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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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★ ★ ★
kunlunlx(金幣+160, 翻譯EPI+1): 辛苦了~感激萬分�。�！ 2011-06-03 09:47:24
Mally89(金幣+3): 感謝應(yīng)助！~ 2011-06-03 11:32:42

如圖2所示，（a）到（e）五個(gè)圖分別是在Ni , Ni-WC, Ni-CB , Ni-CNT, 和 Ni-SiC復(fù)合材料的樣本的形貌。圖二（a）為Ni涂層的掃面電鏡形貌，具有與典型的Ni晶體顆粒一樣得到均勻的金屬Ni的金屬結(jié)構(gòu)，尺寸可能超過5 lm.
如圖二(b)所示，可以觀察到，WC顆粒均勻的分散在Ni-WC膜的表面，也表明了由于WC的存在使得Ni晶體的顆粒尺寸變小�？梢栽趶�(fù)合鍍層的掃面電鏡上看到，和純Ni鍍層相比，盡管有些團(tuán)聚形成了簇，但是尺寸變小了。
可以觀察到，如圖二（c）（d）所示，Ni-CB 和 Ni-CNT圖層的表面形貌很粗糙。在大電流下，形成粗糙的表面形貌的可能原因是，除了鍍?cè)贜i層的可見的CNTs/ CB簇以外，在Ni-CB 和 Ni-CNT沉積過程中的孔洞或者縫隙。并且，注意由于存在CB/CNTs，因而電流密度分布不均勻。CB/CNTs是具有一種小半徑曲率半徑的良導(dǎo)體，這使得在CB/CNTs簇周圍的電場(chǎng)強(qiáng)度比其他地方要高，進(jìn)而使得在電工沉積過程中的電流密度的增加，導(dǎo)致了涂層厚度的不均勻。
如圖二（e）所示，可以看到Ni-SiC 顆粒在表面是團(tuán)聚成為球形，并且尺寸小于1 lm。
m表二所示由EDS計(jì)算結(jié)果得知的在復(fù)合物涂層里面的水浴重量百分比的影響（如圖三所示）。在復(fù)合物電鍍液中，CB 和CNT的比例與加入的物質(zhì)事成比例的，但是WC和SiC 的比例表偏低。相對(duì)于大顆粒的（ＷＣ和SiC），用小顆粒（CB和CNT）的涂層表現(xiàn)出了更高的活性，這可能是因?yàn)橹亓Ρ容^大，使得其由Ni粒子攜帶的分散性比較差的緣故。隨著水浴負(fù)載量的增加，涂層的質(zhì)量比也增加。在合金中的CNT/CB 濃度的增加的其他原因（a）主要是增加物的導(dǎo)電能力增加了布散能力,(b)沉積速率提高了沉積的性能，因?yàn)槠錅p少了殘余應(yīng)力和孔道。
圖四表明了附加物的負(fù)載量對(duì)鎳基復(fù)合鍍層的涂層厚度的影響。厚度為24-65lm,取決于加固的類型和負(fù)載的種類。觀察到改變?cè)谒≈械募庸填愋蜁?huì)影響涂層的厚度，并且與加固類型相同。在所有類型中，涂層厚度隨著負(fù)載的增加而增加.Ni-CNT由于其維數(shù)和電導(dǎo)率而有最高的厚度，Ni-SiC在旨在邊緣上的涂層厚度有所增加。Ni-WC 和Ni-CB的厚度在Ni-CNT 和 Ni-SiC復(fù)合涂層之間。
如圖5所示，WC, CB, CNT, 和 SiC對(duì)復(fù)合涂層的硬度有影響，使得其硬度從純Ni的510 kgf mm 2增加到920 kgf mm （24 g/L WC and 0.4 g/L CNT)。水浴鍋中的加固類型和內(nèi)容對(duì)復(fù)合涂層的微硬度有影響。隨著加固的增加，微硬度增加到最高點(diǎn)之后開始下降。隨著加固的增加，粒子細(xì)化和色散強(qiáng)度的增加，使得隨著加固的增加，鎳基復(fù)合涂層的微硬度也增加。Ni-WC和Ni-CNT復(fù)合涂層相對(duì)于其他類型來說，表現(xiàn)出了更高的硬度，這一結(jié)果表明經(jīng)過WC/CNT共沉積的鎳的任性和強(qiáng)度都增加了。而由Ni-CB復(fù)合的涂層的強(qiáng)度比其他三種都要小，并且由圖二（c）所示，可以看到有更多的表面縫隙，因而表面更不規(guī)則。