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On high speed machining of titanium alloys : analysis and validation

  • Authors: Sonnekus, Reino
  • Date: 2010-08-30T06:55:07Z
  • Subjects: Titanium alloys , High-speed machining
  • Type: Thesis
  • Identifier: uj:6906 , http://hdl.handle.net/10210/3418
  • Description: M.Ing. , This report documents the steps taken to gain insight into the phenomena of high speed machining (HSM) of titanium alloys. This was done by firstly studying titanium alloys and the problems associated with machining titanium alloys. An experimental set-up and procedure was developed for measuring and recording both the machining temperature and component forces. A sufficient set of experimental data was collected through extensive experimentation. The cutting temperatures and component forces in HSM of Ti-6Al-4V were examined simultaneously. The cutting speed was found to be the most influential and limiting parameter on the machining temperature and component forces. A new approach for modeling the temperatures in HSM of titanium alloys was developed. Analytical predictions of the cutting temperatures were performed and used to evaluate the influence of a variation in the process parameters on the cutting temperature. The research provides insight for future work into the phenomena of HSM of titanium alloys . The results of the analytical model were found to be representative and comparable to the experimental data. It is however expected that the deviation between the predicted and measured result may be significantly reduced by changing the experimental approach. It is recommended that a complete set of experiments be done, using a new tool insert for every cut, thus removing the effect of possible tool wear on the experimental data obtained. In addition it is recommended that the iterative solution be improved through more in depth programming, considering the change in both the thermal and mechanical materials properties with a change in temperature. Ultimately the assumptions made in order to simplify the problem addressed in this report needs to be improved upon, in order to analyze data trends and even magnitudes to a greater degree of certainty.
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An investigation on the effects of high speed machining on the surface integrity of grade 4 titanium alloy

  • Authors: Mawanga, Philip
  • Date: 2012-08-01
  • Subjects: Titanium alloys , High-speed machining , Titanium alloys - Testing
  • Type: Thesis
  • Identifier: uj:8924 , http://hdl.handle.net/10210/5394
  • Description: M.Ing. , Grade 4 titanium is a commercially pure grade titanium alloy extensively used in various industries including the chemical industry and more recently in the biomedical industry. Grade 4 has found a niche as a biomedical material for production of components such as orthopaedic and dental implants. Its physical properties such as high corrosion resistance, low thermal conductivity and high strength make it suitable for these applications. These properties also make it hard-to-machine similar to the other grades of titanium alloys and other metals such as nickel based alloys. During machining of titanium, elevated temperatures are generated at the tool-workpiece interface due to its low thermal conductivity. Its high strength is also maintained at these high temperatures. These tend to impair the cutting tool affecting its machinability. Various investigations on other grades of titanium and other hard-to-machine materials have shown that machining at high cutting speeds may improve certain aspects of their machinability. High speed machining (HSM) is used to improve productivity in the machining process and to therefore lower manufacturing costs. HSM may, however, change the surface integrity of the machined material. Surface integrity refers to the properties of the surface and sub-surface of a machined component which may be quite different from the substrate. The properties of the surface and sub-surface of a component may have a marked effect on the functional behaviour of a machined component. Fatigue life and wear are examples of properties that may be significantly influenced by a change in the surface integrity. Surface integrity may include the topography, the metallurgy and various other mechanical properties. It is evaluated by examination of surface integrity indicators. In this investigation the three main surface integrity indicators are examined. These are surface roughness, sub-surface hardness and residual stress. White layer thickness and chip morphology were also observed as results of the machining process used. The effect of HSM on the surface integrity of grade 4 is largely unknown. This investigation therefore aims to address this limitation by conducting an experimental investigation on the effect of HSM on selected surface integrity indicators for grade 4. Two forged bars of grade 4 alloy were machined using a CNC lathe at two depths of cut, 0.2mm and 1mm. Each bar was machined at varying cutting speeds ranging from 70m/min to 290m/min at intervals of approximately 20m/min. Machined samples were prepared from these cutting speeds and depths of cut. The three surface integrity indicators were then evaluated with respect to the cutting speed and depth of cut (DoC). iv Results show that a combination of intermediate cutting speeds and low DoC may have desirable effects on the surface integrity of grade 4. Highest compressive stresses were obtained when machining with these conditions. High compressive stresses are favourable in cases where the fatigue life of a material is an important factor in the functionality of a component. Subsurface hardening was noticed at 0.2mm DoC, with no subsurface softening at all cutting speeds. Surface hardness higher than the bulk hardness tends to improve the wear resistance of the machined material. Though surface roughness values for all depths of cut were below the standard fine finish of 1.6μm, roughness values of samples machined at 0.2mm DoC continued to decrease with increase in cutting speed. Low surface roughness values may also influence the improvement of fatigue life of the machined components. These machining conditions, (intermediate cutting speeds and low DoC), seem to have promoted mechanically dominated deformation during machining rather than thermal dominated deformation. Thermal dominated deformation was prominent on titanium machined at DoC of 1mm.
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A process planning framework for milling of titanium alloys

