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求有关复合材料的翻译~单词有点多，金币有点少，谢谢你了啊~160全部给你吧
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Figure 2(a) to (e) shows the morphology of the deposited specimens with Ni , Ni-WC, Ni-CB , Ni-CNT, and Ni-SiC composite coatings. SEM micrographs of the Ni coating shown in Fig. 2(a) exhibit a homogeneous metallic structure of pure Ni with a typical shape of nickel crystallites,which may exceed a size 5 lm. From Fig. 2(b) it can be observed that the WC particles are homogeneously dispersed in the Ni-WC film. The figure also shows the reduction grain size of Ni crystallites due to the presence of WC reinforcement. This reduction is also discernible in SEM micrographs of composite deposits as compared with those of pure Ni deposits even though some of them have formed agglomerated clusters. Both Ni-CB and Ni-CNT coating surface morphology was very rough as observed in Fig. 2(c) and (d) respectively. The possible reasons for the coarse surface under larger current density are many voids or gaps in the deposits of Ni-CB and Ni-CNT apart from clusters of CNTs/ CB are seen in the deposited Ni layers. Also, notice the uneven distribution of the deposition current density due to the existence of CB/CNTs. CB/CNT that are good conductors with a small radius of curvature radius. This fact results in an electric field is stronger around the cluster of CB/CNTs the than in other areas, resulting in increased local deposition current densities during electro-co-deposition and leading to an uneven coating thickness. Figure 2(e) shows Ni-SiC grains that are smaller than 1 lm with some globular grain-agglomerates visible on the surface.Table 2 shows the effect of bath loading on the percentage weight (wt.%) of reinforcement in the composite coating by computing from EDS results (as shown in Fig. 3). The wt.% of reinforcement in the coating in CB and CNT are proportional to loading content in the composite plating bath, but WC and SiC reinforcements showed lower wt.% in the coating. Coating with smaller particles (CB and CNT) exhibited higher activity than coating with larger particles (WC and SiC). This may be attributed to the fact that heavy particles are difficult to be carried by the Ni ions due to lower effect of their throwing power (Ref 12). wt.% of reinforcement in the coating increased with increasing bath loading. The other reason for increasing the CNT/CB concentration in the alloy was to check (a) whether conductivity of reinforcement increased the throwing power, (b) the deposition rate improves the properties of the deposit in terms of reduction of residual stress and porosity (Ref 13).Figure 4 shows the effect of reinforcement loading on the coating thickness of Ni-based composite deposits. The thicknesses of the coatings range from 24 to 65 lm, depending on the reinforcement type and load used. It was observed that varying the reinforcement loading in the bath clearly affects the thickness of the coatings, and also varies with reinforcement. In all cases the coating thickness increased with increasing reinforcement loading. Ni-CNT showed the highest coating thickness due to the dimension and conductivity of CNT. Ni-SiC showed only marginal increment in coating thickness. The thickness of Ni-WC and Ni-CB was in between Ni-CNT and Ni-SiC composite coatings. The WC, CB, CNT, and SiC have a hardening effect on the composite coating and hardness of the coating increases from 510 kgf mm 2 for pure Ni coating to 920 kgf mm 2 (4 g/L WC and 0.4 g/L CNT) as observed in Fig. 5. The effect of reinforcement types and reinforcement content in the bath on the microhardness of the composites layers. The microhardness increased to a maximum and then decreased with reinforcement content. The grain-refining and dispersive strengthening effect become stronger with increasing reinforcement content, resulting in the microhardness of the Ni-based composite coatings increasing with larger reinforcement content. Ni-WC and Ni-CNT composite coatings showed higher hardness compared to other types. These results show improved both toughness and strength of the composites with co-deposition of WC/CNT s with nickel. Ni-CB composite coating showed lower hardness than the other three types of coatings. Ni-CB has more irregular surface finish as also more porosity that can be seen in the microstructure illustrated in Fig. 2(c). Ni-SiC composite coating hardness lies between Ni-CNT and Ni-CB due to its lower strength and lower SiC content in the coatings. The hardness increase noted in these composite coatings could be linked to a dispersion strengthening effect (Ref 14). With increasing the WC (4 g/L), CB (1.0 g/L), CNT (0.4 g/L), and SiC (15 g/L) content Ni composites coatings, the hardness was improved from 510 to 920, 760, 920, and 810 vH. However, the hardness dropped drastically to 750, 720, 850, and 730 vH for the specimen with the 6 g/L WC, 1.5 g/L CB, 0.6 g/L CNT, and 20 g/L SiC, respectively. This might be due to the porous microstructure of the higher loading composites. The stress strain curves of the Ni-WC coatings (Fig. 6a), Ni-CB coatings (Fig. 6b), Ni-CNT (Fig. 6c), and Ni-SiC (Fig. 6d) are compared with pure Ni coating. For all tests the strain was determined by a sudden drop in the flow curve (catastrophic failure of coatings). Figure 6 shows the addition of reinforcement significant contribution on the composite coating behavior. In pure Ni coating curves show sooth behavior, which due to dynamic recovery and re-crystallization process occurring within the coating. For composite coatings the apparent softening after a strain of 0.2 is due to micro-crack formation at the specimen surface and in the interior as shown in Fig. 6. All graphs clearly show an increase in tensile strength, compared to pure Ni coating with the addition of reinforcement. The composite coating containing WC and CNT show the tensile strength was significantly higher than pure Ni coating, but SiC and CB coating show only a nominal increase in tensile strength. This can be attributed to the higher propensity of particle fracture in Ni-SiC composite coating.Variation in bath loading and reinforcements were found to have a significant effect on the tensile properties of the composites. Figure 7 shows the variation of the tensile strength with different reinforcements and bath loading. It is also important to note that the reinforced particulate clusters also have a significant effect on the tensile properties of the composites coating. With increase in the WC (4 g/L), CB (1.0 g/L), CNT (0.4 g/L), and SiC (15 g/L) content in Ni composites coatings, the tensile strength improved from 620 to 810, 740, 910, and 808 MPa respectively. However, the tensile strength dropped to 740, 710, 860, and 710 MPa for the specimen with the 6 g/L WC, 1.5 g/L CB, 0.6 g/L CNT, and 20 g/L SiC, respectively. Increase in reinforcement (WC, CB, SiC, and CNT) loading into the bath caused more particles clustering as seen in coated materials.XRD diagrams of the Ni and Ni-based coatings are shown in Fig. 8. The average crystal size of the coating was 43, 10.3, 9.1, 8.2, and 13, 5 nm for Ni, Ni-WC, Ni-CB, Ni-CNT, and Ni-SiC composite coatings, respectively. Fine-grained deposits are generally obtained at higher rate of formation of nuclei (Ref 15). The addition of reinforcement may provide a larger number of cathodic sites and consequently more number of fresh nuclei are formed on the metal surface. This results in a fine-grained composite deposit.It is apparent that the diffraction pattern of pure Ni deposit is characterized by the intense (200) diffraction line corresponding to a (100) texture shown in Fig. 8(a), where the diffraction pattern of Ni-WC (Fig. 8b), Ni-CB(Fig. 8c), Ni-CNT (Fig. 8d), and Ni-SiC(Fig. 8e) reinforcements is characterized by (311) and (111) lines accompanied with an attenuation of the (200) line (Ref 7). It is of interest to note that the reinforcement of lines (311) and (111) are attributed to a dispersed (211) orientation (Ref 7). Hence, the composite coatings show maximum strength and hardness. The other reason for improvement in the strength is the reduction of grain size of Ni crystallites due to the presence of reinforcement in the composite coatings as compared with those of pure Ni coatings. |
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