由于其比較低的強(qiáng)度和ＳｉＣ的濃度比較低，Ni-SiC復(fù)合涂層的硬度介于Ni-CNT 和Ni-CB之間。那些硬度增加的復(fù)合涂層，可能是由于其彌散強(qiáng)化效果。當(dāng)用WC (4 g/L), CB (1.0 g/L), CNT (0.4 g/L), 和SiC (15 g/L)來做鎳基復(fù)合涂層的時(shí)候，隨著濃度的增加，強(qiáng)度也有所增加。分別從510增加到920, 760, 920, and 810 vH.但是，當(dāng)起始濃度為6 g/L WC, 1.5 g/L CB, 0.6 g/L CNT, 20 g/L SiC時(shí)，硬度急劇的下降到720, 850, and 730 vH，這可能是由于高負(fù)載的復(fù)合物產(chǎn)生了多微孔結(jié)構(gòu)所致。
如圖六所示，四條曲線分別為相對(duì)于純鎳的Ni-WC 涂層 Ni-CB涂層, Ni-CNT涂層和Ni-SiC 涂層的應(yīng)力應(yīng)變曲線。在所有實(shí)驗(yàn)中，所有的應(yīng)力都是通過測(cè)量曲線上的突然驟減得到的。圖六顯示了加固的增加對(duì)于復(fù)合涂層材料的作用。在純鎳曲線中，平滑的曲線，主要是由于在涂層過程中出現(xiàn)了動(dòng)態(tài)的恢復(fù)以及重結(jié)晶過程。對(duì)于復(fù)合涂層在應(yīng)力大于0.2之后出現(xiàn)的明顯的軟化是由于如圖六所示在試樣表面和內(nèi)部形成微裂。所有的曲線相對(duì)于純鎳來說，在拉伸強(qiáng)度上都有所提高。被含有WC 和CNT的涂層包覆的復(fù)合材料的拉伸強(qiáng)度明顯強(qiáng)于純鎳的，但是被SiC和CB包裹的就幾乎在拉伸強(qiáng)度上所有增加。這可能是由于在Ni-SiC復(fù)合材料中的的粒子更容易發(fā)生粒子的斷裂所致。水浴載荷的不同和強(qiáng)度的不同都會(huì)對(duì)復(fù)合材料的拉伸強(qiáng)度有明顯的影響。
圖七為不同種類的加固以及水浴載荷對(duì)于拉伸強(qiáng)度的影響，我們注意到增強(qiáng)的顆粒簇對(duì)于復(fù)合材料涂層的拉伸強(qiáng)度也有很大的影響。當(dāng)鎳基上的濃度為WC (4 g/L), CB (1.0 g/L), CNT (0.4 g/L), 和 SiC (15 g/L)時(shí)，隨著濃度的增加，拉伸強(qiáng)度明顯的分別從620到810, 740, 910, 808MPa，但是當(dāng)鎳基上的濃度為6 g/L WC, 1.5 g/L CB, 0.6 g/L CNT, 和20 g/L SiC時(shí)，拉伸強(qiáng)度又分別降低到740, 710, 860, 710 MPa�？梢钥吹皆谕繉硬牧现�，水浴里面負(fù)載的增加引起顆粒的簇的形成。
如圖八所示為純鎳和鎳基涂層的XRD圖。對(duì)于純鎳和Ni-WC, Ni-CB, Ni-CNT, 和 Ni-SiC 復(fù)合涂層來說，其平均的晶體尺寸分別為43, 10.3, 9.1, 8.2,和 13, 5 nm。通過快速成核可以得到比較精細(xì)粒子的沉積。加固的增加可以提供很多數(shù)量的陽(yáng)極，從而在金屬表面形成更多的新的核，因而生成了具有精細(xì)粒子的復(fù)合物沉積。在圖8（a）中，很明顯可以觀察到，純鎳沉積的很高強(qiáng)度的(200)面的衍射峰，相應(yīng)于(100)結(jié)構(gòu)，而相對(duì)于Ni-WC (Fig. 8b), Ni-CB(Fig. 8c), Ni-CNT (Fig. 8d), Ni-SiC(Fig. 8e)中，（311）和（111）面衍射峰很明顯，伴隨著（200）面的減小。很有趣的是，（311）和（111）面使得（211）面消失。所以，復(fù)合物涂層具有很大的硬度和拉伸強(qiáng)度。提高強(qiáng)度的其他的可能原因就是相對(duì)于那些純鎳涂層來說，由于在復(fù)合物涂層中的加固的存在使得鎳晶體的顆粒尺寸減小了。

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