  • Authors: Dimitrov, D. , Conradie, P.J.T. , Oosthuizen, G.
  • Date: 2013
  • Subjects: Titanium alloys , Milling , High speed cutting , High performance machining
  • Type: Article
  • Identifier: uj:4949 , http://hdl.handle.net/10210/13049
  • Description: Titanium alloys are being used increasingly in new generation aircraft, creating a market for high value components. It is argued that knowledge development is the key factor for South African machining suppliers to penetrate the global aerospace supply chains. This paper discusses current results of a collaborative project aiming at systematic research towards improved and more efficient utilisation of the High Speed Cutting (HSC), and particularly the High Performance Machining (HPM) technologies for selected titanium alloys. A process planning framework for milling of titanium alloys has been developed. Using as point of departure prominent tool demands, this framework combines a tool wear map approach and cost modelling that enables process planners as well as machine operators to act towards optimised machining. In this way the targeted cost minimisation and lead time shortening could be modelled and practically achieved.
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Experimental investigation of laser beam forming of titanium and statistical analysis of the effects of parameters on curvature

  • Authors: Akinlabi, Stephen A. , Akinlabi, Esther Titilayo
  • Date: 2013
  • Subjects: Laser beam forming , Titanium alloys
  • Type: Article
  • Identifier: uj:4746 , ISSN 2078-0966 , http://hdl.handle.net/10210/11732
  • Description: Laser beam forming, a non-contact manufacturing process has become a viable manufacturing process for shaping metallic components. The capability of laser beam forming and bending demands more experimental studies to identify an optimized parameter setting and the likely parameters influencing the formed curvature. This paper investigates experimental laser beam forming of Ti6Al4V titanium alloy using a 4.4 kW Nd: YAG laser and studied the effects of the process parameters on the formed curvature. It was established that an increase in both the laser beam power and the number of scan tracks reduces the radius of curvature in the formed sheets having a more dome shape. The scan speed on the other hand, achieved the same good curvature at a slower or reduced scan speed to allow enough laser – material interaction. Furthermore, both the ANOVA and the regression analysis confirmed the repeatability of the experimental data. A simple regression model was developed based on the known active parameters to determine approximate curvatures instead of running a series of experiments.
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Towards energy management during the machining of titanium alloys

  • Authors: Oosthuizen, G. , Laubscher, R.F. , Tayisepi, N. , Mulumba, J.
  • Date: 2013
  • Subjects: Manufacturing industry - South Africa , Machining - South Africa , Titanium alloys , Energy management
  • Type: Article
  • Identifier: uj:4955 , http://hdl.handle.net/10210/13055
  • Description: The manufacturing industry needs to address challenges as regards to the machining process in the multifaceted context of sustainability. The current cost of energy and the reduction in material reserves highlights the need for machining systems to be more energy-efficient. This paper aims to provide a systematic overview of advanced approaches to manage energy and resource efficiency in cutting operations. The research experimentation focuses on the machining of a selected titanium alloy, Ti6Al4V, using carbide cutting tools. Tool wear, chip formation, cutting force and energy use were measured and analysed for selected cutting parameters. The experimental results illustrate the importance of selecting optimum cutting parameters and machining strategy. The results further help to define the boundary conditions for the various input parameters. Future research is also discussed.
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An investigation of high speed machining of selected titanium alloys : process and thermal aspects

