SCANNING SPEED INFLUENCE ON THE PHYSICAL PROPERTIES OF LASER METAL DEPOSITION TITANIUM ALLOY

The most commonly used aerospace titanium alloy, Ti6Al4V, was deposited on Ti6Al4V plate of dimension 72 x 72 x5mm. The laser power of 3 kW, powder flow rate of 1.44 g/min and gas flow rate of 4 l/min were used throughout the deposition process. The transverse/ scanning speed was varied between 0.005 to 0.095 m/sec according to established result of the preliminary study that produces full dense and pore free deposits. The mass of the deposited powder was obtained by weighing the substrate before the deposition and reweighing after the deposition. The substrate and the deposits were thoroughly cleaned using wire brush and acetone to remove unmelted powder particles from the surface of the substrate and the deposit. The height and width of the deposits were measured with Venier Caliper and the material efficiencies were determined using developed equations. The objective of this research is to determine the influence of the scanning speed on the material efficiency and deposit height in laser metal deposition of titanium alloy- Ti6Al4V. The results of this study showed that, for the set of processing parameter used in this study, the optimum scanning speed was at 0.015 m/sec with the optimum material utilization efficiency of 83.33% and the deposition height of 1.09 mm.  http://dx.doi.org/10.4314/njt.v36i1.1

Revolutionary additive manufacturing : an overview

Consumer demands are moving away from standardized to customized products, as such, the evolution of alternative manufacturing techniques has become imperative. Additive manufacturing (AM) is a process of building components layer by layer as against the traditional methods which are subtractive in nature. Though AM offers lots of advantages over traditional manufacturing techniques, its wide application is still however in the infancy phase. Despite all the benefits derived from AM technology, there are still a lot of unresolved issues with the technology that has hindered its performance thereby limiting its application to high tolerant jobs. This paper takes a look at some important AM technologies, some problems currently facing AM technology at large and proposes some solutions to these problems. A major known drawback in AM is poor dimensional accuracy and poor surface finish, only the layer height and melt pool temperature are controlled to solve this problem in the literature. The stair-stepping effect in adaptive manufacturing is rooted in a natural phenomenon of surface tension which is the cause of the poor surface finish and in combination with other factors is responsible for the poor dimensional accuracy. An adaptive controller is proposed for removing stair-stepping effect to improve the dimension accuracy, the surface finish and the mechanical properties of the components. Successful implementation of these proposed controllers will greatly improve the performance of AM technologies and also aid its wide application for end use products. Further research work is also suggested to improve the overall AM performance

Influence of laser power on microstructure of laser metal deposited 17-4 ph stainless steel

Abstract: The influence of laser power on the microstructure of 17-4 PH stainless steel produced by laser metal deposition was investigated. Multiple-track of 17-4 stainless steel powder was deposited on 316 stainless steel substrate using laser metal deposition, an additive manufacturing process. In this research, laser power was varied between 1.0 kW and 2.6 kW with scanning speed fixed at 1.2 m/s. The powder flow rate and the gas flow rate were also kept constant at values of 5 g/min and 2 l/min respectively. The microstructure was studied under optical microscope and it revealed that the microstructure was dendritic in structure with finer and lesser δ-ferrite at low laser power while the appearance of coarse and more δ-ferrite are seen at higher laser power

Supermassive Black Holes: Connecting the Growth to the Cosmic Star Formation Rate

In this Letter, we present a model connecting the cosmic star formation rate (CSFR) to the growth of supermassive black holes. Considering that the evolution of the massive black hole is dominated by accretion (Soltan's argument) and that the accretion process can be described by a probabilistic function directly regulated by the CSFR, we obtain the evolution of the black hole mass density. Then using the quasar luminosity function, we determine both the functional form of the radiative efficiency and the evolution of the quasar duty-cycle as functions of the redshift. We analyze four different CSFRs showing that the quasar duty-cycle, $\delta(z)$, peaks at $z\sim 8.5-11$ and so within the window associated with the reionization of the Universe. In particular, $\delta_{\rm max}\sim 0.09-0.22$ depending on the CSFR. The mean radiative efficiency, $\bar\eta(z)$, peaks at $z\sim 0.1-1.3$ with $\bar\eta_{\rm max}\sim 0.10-0.46$ depending on the specific CSFR used. Our results also show that is not necessary a supercritical Eddington accretComment: accepted for publication in MNRAS Letters (5 pages, 6 figures), Some typos fixed; MNRAS Letters 17 Aug 201

