Browsing by Author "Tlotleng, Monnamme"
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Item Application of laser assisted cold spraying process for metal deposition(IGI Global, 2014-02) Tlotleng, Monnamme; Akinlabi, ET; Shukla, M; Pityana, Sisa LLaser assisted cold spraying (LACS) process is a hybrid technique that uses laser and cold spray to deposit solid powders on metal substrates. For bonding to occur, the particle velocities must be supersonic which are achieved by entraining the powder in a highly compressed Nitrogen gas at about 30 bar which is passed through de Laval supersonic nozzle. LACS can be referred to as a surface engineering technique and is desirable in rapid prototyping and manufacturing; particularly for biomedical applications. Current world research revealed that the capability of the LACS regarding the enhancement of surface properties of coating titanium alloys with hydroxyapatite will be essential for fabricating scaffolds for bone implants using laser engineered net shaping (LENS) technique. This chapter reports the success of using LACS to deposit composite powders of titanium and hydroxyapatite on Ti-6Al-4V substrate. The obtained X-ray diffraction (XRD) and optical microscopy results for LACS compare well with the results obtained for traditional thermal spray and cold spray techniques. Also, the XRD results were found to be similar to the precursor powders. It was found that the resulting coats did not contain new material phases and the coatings were continuous.Item Assessing the nanomechanical, wear and thermal stability of Ti-Al-Si-V alloys produced via laser engineered net shaping (LENS) in-situ alloying(2024-12) Raji, SA; Popoola, API; Pityana, Sisa L; Tlotleng, MonnammeTitanium aluminide (TiAl) intermetallic alloys are highly recognized because of their lightweight qualities and are particularly useful for replacing heavier Nickel-based (Ni-based) superalloys in high- temperature components. This study fossed on the investigation of the nanomechanical, wear, and thermal stability of intermetallic Ti-Al-Si-V alloys fabricated by in situ alloying with elemental metal powders using the laser engineered net shaping (LENS) technology. The impact of Vanadium (V) feed rate was examined both before and during the annealing heat treatment, which involved 60mins at temperatures of 1200 and 1400°C, and furnace cooling (FC) conditions. After heat treatment (1200°C and 1400°C), it was discovered that V addition enhances the Ti-Al-Si-V alloy's nanomechanical properties. According to the nanoindentation results, the mechanical characteristics of the heat-treated samples were typically better than those of the as-deposited alloy and were equivalent to the qualities of commercially available TiAl alloys. The alloy that was heat-treated at a temperature of 1200°C exhibited better tribological and thermal stability. Lastly, the as-deposited sample performed better in terms of tribological and thermal stability aspects than the sample that was heat-treated at 1400°C.Item Bioceramic hydroxyapatite coating fabricated on TI-6Al-4V using Nd:YAG Laser(BA Crawford Specialised Publications, 2014-11) Tlotleng, Monnamme; Akinlabi, E; Shukla, M; Pityana, Sisa L; Mathebula, T; Chauke, LevyA method of synthesising a biocompatible HAP coating is presented. In the current study, Nd:YAG laser was used to directly melt pre-place HAP powder beds on Ti-6Al-4V. The processing parameters used were 750 W laser power, 5 mm/s scanning speed and 27° inclined beam plane. The coating was studied under white light and scanning electron microscope where it was possible to characterise the microstructures. The produced coating was characterised of mixed morphologies of HAP, short and elongated titanium needles at the surface while in the middle of the coating dendrite trunks without arms were observed. This observation is related to the heat inputs, dilution and melting of the substrate and powder during processing. The absence of the arms growing from the trunks indicated low heat inputs. In addition, the microstructure of the HAP after soaking in Hanks’ solution indicated octagonal and hexagonal crystals of HAP. The hardness values indicated good metallurgical bonding at the interface. In conclusion, this study was successful in fabricating a desirable coating of HAP on Ti-6Al-4V for biomedical applications. This work highlights that even though laser power and scanning speed are predominantly influential parameter settings, it is also necessary to consider the angle at which the laser beam is scanned across the material.Item Characteristics of laser In-situ alloyed titanium aluminides coatings(Elsevier, 2017-01) Tlotleng, Monnamme; Masina, Bathusile N; Pityana, Sisa LThe 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).Item Commissioning of laser assisted cold spraying technology(2012-10) Tlotleng, Monnamme; Olakanmi, E; Pityana, Sisa L; Shukla, M; Akinlabi, E; Burger, H; Meacock, C; Doyoyo, MThis study demonstrates the potential of a newly designed, assembled and commissioned laser assisted cold spraying (LACS) technology at the National Laser