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Microscopic hardness on free surface of polycrystalline metal during plastic deformation is closely related to the inhomogeneous deformation in respective grains. Uniaxial tensile tests were carried out on annealed pure aluminum sheet specimens with different averaged grain size and also on annealed pure titanium sheet specimen. The microscopic hardness was measured with the Vickers type micro-hardness testing machine. The increase in micro-hardness is larger at the grain boundary area than the central area of grains. The increase in the hardness is dependent on the averaged grain size of polycrystalline metals. The experimental results are discussed in relation to Hall-Petch relation concerning the grain size dependence of the yield stress or the flow stress.

This study focuses on effects of number of shots and the distance from the top of anode on Mo–N deposition process on the surfaces of AISI304 samples using a low energy (2.8 kJ) plasma focus device (AECS PF-1) at room temperature. The structural, morphological, elemental composition, surface roughness and micro-hardness properties of treated surfaces were investigated versus the number of shots and the axial distance from the anode. The obtained XRD spectra show that some of the treated surfaces were in crystalline phase with $\gamma$-Mo₂N (FCC) structure (at 3 cm with 10–40 shots and at 5 cm with 30 and 40 shots) and some others had amorphous structure at 5 cm with 10 and 20 shots and at 7 cm with 10–40 shots. SEM images indicate that the thermal effect occurred at 3 cm and the deposition process of Mo–N at 5 cm and 7 cm from the anode with an increase in number of shots. The atomic ratio for nitrogen was 10.62%, 12.88%, and for molybdenum it was 0.23%, 3.36% at 3 cm, respectively. The atomic ratio for nitrogen has achieved 14.95% and 22.17%, however, the atomic ratio for molybdenum was 2.11% and 7.17 % at 5 cm, respectively. The surface roughness and size of grains on the surface of deposited layers were investigated by AFM analysis. Furthermore, the variation in the micro-hardness of the Mo–N thin layers deposited by different number of shots at different distances from the tip of anode was explained, qualitatively, on the basis of morphological characteristics of the thin layers. The decreasing rates of hardness in the case of 10 shots were 146%, 117% and 112%, and at 40 shots were 237%, 149% and 141% with the increasing of distances 3, 5 and 7 cm, respectively.

Ceramic coatings have been synthesized on 6063 aluminum alloy by micro-arc oxidation (MAO) technique. The effects of current intensity on the chemical and mechanical properties of MAO coatings have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-hardness test, adhesion measurement, and friction and wear tests. The fabricated samples consist mainly of α-Al₂O₃ and γ-Al₂O₃ phases. SEM results show that the surface of the prepared coatings is dense except some pores distributed over the coating surface. Mechanical measurements show that these kinds of samples have high hardness, excellent adhesion, and high friction resistance. The coating consists of a thin buffer layer at the metal surface followed by a relatively compact inner layer and finally a higher porous ceramic layer. Meanwhile, there is a nonuniform distribution of hardness for the samples in the plane parallel to the substrate.

Ceramic coatings have been synthesized on 6063 aluminum alloy by micro-arc oxidation (MAO) technique in the solution of Na₂B₄O₇ electrolyte with and without α-Al₂O₃ nanoadditive. Effects of α-Al₂O₃ nanoadditive on the phase composition, micro-structure, micro-hardness, adhesion and wear resistance of the prepared ceramic coatings have been investigated in this paper. The phase composition and microstructure of the MAO coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDX) analyses, respectively. Micro-hardness, adhesion and tribological and wear tests were also performed. The results showed that the α-Al₂O₃ nanoadditive doped in the electrolyte had great influence on the structural and mechanical properties of the ceramic coatings.

Pure potassium chloride (KCl) and lead chloride (PbCl₂)-doped KCl crystals were grown from saturated aqueous solutions by a solvent evaporation process. The effects of Pb²⁺ on the surface morphology, structural and mechanical properties of KCl crystal were investigated. The surface morphology of the cubic structured crystals was studied by scanning electron microscopy (SEM), X-ray diffraction and the elemental mappings at the microstructural level were determined by energy dispersive X-ray (EDX) spectroscopy. The mass growth rate was found to decrease when the Pb²⁺ ions were present and the volume growth flux was also found to decrease with time and initial concentration of impurity. A Vickers micro-hardness study shows that Pb-doped KCl crystals are harder than pure KCl crystals.

The present study investigates the effect of titania particles on the micro-hardness, wear resistance, corrosion resistance and friction of electroless Ni–P–TiO₂ composite coatings deposited on mild steel substrates at different annealing temperatures. The experimental results confirmed that the amount of TiO₂ particles incorporated in the coatings increases with increase in the concentration of particles in the electroless bath. In presence of TiO₂ particles, hardness, wear resistance and corrosion resistance of the coating improve significantly. At higher annealing temperature, wear resistance increases due to formation of hard Ni₃P phase and incorporation of titania particles in the coated layer. Charge transfer resistance and corrosion current density of the coatings reduce with an increase in TiO₂ particles, whereas corrosion potential increases. Microstructure changes and composition of the composite coating due to heat treatment are studied with the help of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) analysis.