  • Authors: Kruger, Pieter
  • Date: 2013-11-21
  • Subjects: Titanium alloys , High-speed machining , Titanium alloys - Heat treatment
  • Type: Thesis
  • Identifier: uj:7784 , http://hdl.handle.net/10210/8679
  • Description: M.Ing. (Mechanical Engineering) , High strength alloys such as titanium are widely used within applications that require specific material properties. These include high strength, high temperature as well as low weight applications. Thus a need arises to investigate the fundamental to understand the mechanics of how these materials are machined. Titanium alloys are known for the difficulties that arise during the machining thereof. Complexities arise due to its inherent material properties, the most important property being the retention of strength at high temperatures. In addition to maintaining its strength, it becomes highly chemically reactive with other materials at increased temperatures. All these factors contribute to extreme temperatures at the tool chip interface contributing to increased tool wear and shortened tool life. The aim of the research is to investigate the effect of machining on various cutting process parameters including cutting force, temperature, tool wear and surface finish for grade 2 and grade 5 titanium alloys during high speed turning. Grade 2 titanium is a commercially grade with lower mechanical properties, while Grade 5 is titanium alloy with substantially higher mechanical properties and is the most widely used titanium alloy. In addition an experimental setup was developed and verified to conduct fundamental research on the high speed machining of titanium alloys. A literature review was concluded with focus on the machining of titanium alloys. This was followed by the development of the experimental setup, measurement and compilation of data. The data was compiled into graphs and compared with the current research available. The research found that for the cuts performed, that cutting forces are independent of cooling applied and that no substantial variation was noted between the two grades. When temperatures were evaluated, dramatic drops in temperature were noted when coolant was applied. As temperatures increased, specifically during un-cooled cutting, the inserts deteriorated having an effect on the quality of the surfaces obtained. When coolant was applied, substantial temperature drops were achieved, improving tool life and directly improving surface finishes. The best surface finish was achieved for higher cutting speeds as and lower feed rates. This phenomenon was found for both grades of titanium evaluated. The largest amount of tool wear was noted for the highest cutting speeds, with increased values noted for Grade 5 in comparison with Grade 2. This phenomenon is noted for crater as well as flank wear.
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Characterizing the effect of laser power on laser beam formed titanium sheets

  • Authors: Akinlabi, Esther Titilayo
  • Date: 2014
  • Subjects: Laser beam formation , Titanium alloys
  • Type: Article
  • Identifier: uj:4751 , ISSN 978-93-81505-62-5 , http://hdl.handle.net/10210/11737
  • Description: Laser forming is a new advanced technology in manufacturing for the bending of sheet metals and the joining of metallic components in automobile, microelectronics and the aerospace industries. In the laser forming process, various factors such as the laser parameters and the material properties need to be considered in order to achieve optimum properties after laser forming. This paper reports the effects of the laser power on the resulting curvatures of the laser beam formed Titanium sheets. The laser formed samples were characterized through the microstructure and the mechanical properties. The results obtained during the microscopic evaluation of the specimen showed that the grain sizes of the formed samples increases and is proportional to the laser power employed to form the samples. It was also found that the Vickers microhardness is directly proportional to the laser power and the radius of curvature increases with a decrease in the Laser power. Hence, the grain size is also directly proportional to the Vickers microhardness of the sample
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Effect of constitutive modeling during finite element analysis of machining-induced residual stresses in Ti6Al4V

  • Authors: Oosthuizen, Gert A. , Laubscher, Rudolph F. , Styger, Gary
  • Date: 2014
  • Subjects: Residual stresses , Titanium alloys , Finite element method , Machining
  • Type: Article
  • Identifier: uj:5028 , http://hdl.handle.net/10210/13547
  • Description: Residual stress is an important surface integrity descriptor that may have a marked effect on the functional performance of machined alloy parts. This paper describes a finite element evaluation of the effect of different constitutive models on machining induced residual stresses for Ti6Al4V titanium alloy. A two dimensional orthogonal turning process is modelled and the results compared to experimental data. Residual stress is evaluated with respect to different elastic-viscoplastic constitutive models at certain cutting speeds and feeds. The general-purpose finite element code MSC Marc@ was used with comparisons with experimental data made relative to residual stress, cutting force and temperature. The magnitude and extent (depth) of the residual stress field is evaluated with regards to the different material models and compared with experimental data.
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Effect of number of laser scans on the corrosion behavior of laser formed titanium alloy

