Key Engineering Materials Vol. 813

Abstract: Ti alloys have been widely used for biomedical applications.The generated wear debris due to its low wear resistance lead to inflammations and reduce the lifetime of the implant. So, the coating has been used to improve corrosion and wear resistance. In the present work, we report the assessments of TiN coating deposited by CA-PVD on Ti6Al4V alloy for dental applications. The deposited coating was characterized by XRD and SEM. Mechanical properties were assessed using micorindentation. The in vitro corrosion properties was investigated using PDP and EIS in artificial saliva. The wear rate was characterized using the linear reciprocating tribometer. The results showed that a TiN layer with 1.8 µm thickness was deposited with a hardness of 24.9±8.123 GPa and a Modulus of elasticity of 244.7±14.8 GPa. The corrosion study revealed enhancement in the corrosion performance of the coated sample in artificial saliva. The wear rate of the coated samples was also enhanced for the coated sample. The improved surface hardness, corrosion and wear characteristics of the TiN coating suggests that TiN coating would be a potential candidate for dental applications.

Abstract: Cold gas dynamic spray (CGDS) is a solid-state material additive manufacturing method where the particulate feedstock is accelerated under high pressure and relatively low temperature to supersonic condition to develop thin coatings or 3D freeform objects. In this paper, a literature review of the CGDS state-of-art, explanation of fundamentals of gas dynamic principles required to generate supersonic flow condition, and demonstration of a flow model based on computational flow dynamics (CFD) are presented. The focus of the preliminary 3D CFD model validation is the demonstration aerodynamics structures such as shocks that appear in the CGDS problem.

Abstract: On the CCDS2000 installation, detonation spraying of coatings from M28 and METCO 6103 aluminum oxide powders on steel substrates was carried out, and the dependence of the electrical resistivity of coatings on the atmosphere humidity was studied. It is shown that when the relative humidity changes from 14 to 80%, the specific electrical resistance of the coating decreases by 2-3 orders of magnitude from ρ ˃10¹³ Ω·cm to ρ ≈ 10¹¹ Ω·cm. On the base of obtained data, the model of coating microstructure is proposed, according to which alumina layer contained through defects in a form of nanochannels with diameter in the range 1-10 nanometers. In a coating cross section, the area of nanochannels sums up to 1%. In presence of high atmospheric humidity, these nanochannels can be filled with absorbed water, increasing drasticcaly the coating electrical conductivity.

Abstract: Leaves of an obscure plant “oxalis deppei” are so hydrophobic that showered water droplets are almost completely repelled and hardly remained on their surfaces. For this reason, surface configurations were investigated. On the live leaves, there formed protrusions somewhat similar to those observed on lotus leaves which are well known as super hydrophobic leaves. However, in winter, it was found that even dead leaves were hydrophobic also. Because leaf tissues were shriveled and dried half, heights of protrusions with sizes of 20-50 μm were low, and undulations of surfaces were gentle and smooth, and pitches of undulations were as large as 30-70 μm. It was thought that such gentle lens-like protrusions would be probably formed on versatile stainless-steel plates using lithography and wet chemical etching. For this reason, arrays of protrusions with a size of 20 μm, a pitch of 35 μm, and heights of 6-7 μm were formed, and change of hydrophobic properties were investigated. As a result, the hydrophobic properties were effectively improved by forming even such gentle and smooth protrusions. It was also clarified that contact angles were improved almost in proportion to etched depths.

Abstract: Electron beam Surfi-Sculpt^TM is a novel surface treatment technique applied to produce high level performance Composite-Metal-Weld (Comeld^TM) joints. Investigation on forming process during electron beam Surfi-Sculpt^TM on Ti-6Al-4V alloy showed protrusions were formed via a layer-by-layer mode like additive manufacturing process. The near-surface region of electron beam Surfi-Sculpted Ti-6Al-4V alloy was occupied by fusion zone, heat-affected zone and base metal from the outermost surface to the underlying bulk alloy. The microstructure of fusion zone was characterized by a high density of fine acicular martensite phase, leading to a higher micro-hardness. A heat-affected zone was sandwiched between fusion zone and the underlying base metal, with different microstructural features compared to both fusion zone and the base metal.