Centre, Pretoria, South Africa, to deposit Al-12wt%Si coatings on stainless steel substrate for low temperature corrosion application. The effects of laser power on the microstructure and thickness of LACS deposited Al-12wt%Si coatings on stainless steel substrate are also presented.Item A comparative study on laser processing of commercially available titanium aluminide (TI-48AL-2CR-2NB) and in-situ alloying of titanium aluminide(http://www.rapdasa.org, 2017-11) Hoosain, Shaik E; Pityana, Sisa L; Tlotleng, Monnamme; Legopeng, TTitanium aluminides (TiAl) are acknowledged as promising high temperature structural materials due to their high melting point, high strength to density, high elastic modulus and high creep strength. Due to their low ductility, it is difficult to machine post manufacturing with conventional manufacturing techniques. TiAl components have been successfully produced using the cast methods, but prove to be very expensive and time consuming. In situ alloying, using laser processing, is a potential method of manufacture of these alloys; as elemental powders can be fed separately from different powder feeders and the feed rate can be controlled, independently, to control the composition and resulting microstructure.Item Deposition mechanism and microstructure of laser-assisted cold-sprayed (LACS) Al-12 wt.%Si coatings: effects of laser power(Springer, 2013-06) Olakanmi, EO; Tlotleng, Monnamme; Meacock, C; Pityana, Sisa L; Doyoyo, MSurface 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.Item 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 NThis 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.Item 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, MonnammeThe 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.Item Effect of laser scanning speed on surface properties of Ti-Si laser clad intermetallic coatings fabricated on Ti-6Al-4V alloy(Inderscience Enterprises Ltd., 2018) Phala, MF; Popoola, API; Tlotleng, Monnamme; Pityana, Sisa LA binary Ti-Si (1 : 1) alloy coating was fabricated on Ti-6Al-4V alloy using laser cladding technique where Neodymium yttrium aluminium garnet laser was utilised. Micro-atomised powders of Ti and Si were used for deposition of multi-track clad coatings utilising power of 1.5 kW and a varied speed of 1.2 m/min, 1.6 m/min and 2.0 m/min. Scanning electron microscope coupled with energy dispersive spectrometer was used for microstructural characterisation and elemental analysis while a digital light microscope was used for optical imaging and coating thickness measurements. Phase identification was conducted using X-ray diffraction analyser and transverse microhardness evaluated at 100 gf for 10 s dwell time was achieved with the use of a Vickers hardness machine. The laser fabricated coatings were found to exhibit a decrease in grain size with an increase in the laser scanning speed. The microstructure of the coatings ranged from irregular refined grains, faceted grains and lamellar eutectic network of TiSS + Ti5Si3. The hardness of the coatings exhibited Ti, Si, TiS2 and Ti5Si3 phases averaged a 247.4% increase with maximum hardness recorded at 1.2 m/min scanning speed.Item Effects of A1 and heat treatment on the microstructure and hardness of Ti-A1 synthesized via in situ melting using LENS(MDPI, 2019-05) Tlotleng, MonnammeProducing alloys via in-situ laser alloying approach is becoming very easy and a topical issue in the field of laser additive manufacturing. Several studies have emerged, accompanied by a statement by Gasper et al. (2017), who reported the economic benefits and cost savings that can be related to 3D printing of the additive manufacturing (AM) structure using the said in situ synthesis approach. They studied the laser in situ reactive synthesis of producing titanium aluminide (Ti–Al) from elemental powders using the laser materials deposition (LMD) process. This paper highlights how the functional grade Ti–Al alloys can be produced in a single flight using the 850-R Optomec Laser Engineering Net Shaping (LENS) system. The effects of the Al content in the as-built and heat-treated samples were investigated. The as-built samples were cracked, inhomogeneous, and had visible inter-layer boundaries due to the segregation of the alloying elements and different heat profiles that are typically experienced during 3D printing. These characteristics led to wavy hardness profiles. Heat-treated samples were the least hard when compared to the as-built samples and had a homogenized microstructure. Samples with a duplex microstructure were, in particular, the least hard, indicating that they would have better ductility than others. The outcomes of this study show that a structure with different composition can be fabricated with the LENS system. This would lead to adaptive structures being used, especially in the high temperature applications where a structure would have to withstand low and high temperatures during use.Item Effects of heat-treatment on the microstructure of TiAl-Nb produced with laser metal deposition technique(MS&T17, 2017-10) Tlotleng, Monnamme; Lengopeng, Thabo; Seerane, Mandy