Akhlaq Ahmad

Thermo-Physical Properties Measurement of Advanced TBC Materials with Pyrochlore and Perovskite Structures

Thermal barrier coatings (TBCs) serve as thermal insulator in the hot region of an aircraft engine. Besides this, it also protects the underlying metal surface from the harsh corrosive and eroding environment. The associated lower thermal conductivity of TBC ceramic materials plays an important role in the improvement of thermal efficiency of the engine in term of increased combustion temperature and power. The thermal conductivity of the conventional yttria stabilized zirconia (YSZ) and three advanced ceramic materials with perovskite (CaZrO3) and pyrochlore structure (La0.75Nd0.25)2Zr2O7 & Nd2Ce2O7) have been determined using differential scanning calorimetry (DSC). With thin metallic disk on the ceramic samples of different heights were heated / scanned using a standard DSC apparatus. The results were evaluated for the thermal conductivity measurement using well established procedure /calculations. The analyzed results were compared with that of other techniques given by other researchers and found to be in good agreement with an error of 10-15%. The result of coefficient of thermal expansion (CTE) that was measured using a dilatometer up to 1273°K has also given.

Graphene Oxide Coatings Deposited on Steel Substrate Using Electrophoretic Deposition and Electrochemical Evaluation of Coatings in Saline Media

In this study graphene coatings were deposited on mild steel substrate using feasible and environmental friendly method. The successful synthesis of graphite oxide was carried by the modified Hummer’s method. Graphene oxide (GO) coatings were developed from GO/water suspension using electrophoretic deposition (EPD). The EPD parameters voltage and deposition time were varied to deposit uniform adherent coatings. The coatings were post heat treated at 200 °C in vacuum for 4h to assess the effect on coated samples. GO and GO-EPD coating morphology were characterized using Fourier transform infrared spectroscopy (FTIR), Atomic force microscopy (AFM) and Scanning electron microscopy (SEM). Linear polarization (LPR) and electrochemical impedance spectroscopy (EIS) tests were performed in saline solution to evaluate electrochemical response. Coatings were partially reduced due to removal of oxygen containing functional groups during EPD and post heat treatments. The GO post heat treated coating had better corrosion resistance ~2 times than that of bare mild steel and higher charge transfer resistance.

Development of Lightweight Aluminum-Titanium Alloys for Aerospace Applications

Aluminum (Al) and Titanium (Ti) based lightweight alloys have been a topic of discussion and research for a few decades now. Resulting alloys with hard intermetallic phases in Al-Ti binary system have good microstructural and mechanical properties including low densities, high specific strength, better resistance against oxidation and corrosion which are highly desirable in aerospace industry. Such an alloy system was studied in our research. Powder metallurgy (PM) was used as processing route because of its economical and easy operation. Samples were prepared using metallic powders of Aluminum (Al) and Titanium (Ti) with varying compositions of 95 at.% Al-Ti, 90 at.% Al-Ti and 88 at.% Al-10 at.% Ti-2 at.% SiC. After compaction, pressureless sintering was carried out at 620°C for several hours in Argon atmosphere followed by annealing resulting in a reasonably dense Al-Ti alloy. Microstructure and phase composition of alloy was analyzed by Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS), respectively. Hardness was evaluated by Vickers micro indentation test. An increase in hardness was observed. Sample containing reinforcement particles (SiC) demonstrated highest value of hardness.

Characterization of Ta-Doped Titanium Dioxide Nano Particles Produced by Sol-Gel Method

Titanium dioxide also known as titania is a ceramic material. It is probably the most investigated inorganic oxide in recent years because of its non toxic nature, chemical stability and its potential effectiveness for destruction of toxic organic compounds in industrial effluents. In the present study pure and Ta doped TiO2 nanosize particles were prepared by sol-gel method. Samples with doping concentrations varying from 0.50 to 1.50 at % Ta and calcinations temperatures from 300 to 900 oC were synthesized. Changes taken place in phase transformation of the samples doped with Ta and undoped TiO2 were investigated. The effect of dopant concentration, calcinations temperature and particles size on anatase to rutile phase transformation was studied in detail. The samples were analyzed by various standard analytical tools.

Role of Equiaxed Primary Alpha (α׳) and Mechanical Properties of Ti-6Al-4V Alloy

The paper presents the role of equiaxed α׳ in the bimodal microstructure to attain an optimal combination of ductility and strength. The study revealed that the production of bimodal microstructure and volume fraction of equiaxed α׳ were reliant on the forging temperature and subsequent heat treatment. The Ti-6Al-4V alloy was forged in the two phase region and different heat treatment cycles were employed to get the desired bimodal microstructure and thus the combination of strength and ductility. The mechanical properties of fully lamellar microstructure were compared with bimodal microstructure containing equiaxed α׳. The experimental results showed that the amount of equiaxed α׳ in the bimodal microstructure was critical for achieving a well-balanced profile of mechanical properties.

Microstructural and Electrochemical Characterization of Ni/Ti2N Composite Coating for Sintered NdFeB Permanent Magnets

Sintered NdFeB magnets have complex microstructure that makes them susceptible to corrosion in humid or moist environments. The paper presents the anticorrosion characteristics of a novel Ni/Ti2N composite coating applied through electrodeposition and cathodic arc physical vapour deposition (CAPVD) to sintered NdFeB permanent magnets. The performance of composite coating was evaluated in simulated marine environment with the help of dc polarization techniques. The rate of coating degradation was also determined by employing ac electrochemical impedance spectroscopy (EIS). The coating morphology and surface chemistry were studied with scanning electron microscope (SEM). X-ray diffraction (XRD) was used for identification of component phases in the coating-substrate system. The results showed that the composite coating provided an adequately improved corrosion protection to the sintered NdFeB magnets in the simulated marine environment compared to the earlier reported ceramic and metallic coatings. The composite coating did not damage the magnetic properties of coating-substrate system that remained at par with the ceramic and nickel coating having copper interlayer.