Based on the background of automotive mold surface strengthening, the effects of three different enhancements on the microstructure evolution, micro-hardness and wear resistance of laser cladding cobalt-based coatings were studied. The three reinforcing materials were Co45 alloy powder, Co45/8% B₄C mixed powder and Co45/8% B₄C/5% Cr₃C₂ mixed powder. They were respectively used to conduct laser cladding on the surface of die steel with preset powder method, with laser power of 2000W and scanning speed of 4mm/s. According to the test results, the hardness and wear resistance of the cladding coating were the best when Co45/8% B₄C powder was added. In addition, the study also found that B₄C reacted with Cr₃C₂ during laser cladding to eventually generate Cr₂B. The CrB₂ generated for the first time during the reaction was transformed into the most stable Cr₂B with an orthorhombic Fddd symmetry due to its poor stability. Therefore, the sample with Co45/8% B₄C/5% Cr₃C₂ mixed powder was affected with a slight decrease in microhardness and wear resistance.

Public transport via trams has become increasingly important in daily life to meet the growing demand for economic and environmental considerations. In order to ensure the safety of the railway system and reduce service costs, it is necessary to understand the tribological behavior of the system. There are various types of damage such as fatigue, wear, and cracking that can harm the wheels and rails. To determine the wear mechanisms and identify the situations in which wear movements occur, it is crucial to monitor factors such as temperature, surface roughness, and contact micro-hardness between the wheel and the rail. The objective of this study is to analyze the tribological behavior and the impact of climatic conditions on the wheel–rail contact system in the desert area of the Ouargla tramway in Algeria. To achieve this, an intelligent sensor programmed by a microcontroller was utilized to measure the temperature of the wheel–rail contact. Additionally, a hardness tester was used to measure the micro-hardness of the rail, and a roughness tester was utilized to monitor the surface condition of the rail. The measured temperature values during the passage of the tramway varied between ambient temperature and a temperature of 450^∘C. The micro-hardness values ranged from 270 Hv to 440 Hv, and the roughness values varied between 0.4$\mu$m and 2.7$\mu$m.

Selecting materials and alloys, fabrication methods, surface characteristics and coatings, and topology design, all affect the mechanical properties, biocompatibility, and functionality of dental implants. The success in embedding implants in mouth and improving biocompatibility and consequently useful life of implants depends directly on proper adhesion of tissue to implant surface of a biocompatible alloy. In this research, experimental surface hardness and in vitro tests are carried out on samples with different alloys and different manufacturing methods. Various fabrication techniques, such as machining and 3D printing (Selective laser melting (SLM)), are considered for steel and titanium specimens. Results show that the hardness values of specimens made by the SLM method are higher than machined samples about 8% and also stainless steels samples have higher hardness than titanium specimens. A comparison of scanning electron microscopy (SEM) surface pictures indicates that applying modern fabrication methods for production which includes SLM improves the performance of implants in terms of mechanical and biocompatibility by increasing cell adhesion up to 21 times. In addition, results indicate that titanium alloys have almost 13% higher adhesion property than stainless steel and generally exhibit a higher balance of adhesion and cell growth.

The process of electroless plating Ni-P and Ni-P/nano-SiO₂ on API-5L X65 carbon steels was improved. The Ni-P/nano-SiO₂ composite coatings were prepared from the bathes containing different concentrations of nano-SiO₂ particles. The coatings surface and morphologies were observed via scanning electron microscopy (SEM). The chemical compositions were analyzed by EDAX. The corrosion behaviors were evaluated by electrochemical impedance spectroscopy tests. The experimental results indicated that SiO₂ nano-particles co-deposited but some agglomeration occurred. Micro-hardness of electroless Ni-P-SiO₂ composite coatings increased due to the existence of nano-particles. Corrosion tests showed that both electroless Ni-P and Ni-P/nano-SiO₂ composite coatings demonstrated significant improvement of corrosion resistance of substrate in salty atmosphere and latter coating type appeared to offer a better corrosion protection.

AZ91 magnesium on SiC poroues preform and interfacial reaction between SiC and AZ91 magnesium were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), friction and wear testers and micro-hardness testers. The results indicate that magnesium has a good wettability on SiC and can spontaneously infiltrate the porous SiC/starch preform after a 5h infiltration at 750□. Moreover, interface reaction at the front of magnesium melt was found between the SiC and AZ91 magnesium, which improves wettability between each other. The massive oxidized SiC powders have uniform distribution in AZ91 magnesium metal matrix. The micro-hardness of SiC/Mg composites is 383HV_0.2 and more than 5 times higher than that of AZ91 magnesium (72HV_0.2). Under the conditions of dry sliding wear and 4N loads, compared with the unreinforced AZ91 magnesium matrix, the friction curve of the SiC/Mg composite fabricated by pressureless infiltration is much lower than that of AZ91 magnesium, which means SiC/Mg composites have a better wear resistance.

Microscopic hardness on free surface of polycrystalline metal during plastic deformation is closely related to the inhomogeneous deformation in respective grains. Uniaxial tensile tests were carried out on annealed pure aluminum sheet specimens with different averaged grain size and also on annealed pure titanium sheet specimen. The microscopic hardness was measured with the Vickers type micro-hardness testing machine. The increase in micro-hardness is larger at the grain boundary area than the central area of grains. The increase in the hardness is dependent on the averaged grain size of polycrystalline metals. The experimental results are discussed in relation to Hall-Petch relation concerning the grain size dependence of the yield stress or the flow stress.