Material’s tensile strength can be improved by the presence of a body-centered cubic (BCC) phase, which is essential in highstrength applications and highly corrosive environments. Thus, synthesizing a BCC single-phase, equiatomic AlCoCrFeNi high-entropy alloy (HEA) feedstock particle using a highenergy mechanical alloying (HE-MA) method was investigated. The transient alloy particles were developed using a planetary mill at a constant rotational speed of 580 rpm employing milling times in the range of 4 to 24 hours. During the process, stearic acid of 3 wt.% of the precursor composition was used as a process-controlling agent (PCA). Two HE-MA manufacturing regimes were utilized: i) conventional (milling constituent elements simultaneously), and ii) sequential (progressive milling while adding elements in a certain order). In addition to the conventional method, a sequential regime was employed to develop FeNiCoCrAl, wherein individual elements were added every 4 hours to the starting/milled Fe + Ni mixture. Based on the results, the HE-MA FeNiCoCrAl showed a BCC single-phase formation after 24 hours, with no intermetallic or contamination traceability. Finally, a nanoindentation hardness measurement was carried out to support the observed phase transformation before and after the HE-MA process.

Hybrid aerosol deposition (HAD) is a new coating method to deposit homogeneous nano-structured ceramic coatings. An accurate evaluation of the fabricated coating properties is required. In this study, α-Al 2 O 3 fine powder was sprayed by HAD. The obtained coatings were dense and uniform with a nanocrystalline structure. An X-ray diffraction measurement revealed that the fabricated HAD Al 2 O 3 coatings mainly consisted of α-Al 2 O 3 phase. The hardness and Young's modulus of the HAD Al 2 O 3 coatings were evaluated by a micro-Vickers method and a nanoindentation method using the Weibull distribution. The hardness of HAD Al 2 O 3 coatings measured by micro-Vickers was ~1400 HV (~15 GPa). The variation of mechanical properties of HAD coatings measured by the nanoindentation method was extremely small compared to those of plasma-sprayed coatings, which also indicates that HAD coatings contain less pores and cracks than plasma-sprayed coatings.

In this study, a water-based corundum suspension was used to deposit 60 μm alumina coatings onto carbon steel substrates by HVOF spraying. The aim was to develop thin coatings with superior wear properties. Hydrogen was used as a fuel gas and process parameters were varied to determine their effect on microstructure and properties. Coating microstructure was examined by SEM to assess particle melting and morphology and XRD was used to study the phase transformation of the feedstock suspension. At higher combustion flame energy, the coating transformed primarily to gamma alumina, while at lower energy, it was found to be a mixture of alpha and gamma alumina. Nanoindentation tests were used to measure the hardness and elastic modulus of individual phases. Ball-on-plate wear tests helped reveal the relationship between wear performance and the alpha-gamma ratios in the coatings.

This work evaluates the tribological properties of conventional and nanostructured Al 2 O 3 -13TiO 2 coatings obtained by atmospheric plasma spraying. The structure and composition of the composite coatings and powders were analyzed by SEM, TEM, and x-ray diffraction. Nanoindentation and ball-on-disc tests were conducted and surface topography was examined by noncontact 3D profiling. Coating samples of both types were polished and their friction coefficients were measured. The coefficient of friction for nanostructured coatings was 0.51, while that of conventional coatings was 0.62.

In this paper Al-Al 2 O 3 -CrC nanostructured composite coating was presented, fatigue and fracture of the composite coating were investigated by nanoindentation, and in situ experiments performed in a scanning electron microscope to permit examination of freshly exposed surfaces. Crystallographic and morphological texture was characterized and the fracture resistance measured using fracture-mechanics. A CrC layer may improve the fracture resistance of an oxide aluminum layer. A CrC layer produced by pyrolitic deposition effectively heals the pores and defects of an oxide aluminum layer. It results in high load rating of the coating. Experiments revealed that in all cases, detection of an acoustic signal corresponded to an appearance of circular cracks seen on the surface; in a very few cases, examination of the surface after detection of a signal revealed the presence of two ring cracks. The degree of toughening associated with crack healing is determined by the number of healed defects and the effectiveness of the individual healing. Macroscopically, a crack path in the oxide aluminum appears to be straight, propagating along pores and internal voids. However, microscopically, a crack path exhibits a high degree of intergranular fracture. Because cracks generally deflect at small angles in the oxide aluminum layer, a crack path moves through pores and internal voids that usually concentrate internal stresses. The crack path is primarily intergranular at all velocities.

Static mechanical properties such as Young's Modulus, Yield Stress and Ultimate Tensile Strength and especially fatigue behavior are important material properties for thermal spray coatings and their industrial application in automotive and aerospace industry. The static and dynamic mechanical properties of Al-Si, Al-Sn, Fe-Cr and Fe-Cr-B based coating materials deposited by APS, TWAS and HVOF were investigated by nanoindentation and in a three point bending test using DMA (Dynamic Mechanical Analysis). This method permits the determination of pure coating material static and dynamic mechanical properties without substrate influence over a wide temperature range. In this investigation all measurements were carried out at room temperature. The DMA method was verified by comparison of Young's modulus to those obtained by nanoindentation.

The nanoindentation technique has been applied to thermal-sprayed metal, cermet and ceramic deposits. The hardness and elastic modulus were determined from the load-displacement curves. Each test was implemented by varying the penetration depth (100, 200, 300 and 400 nm) in the same test location and at least 20 tests were performed. The results were compared to those from microindentation tests. The nanoindentation test, essentially, measured the submicrometer scale properties of thermal spray deposits, which can be considered as "near-intrinsic" properties of the coatings. Thus, these measurements exclude most of the microstructural factors that influence the "macroscale" properties. The nanoindentation test exhibits significantly greater hardness and elastic modulus values than the microindentation test.