown that the PMS-derived binder confers the desired strength to the SiC preforms without impairing the mechanical properties of the resulting Al/SiC composites.     

Infiltrated Cu8Al–Ti alumina composites

The effect of titanium additions on the interface and mechanical properties of infiltrated Cu8 wt%Al–Al₂O₃ composites containing 57 ± 2 vol% ceramic are investigated, exploring two different Al₂O₃ particle types and four different Ti concentrations (0, 0.2, 1, 2 wt%Ti). Addition of 0.2 wt%Ti leads to the development of a thin (5–10 nm) layer enriched in Ti at the interface between Cu alloy and Al₂O₃ particles; this Ti concentration produces the best mechanical properties. With higher Ti-contents Ti₃(Cu, Al)₃O appears; this decreases both the interface and composite strength. Composites reinforced with vapor-grown polygonal alumina particles show superior mechanical properties compared to those reinforced by angular comminuted alumina particles, as has been previously documented for aluminum-based matrices. Micromechanical analysis shows that damage accumulation is more extensive, as is matrix hardening by dislocation emission during composite cooldown, in the present Cu8 wt%Al matrix composites compared with similarly reinforced and processed Al-matrix composites.     

Mechanical properties of rolled A356 based composites reinforced by Cu-coated bimodal ceramic particles

Three kinds of A356 based composites reinforced with 3 wt.% Al₂O₃ (average particle size: 170 μm), 3 wt.% SiC (average particle size: 15 μm), and 3 wt.% of mixed Al₂O₃–SiC powders (a novel composite with equal weights of reinforcement) were fabricated in this study via a two-step approach. This first process step was semi-solid stir casting, which was followed by rolling as the second process step. Electroless deposition of a copper coating onto the reinforcement was used to improve the wettability of the ceramic particles by the molten A356 alloy. From microstructural characterization, it was found that coarse alumina particles were most effective as obstacles for grain growth during solidification. The rolling process broke the otherwise present fine silicon platelets, which were mostly present around the Al₂O₃ particles. The rolling process was also found to cause fracture of silicon particles, improve the distribution of fine SiC particles, and eliminate porosity remaining after the first casting process step. Examination of the mechanical properties of the obtained composites revealed that samples which contained a bimodal ceramic reinforecment of fine SiC and coarse Al₂O₃ particles had the highest strength and hardness.     

Sintering and technological properties of alumina/zirconia/nano-TiO2 ceramic composites

The present work focuses on studying the effect of nano TiO₂ (0.0–25 mass%) on the sintering behavior and mechanical properties of alumina/zirconia ceramic composites. Al₂O₃–ZrO₂–TiO₂ oxides mixture was sintered at 1600 °C to obtain the desired composites. The sinterability and the technological properties of these ceramic composites, i.e. the sintering parameters and microhardness as well as thermal shock resistance were investigated. Moreover, phase composition and microstructure of the sintered bodies were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results revealed that nano TiO₂ is a beneficial component for alumina/zirconia ceramic composites. The batch containing 20 mass% TiO₂ exhibited the highest sintering and mechanical properties as well as resistance to thermal shock. The obtained microstructure exhibited high compacted ceramic matrix composites.     

New type of mechanical damping composites composed of piezoelectric ceramics,carbon black and epoxy resin

New types of piezoelectric damping materials, piezoelectric ceramic (PZT) powder/carbon black (CB) powder/epoxy (EP) resin composites, were developed, and their mechanical and damping properties were studied. Here the mechanical energy of vibrations and noises were transformed into electric energy (current) by PZT, and the electric current was conducted to an external circuit through CB powders and then dissipated as thermal energy through a resistor. When CB was added to PZT/EP (70/30 in wt%), the mechanical loss factor (η), a measure of mechanical of damping intensity, showed a maximum value of ∼0.08 at the CB content of ∼0.51 wt%, at which the CB particles electrically just contact each other. In the present work, it was found that the PZT/CB/EP composite of 90.0/0.5/9.5 shows a large η value of ∼0.15.     

