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This study explores the effects of excess Al and annealing at high temperature on the purity of Ti3AlC2 MAX phase synthesized by the mechanochemical route. In this regard, a constant stoichiometric ratio of Ti: Al: C = 3: 1: 2 along with three blends of nonstoichiometric ratios with excess Al (Ti: Al: C = 3: X: 2, X = 1.1, 1.2, and 1.5) were ball milled. Then, to examine the annealing at high‐temperature effects, the compacted ball‐milled powders were heated at 900 and 1200°C for 1 h. The phase identification revealed that 10 h of ball milling caused a reaction between the elemental powders, and Ti3AlC2 and TiC were formed. The mechanism of the reaction during the high‐energy ball milling process is assigned to a mechanically induced self‐propagating reaction. Addition of excess Al to primary powders caused to increase the purity of Ti3AlC2 significantly. Furthermore, annealing at high temperature leading to complete reactions of the ball‐milled powders and increased Ti3AlC2 purity. The maximum Ti3AlC2 content of 88% was obtained of initial powder of Ti: Al: C = 3: 1.2: 2 ratio after annealing at 1200°C. [ABSTRACT FROM AUTHOR]

In this research work, wear characteristics of the Al2024 alloy exposed to friction stir processing (FSP) with/without addition of the Ti2SC MAX phase have been investigated. Microstructural investigations revealed a good correlation between SZ and base alloy, and no defects such as cracks, etc. were detected. SEM micrographs confirmed the uniform dispersion of the Ti2SC particles in the Al2024 matrix after FSP. Also, redistribution of the precipitates of Al2024 alloy was observed. A decrease in the hardness of the 3-pass FSPed specimen without Ti2SC was observed due to the grain size increase and coarsening of the precipitates. The considerable improvement in wear rate and friction coefficient was realised by adding the Ti2SC MAX phase in the base alloy. Abrasive abrasion properties such as ploughing, plastic deformation, and grooves on surfaces indicate abrasive abrasion is the predominant wear mechanism for all specimens. [ABSTRACT FROM AUTHOR]

In this research, Cr3C2-NiCr and WC-Co-Cr cermet coatings were developed on A356 aluminum-based alloy substrate by the high-velocity oxy-fuel (HVOF) technique for use in wear and corrosion applications. The substrate and coatings were characterized using a field emission scanning electron microscope (FESEM) equipped with the energy dispersive spectroscope (EDS), microhardness, wear, and corrosion test instruments. Microstructural observations revealed that the coatings with an average thickness of about 250 μm were well bonded with the substrate. The microhardness of the Cr3C2-NiCr (~930 HV) and WC-Co-Cr (~1300 HV) coatings were about eleven and sixteen times higher than that of the A356 substrate (~80 HV), respectively. Cermet coatings showed significantly lower mass losses, wear rates, and friction coefficients in comparison with the A356 substrate. WC-Co-Cr coating illustrated higher tribological performance in comparison with Cr3C2-NiCr coating. The mass loss and friction coefficient of the WC-Co-Cr coating under an applied load of 10 N was about 0.2 mg and 0.13 (about 99.5% and 79.7% lower than that of the A356 substrate, e.g., 41.5 mg and 0.64), respectively. Rising applied load increased the wear characteristics of the A356 substrate with the more pronounced degrees. FESEM observations on wear test specimens illustrated the different wear mechanisms on the surfaces. The results illustrated significant improvements in the corrosion performances of the coated samples. [ABSTRACT FROM AUTHOR]

In this research, expanded graphite (EG) was successfully fabricated using a simple ball milling process followed by hydrofluoric (HF, 10 wt. %) leaching. The effect of ball milling time (0-15 h) and leaching time (1-24 h) on the exfoliation of graphite were examined by XRD and Raman spectroscopy. Furthermore, the morphological evaluation of the obtained expanded graphite samples was carried out by scanning electron microscopy (SEM). The XRD results of the ball-milled and HF treated samples showed a slight peak shift and broadening of (002) plane for expanded graphitein in comparison to the precursor and HF-treated samples. Moreover, the intensity of the (002) planes remarkably decreased by the ball milling process but remained constant after HF treatment. Raman spectra of the samples confirmed the ordering process only in HF-treated specimens. Moreover, the intensity ratio of 2D1 to 2D2 band gradually increased with enhancing the HF treatment time up to 5 hrs, indicating a decrement in the number of graphite layers by leaching in the HF solution. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the electrochemical corrosion properties of flame‐sprayed Al and Al/(5, 10, 15)% Ti3SiC2 coatings in a 3.5% NaCl solution. Scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS) were used for analyzing the microstructural characteristics of the coatings. For examining the corrosion behavior of the coatings, a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) were used. After the potentiodynamic polarization test, the SEM micrograph of coatings indicated that Ti3SiC2 particles played a significant role in pitting corrosion. The results of potentiodynamic polarization tests revealed that Al/Ti3SiC2 coating is nobler than that of the pure aluminum coating. On the contrary, the addition of Ti3SiC2 particles reduced the process of thickening the passive layer. The results of the EIS tests demonstrated that the presence of Ti3SiC2 particles significantly enhances the corrosion resistance of the coatings. [ABSTRACT FROM AUTHOR]

