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- ItemOpen AccessAssessing Susceptibility to Chromium Carbide Precipitation in Cr-Mn Austenitic Stainless Steel Welds(University of Lagos Press, Akoka, 2017) Amuda, M.O; Enumah, K.S; Onitiri, M.A; Osoba, L.OChromium-manganese austenitic stainless steel is a low cost grade with metallurgical and mechanical properties approximating a standard nickel-chromium austenitic stainless steel. It serves as a good substitute to the standard nickel-chromium grade owing to the high cost of nickel. But, there is little information on its weldability particularly the influence of welding parameters on chromium carbide precipitation in the heat affected zone. This limits its structural application through fusion welding. Therefore, in this paper, carbide precipitation in chromium-manganese austenitic stainless steel welds was investigated in the heat input range 180 - 300 J/mm under different combinations of arc current and welding speeds. Microstructural analysis after 10% oxalic acid electrolytic etch revealed that increasing heat input produced significant changes in microstructure of the welds with wider sensitized structure at heat input greater than 206 J/mm. Microstructure of welds produced at heat input lower than 206 J/mm was free of chromium carbide precipitation. This level of heat input which corresponds to arc current of 110 -125A and welding speeds in the range 319- 395 mm/min show that sensitized region associated with chromium carbide precipitation can be safely avoided during fusion welding of this grade of austenitic stainless steel through carefully selected welding parameters.
- ItemOpen AccessWear Behaviour of Low Alloy Grey Cast Iron (NF-Grey 7): The Effect of Ferrosilicon and Carbonised Coconut Shell Nanoparticle Addition(University of Lagos Press, Akoka, 2017) Agunsoye, J.O; Bello, S.A; Odunmosu, A.KEffect of ferrosilicon and carbonised coconut shell nanoparticle additions on wear resistance of (NF-Grey 7) cast iron were studied. Alloys of (NF-Grey 7) cast iron were produced by a gradual increase in masses of the ferrosilicon and carbonised coconut shell nanoparticle additions using a green sand mould and stir cast technique. The behaviour of the material under shock energy impact and dry sliding wear conditions were studied. Results revealed that addition of the ferrosilicon and carbonised coconut shell nanoparticle additions to the (NG-Grey 7) cast iron enhanced the wear resistance and impact energy absorption more than what obtained in the earlier NG-Grey 7 cast iron reinforced with ferrosilicon and graphite micro particles. Hence, new alloy of cast iron for jaw crusher and other heavy equipment applications where wear resistance and energy absorption are a prime prerequisite has been developed.
- ItemOpen AccessTechnical Feasibility and Economics of Direct Aplication of the Nigerian Tar Sand Deposits as Road Asphalt(University of Lagos Press, Akoka, 2017) Akinmosun, A; Olufowobi, S.OThis study present, the technical feasibility and the Economics of the direct application of Nigerian Tar sand deposits as road asphalt. Twenty Tar sand samples were selected from nine locations in parts of Southwestern Nigeria and several engineering tests were conducted on twenty samples. The tests involved Bitumen extraction to determine the percentage of bitumen content, Sieve analysis, Specific gravity and Marshall tests which include the Stability, Flow, Density and Void determination. The percentage of bitumen saturation ranges from 5.6 to 28.6%, the stability values ranges from 2.1 to 6.3KN, the flow values ranges from 27.8 to 63.1mm10, specific gravity values ranges from 1.79 to 2.35g/ml and density values ranges from 1.75 to 2.01g/ml. The sieve analysis results indicate that none of the samples could be applied directly in road construction, though some of them possess stability and flow values that meet the standard specification for wearing course of asphalt. Design mix analysis which involves modification of mineral aggregates was carried out on ten out of the twenty samples to improve their gradation. From economic point of view, using the modified aggregates of tar sand (@₦7,000-9,500 per ton) as against current asphalt concrete (₦20,000 per ton) would have potentially large cost saving in Nigeria.
- ItemOpen AccessMechanical and Wear Characteristics of Aluminium Brass(University of Lagos Press, Akoka, 2017) Esezobor, D.E; Agbeleye, A.A; Onovo, H.O; Bodude, M.AIn this paper, the influence of the processing parameters on the wear and mechanical properties of 5 – 12 % aluminum red brass (Al-brass) was studied. The wear characteristics of developed Al brass in dry sliding conditions were exposed through a series of pin-on-disc sliding wear tests. Three load levels of 2, 7 and 12N, sliding speeds of 125 and 250 rpm and two sliding distances of 392.7 and 785.4m were investigated. The mechanical properties of the Al brass were determined using standard techniques. The results showed an increase in tensile strength from 225 MPa at 5 % aluminum addition to a maximum of 248 MPa at 10% Al and then a decline to 240 MPa at 12 % Al. The peak stress value increases as the weight percentage composition of Al increases until at 11%Al when it reduces. The impact energy and the hardness values of the as-cast Al brass rose from 54.2 Joules and 81HRC to 122 Joules and 92.4 HRC respectively at 12 % aluminum addition. At lower load of 2N, the addition of 5 % of Al brought a drastic improvement (65 %) to the wear resistance at 125 rpm and 250rpm, but the improvement became consistent thereafter. The same trends occurred at load of 7 N, but with lower degree of improvement (approximately 40 %). In contrast, under higher load of 12 N, the addition of Al brought slight and consistent improvement (10 -15 %) to the wear resistance.
- ItemOpen AccessInvestigation of Metallurgical and Microhardness Properties of Titanium Alloy in Laser Metal Deposition Process(University of Lagos Press, Akoka, 2017) Mahamood, R.M; Abdulkareem, S; Ajao, K.R; Aweda, J.OThis paper reports on the investigation of metallurgical and microhardness properties of laser metal deposition of Titanium alloy- Ti-6Al-4V. Ti-6Al-4V substrate and Ti-6Al-4V powder (150-200 μm) both at 99.6% purity were used in this study. The input laser power varied between 0.8 and 4.0 kW while other processing parameters were kept constant. They include the scanning speed of 0.005 m/sec, powder flow of 1.44 g/min and the gas flow rate of 4 l /min. The microstructure and the microhardness were examined under the optical and scanning electron microscope. The microhardness was measured using the Vickers hardness tester. The study revealed that the layer band occurred in all the samples except those samples at very high laser powers. The microstructure of the heat affected zone is characterized with fine globular primary alpha and beta grains at low laser power and become coarse as the laser power was increased. The microhardness was found to initially increase and then decrease as the laser power was increased beyond 3 kW.