Materials Science Forum Vol. 848

Abstract: A series of the blending membranes comprised of the different mass ratio of silk fibroin peptide (SFP) power, silver nanoparticles (NanoAg) and polyurethane (PU) were prepared with mixing the SFP power, silver nitrate and PU, and the silver nitrate was reduced to NanoAg by SFP in this mixing process. UV spectrum was used to detect the nanoAg. The experimental results confirmed the formation of NanoAg. The dissolution of the obtained membranes in simulated body fluid (SBF) were determined, and showed that the membranes had good stability. Their mechanical properties were also determined. The results revealed that the mass ratio of SFP to PU was an important influence factor, and the mass ratio 30/70 (SFP/PU) of the membrane was the optimum. The Antibacterial properties against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, were examined, the results of which indicated that the membranes containing NanoAg had a good bactericidal effect. The SFP/PU/NanoAg membranes also showed good cell and blood compatibility, and then they have application prospect as an antibacterial materials using for medical catheters.

Abstract: In order to evaluate the cytocompatibility and hemolytic properties of n-HA/PEEK biocomposites the nanohydroxyapatite/polyetheretherketone (n-HA/PEEK) biocomposites were successfully prepared. The mechanical properties of the biocomposites were proximal to human bone, at the same time, they had the optimal value with the HA volume content of 5%. The PEEK and n-HA/PEEK biocomposites with different HA content extraction medium was prepared with fresh medium. Simple DMEM culture solution was taken as negative control group. The pure PEEK and 5vol.%, 15vol.%, 30vol.% n-HA/PEEK biocomposites were the testing group. The relative proliferation rate of L929 cells was determined on the 1^st, 2^nd, 3^rd and 6^th days with CCK-8 assay. The cytotoxicity of n-HA/PEEK biocomposites were evaluated according to ISO 10993-5: 2009. The L929 cells morphology and growth on the 1^st, 2^nd, 3^rd and 6^th days were determined under inverted microscope. The hemolysis test in vitro of n-HA/PEEK biocomposites were evaluated through measuring erythrocyte lysis and ferro-hemoglobin freeing degree with indirect contact method basing on ISO 10993-4:2009. The experimental results showed that the growth and morphology of cells in pure PEEK and n-HA/PEEK biocomposites extraction medium had no difference from negative control group. Cytotoxicity test showed that PEEK and n-HA/PEEK biocomposites did not have obvious toxicity on L929 cells, and the cytotoxicity of these extracts was in grade 0-1. Hemolysis test suggested that PEEK and n-HA/PEEK biocomposites did not have obvious hemolysis reaction, and the hemolysis rate of PEEK and n-HA/PEEK biocomposites were 2.37%, 1.71%, 1.05% and 1.32% respectively, which are less than the national standard (5%). It may be concluded that the n-HA/PEEK biocomposites did not have obvious cytotoxicity and hemolysis reaction, which demonstrated that n-HA/PEEK biocomposites had good cytocompatibility.

Abstract: Mn_100-xFe_x (x=50, 58) alloys were prepared by spark plasma sintering (SPS), and the structure, magnetostriction and magnetic properties of the polycrystalline Mn_100-xFe_x alloys were investigated. The results of XRD and SEM showed that the as-cast and annealed samples presented a single face center cubic γ-phase, which is austenite structure. The magnetic measurement showed that Mn_100-xFe_x (x=50, 58) alloys annealed at 700^oC were a typical ferromagnet at low temperature and there was a gradual transition from the ferromagnetic phase to the paramagnetic phase in a wide temperature region (about 150-250K). The magnetostriction for the annealed samples, measured by strain-gauge bridge up to 3T, was ~100 ppm at 300K, but the results was chaotic. The results are not in agreement with the results reported. The further research on the mechanism of the magnetostriction is needed.

Abstract: Cu and Cu-30wt.%Zn alloys with stacking fault energies (SFEs) of 78 mJ/m² and 14 mJ/m² were processed by surface mechanical attrition treatment (SMAT) at room temperature and liquid nitrogen (LN) temperature, respectively. The effect of SFE and deformation temperature on tensile properties of these samples was investigated. The tensile testing results indicated that the yield strength and uniform elongation of these samples enhanced simultaneously with decreasing SFE. Meanwhile, the LN-SMAT processed samples exhibited remarkably higher strength and slightly lower ductility compared to those processed at room temperature. The SFE affected the deformation mechanisms of metals greatly. X-ray diffraction (XRD) measurements indicated that the twin density increased while the average grain size decreased with SFE decreasing, and twinning became the dominant deformation mechanism. The relationship between microstructure and mechanical property is also discussed.