N; Pityana, Sisa LTi and its intermetallic alloys are light-weight and have good creep properties. Materials of this nature are desired for the manufacturing of parts for the aerospace, automotive and power plants. Titanium aluminides, in particular, are preferred due to their lightness and excellent creep properties when compared to nickel super-alloys. This paper looked into the production of titanium aluminide microstructures, the so-called ordered a2-Ti3Al-Nb, making use of the in-situ laser metal alloying additive manufacturing approach, and the impact of heat treatment on microstructural evolution and hardness measurements. Ti-33Al-8Nb alloy was produced by melting the elemental powders in a laser melt-pool. The resulting microstructure was characterised for composition and hardness measurements before and after heat treatment. The As-produced sample was dense and had lamella with the observed grains. Micro-hardness of 5550.5 was reported. Heat treatment at 1200°C, as oppose to other heating profiles, resulted in a homogeneous structure with refined lamella observed inside the preserved grain structures. Contrary, non-homogeneous structure with coarsened lamella inside elongated grains was observed at 1400°C. Micro-hardness of 4520.5 was reported. These results are summarised in Figure 4.Item Effects of laser power during laser assisted cold spraying of Al-12wt%Si on stainless steel(2012-10) Tlotleng, Monnamme; Olakanmi, E; Pityana, Sisa L; Shukla, M; Akinlabi, EThis study seeks to demonstrate Laser Assisted Cold Spraying (LACS) by depositing Al-12wt%Si on stainless steel substrate. LACS is a newly designed, assembled and commissioned technology in the CSIR, laser materials processing laboratories. The basis on which Al-12wt%Si powder is used are validated by the idea that this powder was available, cheap and its spherical nature is suitable to be used with technology. Also, this study wanted to demonstrate that any powder can be deposited on substrate using cheap gases like nitrogen, under no controlled environment , without pre-heating the gas. In addition, sufficient power used to soften the substrate will lead to efficient coatings.Item The effects of LENS process parameters on the behaviour of 17-4 PH stainless steel(Springer, 2020-02) Mathoho, Ipfi; Akinlabi, ET; Arthur, Nana KK; Tlotleng, Monnamme; Makoana, Nkutwane W17-4 PH stainless steel has proven to be one of the workhorse materials in industries such as aerospace, chemical, and energy. The attraction of this alloy to the aforementioned industries is derived from the fact that 17-4 PH stainless steel possesses a combination of excellent mechanical properties and corrosion resistance. Manufacturing of 17-4 PH stainless steel through 3D printing will further inspire confidence in the aforementioned industries. The current study investigated the effects of LENS process parameters on porosity, microstructure, and microhardnesss. The scanning speed and powder feed rate were varied at 7.62 mm/s-12.7 mm/s and 4.70 g/min-5.98 g/min rpm, respectively, while laser power was kept constant at 300 W. The optimum scanning for both 4.70 g/min and 5.98 g/min was 10. 16 mm/s and 12.7 mm/s, respectively. The current study deduced that varying both scanning speed and powder feed rate had an impact on both the microstructure and microhardnessItem Effects of niobium (Nb) on mechanical properties of laser coated Nitinol (NiTi) used for surface modification of Ti6Al4V alloy(Cambridge University Press, 2020-03) Skhosane, Besabakhe S; Tlotleng, Monnamme; Pityana, Sisa LLaser surface treatment is widely used as an engineering technique due to its special characteristics and several advantages over other surface modification techniques. In the present study, elemental mechanically pre-alloyed powder consisting of Niobium, Titanium and Nickel was deposited onto a grade 5 Titanium alloy substrates to form a high wear resistance coating. This was such that the surface mechanical properties of the base metal can be improved. The fabricated samples were characterised using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Differential Scanning Calorimeter (DSC), micro hardness tester and wear machine. The deposited coatings were well bonded and consisted of various phases. Hardness was seen decrease with increase in Nb content while wear resistance increasing with increase in niobium content.Item 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 NThis 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.Item Electrochemical and tribological performance of Ti–Al with xNb addition synthesized via laser In situ alloying(2024-01) Kanyane, LR; Raji, SA; Tlotleng, MonnammeAdditive manufacturing is a growing technique of producing 3D parts directly using metal powders or wires melted with a high-powered intensity beam or laser. It is still a challenging process as to how laser processing parameters such as gas flow rate and powder flow rate can profitably be adopted to significantly produce Ti–Al-based materials from elemental powders to synthesize alloys that are defect-free and have good mechanical