ResearchSpace :: Browsing by Author "Masina, Bathusile N"

Browsing by Author "Masina, Bathusile N"

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An all optical system for studying temperature induced changes in diamond
(CSIR, 2010) Masina, Bathusile N; Forbes, A
Industrial diamonds are heated by a laser beam and the resulting temperature is optically measured on the surface of the diamond. The ultimate aim is that with the heating and temperature known and measurements being repeatable, the temperature-driven defects in industrial diamonds can be studied.
An all optical system for studying temperature induced changes in polycrystalline diamond deposited on a tungsten carbide substrate
(CSIR, 2010-09) Masina, Bathusile N; Forbes, A; Bodkin, R; Mwakikunga, Bonex W
In this poster the authors discussed the ability to heat an industrial diamond sample by means of optical absorption of a CO2 laser beam, and then measure the resulting temperature on the surface of the diamond optically by means of radiometry principles. A model for the temperature on the surface of the diamond was developed and they show that it agrees qualitatively with experimental data. In particular, they show that it is possible to engineer the boundary conditions and initial beam such that uniform temperature gradients can be created, thus allowing the study of thermal effects in the absence of thermal stresses. They make use of the known grey body emission from polycrystalline diamond (PCD). They show that uniform temperature alone can account for significant structural changes in PCD diamond.
An all-optical system designed for the heating and temperature measurement of the diamond tool
(CSIR, 2012-07) Masina, Bathusile N; Forbes, A; Bodkin, R; Mwakikunga, Bonex W
Diamond tools are used in industry for abrasive applications such as grinding, and drilling. One of its important applications is in drill bits used for drilling through rock in search of oil. The early failure of drill bits used in oil drilling rigs has huge financial implications. Therefore, we have undertaken a study trying to understand this problem and solving it by applying the science of light. In this work we outline how a non-contact of all-optical system was designed for the heating and then subsequent temperature measurement of the diamond tool. A laser beam was used as the source to raise the temperature of the diamond tool, and the resultant temperature was measured by using the blackbody principle. In this poster, we have successfully demonstrated temperature profiles across the diamond tool surface using two laser beam profiles and two optical setups, thus allowing a study of temperature influences with and without thermal stress. The generation of such temperature profiles on the diamond tool in the laboratory is important in the study of changes that occur in diamond tools, particularly the reduced efficiency of such tools in applications as rock drilling where extreme heating due to friction is expected. The results show that laser heating does not result in graphitization of the diamond tool, but rather cobalt and tungsten oxides form on the diamond tool surface.
Blue- and red-shifts of V2O5 phonons in NH3 environment by in situ Raman spectroscopy
(IOP Publishing, 2018-01) Akande, Amos A; Machatine, AGJ; Masina, Bathusile N; Chimowa, G; Matsoso, B; Roro, Kittessa T; Duvenhage, M-M; Swart, H; Bandyopadhyay, J; Ray, Suprakas S; Mwakikunga, Bonex W
A layer of ~30 nm V2O5/100 nm-SiO2 on Si was employed in the in situ Raman spectroscopy in the presence of NH3 effluent from a thermal decomposition of ammonium acetate salt with the salt heated at 100 °C. When the layer is placed at 25 °C, we observe a reversible red-shift of 194 cm−1 V2O5 phonon by 2 cm−1 upon NH3 gas injection to saturation, as well as a reversible blue-shift of the 996 cm−1 by 4 cm−1 upon NH3 injection. However when the sensing layer is placed at 100 °C, the 194 cm−1 remains un-shifted while the 996 cm−1 phonon is red-shifted. There is a decrease/increase in intensity of the 145 cm−1 phonon at 25 °C/100 °C when NH3 interacts with V2O5 surface. Using the traditional and quantitative gas sensor tester system, we find that the V2O5 sensor at 25 °C responds faster than at 100 °C up to 20 ppm of NH3 beyond which it responds faster at 100 °C than at 25 °C. Overall rankings of the NH3 gas sensing features between the two techniques showed that the in situ Raman spectroscopy is faster in response compared with the traditional chemi-resistive tester. Hooke's law, phonon confinement in ~51 nm globular particles with ~20 nm pore size and physisorption/chemisorption principles have been employed in the explanation of the data presented.
