http://hdl.handle.net/10204/455 2013-05-21T12:10:39Z http://hdl.handle.net/10204/6708 Title: Effects of Ti and TiC ceramic powder on laser-cladded Ti-6Al-4V in situ intermetallic composite Authors: Ochonogora, OF; Meacock, C; Abdulwahaba, M; Pityana, S; Popoolaa, API Abstract: Titanium metal matrix composite (MMCs) was developed on titanium alloy (Ti–6Al–4V) substrate with the aim of improving the hardness and wear properties by laser cladding technique using a Rofin Sinar 4 kW Nd: YAG laser. Wear investigations were carried out with the aid of three body abrasion tester. The resultant microstructure show homogeneous distribution of TiC particles free from cracks and pores. Multiple track deposited systems with 50% overlap revealed micro-hardness increase from 357.3 HV0.1for the substrate reaching a peak as high as 922.2 HV0.1 for 60%Ti + 40%TiC and the least 665.3 HV0.1 for 80%Ti + 20%TiC MMCs. The wear resistance of the materials improved significantly, indicating a fifteen-fold wear rate reduction due to the proper distribution of ceramic particles thereby forming interstitial carbides as revealed by the X-ray diffraction spectrum. Description: Copyright: 2012 Elsevier. This is an ABSTRACT ONLY. The definitive version is published in Applied Surface Science, vol. 263, pp 591-596 2012-12-01T00:00:00Z http://hdl.handle.net/10204/6702 Title: Impact toughness of laser surface alloyed Aluminium Authors: Mabhali, LAB; Sacks, N; Pityana, S Abstract: Laser surface alloying of aluminium AA1200 was performed with a 4kW Nd:YAG laser and the impact resistance of the alloys was investigated. The alloying powders were a mixture of Ni, Ti and SiC in different proportions. Surfaces reinforced with intermetallic phases and metal matrix composites were achieved during laser alloying. Brittle fracture of the SiC particles and transgranular cracking of the intermetallic phases was observed for the laser alloyed samples, while ductile fracture was observed for the bulk aluminium. The aluminium metal absorbed more energy during fracture compared to the laser alloyed samples due to its high ductility. Laser alloyed layers with a high Ti content had high absorbed energies which represent a reduction in brittleness, while alloyed layers with a high Ni content had low absorbed energies which indicate a preference for brittle fracture. Description: Copyright: 2012 Elsevier. This is the Pre/post print version of the work. The definitive version is published in Journal of Materials Science & Technology, pp 1-29 2012-03-01T00:00:00Z http://hdl.handle.net/10204/6693 Title: Fingerprint pores extractor Authors: Mngenge, NA; Nelufule, NN; Nelwamondo, FV; Msimang, M Abstract: Automatic Fingerprint Recognition Systems (AFRSs) rely on minutiae position and orientation within the fingerprint image for matching. Minutiae information is highly accurate provided that the fingerprint image matched is of high quality. However, this is not always the case because of diseases and hash working conditions that affect fingerprints. In order to maintain high level of security independent of varying fingerprint image quality research suggests the use of other fingerprint features to compliment minutiae. These are things like ridge contours, sweat pores, dots, and incipient ridges. Sweat pores have been proven as one of the most distinctive among these feature. Thus in order to improve accuracy of AFRSs pores can be fused with minutiae or used alone. Sweat pores have been less utilized in the past due to constraints imposed by fingerprint scanning devices and resolution standards. Recently, progress has been made on both scanning devices and resolution standards to support the use of pores in AFRSs. However, very few techniques exist for extracting, matching and fusing them with minutiae. Matching and fusion can only be possible if pores are available. Some techniques have been proposed to reliable extract pores. However, existing techniques can only work on one resolution i.e. an algorithm proposed and tested on 500dpi cannot work on 1000dpi without minor modifications because pores size change if resolution changes. In addition, existing pore extraction techniques are computationally expensive. In this paper an algorithm to extract feature level 3 (pores) is proposed. The algorithm uses Laplacian of Gaussian (LoG) in Fourier domain in order to reduce computation. The performance of the proposed algorithm is tested on two distinct databases with different resolutions in order to validate its accuracy. The accuracy of the proposed algorithm is further measured using false detection rate (FDR) and true detection rate (TDR). Results show that FDR ranges from 10-35% while TDR ranges from 65-90%. Description: 2012 National Conference on Computing and Communication Systems, Durgapur, West Bengal, India, 21- 22 November 2012. To be published in IEEE Xplore 2012-11-01T00:00:00Z http://hdl.handle.net/10204/6684 Title: Process control & monitoring for laser micromaching of Si3N4 ceramics Authors: Tshabalala, L; Pityana, S; Styne, J; Höfer, M; Schäfer, L Abstract: Laser machining which is a non-contact process that offers the advantage of machining advanced ceramics. In laser machining Si3N4, surface temperature is increased and controlled to evaporate the YSiAlON glassy phase of the Si3N4. However, the formation of deep grooves often produced cracks that reduce the material strength. This work explores the diagnostic parameters of solid state lasers varying wavelength and pulse duration for ceramic micromachining. The micromachining process parameters that were monitored and controlled for laser performance are pulse energy, repetition rate and pulse duration. The focused beam size of the ultrashort laser (ns) and the longer (ns) laser pulses were 16µm and 40µm respectively. The primary aim for this research is to evaluate the two types of laser that would offer the best results with respect to material removal mechanism, micro-crack reduction, surface composition and surface roughness. Description: International Congress on Applications of Lasers and Electro-Optics (ICALEO), Anaheim Marriott Hotel® Resort, USA, 23-27 September 2012 2012-09-01T00:00:00Z