فصلنامه علوم و مهندسی سطح ایران
پیاپی 59 (بهار 1403)

In metal forming processes, surface roughness and hardness of the die and workpiece are effective parameters in friction, which is caused by the manufacturing process of the die and workpiece. In this research, effect of die manufacturing processes on the surface roughness and hardness of the deformed parts has been investigated. The inserts of the dies are made with six machining methods, and the effect of the machining method, lubrication, and percentage of deformation on the surface roughness and hardness of the part has been investigated by performing the heading operation on a ring-shap part. The results show that the surface texture of the parts is affected by the surface texture of the inserts and the surface roughness of the parts is proportional to the surface roughness of the inserts. The surface roughness of the parts increases significantly by increasing the amount of cold work, and the use of lubricant reduces slightly the surface roughness in turning, vertical milling and electric discharge machined inserts but it does not have considerable effect in the rest of the inserts. In the case of using lubricant, the surface hardness of the parts decreases by about 5% on average. With the increase of cold work from 25% to 50%, the surface hardness of the parts increases by about 25% on average. Forming with the electrical discharge machined insert causes the lowest surface hardness of the parts, and the highest surface hardness of the parts is related to the grinded and polished inserts. The texture of the surface of the parts is affected by the texture of the surface of the inserts and the roughness and hardness of the surface of the parts is affected by the machining method of the inserts

The aim of this study is to develop a novel nickel-boron-graphite (Ni-B-Gr) composite coating via electroless plating, endowed with self-lubricating properties, and to analyze its wear characteristics. Electroless deposition of Ni-B-Gr coatings was achieved on AISI 4140 steel utilizing a sodium borohydride-based electroless nickel bath. The resulting composite features a nickel-boron matrix, characterized by a skewness index of -0.12, offering both hardness and fluid-retaining capabilities, augmented by graphite flakes (< 20 μm) at a concentration of 0.275 g/L, serving as a solid lubricant component. Plasma nitriding treatments were conducted at 400°C for varying durations (30, 60, 120, 180, and 240 minutes) in a gas mixture of 25% nitrogen and 75% hydrogen. Comprehensive characterization of the Ni-B-Gr composite coatings encompassed microstructural analysis via X-ray diffraction (XRD), morphology examination using field emission scanning electron microscopy (FE-SEM), microhardness testing, roughness measurements, and wear assessment through pin-on-disk tests. Notably, the plasma nitrided Ni-B-Gr composite coatings for 60 minutes exhibited a significant enhancement in hardness, with a hardness of 1060 HV0.1. Moreover, compared to as-plated Ni-B-Gr coatings, the 60 minutes plasmanitrided composites demonstrated a remarkable 75% reduction in specific wear rate and a 31% decrease in friction coefficient. The incorporation of graphite as a self-lubricating agent effectively mitigated adhesive wear and oxidation by reducing the contact surface between the steel pin and the coating, thereby enhancing the wear resistance of the composite.

Studies show that by applying coatings with amorphous structure on surgical instruments, the biocompatibility and corrosion resistance of these instruments can be increased. One of these coatings is Zr-based metal glass thin layer coatings. Therefore, in this research, after investigating the effect of different elements on the biocompatibility and corrosion behavior of coatings, first an alloy with the chemical composition of Zr30Cu20Al10Ag10Cr10Si10Br10 was designed and a thin disk of this alloy was produced using Spark Plasma Sintering, SPS, device. Then, thin layers of the alloy produced were applied on the 316 steel substrate using a Magnetron Sputtering machine. Initial investigations showed that the production coatings have a glass structure. Next, the hydrophobicity of the coating and its corrosion behavior in two environments, NaCl solution and Simulated Body Fluid was studied. The conducted tests showed that the application of the designed coating, by reducing the surfaces energy, increased the contact angle and as a result increased the hydrophobicity of the surfaces, transformed the surface of 316 steel from hydrophilic to hydrophobic. Also, the application of this coating due to its amorphous structure increases the corrosion resistance in the two environments of sodium chloride solution and Simulated Body Fluid. Examining the corroded surfaces indicates the occurrence of pitting corrosion phenomenon for the created coatings.

Electrodeposition of Fe-P coatings have been recently attracted many attentions for applications such as temporary biodegradable bone replacement material, Li ion storage anode and environmentally friendly alternative to hard chrome plating. In this study, the effects of bath temperature and bath chemical composition (concentration of glycine, iron sulfate and sodium hypophosphate) on the microstructure of electrodeposited Fe-P coating has been investigated. Electro deposition was carried out at the current density of 50 mA/cm2 for 1h. Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectrometer (EDS) were used to characterize the coatings. Results showed that the P content and the morphology of the coating is affected by temperature and the concentration of glycine and iron sulfate. The coatings obtained from baths containing low amounts of iron sulfate are coatings with a morphology containing large nodules, and by increasing the concentration of iron sulfate, a uniform surface without defects is obtained. Investigations showed that by increasing the concentration of glycine 0.21 to 0.64 M as a complexion compound, the phosphorus content of applied Fe-P coatings increases from 9.29% to 12.55%. Coating deposited at temperature 60 ºC were micro structurally intact while coatings obtained at temperatures 30 ºC had micro-cracks.

One of the unique features of semiconductors is the ability to alloy them with each other, so that the intermediate properties are extracted from two materials. Here, thin layers of MgxZn1-xO (x=0-0.9) were deposited by combining zinc and magnesium by spray pyrolysis method. The obtained optical results showed that with the increase of Mg content in the structure, the energy gap becomes larger. Also, the results extracted from the X-ray diffraction spectrum and scanning electron microscope revealed that with the increase of Mg in the ZnO layer, the grains grown on the surface have a finer structure. Also, in order to compare the optoelectronic behavior of these layers, hybrid light-emitting diodes were made, and the highest efficiency and efficiency was related to the diode made with x=0.5.

In this research, BiVO4 thin films were prepared by spray pyrolysis deposition. The important parameters of the spray pyrolysis deposition method, namely the substrate temperature, the distance between the nozzle and the substrate, the nozzle aperture diameter and the carrier gas pressure were syste matically investigated and optimized to achieve uniform and porous thin films in different dimensions with excellent adhesion to the substrate (stable layers). It was found that by selecting these parameters as 200 oC, 40 cm, 0.1 mm and 3.5 atm, respectively very uniform layers were deposited on the glass and indium doped tin oxide substrates. But these layers could be easily removed from the substrate and showed weak adhesion to the substrate. In order to improve the adhesion, the pulse deposition approach was investigated and by adjusting the deposition time of each pulse, the number of pulses and the interval time between pulses, BiVO4 layers with appropriate adhesion were obtained. The results of the confocal microscopy showed that the layers with higher roughness (437 ± 25 nm) and lower roughness (173 ± 10 nm) can be achieved by choosing a short (30 seconds) and long (2 minutes) interval time between pulses, respectively.