Characteristics of laser In-situ alloyed titanium aluminides coatings
(Elsevier, 2017-01) Tlotleng, Monnamme; Masina, Bathusile N; Pityana, Sisa L
The use of titanium aluminides as high temperature materials in the aerospace and automobile industries is becoming a reality since their early research and development in 1955. Their mechanical properties at elevated temperatures make them attractive in spite of their poor ductility at room temperature. The progress on their production using powder metallurgy processes seem to be significantly positive; at least on microstructure tailoring and mechanical properties. This research work sought to study the in-situ alloying of the elemental Ti and Al using laser metal deposition (LMD) process. The effects of laser power on the microstructure evolution, composition and micro-hardness were evaluated on the as-produced TiAl coatings. The results indicated that lamellar microstructures formed at 1.0, 1.3 and 1.5 kW laser powers while at 2.0 kW a refined dendritic structure was observed. The phase composition by XRD concluded the presence of TiAl(sub3), TiAl, Ti(sub3)Al(sub5), and the oxide phases of Ti and Al. Generally, the Ti(sub3)Al(sub5) phase is indicative of high temperature process during TiAl processing while TiAl(sub3) is known as a twinning phase to TiAl. The average HV(sub0.3) values for 1.0, 1.3, 1.5 and 2.0 kW coatings were 327(sub0.3), 281(sub0.3), 333(sub0.3) and 367(sub0.3), respectively. These hardness values are indicative of the presence of TiAl/TiAl(sub3).
The control of magnetism near metal-to-insulator transitions of VO2 nano-belts
(Elsevier, 2016-12) Nkosi, SS; Lafane, S; Masina, Bathusile N; Ndwandwe, OM
The magnetic properties of paramagnetic/weakly ferromagnetic films are strongly affected by the proximity to materials that undergo a metal to insulator phase transition. Here, we show that under the deposition conditions associated with structural changes near the metal-insulator phase transition of VO(sub2) produces magnetoelastic anisotropy. We observe intrinsic paramagnetic centres (PM-C) both at the near film surface and bulk/deep PM-C that are affected by the metal-insulator phase transition in VO2. We study the evolution of vibrational modes of VO(sub2) thin films in the vicinity of the phase transition by using temperature controlled-Raman microscopy.
Diffusion of Co and W in diamond tool induced by 10.6 µm CO2 laser radiation
(2011-05) Masina, Bathusile N; Forbes, Andrew; Mwakikunga, Bonex W; Bodkin, R
At present it is known that diamond tools degrade with time as it is normally used at high temperatures. One of the questions the authors like to answer in this study is whether thermally induced problems in diamond tool arise as a result of the temperature value itself? They raised the temperature of the diamond tool sample by laser heating it. Initially, the PCD layer was made of C and trace amount of Co. They observed the increment of Co and W on the PCD layer, and observed the formation of microstructure oxides at the surface of the PCD layer. They have successfully raised the temperature of the diamond tool sample and measure it, and successfully observed the increment of Co and W content on the PCD layer. The authors successfully observed the formation of microstructure oxides on the PCD layer, and showed that the temperature in the diamond tool is sufficient to radically alter its physical and chemical properties, resulting in critical fracture. Future work will be to determine by how much Co and W migrate on the PCD layer during the raising of the diamond tool temperature.
Effect of heat treatment on microstructure, hardness and tensile properties of high-speed selective laser melted Ti6Al4V
(2022-11) Lekoadi, Paul M; Tlotleng, Monnamme; Annan, K; Maledi, N; Masina, Bathusile N
This study presents the investigation of the influence of heat treatment on microstructure, hardness and tensile properties of high-speed selective laser melted Ti6Al4V components. Heat treatment was performed to obtain an improved microstructure with enhanced hardness and tensile properties. It was found that the acicular martensitic a' structure on the asbuilt sample lead to high hardness, yield strength and ultimate tensile strengths of 389±10 HV0.3, 949 ± 10 MPa and 1045 ± 3 MPa, respectively, with a low ductility of 5%. Heat treatment transformed the martensitic a' structure into lamella a + ß phases, with heat treatment at 1000 °C resulting in the most improved hardness and ductility from 389 ± 10 HV0.3 and 5% to 325 ± 20 HV0.3 and 13%, and a decrease in yield and ultimate tensile strength from 949 ± 10 MPa and 1045 ± 13MPa to 835 ± 11 MPa and 911 ± 5 MPa, respectively.
