Surface Review and Letters

Modern technology demands have raised the popularity of aluminum metal matrix composites (AMMCs) as it best suits diverse industrial applications. The need to develop an advanced functional material for specific applications attracts global researchers. Commercial needs for cost-effectiveness, quality improvement, superior performance and high strength to low weight ratio are met by composites. Mass production of AMMCs for specific industrial applications prefer stir casting as a simple and cost-effective manufacturing method. In addition, the production of composites turn more economic by reducing the weight percentage of ceramics and adding natural fibers either in the form of fibers, milled powder or ash to achieve the targeted properties. Process parameters being a dominating factor for minimal defect composites, their effect on final cast products are discussed along with strengthening mechanisms. This paper also discusses the applications, challenges and future scope of natural fiber reinforced AMMCs.

This paper deals with experimental investigation on chip formation of machining of Monel K500 and its characteristics are studied. Two different nanocutting fluids namely nanoCuO and nanographenes are used for turning operation and the performance of the two cutting fluids is evaluated and the corresponding responses are recorded for the selection of better cutting fluid. This experiment is carried out with the help of SEM which picturizes the microstructure and surface distribution of the chips. The various output responses like chip thickness, chip compression ratio, and surface roughness are portrayed. The desirable effects on the properties of the machined material obtained by the variation of process parameters like cutting speed, cutting depth, and feed rate are analyzed. Results show that the thickness of chips (corresponding metal removal rate) is reduced considerably by 10–15% and the surface roughness is reduced by 20–30% when nanographene cutting fluids are used.

The drilling of film cooling holes on gas turbine blades made out of ceramic-coated superalloy improves the efficiency of the gas turbine and prolongs the life of the turbine blade. The purpose of this study was to investigate the effects of different stand-off distances (SODs) on abrasive water jet (AWJ)-pierced holes, in which the machining time, entry and exit hole diameters, overcut, hole taper, and surface morphology were studied. In this study, the water jet pressure (WJP) of 275MPa, piercing angle of $90^{\circ }$, dwell time of 0.2s, and abrasive flow rates (AFRs) of 350g/min and 400g/min were considered for the AWJ piercing operations. The entry and exit hole diameters and overcut linearly increased with an increase of SOD with different abrasive flow rates. And hole taper was observed at the coating and substrate sections in which it decreased with an increase of SOD up to 2mm, and a further increase of SOD increased the hole taper. Besides, the drilled holes were found to have an absence of delamination, cracks, and thermal defects. It was also noted that there is a transformation from a brittle to a ductile mode of erosion that may occur in the high-erosion kinetic energy impact region in the YSZ material section. Based on the experimental results, it is confirmed that SOD of 2mm became an influencing factor in AWJ for piercing quality holes in the YSZ-coated superalloy.

The study shows that the materials of interfacial formations formed at the interface of two immiscible liquids, an aqueous solution of a lanthanide salt and a solution of di(2-ethylhexyl)phosphoric acid in a solvent, can have different hydrophobicity depending on the synthesis time. The surface roughness and the contact angle of the substance transferred to different substrates (glass, duralumin, copper) were measured. It was established that external vibration in the interfacial layer of the system during synthesis and self-assembly affects the hydrophobicity of the substance. A dependence between the contact angle and the surface roughness was established.

After appropriately preparing the surface of AISI316 steel, the Ni–Co–P coating layer was deposited on the substrate using the electroless method using baths with different mole ratios of CoSO₄/NiSO${}_4+{\mathrm{\text{CoSO}}}_4$. Coating rate, weight percentage of the alloy elements, corrosion rate and coating layer hardness were studied in the achieved coating layers. The coating rate of the Ni–Co–P coating layer is a function of the mole ratio of CoSO₄/CoSO${}_4+{\mathrm{\text{NiSO}}}_4$, sodium hypophosphite concentration, bath temperature, bath pH and plating time. The electroless deposits studied in this paper are in crystal form. The XRD pattern of the Ni–Co–P deposits shows the peaks related to Ni-fcc and tetragonal Ni${}_{12}$P₅. X-ray diffraction pattern confirms the formation of the Ni₃P phase during annealing for 1h at 400^∘C.

