Monnamme Tlotleng | Council for Scientific and Industrial Research (CSIR) (original) (raw)

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Papers by Monnamme Tlotleng

Materials Science and Engineering: C, 2014

Hydroxyapatite (HAP) coatings on bioinert metals such as Ti-6Al-4V are necessary for biomedical a... more Hydroxyapatite (HAP) coatings on bioinert metals such as Ti-6Al-4V are necessary for biomedical applications. Together, HAP and Ti-6Al-4V are biocompatible and bioactive. The challenges of depositing HAP on Ti-6Al-4V with traditional thermal spraying techniques are well founded. In this paper, HAP was coated on Ti-6Al-4V using direct laser melting (DLM) process. This process, unlike the traditional coating processes, is able to achieve coatings with good metallurgical bonding and little dilution. The microstructural and mechanical properties, chemical composition and bio-activities of the produced coatings were studied with optical microscopy, scanning electron microscope equipped with energy dispersive Xray spectroscopy, and Vickers hardness machine, and by immersion test in Hank's solution.

Industries such as the automotive, marine, power generation, petrochemical and mining experience ... more Industries such as the automotive, marine, power generation, petrochemical and mining experience problems which results in huge financial constraints due to damaged engineering components. Due to the exposure of materials for various components to aggressive corrosive, contaminating and erosive environments which may be further aggravated by environmental degradation, coatings must generally be used to prolong the life of the parts. Laser Assisted Cold Spray (LACS) is a relatively new deposition process in the laser materials processing field which is employed to produce surface modification of engineering components for enhanced functionality. LACS can be classified as a hybrid coating technique which combines the use of a laser to soften the powder along with the spraying mechanism to deposit powder particles at accelerated rates via a high temperature – high pressure gas onto a metal substrate. The particles then impact the substrate and adhere due to localized conditions to form...

High-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications IV, 2015

ABSTRACT

Research Advancements, 2014

Metal surface amending and modifications using metallurgical processes are desirable and conseque... more Metal surface amending and modifications using metallurgical processes are desirable and consequently are profound in the literature. This is because for whatever application, different challenges arise which require further in-depth knowledge and solutions to these problems.

Journal of Alloys and Compounds, 2011

Production of bulk Al-TiB 2 nanocomposite from mechanically alloyed powder was studied. Al-20 wt.... more Production of bulk Al-TiB 2 nanocomposite from mechanically alloyed powder was studied. Al-20 wt.% TiB 2 metal matrix nanocomposite powder was obtained by mechanical alloying (MA) of pure Ti, B and Al powder mixture. A double step process was used to prevent the formation of undesirable phases like Al 3 Ti intermetallic compound, which has been described in our previous papers. The resultant powder was consolidated by spark plasma sintering (SPS) followed up by hot extrusion. The structural characteristics of powder particles and sintered samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness measurements were conducted on the cross section of powder particles and sintered sample and the tensile behavior of extruded samples was evaluated. The results showed that the prepared Al-20 wt.% TiB 2 nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20 wt.% TiB 2 showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively, which are much higher than those reported for similar composites made by other processes.

$Research paper thumbnail of Distribution of selected trace elements in density fractionated Waterberg coals from South Africa$

International Journal of Coal Geology, 2012

The Waterberg Coalfield, located in the Limpopo Province (north-western area) of South Africa, co... more The Waterberg Coalfield, located in the Limpopo Province (north-western area) of South Africa, contains a significant proportion of the South African coal resource. This Permian coalfield typically contains high vitrinite, high ash coals in the Kungurian Grootegeluk Formation, and high inertinite, low ash coals in the Artinskian Vryheid Formation. Four run-of-mine coals and density fractioned samples were analysed to determine their trace element content. The concentrations of most trace elements in the run-of-mine coals exceed the global averages and certain global ranges, and generally exceed values reported for other South African coalfields. Specifically, Hg concentrations are high to very high in all the coals (up to 2.43 ppm in a sample from the Vryheid Formation), Cd and Se concentrations are comparable to or lower than global averages, and As is very low in the Vryheid Formation (1.57 ppm). A sample from the Grootegeluk Formation is enriched in siderophile elements, and a sample from the Vryheid Formation is depleted in chalcophile elements. Studies of the density fractionated samples indicate that Cd exhibits an organic affinity in the Grootegeluk Formation samples, and possibly a pyritic (or sulphide) affinity in the Vryheid Formation sample. Selenium has a greater affinity for the middle, clay-rich density fractions in all samples. Arsenic reports to the mineral-rich sink fractions, specifically the fractions enriched in pyrite. Mercury reports to both the float and sink fractions, indicating an organic and inorganic affinity in these coals, although there is more enrichment in the sink fractions in the Grootegeluk Formation samples, and a definite organic correlation in the Vryheid Formation sample.

Materials Science and Engineering C, Jul 8, 2014

Hydroxyapatite (HAP) coatings on bioinert metals such as Ti-6Al-4V are necessary for biomedical ... more Hydroxyapatite (HAP) coatings on bioinert metals such as Ti-6Al-4V are necessary for
biomedical applications. Together, HAP and Ti-6Al-4V are biocompatible and bioactive. The
challenges of depositing HAP on Ti-6Al-4V with traditional thermal spraying techniques are
well founded. In this paper, HAP was coated on Ti-6Al-4V using direct laser melting (DLM)
process. This process, unlike the traditional coating processes, is able to achieve coatings
with good metallurgical bonding and little dilution. The microstructural and mechanical
properties, chemical composition and bio-activities of the produced coatings were studied
with optical microscopy, scanning electron microscope equipped with energy dispersive Xray
spectroscopy, and Vickers hardness machine, and by immersion test in Hank’s solution.
The results showed that the choice of the laser power has much influence on the evolving
microstructure, the mechanical properties and the retainment of HAP on the surface of the
coating. Also, the choice of laser power of 750 W led to no dilution. The microhardness
results inferred a strong intermetallic-ceramic interfacial bonding; which meant that the 750
W coating could survive long in service. Also, the coating was softer at the surface and
stronger in the heat affected zones. Hence, this process parameter setting can be considered as
an optimal setting. The soak tests revealed that the surface of the coating had unmelted
crystals of HAP. The CaP ratio conducted on the soaked coating was 2.00 which
corresponded to tetra calcium phosphate. This coating seems attractive for metallic implants
applications.

Surface treatment is one of the most costly processes for treating metallic components against co... more Surface treatment is one of the most costly processes for treating metallic components against corrosion. Laser-assisted cold spray (LACS) has an opportunity to decrease those costs particularly in transportation systems, chemical industries, and renewable energy systems. This article highlights some of those potential applications. In the LACS process, a laser beam irradiates the substrate and the particles, thereby softening both of them. Consequently, the particles deform upon impact at the substrate and build up a coating. To circumvent the processing problems associated with cold-spray (CS) deposition of low-temperature, corrosion-resistant Al-12 wt.%Si coatings, a preliminary investigation detailing the effect of laser power on its LACS deposition mechanism and microstructural properties is presented. The deposition efficiency, the microstructure, and the microhardness of the LACSdeposited coatings produced by a 4.4-kW Nd:YAG laser system were evaluated. The outcome of this study shows that pore-and crack-free Al-12 wt.%Si coatings were deposited via softening by laser irradiation and adiabatic shearing phenomena at an optimum laser power of 2.5 kW.