The aim of this research was to create Ni-B4C composite coatings on copper substrate by the electroplating process. The effects of current type on the microstructure, hardness, wear and corrosion behavior of coatings were also studied. Different process parameters (particle concentration in the solution, mixing condition in the electroplating Watts bath, current density and process time) were examined using pulse reverse current in the presence of B4C micro particles into the electroplating Watts bath. Afterward, Ni-B4C micro-composite coatings were prepared at the optimum conditions using three different current types: direct current (DC), Pulsed current (PC) and pulsed reverse current (PRC). The same conditions were used in the presence of B4C nano particles in electroplating Watts bath by using pulse reverse current. The effect of particle concentration in the solution on the resultant microstructure was examined. Ni-B4C nano-composite coatings were prepared with three types of currents: direct current (DC), pulsed current (PC) and pulsed reverse current (PRC) with the optimum bath consentration. Morphology and microstructure of the coatings were studied by optical microscopy (OM), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). To evaluate the hardness, wear and corrosion behavior of the coatings vickers hardness testing, wear testing and potentiodynamic polarization were conducted, respectively. The results showed that the coating obtaind by using pulse reverse current (PRC) showed higher hardness and better corrosion and wear resistance compared to the other coatings. Meanwhile, best co-deposition and distribution of particles in the nickel matrix composite coating was attained by using pulse reverse current (PRC).

The aim of this study was to fabricate of Ni-SiC composite coating by electroplating technique emphasing on the effect of magnetic field using Ni pre-coated SiC particles. In order to obtain a coating with desired microstructure different electroplating process parameters (particle concentration in the solution, process time) were examined during the electroplating of St37 plain carbon steel in the presence of a magnetic field SiC particles and electroless Ni coated SiC particles were used, as the reinforcing phase. Microstructural evaluation and phase identification of the coatings were conducted by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD), respectively. Experimental results showed that the coatings contained nickel matrix with different amount of SiC particles distributed in the matrix. Increasing the time of process, and the concentration of SiC particles in the solution as well as applying magnetic field resulted in, increasing of SiC content and the hardness of the coating. Moreover, using Ni coated SiC particles by applying magnetic field during the process, resulted in the modification of the coating with higher amount of SiC (3.6 volume percent) with uniform distribution and maximum hardness value (734.5 HV).

 In this research, one stage pack cementation process was applied to estimate the optimized conditions for creating a desirable silicon aluminide diffusion coating on IN738LC superalloy. Thermochemical calculations indicated the possibility of
co-deposition of Al and Si with NH4Cl activated pack powder at 750C and 900C by stabilizing the Al source within the pack. In order to create a coating with desirable structure, packs of powder with different Si/Al ratio and NH4Cl and Al2O3 (as activator and filler, respectively) were used. Microstructural evaluation and phase characterization of created coatings were conducted by field emission scanning electron microscope (FESEM) equipped with energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). According to the results, NiSi and AlNi2Si compounds (individually or together) were identified as dominant phases. It was found that inward diffusion of Al was dominant in first stages, there in after, inward diffusion of Si led to the conversion of NiAl phase to AlNi2Si and finally to NiSi phase, gradually. For most samples, outward diffusion of Ni became dominant in final stages. Therefore, A porous and brittle layer of NiSi was formed on the surface, deteriorated the properties of the coating. The sample coated by pack powder with Si/Al=4 at 900C showed superior microstructural characteristics and contained desirable AlNi2Si phase without unwanted NiSi phase.

In this research, microstructures, wear properties and hardness of Stellite 6-B4C composite layers were evaluated.Composite layers of Stellite 6 with different B4C percentages were cladded on plain carbon steel substrates by GTAW method. X-ray Diffractometery (XRD) was used for investigating the structure of clad layers. Microstructural evaluation of clad layers was conducted by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometery (EDS). Hardness and wear resistance of clad layers were studied by microhardness testing and pin on disc wear testing, respectively. Experimental resultes illustrated the existence of cobalt-rich matrix together with eutectic carbides such as Cr7C3 and Cr23C6 and other phases such as CrB2, W2B, Co2B, WC. It was proposed that B4C particles dissolved during the welding process, and elemental B, C reacted with other elements in the clad layer. Furthermore, the addition of B4C particles up to 20 wt% leads to a finer microstructure and rised hardness of the coating. Addition of B4C particles to the coating reduced the wear rates and the coting containing 20 weight percent B4C showed the highest wear resistance.

  Graphene, a single 2D carbon sheet, has attracted considerable interest for its remarkable and unusual chemical and physical properties since its discovery in 2005. Graphene is regarded as the “thinnest material in the universe” with the highest-known intrinsic strength of 130 GPa and a Young’s modulus of 1 TPa. In this study, Ni-P-Graphene nanocomposite coatings were deposited on copper substrates by electroless plating with different concentrations of graphene in electroless bath. X-ray diffractometery (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were used to characterize and evaluate the microstructure of composite coatings. The effect of co-deposition of graphene nano sheets on friction and wear behavior of nanocomposite coatings was investigated by Vickers micro-hardness testing and pin-on-disk wear testing. Microstructural studies of Ni-P-Graphene coatings showed a good distribution of graphene sheets within the matrix without obvious signs of agglomeration. Comparison of Ni-P and Ni-P-Graphene coatings indicated that due to the addition of graphene nano sheets, a remarkable improvement in the tribological behavior of nanocomposite coating occurred. This enhancement in properties is attributed to the superior mechanical properties and unique topological structure of graphene.