Abstract: To provide insight into the mechanical behavior and microstructural evolution of bulk nanograined (NG) Ni-based alloys during annealing, the Ni-based alloy sheets with grain size about 50 nm was produced through severe cold-rolling at room temperature, and then the cold rolled (CRed) Ni-based alloys were annealed at different states. The evolution of the nanostructure of the CRed Ni-based alloy during annealing and corresponding change in mechanical properties was investigated. The results showed that the CRed Ni-based alloy exhibited prominent enhancement in the yield strength (YS), ultimate tensile strength (UTS), which increased respectively from 253 MPa to 1455 MPa, 684 MPa to 1557 MPa. Further increase of the YS and UTS were obtained in the annealed-CRed Ni-based alloy with dual-phase. The YS and UTS of the NG dual-phase Ni-based alloy was respectively 2013 MPa and 2061MPa, which was annealed at 700 °C for 1h. In terms of the microstructural evolution, lower density of defects on the grain boundary were observed and the nanograins can be maintained about 100 nm even when annealed for 30 h at 700 °C, which suggests high thermal stability at this temperature. Both the high thermal stability and strength are due to the formation of the γ′ precipitates and slight grain growth of the NG matrix.

Abstract: The Hall-Petch relation in a spheroidized steel with bimodal cementite particle size distribution has been investigated in this study, with an emphasis on considering the effect of the large particles at ferrite grain boundaries and triple junctions. A medium carbon steel was processed by variable thermomechanical procedures to achieve spheroidized structures with different combinations of microstructrual parameters, but all exhibiting a bimodal particle size distribution, in which large intergranular particles and small intragranular particles coexisted in the ferrite matrix. A quantitative relationship between the Hall-Petch parameter k_y and the volume fraction of the intergranular cementite particles is presented, by considering a composite model. The contribution of the large intergranular particles to grain boundary strengthening wa substantiated by the increment of the k_y parameter, since the average orientation factor of the composite, is increased. After correction of the k_y parameters based on the constants from literatures, the predicted stresses show good agreement with the experimental stresses. A linear fit between the experimental stresses and the reciprocal square root of grain sizes is performed, the slope constant k_y derived agrees to within 11 % of the corrected k_y parameters based on the constants from literatures.

Abstract: AlMgB₁₄ is a very hard and brittle material which need be modified for utilizing as cutting tool materials. In present study, TiB₂ and Ni₃Al were used to strengthen and toughen AlMgB₁₄ material. The microstructure of the AlMgB₁₄-TiB₂-Ni₃Al composites was analysized by scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) and an X-ray diffractometer (XRD). The hardness and fracture toughness of the AlMgB₁₄-TiB₂Ni₃Al composites were also examined. The results showed that the major phases in AlMgB₁₄-Ni₃Al composites were TiB₂, AlMgB₁₄, MgAl₂O₄ , Ni₃Al and NiAl. With the increasing of the amount of Ni₃Al, more intergranular fractured features can be found in the fractured surface of the composites, the hardness and fracture toughness of the composites were both decreased comparing to the synthesised AlMgB₁₄. The AlMgB₁₄-TiB₂-4wt.% Ni₃Al composite has a hardness of 28.1 Gpa and a fracture toughness of 3.14 MPa·m^1/2.

Abstract: In this paper, nanocrystalline diamond with the average grain size of 50nm was prepared under different sintering pressure, temperature and sintering time. The microstructure of the sample was analyzed by SEM, EDS and XRD, and the mechanical properties tested by micro-hardness tester and wear ratio instrument. The results show that the sample sintered under the optimum conditions of oil pressure 87MPa, heating power 4000W and sintering time 120s possessed hardness of 706.41HV and wear ratio of 3280. It indicated that high performance n-PCD sintered from nanodiamond and silicon system can be formed hardly with diamond to diamond bonding but can be formed with diamond to silicon carbide bonding. The poor mechanical properties of the samples were due to the surface adsorption groups and surface graphitization of nanodiamond during high pressure sintering.

Abstract: In the present study, high-quality chemical vapor deposition (CVD) micro-crystalline diamond (MCD) film was successfully deposited on the surface of the Φ0.5 mm×120 mm tungsten wire using a special designed graphitic jig for supporting the substrate and a two-step deposition procedure for guaranteeing the uniformity of as-deposited diamond film. It is proved that as-deposited film indeed presented much more uniform thickness than that obtained using a conventional jig described in the previous literature, and a very thick WC interlayer spontaneously formed between the substrate and the diamond film, which together with as-deposited MCD film have significant effects on mechanical properties of the wire. Generally speaking, the coated wire remains extremely high surface hardness of the MCD film and considerable toughness of the substrate, along with favorable film-substrate adhesion. It is recognized that these the coated tungsten wires have broad application prospects, but the technologies for depositing diamond films that are thick enough on even longer and thinner wires still need further investigation.

Abstract: In order to investigate the effect of austenite grain size on martensite start temperature of Nb-V-Ti micro-alloyed ultra-high strength steel, the phase transformation features of Nb-V-Ti micro-alloyed steel was investigated. It has been found that martensite start temperature increased with the increase of austenite grain size as a consequence of the increase of austenitizing temperature. Based on microstructure observation, two types of MX carbonitrides with different compositions and morphologies have been identified. With the increase of the austenite grain size, both the volume fraction of precipitates and the dislocation density decreased, which may be induced by the strengthening of the austenite matrix directly and increasing the resistance of austenite to plastic deformation. Hence, the increase of martensite start temperature could be attributed to a decrease in volume fraction of precipitates and dislocation density.