Effects of wire electrical discharge machining on fracture toughness of grade 5 titanium alloy

  • Authors: Madyira, Daniel M. , Akinlabi, Esther Titilayo
  • Date: 2014
  • Subjects: Titanium alloys , Electrical discharge machining , Fracture toughness , Compact tension
  • Type: Article
  • Identifier: uj:4752 , ISSN 2078-0958 , http://hdl.handle.net/10210/11738
  • Description: Grade 5 titanium (Ti6Al4V) is considered as the workhorse material when it comes to automotive and aerospace applications. It is widely referred to as an aerospace alloy and is relatively a new engineering material. The main attraction of this material is its high strength to weight ratio when compared to such common engineering materials such as steel and aluminum alloys. One of the major challenges in the use of this aerospace material is its machinability. Its high strength which is maintained at elevated temperatures, low thermal conductivity, low elastic modulus and high reactivity with oxygen is a perfect recipe for machining challenges. This leads to high tool wear and long production times. Such challenges are sometimes overcome by electrical discharge machining (EDM). Given that titanium is usually applied to mission critical components (gears, shafts, wing sections), it is important to understand the possible effect of wire EDM on their structural performance. One of the structural integrity indicators in such applications is fracture toughness. Fracture toughness is widely used for damage tolerance analysis of aerospace components in which critical crack sizes are computed for given loading conditions to arrive at safe inspection and maintenance intervals. It is therefore the purpose of this paper to conduct a study on the effect of wire EDM on the fracture toughness of this aerospace material. Standard test procedure using compact tension (CT) specimen is used to measure the fracture toughness. Four specimens are produced using wire EDM. This includes the pre-crack which is usually produced by fatigue cycling. Obtained results indicate a slight decrease in fracture toughness compared to that reported in literature. In addition, it can also be concluded that wire EDM can be used as an alternative to fatigue pre-cracking in fracture toughness testing of titanium alloys.
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Laser metal deposition of Ti6Al4V/Cu composite : a study of the effect of laser power on the evolving properties

  • Authors: Erinosho, Mutiu F. , Akinlabi, Esther Titilayo , Pityana, Sisa
  • Date: 2014
  • Subjects: Porosity , Laser metal deposition , Titanium alloys
  • Type: Article
  • Identifier: http://ujcontent.uj.ac.za8080/10210/375937 , uj:4740 , ISSN 978-93-81505-62-5 , http://hdl.handle.net/10210/11726
  • Description: A study of the effect of laser power was investigated over the volume of deposited composite, microstructure and microhardness. The laser power was varied between 600 and 1800 W while keeping all other parameters constant. An indication shows that the area and the volume of the deposited composites are directly proportional to the laser power employed. The volume of the deposit obtained falls between 358.6 mm3 and 1009 mm3. The microstructures were analyzed and found that the formation of the Widmanstatten structures improved the hardness of Ti6Al4V/Cu composites. The hardness values of the deposits varied between HV335 and HV490. The percentages of porosities of the samples were also presented and found to have an inverse relationship with the laser power. The results are presented and discussed.
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A numerical analysis of machining induced residual stresses of Grade 5 titanium alloy

  • Authors: Laubscher, R.F. , Styger, G. , Oosthuizen, G.A.
  • Date: 2014-06
  • Subjects: Numerical analysis , Machining , Residual stresses , Titanium alloys
  • Type: Article
  • Identifier: uj:5055 , http://hdl.handle.net/10210/13603
  • Description: Machining induced residual stresses may have a significant effect on the mechanical performance of machined parts. AdvantEdge is an advanced finite element code dedicated to the modelling of the machining process. This paper describes a comparative evaluation of modelling results obtained with AdvantEdge with experimental results obtained during turning of Grade 5 (Ti6Al4V) titanium alloy. A two dimensional orthogonal turning process is modelled and compared with experimental data. Comparisons are made relative to residual stress, cutting force and cutting temperature for various different cutting parameters including cutting speed, feed rate and cut depth.
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Characterization of aluminium and titanium carbide metal matrix composites produced via friction stir welding