The aim of this research is producing Al-B4C and Al-B4C-TiB2 mono and hybrid surface composite layer by Friction Stir Processing (FSP). Al-B4C surface composite layer was produced with two different tool dimensions and different rotational speeds by friction stir processing. In order to produce surface hybrid composite layer, TiB2-Al composite nano particles were produced by mechanical alloying. Friction stir processing was used to produce mono and hybrid composite layers of B4C and TiB2-Al particles in aluminum matrix by optimized process parameters. Microstructural evaluation implemented by optical microscopy (OM) and scanning electron microscopy (SEM). Vickers microhardness test was used to quantify hardness values and pin on disk wear test was used to evaluate the wear behavior of composite layers. The result showed that the addition of B4C and TiB2 on AA6061 led to significant enhancement of hardness and wear behavior in composite layers. Also in hybrid surface composite layers by increasing in TiB2 nano particles content the hardness values and wear resistance improved nearly twice in comparison with AA6061..
 

 A356 -5 vol. % (micro/nano) Al2O3 composites containing different weight ratios of micro and nano size alumina particles were fabricated by stir casting method. Different mixtures of 50 m and 80 nm Al2O3 particles were mixed and milled with pure aluminum powder before introducing to the melt. The milled powder mixtures were added to the molten A356 alloy during stir casting process and poured in metal dies. Microstructural characterization of as-cast samples conducted by scanning electron microscopy (SEM) revealed a fairly uniform distribution of the particles and some amount of grain refinement in the specimens with the addition of bimodal Al2O3 reinforcing particles. The effect of Al2O3 micro/nano particles weight ratio on the mechanical properties of composites such as hardness and tensile strength was investigated. The results showed the improvement of hardness and tensile strength of the composites with increasing the fraction of nano size particles.

Microstructural characteristics and wear behavior of stellite6-B4C composite clad layer were evaluated. Composite layers of stellite6 with different B4C percentages were Cladded method on low carbon steel substrates by GTAW welding. X-ray diffractometery (XRD) was used for structural investigation of clad layers. Microstructural evaluation of clad layers was conducted by optical microscope (OM) and scanning electron microscope (SEM) equipped with energy dispersive spectrometery (EDS). Hardness and wear resistance of clad layers were studied by microhardness and pin-on-disc wear testing, respectively. According to the results the microstructure of composite clad layers contained a hypoeutectic structure. X-ray diffraction analysis showed the existence of cobalt-rich matrix together with eutectic carbides such as Cr7C3 and Cr23C6. It was suggested from the investigations that during the cladding process, boron carbides which were added to clad matrix, melted completely and solidified again. B4C was found to have a preventing effect against the growth of dendrites tending to refinement of microstructure. Hardness and wear resistance increased with increasing B4C content up to 30 %wt, but more incensement of B4C resulted in degradation of hardness and wear resistance of composite clad layers. Investigations showed that in the composite claddings due to a compact oxide layer formation on wear surface, weight loss and friction coefficient was reduced towards stellite6 cladding.

Nowadays we need materials to reduce friction, wear and corrosion because of rapid development of machines and tools. For this purpose, modern techniques such as electroplating, physical vapor deposition, chemical vapor deposition and plasma spray were used to deposit wear resistant coatings. In recent years, nickel-boron coatings were used to improve friction and erosion properties of the surfaces. Electroless Ni-P and Ni-B coatings have the same Properties. The main advantage of electroless Ni-B coatings is high hardness and good wear resistance. Electroless Ni-B coatings have higher wear resistance by comparison with tool steel and hard chromium coatings. We could improve wear resistance and friction coefficient of electroless coatings by adding reinforcing element such as silicon carbide. The aim of this study is to obtain Ni-B-SiC coatings by electroless process and evaluate its hardness and wear resistance. In this study the basic parameters such as temperature, plating time and changing the amount of SiC were optimized and Ni-B-SiC coating were deposited on high phosphorous electroless coating sublayer on carbon steel (CK45) substrate and the effect of carbide on the mechanical properties of the coating was investigated. Some of the samples were heat treated at different temperature for 1 hour. Finally, samples with and without heat treatment tested by SEM, XRD, EDS, microhardness, corrosion and friction coefficient at room temperature. It’s concluded that after heat treatment amorphous structure of the coatings were transformed to nanocrystalline structure and this phenomena could increase microhardness of the coating even to 1288 Hv0.1. wear results were shown that adding SiC to the coatings could reduced significantly wear lose of the coatings.