Mohammad Sakhawat Hussain

Improvement of thermally grown oxide layer in thermal barrier coating systems with nano alumina as third layer

Abstract A thermally grown oxide (TGO) layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni(Cr,Al)2O4 mixed oxides (as spinel) and NiO onto the Al2O3 (TGO) layer. The formation of detrimental mixed oxides (spinels) on the Al2O3(TGO) layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.

The Role of Nanostructured Al2O3 Layer in Reduction of Hot Corrosion Products in Normal YSZ Layer

YVO4 crystals and monoclinic ZrO2 are known as hot corrosion products that can considerably reduce the lifetime of thermal barrier coatings during service. The hot corrosion resistance of two types of air plasma sprayed thermal barrier coating systems was investigated: an Inconel 738/NiCrAlY/YSZ (yttria-stabilized zirconia) and an Inconel 738/NiCrAlY/YSZ/nano-Al2O3 as an outer layer. Hot corrosion test was accomplished on the outer surface of coatings in molten salts (45% Na2SO4 + 55% V2O5) at 1000°C for 52 hour. It was found that nanostructured alumina as outer layer of YSZ/nano-Al2O3 coating had significantly reduced the infiltration of molten salts into the YSZ layer and resulted in lower reaction of fused corrosive salts with YSZ, as the hot corrosion products had been substantially decreased in YSZ/nano-Al2O3 coating in comparison with normal YSZ coating after hot corrosion process.

Characteristics of Electroplated Nickel Layer on Tungsten Carbide

Diamond coating on tungsten carbide (WC-Co) cutting tools with cobalt binder experiences delaminating failure due to the deleterious effect of cobalt. One of the methods used to reduce this effect is by coating an interlayer onto the substrate surface prior to diamond deposition. Different materials have been used as an interlayer which is normally deposited to the substrate surface using CVD and PVD techniques. Among different materials used as interlayer on WC-Co, nickel is considered as an attractive candidate due its good chemical and physical properties. In this study the potential of the electroplating technique for deposition of nickel interlayer on WC-Co will be investigated. Nickel deposition on WC-6%Co substrate was carried out by electroplating in a standard watts solution at constant plating parameters (Current: 0.1 Amp, electric potential: 1.0 V and pH: 3.5). The gap between anode and cathode was varied (5mm, 10mm and 15mm). The nickel coating formed on the hard metal surface was characterized in terms of the coating thickness, layer uniformity and coating hardness by using SEM and the micro hardness tester. Based on the results, desirable nickel coating properties were obtained when the separation distance between anode and cathode was 15mm.

Evaluation of normal and nanolayer composite thermal barrier coatings in fused vanadate-sulfate salts at 1000°C

Hot corrosion behavior of yttria stabilized zirconia (YSZ), YSZ/normal Al2O3, and YSZ/nano-Al2O3 coatings was investigated in the presence of molten mixture of Na2SO4

Inhibiting Sulphate Attack on Concrete by Hydrophobic Green Plant Extract

Organic base (Amine) and inorganic base (Nitrite) have been known for protection of concrete structures but are not commercially indigenous to most developing economies due to manufacturing difficulties and are toxic to the environment. Also inhibitors are not known to stop sulphate attack in concrete. Hence, the objective of the present investigation was to study a novel, eco-friendly and hydrophobic green plant extracts inhibitor and compares its effectiveness with established calcium nitrite and ethanolamine inhibitors. Bambusa Arundinacea (Green plant extracts), calcium nitrite and ethanolamine corrosion inhibitors were selected for the present investigation. Compressive strength of 100×100×100mm concrete cubes after 7, 28 and 90 days of curing test was used. The results of the inhibitors studied showed that Bambusa Arundinacea has superior compressive strength compared to calcium nitrite and ethanolamine. Bambusa Arundinacea may be considered a better substitute for nitrite and amine- based corrosion inhibiting admixtures for durable concrete structures due its pore blocking effects.

Nanomechanical characterization of nanocrystalline Ni directly plated on aluminium

Aluminium is the second largest consumer industrial item after steel. The high strength to weight ratio of aluminium allows a substantial savings in most applications. There is always a high demand for plating on Al and its alloys i.e. in automotive and aerospace products, house-hold goods, artificial jewellery, to name some. The achievable properties that can be added to aluminium are mechanical, magnetic, electrical, thermal, corrosive and decorative. As an example it could be interesting to add wear resistance (abrasive or adhesive wear), hardness and corrosion protection to aluminium. However, as soon as aluminium is exposed to the atmosphere a thin oxide film forms almost instantaneously. In its natural form this oxide film is less than 0.10µm thick. Although this natural oxide film is very hard, tenacious, abrasion resistant and an insulator but as it is attached to a soft ductile metal, it is easily damaged. The presence of the same oxide film (which makes the surface of the aluminium act as a non-conductor) has made it impossible to deposit any decorative or wear resistant coatings by electrodeposition on aluminium. This paper will for the first time discuss a new, an innovative and worlds first ever process for directly electrodepositing nanocrystalline Ni on aluminium surfaces without the need to pre-treat the aluminium substrates with acid/s and pre-plate with an intermediate metallic layer. Nanomechanical test instrument was used to evaluate the mechanical properties of the as plated Ni/Al2O3/Al layers. Several partial-unloading nanoindentation tests were performed on the samples using a Berkovich probe to measure the hardness and reduced modulus of the samples as a function of contact depth. These test results will be discussed further to elucidate the mechanism of adhesion of the electrodeposited nanocrystalline Ni with the intermediate non-conductive aluminium oxide (Al2O3) layer at a nano-scale.