This study has investigated the mechanical and tribological performance of epoxy composites filled with different contents of Ti3AlC2 MAX phase particles. The Ti3AlC2 particles were synthesized by the mechanical alloying of Ti, Al and C powders. The ultrasonic blending was used for preparing the mixture of Ti3AlC2 and epoxy matrix. The Vickers microhardness and pin on disc tests were carried out to investigate the mechanical and wear properties of samples, respectively. Moreover, the fracture and worn surface of the samples were analyzed by scanning electron microscopy images. Results showed that the microhardness values were increased due to increasing the content of Ti3AlC2 in the epoxy matrix. In this regard, the highest value of 39.24 Hv was achieved for composites containing 0.75 wt.% Ti3AlC2, which corresponds to the 75.4% improvement in microhardness value, compared to neat epoxy. Moreover, wear results demonstrated that the friction coefficient and wear rate values were decreased by the addition of Ti3AlC2 particles in the epoxy matrix. [ABSTRACT FROM AUTHOR]

An effect of the friction stir processing (FSP), its pass numbers and addition of the SiO2 nanoparticles on microhardness, wear behavior and corrosion performance of the Al6061 aluminum alloy was investigated. Scanning electron microscopy (SEM) and optical microscopy were utilized to characterize the microstructure of the alloy, FSPed and composite samples. SEM observations revealed that the SiO2 particles were not uniformly dispersed in the matrix after two passes of FSP. However, increasing the pass number more than two passes resulted in a great improvement in the distribution of the SiO2 particles. The application of FSP led to overall softening compared to the base metal. Softening of the Al6061 alloy was probably attributed to the coarsening of Mg2Si. Corrosion resistance of the FSPed samples found a significant reduction compared to the base metal. Applying higher pass number of the process and also addition of the SiO2 nanoparticles improved the wear behavior of the samples. [ABSTRACT FROM AUTHOR]

In this study, WC-Al2O3 ceramic composite was incorporated into Al5083 to produce a surface composite by friction stir processing (FSP), and the microstructure, hardness and wear properties of Al5083-WC-Al2O3 surface composite were evaluated. Optical microscopy of FSPed samples showed grain refinement in the stir zone. The addition of WC-Al2O3 particles as well as increase in FSP pass number had a considerable effect on grain refinement, and the grain size of Al5083 base metal of 36 µm reduced to 11 µm for Al5083-WC-Al2O3 surface composite after four passes. The SEM observation of the surface composite revealed that the WC-Al2O3 particles distributed homogenously in the matrix and by increasing the FSP passes, the initial agglomerates of mechanochemically synthesized WC-Al2O3 powders could be fractured. Microhardness evaluation showed a substantial improvement by adding WC-Al2O3 particles and increase in FSP pass number. The maximum microhardness value of 101 HV belonged to surface composite after four passes, while the microhardness of the base metal was 65 HV. Wear test results revealed enhanced tribological behavior with a similar trend of microhardness values. Scanning electron microscopy tests revealed both adhesive and abrasive wear mechanisms on the surface of the wear test specimens. [ABSTRACT FROM AUTHOR]

In this study, the production and characterization of A5083–Al2O3–TiO2 hybrid surface nanocomposite by friction stir processing have been investigated. The effect of different ratios of nanosized Al2O3 and TiO2 particles on microstructural and mechanical properties was investigated. A threaded cylindrical hardened steel tool was used with the rotation speed of 500 r/min and travel speed of 56 mm/min and a tilt angle of 3°. Microhardness of base metal and treated surfaces as well as tensile strength was evaluated. The samples were characterized by means of optical and scanning electron microscopy. The results showed that the maximum tensile strength and hardness value were achieved for a mixture of Al2O3 and TiO2 in the ratio of 25–75, respectively. The microhardness and tensile strength were respectively increased by 50% and 182% while ductility was reduced by 60%. [ABSTRACT FROM AUTHOR]