  • Authors: Abegunde, Olayinka Oluwatosin
  • Date: 2015
  • Subjects: Friction stir welding , Titanium alloys
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/212716 , uj:21011
  • Description: Abstract: The Friction Stir Welding (FSW) process was invented and developed at The Welding Institute of United Kingdom in the year 1991 for solid state joining of aluminum and its alloys. Subsequently, this welding process has been used for joining other materials like magnesium, titanium and copper alloys, stainless steels and thermoplastics. In this research work, ample study was conducted on the material characterization of aluminium (Al) and titanium carbide (TiC) metal matrix composites produced via friction stir welding. Different process parameters were employed for the welding process. Rotational speeds of 1600 rpm to 2000 rpm at an interval of 200 rpm and transverse speeds of 100 to 300 mm/min at an interval of 100 mm/min were employed for the welding on an Intelligent Stir Welding for Industry and Research (I-STIR) Process development System (PDS) platform. The process parameters were carefully selected to represent low, medium and high for the rotation and the translation of the tool. The characterizations carried out include optical microscopy and the scanning electron microscopy analyses combined with Energy Dispersive Spectroscopy (SEM/EDS) techniques to investigate the particle distribution, microstructural evolution and the chemical analysis of the welded samples. Vickers microhardness tests was used to determine the hardness distribution of the welded zone and tensile testing was conducted to quantify the strength of the welded area to the base metal in order to establish the optimal process parameters. Based on the results obtained from the characterization analysis, it was found that the process parameters played a major role in the microstructural evolution. Homogenous distribution of the TiC particles was observed at high rotational speed of 2000 rpm and low transverse speed of 100 mm/min. The highest hardness value was measured at the stir zone of the weld due to the presence of the TiC reinforcement particles. The tensile strength also increased as the rotational speed increased and 92% joint efficiency was found in a sample produced at 2000 rpm and 100 mm/min. The EDS analysis revealed that Al, Ti and C made up the composition formed at the stir zone. The optimum process parameter setting was found to be at 2000 rpm and 100 mm/min and can be recommended. , M.Ing. (Mechanical Engineering Science)
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Characterising the effect of laser metal deposited Ti6Al4V/Cu composites in simulated body fluid for biomedical application

  • Authors: Erinosho, M. F. , Akinlabi, Esther Titilayo , Pityana, S.
  • Date: 2015-01-15
  • Subjects: Hank’s solution , Laser metal deposition , Surface morphologies , Titanium alloys
  • Type: Article
  • Identifier: uj:5120 , ISBN 9789384935108 , http://hdl.handle.net/10210/14078
  • Description: Ti6Al4V alloy has been known to have very excellent corrosion resistance due to the oxide layer formed on its surface. Due to this property, the alloy is found applicable for biomedical implants. Copper shows an excellent antimicrobial property and has been found to stabilize the immune system. In this study, laser metal deposition of Ti6Al4V powder and Cu powder on Ti6Al4V substrates were conducted by varying the laser power between 600 W and 1800 W while the scanning speed, the powder flow rate and the gas flow rate were kept constant. The surface behaviour and the morphologies of the composites were evaluated under the microscope and the SEM after soaking for 4 hours, 5 days and 2 weeks respectively. The simulated body fluid (hank’s solution) was maintained at normal body temperature of about 37±1oC. The surfaces showed fracture topography with porous bone-like structures and some trivial pitting were observed.
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An investigation on the effect of high speed machining on the osseointegration performance of grade 4 titanium alloy