Effect of heat treatment temperature on the microstructure and microhardness of TiC/Ti6Al4V composite manufactured with laser metal deposition
(2023-11) Kgoahla, Reneilwe M; Lekoadi, Paul M; Masina, Bathusile N
This study presented the investigation of the influence of post heat treatment temperature on the microstructure and hardness of TiC/Ti6Al4V composite manufactured with laser metal deposition. Heat treatment was performed to improve the microstructural homogeneity. It was found that the addition of TiC into Ti6Al4V results in the formation of a Widmanstätten microstructure with different grain sizes on the matrix. Heat treatment of the TiC/Ti6Al4V promoted phase transformations from acicular in the as built to lamella (a + ß) and equiaxial phases in the heat treated samples. The 900°C heat treated sample showed a uniform distribution of a and ß phases, and 1100°C showed an increase in ß phases, which resulted in an equiaxial microstructure. Moreover, Heat treatment at 1100°C resulted in the highest microhardness of 665±13HV.
Effect of in-situ heat treatment and process parameters on the laser-deposited IN718 microstructure and mechanical properties
(Cambridge University Press, 2020) Masina, Bathusile N; Skhosane, Besabakhe S; Tlotleng, Monnamme
The direct laser-deposited Inconel 718 (IN718) specimens were produced using 1073 nm, high power continuous wave (CW), IPG Ytterbium fibre laser and in-situ heat treatment. The laser power and in-situ heat treatment temperature were fixed while varying the laser scanning speed from 0.83 to 2.50 cm/s. The microstructure and micro-hardness of the IN718 specimens were characterized using an optical microscope (OM), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS or EDX) and Vickers system. The microstructure of the specimens consists of g-matrix as the primary phase, Nb-rich particles, constitutional liquation cave, liquation cracking and ductility-dip cracks. It was found that the micro-hardness profile of the IN718 specimens was gradually increased with the increase of the distance from the surface.
The effect of laser shock processing on the anti-corrosion performance of LENS-Fabricated Ti-6Al-4V alloy
(2023-05) Arthur, Nana KK; Kubjane, SM; Popoola, API; Masina, Bathusile N; Pityana, Sisa L
Titanium alloys are prone to increased oxidation rates when exposed to higher temperatures during application. As a result, the components suffer mechanical failure due to the formation of the alpha-case layer at 500 °C. To improve its corrosion and oxidation properties, and ultimately its mechanical performance, it is necessary to modify its surface properties. In this study, a LENS 3D-printing system was used to fabricate titanium alloy sample coupons, while surface treatment was performed using laser shock processing (LSP) to improve the surface properties. The characterisation of the samples was performed to establish a basis for the corrosion behaviour of the 3D-printed material and the effect of LSP treatment on the rate of corrosion. The samples fabricated at the moderate laser energy density of 249 J/mm3 showed the best-performing properties as the microstructures that evolved showed elevated hardness profiles, which were associated with material property improvements such as high strength and corrosion resistance. After subjecting the samples to LSP treatment, the properties of the LENS samples showed a further improvement in corrosion resistance.
Effect of laser wavelength in PLD in the orientation and thermochromic properties of VO2 (M1) on a glass substrate
(Materials Research Society, 2019-12) Masina, Bathusile N; Akande, Amos A; Mwakikunga, Bonex W
Highly oriented VO2 (M1) thin films are difficult to produce using non-crystalline substrates. For example, to produce such films on glass has required post-annealing or the use of a ZnO transparent layer. Here, we overcome this challenge and report highly oriented VO2 (M1) in the (100) plane directly on the glass substrate by pulsed laser deposition (PLD). We study the influence of the laser wavelengths (1064, 532, 355 and 266 nm) on the orientation of VO2 (M1) deposited on Corning glass. We find that the laser wavelength of 532 nm leads the most highly a-axis textured VO2 (M1) demonstrating the highest reversible metal-to-insulator at about 62 °C with a lowest hysteresis width of approximately 9°C. One of the conditions is to select the green 532 nm wavelength laser in PLD as this particular laser wavelength also produces films with highest roughness value (of more than 60 nm) when compared to other wavelengths which produce films of roughness values less than 40 nm.
