In vitro dissolution of calcium phosphate-mullite composite in simulated body fluid

In our recent research, we have developed novel CaP-mullite composites for bone implant applications. In order to realize such applications, the in vitro dissolution behaviour of these materials needs to be evaluated. In this perspective, the present paper reports the dissolution behavior of pure hydroxyapatite (HAp) and hydroxyapatite composites with 20–30 wt% mullite in simulated body fluid (SBF). The in vitro dissolution experiments were carried out for different time duration starting from 7 days up to 28 days. XRD and SEM results show almost no dissolution for pure HAp and HAp composite with 30 wt% mullite. However, HAp-20 wt% mullite composite exhibits considerable dissolution after 7 days. The α-TCP phase mainly contributes to the dissolution process. Based on the dynamic changes in pH, ionic conductivity, Ca and P ion concentration in SBF as well as microstructural observations of the bioceramic surfaces after various time frames of immersion in SBF, the differences in dissolution behaviour are discussed.     

Study on the effects of nanoparticulates of SiC,Al2O3, and ZnO on the mechanical and tribological performance of epoxy-based nanocomposites

In this research work, mechanical and tribological characteristics of ortho cresol novalac epoxy (OCNE)-based nanocomposites filled with nanoparticulates of SiC, Al₂O_3, and ZnO have been investigated. Also, in these investigations, the influence of wear parameters such as applied normal load, sliding velocity, filler contents, and sliding distance have been explored. The experimental plan for four factors at three levels using face centered composite design (CCD) has been employed by the response surface methodology (RSM) technique. The friction and wear tests were carried out using a pin on disc wear test apparatus under dry sliding conditions. The hardness and flexural strength of nano ortho cresol novalac epoxy composites filled with nano (SiC, Al₂O_3, and ZnO) particulates increases with an increase in the filler contents. Whereas, the tensile strength of these nanocomposites increases with an increase in the filler contents from 1 to 2 wt%, and with a further increase in filler contents the tensile strength decreases. The results of the study also showed that (2 wt%) filler contents bring superior mechanical and tribological properties. The lowest coefficient of friction and specific wear rate were found with nano Al₂O₃-filled composites. Also, the wear mechanisms of these nanocomposites were studied using a scanning electron microscope (SEM) equipped with an EDS analyzer.     

In situ ring-opening polymerization of hydroxyapatite/poly(ethylene adipate)-co-(ethylene terephthalate) biomimetic composites

Hydroxyapatite/poly(ethylene adipate)-co-poly(ethylene terephthalate) biomaterials (HAp/PEA-co-PET) have been prepared by ring opening polymerization (ROP) of cyclic oligo(ethylene adipate)-co-oligo(ethylene terephthalate) (C-OEA-co-C-OET) in the porous hydroxyapatite (HAp) scaffolds at 250 °C for 24 h under vacuum. The content of ROP-PEA-co-PET in the HAp/PEA-co-PET composite was about 20 wt% with the values of number average molecular weight $({\overline{M}_{{\rm n}}})$ and weight average molecular weight $({\overline{M}_{{\rm W}}})$ of 3380 and 7160 g/mol, respectively. Compressive strength and modulus of the HAp/PEA-co-PET composites were about 29 and 246 MPa, respectively. These mechanical properties were higher than those of the porous HAp templates and natural cancellous bone. In vitro bioactivity of the HAp/PEA-co-PET composites was studied by soaking in simulated body fluid (SBF) under the flowing system at the rate of 130 mL/day for 7, 14, 21 and 28 days. The formation of hydroxyapatite nanocrystals was observed on the composite surfaces through the consumption of calcium and phosphorus from the SBF solution, indicating the bioactivity of these HAp/PEA-co-PET composites. These results indicated the competency of HAp/PEA-co-PET composites for biomedical applications.     