This paper deals with the dry sliding wear behavior of cold-sprayed Inconel 738 (IN 738) coating up to 600^∘ C. The coating was deposited by a high-pressure cold spray system using helium as the propellant on T11 low-carbon steel substrate. The dry sliding wear behavior of uncoated specimens is compared with IN 738 coating using pin-on-disk tribometer (ASTM G99). SEM, EDX, and XRD analyses provide better insights on the worn surface morphology, changes in oxide scales, and phase transformation. At 400^∘C, the tribo-layer developed at the interface contains NiO, which is a lubricious oxide, which reduces the wear rate of the coating. With further increase in temperature up to 600^∘C, there is a formation of a protective layer, which results in the enhancement of high-temperature dry sliding wear resistance of the coating. At 600^∘C, sliding wear resistance offered by the coating is approximately four times higher than T11 low-carbon steel. Therefore, the developed cold-sprayed IN 738 has high potential for usage at elevated-temperature dry sliding applications.

Flake Powder Metallurgy (FPM) is utilized for the processing of Al–Al₂O₃ composites. The effects of contents of 1-$\mu$m-sized alumina (0, 3, 6 and 9 vol.%) on the microstructure, hardness, porosity and wear behavior of these composites are investigated. The as-received aluminum powder particles are milled in a planetary ball mill for different time durations (0.5, 1, 1.5 and 2 h), and the resultant flake powders are characterized by sieving, SEM, optical microscopy and XRD to determine their particle size, morphology and grain size. Al flakes and different amounts of Al₂O₃ powders are stacked into the mold cavity using a floating column filled with alcohol. Then the compacts are cold pressed at 750 MPa and sintered in a tube furnace at 655^∘C for 60min. For comparison, reference samples from as-received aluminum powders are also fabricated. SEM studies showed a uniform distribution of alumina particles within the matrix of FPM-processed composites. These composites, despite their higher porosity, exhibited higher hardness levels and improved wear properties in comparison with the conventionally produced powder metallurgy (PM) counterparts. This is due to: (i) the special morphology of the flake powders that contributed to a more uniform distribution of alumina within the matrix and (ii) their smaller grain size due to work hardening that occurred during milling, which resulted in higher hardness values.

In this research, microsized marble dust is spray-coated on mild steel substrates through a well-designed high-velocity oxy-fuel (HVOF) spraying route. For this, a standard spray set up Hipojet 2700 is used. Marble dust is an ornamental stone waste generated in huge quantities during the depletion and processing of ornamental stones to make them usable. Commercially available spray-grade NiCr powder is added with a proportion of 10% by weight in the marble dust prior to deposition to increase its flowability and adherence. The coating on the mild steel substrates is deposited with a spray distance of 200mm and a fuel (LPG) feed rate of 55–60g/min. Dry-sliding wear trials under controlled conditions on the deposited coatings are conducted as per ASTM G 99-05 using a tribometer capable of operating at a wide temperature range. A parametric analysis of the test results using MINITAB 18 software shows that the control factors such as sliding velocity, specimen temperature, sliding distance and normal load, in the declining sequence, are significant in affecting the specific wear rate (SWR) of the coatings. Based on this, further experimentations are carried out separately for a wider range of the sliding velocity and specimen temperature keeping all other factors constant to study their individual effects on the wear rate more precisely. The morphologies of the worn surfaces are studied to ascertain the possible mechanisms taking place during the wear process leading to coating mass loss.

In this work, we establish a fractal contact model and analyze the effect of the parameters on stress. The study provided a method to make a link between contact characteristics and surface condition. The surface texture model was built based on the process mechanism of point grinding. The experiment for the effect of the surface texture on contour height was carried out on TR300 roughness shape-measuring instrument and the structural function method of fractal theory was used to obtain the fractal dimensions and scale coefficients of surfaces with different surface textures. The fractal contact model was established based on the fractal characteristics of the surface point ground and the simulation was carried out using Matlab. Furthermore, the validation of compression experiment was carried out by WAW-600C universal testing machine, the high-definition pictures before and after the experiment were obtained by KEYENCE VH-Z500R ultra-depth-of-field 3D microscope and the surface topographies before and after the experiment were obtained by NANOVEA PS50 three-dimensional noncontact surface profile meter. The obtained findings can help to choose appropriate surface with the best contact characteristics under certain condition.