  • Authors: Reddy, Andrish
  • Date: 2015-02-12
  • Subjects: Titanium alloys , Titanium alloys - Testing , High-speed machining
  • Type: Thesis
  • Identifier: uj:13323 , http://hdl.handle.net/10210/13339
  • Description: M.Eng. (Mechanical Engineering) , High speed machining (HSM) has the potential to greatly increase productivity and to lower manufacturing costs if workpiece surface integrity can be controlled. The surface fmish of a biomaterial is vitally important for proper implant functioning, and is the focus of this study. Grade 4 titanium was turned on a lathe with cutting speeds increasing from the conventional to the high speed range. The surface finish was assessed using profilometry, atomic force microscopy, and contact angle measurement. The ability of the material to bond directly with bone was predicted by cell adhesion studies. Results indicate that there is a general relationship between cutting speed, surface roughness, contact angle, and cell adhesion. Turning grade 4 titanium at cutting speeds between 150m/min and 200m/min may provide an optimal surface for osseointegration.
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Laser metal deposition of functionally graded Ti6Al4V/TiC

  • Authors: Mahamood, R. M. , Akinlabi, Esther Titilayo
  • Date: 2015-06-20
  • Subjects: Functionally graded materials , Laser metal deposition , Titanium alloys
  • Type: Article
  • Identifier: uj:5119 , ISSN 02641275 , http://hdl.handle.net/10210/14077
  • Description: Functionally graded materials (FGMs) are advanced materials with improved properties that enable them to withstand severe working environment which the traditional composite materials cannot withstand. FGM found their applications in several areas which include: military,medicine and aerospace. Various manufacturing processes are used to produce functionally graded materials that include: powder metallurgy, physical vapour deposition, chemical vapour deposition process and laser metal deposition process. Laser metal deposition (LMD) process is an additive manufacturing process that can be used to produce functionally graded material directly from the three dimensional (3D) computer aided design (CAD) model of the part in one single process. LMD process is a fairly new manufacturing process and a highly non-linear process. The process parameters are of great importance in LMD process and they need to be optimized for the required application. In this study, functionally graded titanium alloy composite was produced using optimized process parameters for each material combination as obtained through a model that was developed in an initial study and the FGM was characterized throughmetallurgical, mechanical and tribological studies. The results showthat the produced FGM has improved properties when compared to those produced at constant processing parameters for all material combinations.
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Effect of laser power on the microstructure and microhardness property of hybrid fabricated Ti6Al4V based metal matrix composite

  • Authors: Ochonogor, O. F. , Akinlabi, Esther Titilayo , Nyembwe, Didier
  • Date: 2016
  • Subjects: Titanium alloys , Laser treatment
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/93318 , uj:20333 , Citation: Ochonogor, O.F., Akinlabi, E.T. & Nyembwe, D. 2016. Effect of laser power on the microstructure and microhardness property of hybrid fabricated Ti6Al4V based metal matrix composite.
  • Description: Abstract: Several surface coatings on Ti-6Al-4V alloy using laser treatment technique have been investigated in this paper. A hybrid Ti-6Al-4V based metal matrix composites system was also successfully fabricated. This was possible using three hoper system which contained 3.8 vol. % of Ti-6Al-4V and a small amount 0.1 B4C and 0.1 BN respectively. Two different laser powers “2000 W and 1400 W with scanning speed of 1.0 were employed. The idea of these powder coatings and reason for investigating the different Laser power is to evaluate the influence of laser power on the surface morphology and hardness property of Ti-6Al-4V/B4C/BN alloy systems. The hardness result of experimental showed a general improvement. The hardness revealed that the Ti-6Al- 4V/B4C/BN system fabricated at 2000W showed a hardness improvement as high as 640.4 HVO.5 compared to the as receive Ti-6Al-4V substrate Hardness value of about 357.3 HVO.5 and that of 1400W recorded a hardness value of 886 HVO.5. The percentage increase from the as received Ti-6Al-4V alloy was 147.9% and 79.2% respectively. Problems to be solved and the prospective application of laser modification of the hybrid titanium alloy formed were also highlighted.
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Effect of powder density variation on premixed Ti-6Al-4V and Cu composites during laser metal deposition

Effect of rapid cooling of high temperature laser fabricated Ti/B4C/BN coating on Ti-6AL-4V alloy