Comparison of friction and wear performances of brake materials containing different amounts of ZrSiO4 dry sliding against SiCp reinforced Al matrix composites

Low friction levels for brake materials dry sliding against Al matrix composites (Al-MMCs) were observed. Al matrix composites reinforced with 30 vol.% SiC_p (34 μm) were used first to fabricate a new brake drum in place of the conventional cast iron brake drum for a Chase Machine. Experimental studies on the brake materials differing in amounts of zirconium silicate (0 wt%, 4 wt%, 8 wt%, and 12 wt% ZrSiO₄) dry sliding against the Al-MMCs drum were performed on the Chase Machine in order to examine their effects on friction and wear performances. The test procedures include friction fade and recovery, load and speed sensitivities at 177 °C and 316 °C, and wear. Experimental results show that the brake material containing 8 wt% ZrSiO₄ had the best wear resistance and higher friction level. The brake material containing 12 wt% ZrSiO₄ had the highest friction level, but wear increased rapidly. The deterioration of the latter wear suggests that this brake material is unreliable in commercial applications.     

莫来石与碳纤维协同填充的聚四氟乙烯基复合材料及其摩擦学性能

为了提高聚四氟乙烯（PTFE）的摩擦学性能,采用机械混匀、带温预压及烧结等工艺制备了莫来石和碳纤维填充的PTFE基复合材料,并通过FTIR、XRD、万能材料试验机、洛氏硬度计、DSC及热机械分析分别表征了PTFE基复合材料的显微结构、力学性能和热学性能;然后,使用MRH-3 型高速环块磨损试验机测定了复合材料的摩擦系数和磨损率,通过自制的硅油砂浆磨损装置测定了复合材料在不同温度下的耐砂浆磨损性能;最后,借助3D测量激光显微镜研究了复合材料摩擦面形貌,并分析了摩擦磨损机制。结果表明:莫来石和碳纤维在PTFE体系中起到填充增强作用,20wt%莫来石-10wt%碳纤维/PTFE复合材料的弹性模量由364 MPa增加至874 MPa;20wt%莫来石-10wt%碳纤维/PTFE复合材料的干摩擦系数较大,但其磨损率与纯PTFE相比降低了3个数量级以上,且此复合材料在水摩擦条件下仍能保持较好的摩擦系数和磨损率,摩擦系数为0.157,磨损率为7.40×10-6 mm3·N-1·m-1;此外,20wt%莫来石-10wt%碳纤维/PTFE复合材料在较高温度下仍能表现出良好的耐砂浆磨损性能。所得结论表明改性得到的PTFE 基复合材料的摩擦学性能显著提高,复合材料可用于有杆抽油井防偏磨。      

Experimental investigation on tribological behaviours of PA6, PA6-reinforced Al<Subscript>2</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>3</Subscript> and PA6-reinforced graphite polymer composites

This article reports on the preparation, characterization and experimental investigation of polyamide 6 (PA6) reinforced with alumina oxide (Al₂O₃) and graphite composites. The test specimens were prepared in an injection-moulding machine by varying the weight proportions of Al₂O₃ and graphite particles blended with PA6. The tribological properties of the composites were observed by using pin-on-disc wear test rig under dry sliding conditions. The worn surfaces of the composites were examined using scanning electron microscope. The addition of Al₂O₃ and graphite significantly enhanced the tribological properties of PA6. The PA6 containing 30 wt% Al₂O₃ and 20 wt% graphite revealed the best tribological behaviours due to the stronger interfacial bonding characteristics with improved wear resistance. Further, the thermal stability of Al₂O₃ and graphite particles was studied through thermogravimetric analysis test. It was also found that further addition of Al₂O₃ and graphite in PA6 had no significant improvement in wear resistance, the co-efficient of friction and heat generation.     

Effect of Graphite as Forming Additive on Wear Properties of (SiCp + Al2O3f)/Al Composites Prepared by Pressure Infiltration

The 2024Al matrix composites reinforced by 30 vol% SiCp and 10 vol% Al₂O_3f as wear-resistant materials are prepared by pressure infiltration. The graphite powders are added during the preparation of the preform to support shaping. In this article, the effect of the size of the graphite powder on the friction and wear properties of the composites is researched. The results showed that at a given conditions, namely, the size of the SiCp is 14 µm and the diameter of the Al₂O₃ fiber is 4–5 µm, the composites made from 5 ～ 30 µm have a more stable friction coefficience and lower wear rate than those from 30 ～ 50 µm and 50 ～ 70 µm graphite because the diameter of the generated pores in the corresponding preforms is smaller and more concentrated, resulting in a uniform distribution of the reinforcements in the matrix. The detailed effect mechanisms of different graphite sizes on wear and friction properties of the composites as well as the porosity of the corresponding preforms are also discussed.     