Effect of LSP parameters on the corrosion and hardness properties of TI6Al4V
(2019-09) Kubjane, SM; Arthur, Nana KK; Masina, Bathusile N; Popoola, API; Pityana, Sisa L
Because of its low density, high corrosion resistance and high strength to weight ratio, titanium and its alloys are widely used in aerospace applications. As a result, the material is exposed to detrimental environment. An enhancement in surface integrity of the alloy is believed to have the potential to prevent the materials from experiencing premature failure in these aggressive environments. One of the promising surface modification techniques for improving the properties of metals is laser shock peening (LSP), which induces compressive residual stresses in the surface of layer of alloy and results in an increase in strength and fatigue life of the part. In the present study, Laser shock peening is employed to modify the microstructure, mechanical properties and corrosion behaviour of LENS-built titanium alloy components. The surface roughness, microstructural evolution, microhardness and corrosion behaviour of the LENS-built is examined before and after laser shock peening treatment. The effect of LSP overlaps on the corrosion and hardness properties of wrought titanium alloy and LENS-built were investigated. LSP treatment with 90, 95 and 99% overlapping were chosen. The mechanical behaviour of the Ti6Al4V was characterized by material hardness measurements to assess the effect of the peening process on material properties. The microstructure of the peened samples revealed a homogeneous a + ß phases. Electrochemical tests indicated that LSP improved the corrosion resistance of Ti6Al4V in sodium chloride. In addition, the hardness of Ti6Al4V increased from 375 HV before LSP to 389 HV after LSP. These results demonstrated that LSP is a promising surface modification method that can be used to improve the mechanical properties and corrosion resistance of Ti6Al4V.
Effects of energy density on the microstructure evolution of TiC/Ti6Al4V-ELI metal composite fabricated with laser metal deposition
(2022-11) Ramasobane, P; Mashinini, MP; Masina, Bathusile N
This study investigated the microstructural evolution of Ti6Al4V-ELI reinforced with TiC, fabricated via in-situ laser metal deposition technique. The 3.85% volume fraction TiC/Ti6Al4V-ELI metal composite samples were fabricated at two different energy densities (ED). It was observed that in-situ reaction resulted in various morphologies (unmelted or partially melted, chain-shaped eutectic, granular eutectic, granular primary eutectic, and dendritic primary) of TiC embedded with the beta grain boundary and the acicular alpha prime matrix. The size of dendritic structures decreases with respect to ED. Additionally, the hardness average of 457.59 ± 39.73 and 455.08 ± 18.03 HV0.3 for 96 and 102 J/mm2 ED respectively.
Effects of substrate heating on the microstructure and hardness of TiB/Ti6Al4V-ELI during laser in-situ metal deposition
(2021-12) Lekoadi, Paul M; Tlotleng, Monnamme; Masina, Bathusile N
This work investigated the influence of heating temperature (°C) on the microstructure and microhardness of TiB/Ti6Al4V-ELI composite clads that were produced via in-situ alloying using laser metal deposition technique. The samples were produced on a Ti6Al4V base plates which were heated at different temperatures (25°C, 200°C, 300°C, 400°C and 500°C) before they were characterised for microstructure and hardness. It was found that the TiB/Ti6Al4V-ELI sample that was produced on a non-pre-heated base plate was characterized by TiB particles and had the lowest hardness of 511 ± 66 HV. Base plate heating resulted in the formation of TiB whiskers that were dispersed within the titanium matrix. 200°C led to a microstructure with clusters of TiB whiskers hence it had an increased hardness of 651 ± 40 HV. A fine microstructure with homogeneous distribution of the TiB whiskers was obtained at 500°C base plate heating temperature and had hardness of 565 ± 14 HV.