  • Authors: Franklin, Ochonogor O. , Akinlabi, Esther Titilayo , Nyembwe, Kasongo D. , Pityana, Sisa , Shongwe, Mxolisi Brendon
  • Date: 2016
  • Subjects: Heat treatment , Titanium alloys
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/214859 , uj:21334 , Citation: Franklin, O.O. et al. 2016. Effect of rapid cooling of high temperature laser fabricated Ti/B4C/BN coating on Ti-6AL-4V alloy.
  • Description: Abstract: A hybrid Ti-6Al-4V based metal matrix composites characterized of martensitic structure was formed using three hoper system. Different volume percentages used were as follows: 3.0 vol. % of Ti-6Al-4V, 3.2 vol. % of Ti-6Al-4V and 3.4 vol. % of Ti-6Al-4V respectively while an equal amount of BN and B4C mixed with the Ti-6Al-4V powder particle was fed through the hoper systems at a constant laser power 2000 W and scanning speed of 1.0 m/s. The influence of rapid cooling and varied powder particle at constant coating temperature on the surface morphology and hardness property of Ti-6Al- 4V/B4C/BN alloy systems was however investigated. The hardness result of experimental showed a general improvement. Further result showed that the Ti-6Al- 4V/B4C/BN system fabricated at 3.0 Ti Vol. percent had a hardness improvement as high as 986.9 HVO.5 compared to the as receive Ti-6Al-4V substrate Hardness value of about 357.3 HVO.5. 3.2 Ti Vol. percent systems recorded a hardness value of 723.4 HVO.5 and 3.2 Ti Vol. percent system recorded a hardness value of 609.6 HVO.5. Optical microscope (OM) Scanning electron microscope (SEM) was also carried out for microstructural evaluation and Energy Dispersive Spectroscopy (EDS) to confirm the elemental composition of coating when necessary.
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Laser additive manufacturing technology for crack repairs in titanium alloy components

  • Authors: Marazani, Tawanda
  • Date: 2016
  • Subjects: Laser welding , Welded joints - Cracking , Manufacturing processes , Titanium alloys
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://ujcontent.uj.ac.za8080/10210/366385 , http://hdl.handle.net/10210/213019 , uj:21067
  • Description: Abstract: Laser additive technology (LAT) uses a laser beam which locally melts the target material surface. The technology has been widely used for high value and critical components mainly in the aerospace and the biomedical industries. Due to its favourable properties, titanium has become a workhorse metal, particularly the grade 5 titanium alloy (Ti-6Al-4V). Recent years have seen increased research and development studies on the application of the laser additive technology in the production of Ti-6Al-4V components. These ranged from free form fabrication, materials processing, manufacturing, maintenance and repairs. Attempts to use the laser additive technology for the repair of cracks in Ti alloy components have been recently reported where V-grooves have been recommended. Further attempts to use narrow U-grooves for crack repairs were not successful and hence not widely adopted. There is limited published work on the use of narrow rectangular grooves for crack repairs in Ti-6Al-4V.There is therefore a need to further investigate the potential repairing of U-cracks using LAT. This research work established through experimental design, mechanical and metallographic characterization, a process that was used for the laser additive repair of cracks in Ti-6Al-4V components. The preliminary repairs were made without laser re-melting. They were analysed for defects using the optical microscopy (OM) and their macrographs revealed lack of sidewall fusion, lack of interlayer fusion, lack of intralayer fusion, unmelted powder and porosity. The matrix used for the preliminary repairs was then optimised using the observations made during the preliminary phase. It was from this preliminary phase optimization that the final experimental matrix of the research was developed. Controlled laser re-melting, reduction of the spot size diameter and lowering of the scanning speed were introduced as main process parameters of the optimized matrix. The optimized repairs were further characterized using the optical microscopy (OM) and the scanning electron microscopy (SEM). The optimized repairs were observed to have very limited defects. The energy dispersive spectroscopy (EDS) analyses revealed that the deposits were dominated by Ti, Al and V which were the main compositions of the material. The Vickers microhardness tests, microhardness-tensile strength correlations and the Charpy impact tests obtained results confirmed mechanically sound repairs with good evolving microstructural properties... , M.Ing. (Mechanical Engineering)
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