Poly(D,L-lactide) (PDLLA) foams with TiO2 nanoparticles and PDLLA/TiO2-Bioglass® foam composites for tissue engineering scaffolds

Porous poly(D,L-lactide) PDLLA foams containing 0, 5 and 20 wt% of TiO₂ nanoparticles were fabricated and characterised. The addition of Bioglass^® particles was also studied in a composite containing 5 wt% of Bioglass^® particles and 20 wt% of TiO₂ nanoparticles. The microstructure of the four different foam types was characterised using scanning electron microscopy (SEM) and their mechanical properties assessed by quasi-static compression testing. The in vitro behaviour of the foams was studied in simulated body fluid (SBF) at three different time points: 3, 21 and 28 days. The degradation of the samples was characterised quantitatively by measuring the water absorption and weight loss as a function of immersion time in SBF. The bioactivity of the foams was characterised by observing hydroxyapatite (HA) formation after 21 days of immersion in SBF using SEM and confirmed with X-ray diffraction (XRD) analysis. It was found that the amount of HA was dependent on the distribution of TiO₂ nanoparticles and on the presence of Bioglass^® in the foam samples.     

Synthesis and characterization of borosilicate glass/β-spodumene/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites with low CTE value for LTCC applications

Glass?+?ceramic composites based on low-softening-point borosilicate (BS) glass, β-spodumene and Al₂O₃ were produced in this work. The influence of ceramic filler composition on the microstructure, sintering quality, mechanical properties, thermal properties and dielectric properties of composites were studied. XRD and DSC indicated that both kinds of ceramic filler as well as the BS glass maintained their characteristics after sintering. The addition of β-spodumene would decrease the coefficient of thermal expansion (CTE) value of composites to match with silicon well. The better wetting behavior between β-spodumene and BS glass would lead to better sintering quality, microstructure and dielectric properties for composites containing more β-spodumene. With appropriate Al₂O₃ content, the flexural strength of composites could be enhanced. Composite with 45 wt% BS glass, 30 wt% β-spodumene and 25 wt% Al₂O₃ sintered at 875 °C showed good properties which meet the requirements of low temperature co-fired ceramic applications: dense microstructure with high relative density of 96.27%, proper CTE value of 3.57 ppm/°C, high flexural strength of 156 MPa, low dielectric constant of 6.20 and low dielectric loss of 1.9?×?10^?3.     

Relationship between thermal and sliding wear behavior of Al6061/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> metal matrix composites

Al6061 alloy and Al6061/Al₂O₃ metal matrix composites (MMCs) were fabricated by stir casting. The MMCs were prepared by addition of 5, 10 and 15 wt% Al₂O₃ particulates and the size of particulates was taken as 16 μm. The effect of Al₂O₃ particulate content, thermal properties and stir casting parameters on the dry sliding wear resistance of MMCs were investigated under 50–350 N loads. The dry sliding wear tests were performed to investigate the wear behavior of MMCs against a steel counterface (DIN 5401) in a block-on-ring apparatus. The wear tests were carried out in an incremental manner, i.e., 300 m per increment and 3,000 m in total. It was observed that, the increase in Al₂O₃ vol% decreased both thermal conductivity and friction coefficient and hence increased the transition load and transition temperature for mild to severe wear during dry sliding wear test.     