properties. The density of titanium aluminide (Ti–Al) intermetallic alloys makes it gain lots of interests due to its potential ability to substitute nickel-based superalloys in gas turbine engines. This work aims to investigate the effects of Niobium (Nb) additions on Ti–Al–xNb ternary alloys created via the use of 3D printing technology, specifically looking at microstructural evolution, microhardness, electrochemical behavior, and tribological properties. Ti–Al–Nb alloy was synthesized at scan speed of 26 in/min and laser power of 450 W. The structural morphology of the alloys produced was investigated using scanning electron microscopy equipped with energy dispersive spectroscopy and the electrochemical studies of the in situ alloyed Ti–Al–xNb were studied using potentiodynamic techniques. Using an Emco microhardness tester, the microhardness characteristics of the produced TiAl–xNb alloys were examined. From the results obtained, it was observed that the microstructure showed not much substantial cracking or crack initiation. The micrographs are evident of refined microstructure associated to increase in Nb feed rate with α-Ti3Al, γ-TiAl and precipitates of β-TiAl phases as the distinctively identified in the microstructure. The highest recorded microhardness value of 679.1 HV0.5 was achieved at Nb feed of 0.5 rpm and gas carrier of 2 L/min. The fabricated Ti–Al–Nb alloys showed good corrosion resistance behavior in HCl and appreciable wear characteristics with coefficient of friction of 0.412, 0.401, and 0.414 µ at B1, B3, and B5, respectively.Item 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 NThis 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.Item Evaluation of microstructure and micro-hardness of 410L SS coatings fabricated using laser assisted cold spraying: process development(RAPDASA, 2014-11) Mathebula, TE; Tlotleng, Monnamme; Malabi, Khorommbi P; Pityana, Sisa L; Camagu, SAutomotive, marine, power generation, petrochemical and mining industries experience problems which results in huge financial constraints due to damage of the engineering components. Sometimes the components are exposed to aggressive, corrosive, contaminating and erosive environments which accelerate the degradation of these components. Surface coatings are generally used to protect and prolong the lifetime of the parts. Laser Assisted Cold Spray (LACS) is a relatively new surface coating process which can be used to protect surfaces of engineering components against these aggressive environments. LACS is a hybrid process that combines the supersonic powder stream with laser heating of the deposition zone. In this process, the deposited particles and the substrate are not melted by the laser beam, but heated to just below the melting. Since no melting is involved, it is referred to “Laser Assisted Cold Spraying”. LACS technique is an emerging mainstream process; which means there are gaps in the knowledge base relating to LACS-dependent applications. This paper will focus on the microstructural evolution, mechanical deformation, the correlation between functional properties and process parameters necessary for the development of required LACS coatings. This paper will provide the basis on which research will follow-on-research that will lead to the development of high-productivity LACS coatings for identified industrial applications. The investigation of the effect of varying experimental parameters such as laser power, laser travel speed and powder feed rate on coating deposition efficiency, microstructure evolution and micro-hardness of the depositedItem Evaluation of single tracks of 17-4PH steel manufactured at different power densities and scanning speeds by selective laser melting(SUNJOurnals, 2016-11) Moller, Hein; Burger, Herman; Tlotleng, Monnamme; Yadroitsev, I; Makoana, Nkutwane WIn Selective Laser Melting, the initial units produced are single tracks that overlap to create a single layer; from the sequence of layers, a 3D object is manufactured. The properties of the parts produced by SLM depend heavily on the properties of each single track and each layer formed by these tracks. This study evaluates the effect of processing parameters on the geometrical characteristics of single tracks manufactured from 17-4PH stainless steel powder. A single-mode continuous-wave ytterbium fibre laser was used to manufacture single tracks at laser powers in the range of 100-300 W with a constant spot size of ~80µm. The single tracks produced were subjected to standard metallographic preparation techniques for further analysis with an optical microscope. Deep molten pool shapes were observed at low scan speeds, while shallow molten pool shapes were observed at high scan speeds. At higher laser power densities, under-cutting and humping effects were also observed. The dimensions of single tracks processed without powder generally decrease with increasing scan speed at constant laser power. However, the geometrical features of the single tracks processed with powder revealed pronounced irregularities believed to be caused by non-homogeneity in the deposited powder layer.