Evaluation of heat treatment parameters on microstructure and hardness properties of high-speed selective laser melted Ti6Al4V
(2021-02) Lekoadi, Paul M; Tlotleng, Monnamme; Annan, K; Maledi, N; Masina, Bathusile N
This study presents the investigation on how heat treatment parameters, which are temperature, cooling method, and residence time, influence the microstructural and hardness properties of Ti6Al4V components produced on Ti6Al4V substrate using high speed selective laser melting technique. Heat treatment was performed on the produced samples before they were characterized for microstructure and hardness. The microstructure of the as-built sample contained large columnar ß-grains that were filled with martensite a’ phase and had a high hardness of 383 ± 13 HV. At 1000 C and residence time of maximum 4 h, better heat treatment parameters were seen for the selective laser melting (SLM) produced Ti6Al4V sample since an improved lamellar a + ß microstructure was obtained at this condition. This microstructure is known to have improved tensile properties.
Fast imaging of laser induced plasma emission of vanadium dioxide (VO2) target
(2013-10) Masina, Bathusile N; Lafane, S; Wu, Lorinda; Kerdja, T; Abdelli-Messaci, S; Forbes, A
The main objective of this study is to fully optimise the synthesis of vanadium oxide nanostructures using pulsed laser deposition. We will attempt to realise this by studying the mechanism of the plasma formation and expansion during the pulsed laser deposition process of vanadium oxide, since the source of the films is a laser- generated plasma composed of neutrals and ionised atoms, molecules and other species. In this poster presentation, a spatio-temporal evolution study of different species such as VI (437.85 nm), VII (326.1 nm), VIII (237.1 nm) and VO (608.56 nm) are presented and compared.
Improving the microstructure of high speed selective laser melted Ti6A14V components by varying residence time during heat treatment
(RAPDASA, 2019-11) Lekoadi, Paul M; Tlotleng, Monnamme; Maledi, N; Masina, Bathusile N
Selective laser melting (SLM) is a powder bed additive manufacturing technique that produces components layerby-layer from computer aided designs as opposed to conventional manufacturing methods. Although this manufacturing technique offers various advantages, the microstructure of the produced components exhibits an acicular martensitic a’ phase which exhibits low ductility and high hardness on the produced components. Heat treatment is known to improve the microstructure and ductility and hardness of SLM produced Ti6Al4V components. This study reports on the effect of residence time during heat treatment of Ti6Al4V samples that were built with Aeroswift 3D printing SLM machine. Samples were heat treated to a temperature of 1000°C and held for 2hrs, 4hrs, 8hrs, 10hrs and 12hrs before furnace cooling. It was found that the microstructure transformed from martensitic to lamella a+ß, then to globular a+ß as residence time was increased. Furthermore, grain growth was observed with an increase in residence time.
In-situ production of WC-Ni using a laser cladding technique
(2022-11) Skhosane, Besabakhe S; Masina, Bathusile N; Lekoadi, Paul M; Pityane, Sisa L
Metal Matrix Composite (MMC) coatings of Tungsten Carbide (WC) and Nickel (Ni) powder were produced using laser cladding process. A crack free and good metallurgically bonded WC-Ni coating of about 5mm thick produced from varying both laser energy density and percent mixture of Ni and WC. In this study, the microstructure of WC-Ni coatings were characterised using optical microscope (OM), scanning electron microscope (SEM) with EDS, while mechanical properties of the coating were studied using Vickers hardness tester and abrasion wear resistance tester. It was found that the hardness and wear resistance increase as the percentage of WC increases.
In-situ synthesis of TiC/Ti-6Al-4V-ELI composite by laser
(2021-10) Ramasobane, P; Mashinini, PM; Masina, Bathusile N
Titanium-based alloys are reported to offer up to 50% strength to weight ratio. These lands titanium-based alloys as a preferred material over steel and nickel-base super-alloys, where strength and stiffness are required. Regardless titanium-based alloys are prone to losing strength and stiffness at elevated temperature applications such as jet engines. This prompted a need for titanium matrix to be braced with a material with superior properties, such as ceramic. In-situ synthesis with laser metal deposition (LMD) of Ti-6Al-4V-ELI braced with discontinuous particulates of TiC resulted in improved hardness and microstructure. It is reported that an increase in the feed rate of TiC during the LMD process directly increases the hardness of the TiC/Ti-6Al-4V-ELI composite and refine the grain size of Ti-6Al4V-ELI. Various fabrication methods and properties of Ti-6Al-4V are well documented in the literature. This paper focuses on the effect of TiC on the microstructure and hardness of Ti-6Al-4V-ELI.

Browsing by Author "Masina, Bathusile N"

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