The preparation and the friction and wear behaviours of TiO2/CNT/PI composite film

Recently, the tribological properties of polyimide composites filled with TiO₂ nanoparticles and short pitch-based carbon nanotubes (CNTs) were investigated. Sliding tests were performed on a co-rotating twin-screw extruder under different temperatures and regular pressure and speed. It was found that the composite with 4 wt% TiO₂ and 6 wt% CNT could reduce the frictional coefficient and wear rate in the most effective way. Compared to the conventional hybrid composites up to now, the above composite was characterised by relatively lower filler content, which would reduce the manufacturing cost. Therefore, it could be largely processed in practice. Increased surface hardness, lubricating effect of the sheet-like wear debris reinforced by TiO₂ and rapidly formed transfer film were believed to be the key issues accounting for the obvious wear-resisting and friction-reducing behaviours.     

(Mg2B2O5w+ND)/ZK60镁基复合材料的摩擦磨损性能研究

在湿球磨条件下以600 r/min高能球磨混粉,并将球磨后的粉末经过热压烧结-热挤压成型制备(Mg2B2O5w+ND)/ZK60镁基复合材料。研究了(Mg2B2O5w+ND)/ZK60镁基复合材料在不同载荷和转速下的干摩擦磨损性能。结果表明:干摩擦条件下,材料的摩擦系数随着滑动距离的增加会经历跑和阶段和稳定阶段;材料的质量磨损率随着转速的增大而降低,随着载荷的增大而增大,且基体镁合金的质量磨损率始终低于复合材料。随着摩擦载荷和转速的增加,材料的摩擦系数减小,然后逐渐趋于平稳。混杂增强的镁基复合材料相比基体合金具有更低的摩擦系数。     

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

Impact of lubrication on the tribological behaviour of PTFE composites for guide rings application

In this study, the friction and wear behaviours of polytetrafluoroethylene (PTFE)-based composites were comparatively evaluated under dry sliding and oil-lubricated conditions. Two PTFE composites filled with bronze and bronze + molybdenum disulfide (MoS₂) were considered. These composites were used as guide rings for hydraulic actuating cylinder. Friction and wear tests of the composite specimens sliding against high chromium steel ball were conducted using reciprocating linear tribometer. The wear mechanisms of the composites under the two different sliding conditions were analysed and discussed based on scanning electron microscopic (SEM) examinations of the worn surface and optical micrographs of the steel counterface. Under the oil-lubricated condition, the friction and wear behaviours of the composites were considerably improved if compared to that under the dry sliding. The oil adsorbed layer limited the transfer of the composite to the steel counterface and avoided the oxidation of the MoS₂ during the sliding test.     

Effects of atomic oxygen exposure on the tribological performance of ZrO2-reinforced polyimide nanocomposites for low earth orbit space applications

The effects of atomic oxygen exposure on pure polyimide and nano-ZrO₂ reinforced polyimide composites were investigated in a ground-based simulation facility. The experimental results indicated that the surface structure of both pure polyimide and ZrO₂/polyimide composites were destroyed by atomic oxygen attack, but the addition of nano-ZrO₂ particles in polyimide could obviously decrease the mass loss, which showed that ZrO₂ could enhance the atomic oxygen resistance. The results of ZrO₂/polyimide composites before and after atomic oxygen exposure showed that atomic oxygen irradiation aggravated the friction and wear of the ZrO₂/polyimide composites. The wear mechanism was mainly abrasive particles wear arising from the ZrO₂-rich layer on the surface of composites. The ZrO₂/polyimide composites with 1 wt% nano-ZrO₂ owns the lowest varying rate of the friction coefficient and wear rate before and after atomic oxygen exposure, which showed stable friction and wear properties and was expected to become a kind of potential tribological materials for practical spacecraft designation.     