Abstract: In the present study, experiments were conducted to compare the effect of oxide layer formation on the piston crown coated using Micro-Arc Oxidation (MAO) with uncoated piston on the combustion and emission characteristics of the port injected Spark Ignition engine fueled by gasoline. The micro-arc oxidation (MAO) coating technique is the modern process to form a ceramic oxide layer on the reactive metal substrate (base metal) by electrochemical and electro-thermal oxidation in an alkaline electrolytic solution. Using MAO technique, an oxide layer of thickness 72 μm was formed on the piston crown. This oxide layer acts as a thermal barrier to reduce the in-cylinder heat rejection and increase the durability of the piston by withstanding high temperature and pressure produced during combustion. Combustion flames have been captured using the AVL combustion analyzer to analyze the development and propagation of flames within the engine cylinder. From the flame images, it was observed that propagation of flame was faster in MAO coated piston compared to uncoated piston. This is because of higher local temperature inside the combustion chamber that was resulted due to low thermal conductivity of MAO layer. It was also found that carbon monoxide (CO) and hydrocarbon (HC) emissions were reduced as a result of efficient fuel combustion, while NOx emissions increased because of increased combustion temperatures for MAO coated pistons. Keywords: Electro-thermal oxidation, Flame propagation, Micro-arc oxidation, Piston crown, Thermal barrie

Abstract: Three different methods were used to obtain nature-inspired superhydrophobic surfaces on aluminum alloys: short-term treatment with boiling water, HF/HCl and HNO₃/HCl concentrated solution etching. Afterwards a thin octadecylsilane film was deposited on all pre-treated surfaces. The surface morphology analysis showed that each method allow to obtain a specific dual nano/micro-structure. The corresponding water contact angles ranged from 160° to nearly 180°. The adhesion force between the water droplets and superhydrophobic surfaces were evaluated. The specimen etched with HF/HCl acid mixture solution showed the lowest adhesion. However, the boiling water treatment sample was characterized by the highest adhesion. Furthermore, the relationship between hydrophobic behavior and surface morphology was discussed compressively. In addition, the electrochemical measurements show that the different superhydrophobic surfaces have an excellent anti-corrosion performance evidencing promising results suitable to obtain large-scale nature-inspired superhydrophobic surfaces for several industrial applications.

Abstract: Ultrasonic Shot Peening (USP) - a novel route of surface modification was employed on biomedical grade Nickel free high nitrogen stainless steel (18Cr-21Mn-0.65N-balance Fe) to obtain a surface nanostructure without changing its chemical composition and microstructural phase transformation. Hardened steel shots of diameter 2 mm and 3mm were repeatedly impacted on the specimen surface at a constant frequency of 20KHz for 2 and 8 minutes duration. Coarse surface grains of size 36±6µm transformed into nanocrystalline grains of size 13-18 nm. The deformed layer resulted by USP treatment increased with increase in shot diameter and duration of USP. The microstructure was characterized by using optical microscope, SEM, XRD and TEM technique. The hardness and roughness of the treated surface was also found to be strongly dependent on the USP process parameters.

Abstract: Vitreous enamel is a very interesting materials thanks to its glassy nature, which permits to obtain high protection against corrosion and fire. In addition, the smooth surface with an elevate hardness favors good abrasion resistance. However, a negative aspect of this kind of coating is the high brittleness, which limits the application in case of impulsive or high loads. The nucleation and propagation of cracks leads to the destruction of layer integrity with loss of properties. In recent years graphene has received increasing attention as toughening addictive for organic and metal coatings as well as composite materials. This work is a first attempt to evaluate if the addition of graphene in an enamel deposit can increase its mechanical properties. The graphene was mixed with the dry frit. A milling process was then carried out before producing the torbida. In this way the formation of graphene clusters and accumulations is prevented. The addition of 1% graphene has shown to be effective in the increase of mechanical properties without negative influence on the deposit microstructure.