Search

The study of laser cladding of 90Ti-10Al2O3, 90Ti-8Al2O3-2Zn and 90Ti-4Al2O3-6Zn coatings onto Ti-6Al-4V alloy, with intention to produce defect-less, high microhardness and wear resistant coating ...

Titanium alloy (Ti-6Al-4V) is one of the materials used in most engineering applications due to its excellent combination of mechanical and corrosion properties. However, the extend application of Ti-6Al-4V alloy is limited because of low hardness and poor wear resistance. In order to overcome this alloy’s limitations, coatings could be fabricated on the surface of the alloy through surface modification technique. In this work, Ti and Al2O3 powders were deposited using laser cladding at different admixed ratios (95Ti-5Al2O3, 92Ti-8Al2O3 and 90Ti-10Al2O3) on Ti-6Al-4V alloy. The coatings were laser cladded at laser power of 900 W, powder feed rate 2.0 g/min, beam spot size 2 mm and gas flow rate 8.0 L/ min while scan speed was varied at 0.6 and 0.8 m/min. The produced coatings were characterized for microstructures and phase constituents by using optical microscope (OPM), scanning electron microscope (SEM) and X-ray diffractometer (XRD). Moreover, Vickers hardness tester and and pin-on-disk Anton Paar tribometer were respectively used to measure hardness and wear resistance. The results showed that hardness values and reduction in wear loss were improved by increasing the Al2O3 content from 5 to 10 wt% in Ti-Al2O3. However, high scan speed of 0.8 m/min prompted non-uniform distribution of Al2O3 which in resulted low hardness and wear resistance compared to coatings fabricated at 0.6 m/min.

Titanium alloy (Ti-6Al-4V) has been mostly used for medical implants due to its good chemical and mechanical properties. However, this alloy has tendency to emanate toxic V and Al due to its low corrosion resistance in body conditions. In this work, an experimental study of laser cladding Ti-Al2O3 coatings with different Al2O3 fractions (5 wt.% Al2O3, 8 wt.% Al2O3, and 10 wt.% Al2O3) was carried out to establish a coating which could improve the hardness and corrosion resistance of Ti-6Al-4V alloy. Laser parameters of 900 W power, 0.6 m/min laser scan speed, and 2 l/min powder feed were used in this research. The microstructure, phase constituents, microhardness, and corrosion of the resultant coatings were characterized by scanning electron microscope (SEM), optical microscope (OPM), X-Ray Diffractometer (XRD), Vicker hardness tester, and potentiostat respectively. Results showed that a defect free coating was achieved at a coating with less Al2O3 content. Increase in Al2O3 addition resulted in increment of hardness with Ti-10 wt.% Al2O3 coating achieving an optimum hardness of about 2.2 times greater than that of the substrate. Moreover, considerable increment in corrosion resistance of Ti-6Al-4V alloy was achieved after laser deposition of various Ti-Al2O3 admixed coatings. An optimal corrosion rate reduction of about 81% and polarization resistance increment of 709% over the substrate were achieved at Ti-5 wt.% Al2O3 due to low porosity within the coating layer. It has been established that fabricating Ti-Al2O3 on Ti6Al4V through laser could be used in improving the surface hardness values and corrosion resistance.

The distinctive properties of Ti-6Al-4V alloy coupled with its poor tribological properties make it a subject of numerous researches. While titanium alloys possesses vast applications and excellent properties, their low hardness and poor tribological behaviour have retarded their applications in engineering applications. In this work, the microstructures and micro - hardness values of Ti-Co intermetallics reinforced on Ti6Al4V, were investigated. Laser surface cladding technique was employed using Nd: YAG high power laser beam for the synthesis of the powders. The feedstock powders were premixed and deposited on Ti6Al4V with varying compositions at scan velocity of 1.2 m/min. Laser power of 900W and beam size of 3mm with argon shield gas flow rate of 1.2l/min were set as the operating laser parameters. Phase identification and morphological studies of the resultant coatings were carried out using scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) respectively. The coatings displayed fine microstructure and good metallurgical bonding with the substrate containing minute or no defects such as cracks and pores. The results revealed the formation of fractions of Ti2Co and TiCo3 inter - metallic phases dispersed within the coating matrix which could be responsible for the enhanced properties attained. The hardness was increased by 150% as against the substrate.

The need for new advanced high temperature materials is in high demand. High Entropy Alloy (HEAs) has been described to possess excellent mechanical oxidation and good corrosion resistance properties even far above the ambient temperature. Attempts are made in this research to study the corrosion, oxidation, microhardness and densification properties of Al15Ti30Si30Mo15Ni10 HEA produced by spark plasma sintering (SPS) for high temperature applications. In addition, the effects of SPS temperature (800, 900 and 1000°C) on the microstructure and phase formation of the developed HEA were reported. The microstructural modification and phases present were examined using the scanning electron microscope (SEM) equipped with the energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD) respectively. Ordered FCC and BCC systems were identified along with clearly defined crystal lattice along with Mo, Ti and Si rich regions were observed. No pores or cracks were observed from the microstructures. Densification of 98.8% accompanied with microhardness of 1445.29HV was achieved for both HEA at 1000°C. The Al15Ti30Si30Mo15Ni10 HEA fabricated at 1000°C displayed a higher polarization value of 3477 Ω.

The indispensable properties of Ti-6Al-4V alloy coupled with poor tribological properties and delayed bioactivity make it a subject of interest to explore in biomedical application. A quite number of numerous coatings have been employed on titanium alloys, with aim to overcome the poor properties exhibited by this alloy. In this work, the possibility of laser cladding different ad-mixed powders (Ti - 5 wt.% Al2O3 and Ti - 8wt.% Al2O3) on Ti-6Al-4V at various laser scan speed (0.6 and 0.8 m/min) were investigated. The microstructure, phase constituents and corrosion of the resultant coatings were characterized by scanning electron microscope (SEM), Optical microscope, X-Ray diffractometer (XRD) and potentiostat respectively. The electrochemical behaviour of the produced coatings was studied in a simulated body fluid (Hanks solution). The microstructural results show that a defect free coating is achieved at low scan speed and ad-mixed of Ti-5 wt. % Al2O3. Cladding of Ti - Al2O3 improved the corrosion resistance of Ti-6Al-4V alloy regardless of varying neither scan speed nor ad-mixed percentage. However, Ti-5 wt.% Al2O3 coating produced at low scan speed revealed the highest corrosion resistance among the coatings due to better quality coating layer. Henceforth, this coating may be suitable for biomedical applications.

MBA, North-West University, Potchefstroom Campus, 2015 Small and medium enterprises (SMEs) are very unique in nature and contribute immensely to the growth of the economy of any country in the world. Hence SMEs can be considered to be the greatest source of growth of the economy. Regardless of these contributions, SMEs seem to be faced with an infinite number of problems and challenges. Although it is quite challenging for all businesses (from micro to large) to sustain and maintain a successful enterprise, SMEs face even more difficult challenges because of their unique small and medium sizes. The majority of which are caused by the Government (through restrictive regulations and a lack of SME focused policies), while some are internal, caused by the owners and/or managers. The fundamental objective of this study was to explore and investigate the challenges and problems faced by SMEs and provide some recommendations to overcome these challenges especially within Klerksdorp Orkney Stilfontein Hartebeesfontein (KOSH) area. A study consisting of 195 SMEs was conducted. Each SME faces its own unique challenges, such as lacking the management skills needed to run the business and difficulty accessing markets. Recommendations are suggested to both the Government and SMEs to help overcome these challenges and problems and to help sustain and grow these businesses successfully Masters