The effect of silane coupling agent on the sliding wear behavior of nanometer ZrO<Subscript>2</Subscript>/bismaleimide composites

The polymer composites filled with nanoparticles have good friction and wear properties and widely used in many fields. The performances of nanocomposites are influenced extensively by the nanoparticles morphology, size, volume fraction and dispersion. Nanometer ZrO₂ particles have good properties, lower prices and shows good foreground in resist-materials of polymer composites. In this paper, the nanometer ZrO₂ particles are treated by silane coupling agent of N-(2-aminoethyl)-γ-aminopropylmethyl dimethoxy silane. The effect of nanometer ZrO₂ content and silane coupling agent on the friction and wear properties of BMI copmposites filled with nanometer ZrO₂ are investigated. The composites filled with untreated ZrO₂ and treated ZrO₂ are prepared by the same way of mechanical high shear dispersion process and casting method. The sliding wear performance of the nanocomposites is studied on an M-200 friction and wear tester. The experimental results indicate that the frictional coefficient and the wear rate of the composites can be reduced by filled with nanometer ZrO₂. The composites containing treated nanometer ZrO₂ have the better tribological performance than that containing untreated nanometer ZrO₂. The results are explained from the SEM morphologies of the worn surface of matrix resin and the composites containing nanometer ZrO₂ and the TEM photographs of the nanometer ZrO₂ dispersion in the matrix.     

Crystallization of gel-derived mullite-zirconia composites

The crystallization of gel-derived mullites containing ZrO₂ content up to 20wt% had been studied. The formation of a metastable solid solution between ZrO₂ and mullite was established. A model was proposed to account for the formation of this solid solution. Grain refinement of mullite grains was observed in the composites containing at least 7wt% ZrO₂.     

流变成形压力对Al2Y/AZ91镁基复合材料摩擦磨损行为的影响

采用销盘式摩擦副,在转速为100 r/min干摩擦条件下,结合OM、SEM结果,考察了不同载荷与成形压力对流变成形Al2Y/AZ91镁基复合材料(质量分数2%Y)摩擦磨损性能的影响,并探究耐磨性与材料显微组织、力学性能之间的关系.研究表明:在相同的实验载荷下,随着制备复合材料流变成形压力的增加,材料的磨损质量和摩擦系数减少,本实验条件下最大成形压力为100 MPa时磨损量和摩擦系数最小,摩擦磨损性能较佳;对于在相同成形压力下制备的镁基复合材料,磨损质量随着载荷的提升而增大,而摩擦系数有所降低.当载荷较小时,Al2Y/AZ91镁基复合材料的磨损机制以磨粒磨损为主;随着载荷的增大,磨损机制逐步发生转变;当载荷较大时,磨损机制以剥层磨损为主.     

Friction and wear behavior of three-dimensional braided carbon fiber/epoxy composites under lubricated sliding conditions

The friction and wear characteristics of three-dimensional (3D) braided carbon fiber-epoxy (C_3D/EP) composites under lubricated sliding conditions against a quenched medium-carbon steel counterface were studied. Wear tests were performed under different loads at two velocities. Comparative wear tests under dry conditions were carried out to investigate the influence of lubrication. Tribological properties of the C_3D/EP composites with various fiber loadings and two different fiber-matrix adhesion strengths were assessed. It was found that the lubricated contact promoted lower wear rates and friction coefficients. Compared to dry sliding, the tribological performance of the C_3D/EP composites under lubrication was less dependent on fiber content, fiber-matrix bonding, load, and velocity than dry sliding. The worn surfaces of the C_3D/EP composites were analyzed by scanning electron microscopy (SEM) to explore the relevant mechanisms.     

Study on the friction and wear behavior of basalt fabric composites filled with graphite and nano-SiO2

To improve the friction and wear behavior of basalt fabric reinforced phenolic composites, single graphite or nano-SiO₂ and both of them were incorporated. The tribological properties of the resulting composites under different sliding conditions were investigated systematically on a model ring-on-block test rig. The friction and wear mechanisms of the composites were studied through analyzing the worn surfaces and transfer films by a scanning electron microscopy (SEM). Experimental results showed that graphite (Gr) was more beneficial than nano-SiO₂ in improving the tribological properties of basalt fabric composites (BFC) when they were singly incorporated. It is well worth noting that the friction and wear behavior of the filled composites was improved further when nano-SiO₂ and graphite were added together, indicating that there was a synergistic effect between them. Tribological tests under different sliding conditions revealed that the BFC/Gr/SiO₂ composites seemed to be more suitable for tribological applications under higher sliding speed and load.