YIELD RESPONSE OF DIALLELIC CROSSED MAIZE (ZEA MAYS L.) GENOTYPES TO VARYING NITROGEN REGIMES IN NIGERIA

Context: Development of early maturing maize cultivars that remain productive under low N fertilizer farming system, consistent with the farmers’ technologies is a prerequisite to improving adoption of new varieties without increasing production cost. Objective: To assess the performance of ten early open pollination maize varieties (OPVs) and their F1 hybrids for grain yield and nitrogen use efficiency (NUE), and also identify productive cultivars under low N fertilizer regimes. Materials and Methods: The trials were set up in a split plot arrangement with three N fertilizer levels (0, 45 and 90 kg N ha-1) as main plot and the genotypes as sub-plot. Each plot within N level was four-row, laid out in a randomized complete block design of four replications. Ten OPVs were crossed in a half diallel to generate 45 F1 hybrids during 2004 and 2005 growing seasons. Planting were carried out on 20th July, 2005 and 2nd July, 2006. Agronomic characters studied were grain yield, maize establishment count, days to 50% tasselling and silking as well as plant and ear heights. Results: The year 2005 growing season was better for all observed characters amongst all the genotypes than the year 2006. Although, expressions of these traits in the hybrids were relatively higher than the OPVs including the grain yield. The total increase in grain yield observed was 1.72 t ha-1 and 1.95 t ha-1 for OPVs and hybrids respectively on application of 90 kg ha-1 over no N-application. However, NUE was optimum at 45 kg N ha-1 in both groups. Grain yield and NUE correlated positively with growth characters measured except for days to 50% silking. Higher genetic gains were recorded for plant and ear heights. Conclusion: Two drought tolerant varieties (Acr 90 Pool 16-Dt and Tze Comp3 Dt) that combined well with specific cultivars for grain yield and NUE probably have gene pools for low N-tolerance. Keywords: Nitrogen use efficiency, diallel crosses, maize cultivars, open pollinated varietie

Multiple urological problems in young age: a case report

Renal stone disease has been regarded as an uncommon problem in children as compared to adult population. The incidence varies in different parts of continent. Posterior urethral valve is also regarded as uncommon urological problem in pediatric population. The incidence is about 1 per 8,000 to 25,000 life births. A combination of renal calculi, posterior uerthral valve and vesicoureteric reflux in any given case is extremely rare especially in pediatri

Structural Behavior of Reinforced Self-Compacted Engineered Cementitious Composite Beams

Eight large-scale reinforced self-compacted engineered cementitious composite (R-SC-ECC) beams with different steel reinforcement ratios have been designed, prepared, cast, cured, and tested to failure at the age of 28 days. The experimental results have been compared with theoretical values predicted using EC2, RILEM, and VecTor2 models. Results show that failure modes in flexure and shear of R-SC-ECC beams are comparable to that of normal reinforced concrete beam. Nevertheless, contrary to VecTor2, models of EC2 and RILEM are not suitable for predicting reasonable ultimate moments for the beams, while results using VecTor2 model have successfully predicted the failure modes and load-deflection curves for all R-SC-ECC beams. It has been concluded that R-SC-ECC fall in the category of ductility class medium to high which gives advantages of using R-SC-ECC beams in regions susceptible to seismic activities

Process Parameter Influence on Tensile Property of Friction Stir Processed Al/Ni-Fe Composite

Friction stir processing (FSP) is a solid-state processing technique that has proven to be an efficient surface modification process for producing aluminium matrix composites (AMCs). However, practical challenges still occur during the processing of AMCs even though extensive progress has been made in recent years. In the present study, the influence of FSP process parameters on the tensile property of Al-Ni-Fe composite has been investigated. The process parameters studied were rotational speed and advancing speed. The rotational speed varied between 600 and 1000 rpm while the advancing speed varied between 70 and 210 mm/min. The rotational speed was kept constant at each setting and the advancing speed varied. Other processing parameters were kept constant throughout the experiments. The results were compared with those of the base metal (Al). The results showed that the tensile strength decreased as the advancing speed increased. The highest tensile strength was obtained at a rotational speed of 1000 rpm and an advancing speed of 70 mm/min

Metallurgical and Corrosion Property of Additive Manufactured Titanium Alloy-Ti6Al4V

Additive manufacturing (AM) is an important manufacturing technology that has changed the way products are designed and manufactured. Laser Metal Deposition (LMD), an AM technology, has the capability of producing components using a 3-Dimensional CAD model, through a layer by layer formation process just like any other AM technology. In this study, the influence of the scanning speed on the corrosion property of Titanium alloy-Ti6Al4V using LMD process was investigated. The scanning speed varied between 0.02 m/s and 0.14 m/s while other processing parameters were kept constant. The electrochemical corrosion test was conducted in sodium chloride (NaCl) solution. The result revealed that the corrosion resistance property was found to increase with the scanning speed

PCNL in horseshoe kidney- the first experience at HUSM

Horseshoe kidney is one of the commonest congenital renal fusion anomalies with an incidence of 0.25% in general population. Disturbances in urine flow, drainage and concomitant infections promote stone formation is common. Percutaneous nephrolithotripsy (PCNL) in horseshoe kidney is a challenge due to its anatomical difference and thus a modified technique is needed. Hereby, we report our first experience with PCNL in this anomaly, a 55 year old with left staghorn renal calculi in a horseshoe kidne