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A gradient three-layer Al-Mo coating was deposited on steel using magnetron sputtering method. The corrosion properties of the coating were studied in 3.5 wt.% NaCl solution using electrochemical techniques, whereas the hydrogen-induced cracking (HIC) resistance was examined by constant-load tests using notched tensile specimens. These results were compared with conventional electroplated cadmium-coated steel. The results show that the gradient Al-Mo coating exhibits better corrosion and HIC resistance when compared to electroplated cadmium. This was due to the excellent corrosion resistance of the bottom aluminum-rich layer, while the top Mo-rich layer provided good lubrication properties.

The hot deformation behaviour of Inconel alloy IN718 was studied in the temperature range of 950–1100 °C and at strain rates of 0.01 and 1 s − 1 with a view to understand the microstructural evolution as a function of strain rate and temperature. For this purpose, a single hit, hot isothermal plane strain compression (PSC) technique was used. The flow curves obtained during PSC exhibited weak flow softening at higher temperatures. Electron backscattered diffraction analysis (EBSD) of the PSC tested samples at the location of maximum strain revealed dynamic recrystallisation occurring at higher temperatures. Based on detailed microstructure and microtexture analyses, it was concluded that single step, large strain deformation has a distinct advantage in the thermo-mechanical processing of Inconel alloy IN718.

In the present study, dynamic elastic constants namely Young’s modulus, shear modulus, Poisson’s ratio, and internal friction properties for polycrystalline Cu-0.68Cr-0.04Zr-0.03Ti-0.015Fe (wt.%) alloy have been evaluated from 25 to 650 °C temperature in argon environment. These properties were determined using resonance-based high-temperature impulse excitation technique. The temperature-dependent elastic constants are very vital for the thermo-structural analysis to predict the performance of the component/structure. The test results revealed that, the alloy exhibits linear reduction in Young’s modulus and shear modulus with increasing temperature. On the other hand, the calculated Poisson’s ratio showed minor increase with temperature. It was shown that, the variation in the internal friction is attributed to in situ aging in the temperature range studied. Overaging beyond 500 °C has led to drastic increase of internal friction. This has been supported by hardness measurement, tensile test, differential scanning calorimetry test, and transmission electron microscopy examination.

For machining a component, it is important to understand the characteristics of work material in order to choose the appropriate cutting tool and to fix a set of machining parameters to achieve optimum output. Analytical models of machining processes require complete understanding of process mechanism and hence are difficult to be developed. Once developed, these models are useful in parametric optimization, process simulation, operation and process planning, process parameter selection, parametric analysis, process performance prediction, verification of the experimental results, and improving the process performance by implementing/incorporating the theoretical findings. Neural network models associated with artificial intelligence are known as artificial neural networks (ANNs) which are simple mathematical models in the form of defining a function. This work presents the details of the experiments carried out for data acquisition, method of building the ANN models and their validation. These models can be used for predicting the output for a chosen set of input variables or for a specific desired output, finding the set of input variables to be chosen. This work resulted in developing models for the turning process for Inconel 718 alloy in a scientific manner. It also enables further scope of identifying the optimized set of turning parameters for Inconel 718 material using the newly developed coated carbide tools, achieving quality surface and productivity.

Alumina coating is given to a 07Х16Н6M stainless steel substrate, to withstand high frictional loads at elevated temperatures. Properties like high hardness, good adhesion and low thermal mismatch are essential for the coating. An 80%Ni-20%Cr bond coat is given for better adhesion of the alumina coating to the substrate. Air plasma spray technique was used for bond coat as well as the alumina coating.The substrate, bond coat and the alumina coating were characterized using optical microscopy, scanning electron microscopy (SEM) and nanoindentation. Hardness was evaluated using nanoindentation in all the three regions at loads varying from 2 mN in the bond coat to 50 mN in the alumina coating. Alumina coating showed the highest hardness of 11.5 GPa, followed by the bond coat – substrate interface having a hardness of 7.4 GPa. Substrate exhibited the least hardness of 6.3 GPa.

Gimbaling the engine nozzle within a specified angle through hydraulic actuator modules is commonly used to control the trajectory path of satellite launch vehicles. During one of the hot test of a liquid engine stage, a drop in system pressure in actuator module was noticed due to cracking of case drain plumbing inside the ferrule. The tensile and fatigue (axial and bending) test of the tube material was carried out to understand the cause of failure, simulating the actual service conditions such as strength and bending moment in assembled tube. Findings of the metallurgical investigation along with the fatigue test results were presented in this paper.

