The results from XRD, SEM-EDAX study on Ni-P-SiC/Ni-P-TiO2-ZrO2 as-plated and heated (400℃) coated surfaces are explained and results are discussed in following section.The FESEM-EDAX photographs (Figures 1a, 1b, 1c and 2) suggests that, inclusion of TiO2 and ZrO2 nano-particles into EL Ni-P matrix results in change in metallic shine surface and with approximately uniform distribution of TiO2 and ZrO2 nano-particles over the coated surface with fine density. The Ni-P-SiC coated surfaces appearance becomes blackish. An one hour heat treatment in presence of Ar for nano-composite coated coupons turnout SiC, TiO2 and ZrO2 nano-particles more packed in, which results reduced porosity of the nano-composite coatings and this may get better corrosion and wear resistance of these coatings .
Fig. 1. SEM micrographs of (a) Ni-P-TiO2-ZrO2 (As-plated) and (b) Ni-P-TiO2-ZrO2 (Heated) nano-composite coatings (c) Ni-P-SiC (Heated) nano-composite coatings.
Fig. 2. EDAX micrographs of Ni-P-TiO2-ZrO2 (Heated) nano-composite coating.
From EDAX analysis (Table 1) it is revealed that Ni-P-TiO2-ZrO2 as-plated depositions has following weight percentage of particles Ni (82.15%), P (11.41%), O (3.17%), Fe (2.13%), Zr (0.43%) and Ti (0.58 %). The heat treated Ni-P-TiO2-ZrO2 coating has Ni (80.50%), P (10.75%), O (3.10%), Fe (4.69%), Zr (0.39%) and Ti (0.47%)
weight percentage of particles. In EDAX analysis (Table 3) of Ni-P-SiC as-plated depositions has following weight percentage of particles Ni (82.24%), P (10.13%), Si (3.20%), Fe (2.10%) and C (2.33%). The heat treated Ni-P-SiC coating has Ni (80.32%), P (10.10%), Si (2.86%), Fe (4.59%) and C (2.13%) weight percentage of particles. In EDAX spectra of Ni-P-TiO2-ZrO2 EL nano-composite coatings besides Ni and P peaks, the weak peaks of zirconium and titania are also observed and similar behavior is observed for Ni-P-SiC coatings. These weak peaks prove codeposition of SiC, zirconium plus titania nano- element into EL Ni-P medium. The weak peaks of SiC, TiO2 and ZrO2 can be because of less amount and uniform co-deposition of silicon carbide, zirconium plus titania nano constituent particle into EL Ni-P medium. In Ni-P-SiC/Ni-P-TiO2-ZrO2 as-plated deposition, the phosphorus (P) amount, to some extent is superior to Ni-P-SiC/Ni-P-TiO2-ZrO2 heat treated. The higher phosphorus (P) content can prevent the nucleation of Ni (FCC) phase which outcomes as amorphous configuration with higher fineness and density of surface structure than Ni-P-SiC/Ni-P-TiO2-ZrO2 heat treated. It is marked from the EDAX analysis that the amount of Ni, Si, C, O, zirconia and titania particles also decreases in case of Ni-P-SiC/Ni-P-TiO2-ZrO2 heated coatings in contrast to Ni-P-SiC/Ni-P-TiO2-ZrO2 as-plated coatings. The EDAX examination further reveals that considerable quantity of iron depositions into edges of depositions and substrate. This may enhance corrosion however in Ni-P-SiC/Ni-P-TiO2-ZrO2 as-plated EL nano-composite coatings a smaller amount of iron put forward less diffusion of plating which supports in prevention of corrosion.
Table 1. EDAX analysis of Ni-P-SiC/Ni-P-TiO2-ZrO2 nano-composite coatings.
The XRD plots of EL Ni-P-TiO2-ZrO2 nano-composite coatings are shown in Figure 3 as-plated and heat treated at 400 °C. These figures divulge that phase of as-plated coupon is more amorphous than crystalline and a solitary extensive peak is existing at diffraction angle of 44.30 (Ni) plus other very low peaks are available at angle of 28.20 (ZrO2) and 28.20 (TiO2).It can be because of co-deposition of TiO2 and ZrO2 nano-particles with high distribution and in very less amount into the EL Ni-P matrix. Secondly for heat treated coupon (400°C) more nebulous nature of coatings gets transformed into semi-crystalline (more crystalline less amorphous) nature with crest on different diffraction angles.
The topmost peak of Ni3P with TiO2 is experienced for diffraction angle 44.10. The Ni-P peaks are experienced at 42.30, 44.50 plus 45.40. The TiO2 peaks are experienced at 35.10, 53.50, 57.80 and 77.40 diffraction angles. The Ni diffraction peaks at 52.10, 76.40 and Fe diffraction peaks are experienced as a substrate at 64.70 and 68.30.Very weak peaks of ZrO2 nano particlesare observed in heat treated case this can be because of very low amounts of ZrO2 nanoparticles into matrix of EL Ni-P. It is also thought that dispersion distributed ZrO2 nano-particles uniformly in Ni-P matrix which further can control the oxidation of the composite coatings and put off the growth of crystal grains and re-crystallization. Thus degree of crystallization and oxidation of EL Ni-P-TiO2-ZrO2 heat treated coating was decreased. The reflections corresponding to (111), (200) and (220) planes, the FCC phase of Ni are able to be hardheaded. The Ni3P (BCC) alloy phase is accountable in favor of strengthens in hardness and wear confrontation of coatings. The grains dimension of depositions is roughly within the range among 4.13 nm to 15.58 nm. For Figure 5, reflections (by indexing) are seen perfectly equivalent through orientation (JCPDS 01 to 1260; FCC Ni), (JCPDS 34 to 0501; BCC Ni3P), (JCPDS 01-074-0508 to 01-071-1166; TiO2) and (JCPDS00-024 to 1164, 01 to 078-0047; ZrO2). These reflections authenticate the crystalline, metallic Ni (FCC) and Ni3P (BCC) alloy phases. In XRD spectra of Ni-P-TiO2-ZrO2 as-plated and heat treated depositions, the Ni-P peak does not carry out any major shift because of incorporation of nano-particles in little concentration as compared with basic EL Ni-P depositions. Similar results are observed for Ni-P-SiC coatings. Hence consequences attained here are into good accordance through the outcome reported by and breadth of foremost crest of Ni (111) point out grain proportions of coatings are in range among 3.97-16.46 nm for as-coated and heat treated samples and observations also validate it.
Fig. 3. XRD micrographs of (a) Ni-P-TiO2-ZrO2 (As-plated) and (b) Ni-P-TiO2-ZrO2 (Heated) nano-composite coatings.
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