Cytocompatibility,degradation, mechanical property retention and ion release profiles for phosphate glass fibre reinforced composite rods

Fibre reinforced composites have recently received much attention as potential bone fracture fixation applications. Bioresorbable composites based on poly lactic acid (PLA) and phosphate based glass fibre were investigated according to ion release, degradation, biocompatibility and mechanical retention profiles. The phosphate based glass fibres used in this study had the composition of 40P₂O₅–24MgO–16CaO–16Na₂O–4Fe₂O₃ in mol% (P40). The degradation and ion release profiles for the composites showed similar trends with the amount of sodium and orthophosphate ions released being greater than the other cations and anions investigated. This was attributed to low Dietzal's field strength for the Na⁺ in comparison with Mg^2 + and Ca^2 + and breakdown of longer chain polyphosphates into orthophosphate ions. P40 composites exhibited good biocompatibility to human mesenchymal stem cells (MSCs), which was suggested to be due to the low degradation rate of P40 fibres. After 63 days immersion in PBS at 37 °C, the P40 composite rods lost ~ 1.1% of mass. The wet flexural, shear and compressive strengths for P40 UD rods were ~ 70%, ~ 80% and ~ 50% of their initial dry values after 3 days of degradation, whereas the flexural modulus, shear and compressive strengths were ~ 70%, ~ 80%, and ~ 65% respectively. Subsequently, the mechanical properties remained stable for the duration of the study at 63 days. The initial decrease in mechanical properties was attributed to a combination of the plasticisation effect of water and degradation of the fibre–matrix interface, with the subsequent linear behaviour being attributed to the chemical durability of P40 fibres. P40 composite rods showed low degradation and ion release rates, good biocompatibility and maintained mechanical properties similar to cortical bone for the duration of the study. Therefore, P40 composite rods have huge potential as resorbable intramedullary nails or rods.     

Mechanical and wear behaviours of nano and microfilled polymeric composite: Effect of filler fraction and size

The addition of ceramic reinforced material, SiC particles, to resin matrices, results in the improvement of the overall performance of the composite, allowing the application of these materials as tribo-materials in industries such as: automotive, aeronautical and medical. Particle-reinforced polymeric composites are widely used as biomaterials, for example as dental filler materials and bone cements. These reinforced composites have improved mechanical and tribological performance and have higher values of elastic modulus and hardness, and also reduce the shrinkage during the polymerisation compared with resin matrices. However, the effect of the filler level in mechanical and tribological behaviour is not quite understood.The aim of this work is to determine the influence of the particle volume fraction and particle size in the wear loss of the composites and their antagonists. Reciprocating wear tests were conducted using a glass sphere against resin polyester silica reinforced composite in a controlled medium, with an abrasive slurry or distilled water. For 6 μm average particle dimension, seven particles contents were studied ranging from 0% to 46% of filler volume fraction (FVF). Afterwards, filler volume fractions of 10% and 30% were selected; and, for these percentages, 7 and 4 average particle dimensions were tested and were evaluated regarding their wear behaviour, respectively. The reinforcement particle dimensions used ranged from 0.1 μm to 22 μm with the 10% filler fraction, and for 30% of filler content the range extended from 3 μm to 22 μm. The results allow us to conclude that in an abrasive slurry medium the composite abrasion resistance decreases with the increase of the particle volume fraction, in spite of the accompanying rise in hardness and elastic modulus. With constant FVF, and abrasive slurry, the composite wear resistance increases with increasing average particle dimension. In a distilled water medium and with several FVF values, the minimum wear was registered for a median particle content of 24%. In this medium and with constant FVF the highest wear resistance occurred for average reinforcement particles of 6 μm. The removal mechanisms involved in the wear process are discussed, taking into account the systematic SEM observations to evaluate the wear mechanisms.     

