Mechanical and tribological characterization nitrided Al-7075/Al2O3 metal matrix composites

This research is mainly intended to evaluate the effect of nitriding on the wear behaviour of Al2O3 reinforced aluminium-7075 metal matrix composite materials. The composites were prepared by using powder metallurgy process. The amount of Al2O3 in these composites was varied from 3% to 7% (by weight) in steps of 2%. Homogeneously mixed powder by using double cone mixture was compacted using hydraulic press with 60KN of load. The compaction load was optimized to get a equal density as base specimens,then the compacted specimens were sintered at 5400 C which is 80% of melting temperature aluminium base alloy. The sintered materials were nitrided with a temperature of 520°C for 72hrs. Two different set of specimens, namely, nitrided composites and non-nitrided composites specimens were tested for their wear resistance and hardness properties. Pin-on-disc equipment was used for wear testing and microhardness testing machine was used for hardness testing. Elemental X-Ray Diffraction technique (XRD) was used to ensure the diffusion of nitrogen to the surface of composites. After all the standard tests it was observed that the nitrided composites have shown better wear resistance than the non-nitrided composite

Application of response surface methodology for parameter optimization of aluminum 7075 thixoforming feedstock billet production

This paper aims to present the experimental work to formulate optimum processing parameters of the direct thermal method (DTM) using response surface methodology (RSM) for high-quality feedstock billet production. The DTM is one of the techniques which is used to produce aluminum 7075 alloy feedstock billets with globular microstructures for thixoforming operations. Based on the central composite design (CCD) techniques, 13 experiments were performed using two factors and levels. Pouring temperature parameters in CCD varied from 645 to 685 °C, with holding times ranging from 20 to 60 s. The size of the microstructures of the produced feedstock billets was measured, and the different parameter combinations were analyzed in detail by RSM. Moreover, the distribution of elements and the impact of primary and secondary phases on microstructures were examined by scanning electron microscopy (SEM)). Statistical analysis showed that R2 values of circularity and aspect ratio were 0.96 and 0.97 and meanwhile probability values (p  p-value) at 95% confidence level, with an acceptable error percentage. RSM results showed that a pouring temperature of 665 °C and a holding time of 60 s produced the optimum globular microstructure. The grain diameter, circularity, and aspect ratio values were 61.12 µm, 0.707, and 1.44, respectively. Moreover, the predicted and experimental values are in good agreement. These experimental results that used the RSM explained the effects of the various combination parameters in detail using a limited number of experiments and have successfully identified the optimum parameters

Cloud computing: survey on energy efficiency

International audienceCloud computing is today’s most emphasized Information and Communications Technology (ICT) paradigm that is directly or indirectly used by almost every online user. However, such great significance comes with the support of a great infrastructure that includes large data centers comprising thousands of server units and other supporting equipment. Their share in power consumption generates between 1.1% and 1.5% of the total electricity use worldwide and is projected to rise even more. Such alarming numbers demand rethinking the energy efficiency of such infrastructures. However, before making any changes to infrastructure, an analysis of the current status is required. In this article, we perform a comprehensive analysis of an infrastructure supporting the cloud computing paradigm with regards to energy efficiency. First, we define a systematic approach for analyzing the energy efficiency of most important data center domains, including server and network equipment, as well as cloud management systems and appliances consisting of a software utilized by end users. Second, we utilize this approach for analyzing available scientific and industrial literature on state-of-the-art practices in data centers and their equipment. Finally, we extract existing challenges and highlight future research directions

Optimization of Output Responses during EDM of AZ91 Magnesium Alloy using Grey Relational Analysis and TOPSIS

Unconventional machining of magnesium alloys through die sinking and Wire electrical discharge Machining (WEDM) processes are preferred over conventional machining processes to overcome the rapid loss in strength and affinity that occurs with tool materials at high temperatures. in the present study, AZ91 magnesium alloy is machined in EDM using a prepared alloy tool (copper alloyed with titanium diboride). Based on Taguchi’s l27 orthogonal array, a total of 27 experiments have been conducted by varying the process parameters such as pulse on time (Ton), gap voltage (Vg) and current (Ip) with three different levels. Techniques for Order Preference by Similarity to ideal Solution (TOPSIS) and Grey Relational Analysis (GRA) have been applied to optimize the response parameters of EDM to obtain maximum Material Removal Rate (MRR) and minimum Tool Wear Rate (TWR) and Surface Roughness (SR). Analysis of variance (ANOVA) is carried out based on F-test at a confidence interval of 95% to confirm the significant influence of individual parameters. From the above two optimization techniques, the obtained optimal values are current 15 A, gap voltage 55 V, pulse on time 30 μs and an error of less than 5% is observed from the confirmation experiments. Scanning Electron Microscope (SEM) images revealed that there is no formation of cracks but micro pits and holes are observed

Dry Sliding Friction and Wear Behaviour of Leaded Tin bronze for Bearing and Bushing Application

Among different bearing materials, copper-based alloys are the most important source for bearing and bushing applications. In this work, the tribological behavior of a leaded tin bronze (Cu-22Pb-4Sn) against an EN31 Steel for various loads (20 N, 70 N, 120 N) and different sliding velocity (1 m/s, 3 m/s, 5 m/s) at 3000 m sliding distance is performed using a pin on disk tribometer. Irrespective of all loads and sliding velocity, a higher specific wear rate is observed at 1 m/s and 120 n that fails to facilitate the formation of lubricating film, whereas a lower specific wear rate is evident when the sliding velocity is increased to 5 m/s. This is attributed to the formation of a stable oxide layer that has been confirmed through the energy dispersive X-ray spectroscopy analysis and scanning electron microscopy. The coefficient of friction is observed in reducing trend from 0.69 to 0.48 for the increasing load (70 N, 120 N) and sliding velocity (3 m/s and 5 m/s) due to stable thin oxide film formation. Also, the increase in frictional force and loading the interacting surface temperature is increased to a maximum of 102°C. The grey relational analysis indicates that the optimal parameters for the minimum specific wear rate and coefficient of friction is 120 N and 5 m/s that has been confirmed with experimental analysis

Creep Behaviour of Aluminium 7075 Feedstock Billet Globular Microstructure at High Processing Temperature

This paper aims to present the determination of the creep behaviour of a globular microstructure aluminium 7075 alloy semi-solid metal feedstock billets under a constant temperature of 250 °C. Globular microstructures are often preferred in thixoforming processes due to their unique properties and favourable mechanical and high-temperature applications. Less attention has been given to globular microstructure even though the contribution of microstructure to creep behaviour is essential. Therefore, for this test, globular microstructure aluminium 7075 alloy feedstock billets were produced by the direct thermal method. The creep tests were conducted at different stress ranges from 30 to 70 MPa, and the effect of globular microstructure was examined. The results showed that the globular microstructure had the least deformation and the lowest creep rate at a longer deformation time. The fracture surface of the samples was then analysed with scanning electron microscopy (SEM). The microstructural changes that occurred during the test were investigated. SEM analysis revealed that the globular microstructure of the feedstock billet exhibits fewer voids and defects due to a uniform microstructure. The strain exponent value of globular microstructure billets was found to be at n = 4.6 in the stress range between 30 and 70 MPa at a constant temperature. This study is expected to provide an understanding of the creep behaviour of globular microstructures at high temperatures and high-stress conditions