Gyroscope is an orientation determining sensor whose performance is mainly dependant on one of the critical element called the gimbal flexure. Thinner the flexure, better is the performance. To have sufficient strength, M300 maraging steel is used to fabricate the thin flexures machined by Electrical Discharge Machining (EDM) process down to the required thickness of 0.05 mm in various stages. After the EDM processing, the recast layer formed can cause degradation in the microstructure and mechanical properties. Micro-abrasive machining was carried out to remove the recast layer. An attempt was made to understand the changes that occurred after EDM and after micro-abrasive machining with respect to the microstructure using optical and Scanning Electron Microscopy (SEM) and with respect to mechanical properties using nanoindentation. Nanoindentation technique was adopted as the recast layer was just few microns thick. Indentations were carried out on the base material, as EDM cut flexure, and the micro-abrasive machined EDM cut flexure to obtain elastic modulus and hardness values for each condition and the results were analyzed.

Results are given for a study of the mechanical properties of aluminum alloy AA2219 after thermomechanical treatment by different regimes, including different (in form and degree) cold plastic deformation.

Hot isostatic pressing (HIPping) technology is used for healing the casting defects for aerospace applications. Castings used for aerospace applications like turbo-pumps need to meet very stringent quality requirements. Complexity of the castings used in these applications, makes it difficult to meet the quality requirements in all the areas. Defects like gas holes, shrinkages, cavities etc. may occur in few locations and need to be repaired by welding or healed by HIPping. In the present study, we attempted to simulate the defect healing capability of HIP in a systematic manner. Artificial defects were created in Austenite-Martensite grade stainless steel cast rod. These rods were then subjected to HIP prcoss cycle at 1150 °C and at a pressure of 1620 bar. Healing of the defects was ensured through X-ray radiography. Detailed microstructural analysis using optical metallography and scanning electron microscopy (SEM) with EDX was carried out before and after HIPping, to understand the defect healing mechanisms. These results are discussed in detail here.

Alumina coating was formed on AA7020 aluminum alloy by micro arc oxidation (MAO) method and its corrosion and stress corrosion cracking (SCC) behaviors were examined in 3.5 wt. % NaCl solution. Potentiodynamic polarization (PP) was used to evaluate the corrosion resistance of the coating and slow strain rate test (SSRT) was used for evaluating the environmental cracking resistance in 3.5% NaCl solution. Results indicated that MAO coating on AA7020 alloy significantly improved the corrosion resistance. However the environmental cracking resistance was found to be only marginal. Key words: aluminum, micro arc oxidation, x-ray diffraction, stress corrosion cracking

Elastic constants are the fundamental key parameters to understand the mechanical behaviour of engineering materials under stressed condition. This paper explains the test methodology and provides results of experiments carried out using resonance based high temperature impulse excitation technique test facility for the measurement of technical elastic moduli i.e., Young’s modulus (E), Shear modulus (G), Poisson’s ratio (ν) and internal friction (Q-1) of two nickel-base polycrystalline super alloys IN718 and Haynes 214 from ambient to 650°C temperature in argon environment during heating and cooling.

The electrochemical corrosion and mechanical properties of ceramic coatings fabricated by plasma electrolytic coating (PEO) and hard anodizing (HA) methods comparatively examined for AA2219. Potentiodynamic polarization results revealed that the corrosion resistance of both coatings are comparable to each other. However, the indentation and scratch testing indicated that the hardness and modulus of the PEO coating was significantly higher when compared to HA coating. The critical load (Lc2) causing adhesive failure of the PEO coating was much high (19N) when compared to HA coating (10N) showing better adhesive strength of the PEO coating.Key words: Plasma electrolytic oxidation (PEO), potentiodynamic polarization, nanoindentation, hard anodizing

While machining a material, it is essential to understand the characteristics of work material for choosing the favorable condition of the material, appropriate cutting tool, machining parameters to achieve desired optimum output. Accordingly, researchers always devise their studies to improve the machining processes resulting in enhanced product quality and increased production rate simultaneously. Such machining studies on super-alloys attract significance, since they are oriented towards overcoming the difficulties involved in machined out a component. Generation of heat in the cutting zone and high cutting forces on the tool being experienced while machining super-alloys, are due to poor thermal conductivity and work hardening characteristics. Above factors contribute to two basic problems viz. the inability of the tool materials to give long tool life and the metallurgical damage to the machined components due to induced stresses. Among the super-alloys, Inconel 718 is the widely used heat resistant super alloy (HRSA), which withstands stringent operating conditions in high and cryo temperature environments for longer duration. Studies on understanding the behavior and the relationship between work piece material, cutting tool materials, cutting conditions and the process parameters is an essential requirement for establishing and optimizing the machining process and the present work is tailored towards this objective. In this work, Inconel 718 alloy was subjected to turning experiments and the experimental data collected was used for constructing empirical models whose performance was assessed through statistical approach. It is established that the models developed could be used for predicting the output parameters for a set of input of parameters through 2-D (surface) and 3-D (contour) plots.