In situ synthesis of hybrid-reinforced titanium matrix composites

Novel hybrid-reinforced (TiB + La₂O₃)/Ti composites were in situ synthesized utilizing the reaction between Ti, LaB₆ and B₂O₃ through homogeneous melting in a non-consumable vacuum arc remelting furnace. The thermodynamics of in situ synthesis reaction were analyzed. The phases in the composites were identified by X-ray diffraction (XRD) and the microstructures of the composites were examined by optical microscope (OM), backscattered scanning electron microscope (SEM) and field-emission SEM. Three kinds of reinforcements were found in the composites: La₂O₃ particles (diameter: ∼ 2 μm), TiB whiskers (width: ∼ 3 μm) and TiB plates (thickness: ∼ 1.5 μm). The reinforcements' sizes were fine and they were homogeneously distributed in the matrix.     

Mechanical and magnetic properties of γ-Ni–xFe/Al2O3 composites

Ultra-fine grained γ-Ni–xFe (x = 20, 50, and 64 (nominal)) dispersed Al₂O₃-matrix composites were fabricated by a mechano-chemical process plus hot-pressing, and their mechanical and magnetic properties were explored. The results indicated that all composites incorporated with different γ-Ni–xFe alloys possessed high densities (relative density D ⩾ 98%) and sub-micrometer-sized matrix dispersed with γ-Ni–xFe particles of sizes below ∼500 nm. As compared to other two composite systems, γ-Ni–20Fe/Al₂O₃ had finer microstructures and displayed superior fracture toughness and strength. In high iron-contained γ-Ni–64Fe/Al₂O₃ composite undesired FeAl₂O₄ phase formed on the matrix grain boundaries, which is mainly responsible for its inferior mechanical properties. Although Young’s modulus and hardness of Ni–20Fe/Al₂O₃ composite system decreased, its fracture toughness increased monotonously with increasing the alloy content in the composition range investigated. Moreover, incorporation of ferromagnetic γ-Ni–xFe particles led all the composite systems to display ferromagnetism with their saturation magnetization increasing almost linearly with increasing alloy content. In addition, experiments showed that their ferromagnetism had high thermal stability (T_c = ∼580 °C), no obvious magnetism degradation and magnetic interactions of the alloys with the matrix being observed. The combination of good mechanical properties with excellent magnetic performance would make this material be very valuable in industry.     

Assessment of three oxide/oxide ceramic matrix composites: Mechanical performance and effects of heat treatments

Mechanical performance of three oxide/oxide ceramic matrix composites (CMCs) based on Nextel 610 fibers and SiOC, alumina, and mullite/SiOC matrices respectively, is evaluated herein. Tensile strength and stiffness of all materials decreased at 1000 °C and 1200 °C, probably because of degradation of fiber properties beyond 1000 °C. Microstructural changes in the composites during exposure at 1000 °C and 1200 °C for 50 h reduce their flexural strength, fracture toughness and work of fracture. A literature review regarding mechanical properties of several oxide/oxide CMCs revealed lower influence of fiber properties on composite strength compared with elastic modulus. The tested composites exhibit comparable stiffness and strength but higher fracture toughness compared with average values determined from a literature review. Considering CMCs with different compositions, we observed an interesting linear trend between strength and fracture toughness. The validity of the linear relationship between fracture strength and flexural toughness for CMCs is discussed.     

Mechanical properties and morphological characterization of exfoliated graphite–polypropylene nanocomposites

This research explores the potential of using exfoliated graphite nanoplatelets, xGnP, (graphene sheets ∼10 nm thickness, ∼1 μm diameter), as reinforcement in polypropylene, PP. xGnP–PP nanocomposites were fabricated by melt mixing and injection molding. The feasibility of using xGnP–PP nanocomposites was investigated by evaluating the flexural strength, modulus and impact strength and studying the morphology of this system as a function of xGnP loading and aspect ratio and by comparing the xGnP–PP with composites made with commercial available reinforcements such as carbon fibers, carbon black and clays. It is concluded that the smaller aspect ratio xGnP has the strongest impact on the mechanical properties of PP, at loadings up to 5 vol.%, compared to the other reinforcements used, which reflects the compatibility between the exfoliated graphite nanoplatelets and the PP matrix and the exceptional mechanical properties of xGnP, similar to crystalline graphite.