Thermal diffusivity behaviour of multi-walled carbon nanotube reinforced Ti6Al4V metal matrix composites

Abstract: This study investigated the thermal diffusivity behaviours of spark plasma sintered (SPS) multi-walled carbon nanotubes (MWCNTs) reinforced Ti6Al4V composites containing 0, 1, 2 and 3 wt. % of the reinforcement respectively, over a range of 50 – 300 °C. The MWCNTs were dispersed into the Ti6Al4V matrices by high-energy ball milling (HEBM) technique and the milled composite powders were consolidated by SPS under a vacuum atmosphere. The sintering conditions employed were heating rate (100 °C/min), holding time at temperature (5 min), sintering temperature (850 °C) and applied pressure of 50 MPa. The relative densities of the composite discs were measured according to Archimedes’ principle while the thermal diffusivities of as-sectioned composite samples were measured using the Laser Flash equipment. Relative densities of the synthesized nanocomposites deteriorated with increase in the weight fraction of MWCNTs added to Ti6Al4V. The thermal diffusivities of the composites containing 1 and 2 wt. % MWCNTs improved with increase in temperature and weight fraction of MWCNTs contents. A reverse trend was observed in the composite containing 3 wt. % MWCNTs, as the measured thermal diffusivities continued to drop with increase in temperature. Although this composite exhibited the best thermal diffusivities compared to the other composites up to 200 °C, a significant drop in thermal diffusivity was recorded between 250 and 300 °C respectively with the values lower than that of the unreinforced Ti6Al4V alloy. However, the thermal diffusivities of MWCNTs/Ti6Al4V composites were generally not dependent on their densification as the composites with higher weight fractions of the reinforcement had higher thermal diffusivities in spite of their lower relative densities

Development of MgAl2O4 grain refiner in Al in-situ composite through H3BO3 addition

Abstract : In the present work, a novel approach has been made for synthesis of in-situ Magnesium Aluminate (MgAl2O4) particles in the Al-4Mg alloy by Boric Acid (H3BO3) precursor addition (1 wt %, 1.5 wt % and 2 wt %) during the casting process. The developed composite has been investigated for its microstructural characteristics and corrosion performance. Scanning Electron Microscopy and Energy Dispersive Spectroscopy examination revealed the formation of MgAl2O4 particles in the composite. Potentiodynamic polarization corrosion experiments were performed on the Al-4Mg/H3BO3 composite specimens (1 wt %, 1.5 wt % and 2 wt %) in three different medium (3.5 % Sodium Chloride-NaCl, 1 M Sulphuric Acid-H2SO4 and 1 M Hydrochloric Acid-HCl). Corrosion results showed that Al-4Mg/1.5 wt % H3BO3 composite specimen exhibited better corrosion resistance in 3.5 % NaCl, 1 M H2SO4 and 1 M HCl medium due to the significant grain refinement produced by MgAl2O4 particles. The developed composite with better corrosion properties can be utilized for marine and naval application

Effects of Mo content on the microstructural and mechanical properties of as-cast Ti-Mo alloys

Abstract : The effects of Mo content on the mechanical and microstructural properties of as-cast Ti-10Mo wt.% and Ti-15Mo wt.% alloys were measured in order to evaluate their possible use in biomedical applications. The microstructure and phase analysis of as-cast specimens were studied using an optical microscopy and X-ray diffraction (XRD). The micro-Vickers hardness properties of the alloys were examined using Vickers equipment and the elastic modulus was determined using the tensile test. Results indicated that the Mo content influenced the structure- property relationship. The relative density increased significantly with the addition of Mo, the optical microscopy results showed that CP Ti was characterised with an α’-phase lamellar structure and with the addition of Mo, the microstructure composed of β phase with equiaxed grains of different sizes with sub-grain boundaries were observed. The measured XRD patterns showed that the CP Ti consisted of α’-phase and with the addition of Mo, the resultant alloys consisted of the β-phase. The micro-Vickers hardness and elastic modulus increased significantly after the addition of 10 wt.% Mo and then decreased significantly when the Mo content was raised to15 wt.%

The microstructural and mechanical characterization of the β- type Ti-11.1Mo-10.8Nb alloy for biomedical applications

Abstract : Ti-Mo alloys are promising biocompatible materials with lower elastic modulus than the extensively used Ti-6Al-4V alloy. However, research work done on these alloys indicate that their elastic modulus is still higher than that of the bone, even after the execution of numerous heat treatment procedures. Therefore, this study was aimed at adding Nb (non-toxic β stabilizer) to Ti-Mo system followed by the characterization of its microstructural and mechanical properties in the as-cast condition. This study will provide systematic preliminary information towards the design and development of novel biomedical components. The microstructure and phase analysis were carried out using optical microscope, SEM, and XRD. Mechanical tests were conducted using the uniaxial tensile test machine and Vickers microhardness tester. The as-cast Ti-11.1Mo-10.8Nb alloy consisted primarily of β phase and a possible small volume fraction of ω phase. The Vickers micro-hardness, elastic modulus, bending strength were measured as 311.62 HV0.5, 56.9 GPa 1671.4 MPa, respectively. The Ti-11.1Mo-10.8Nb alloy also exhibited ductile fracture behaviour during bend testing. The Ti-11.1Mo-10.8Nb design is a promising alloy for biomedical applications

Fretting biocorrosion behaviour of titanium-zirconia composites in foetal bovine serum

Abstract : This work aims at studying the fretting biocorrosion response of newly developed Ti-6Al-4V/ZrO2 in simulated body fluid. Ti-6Al-4V alloy with different volume fractions of ZrO2 produced via powder metallurgy techniques were spark plasma sintered to produce Ti- 6Al-4V composites with improved properties. The microstructures of the resulting spark plasma sintered composites were examined using a scanning electron microscope (SEM). Fretting corrosion tests were conducted for each material composition with a special device used for fretting corrosion investigations with a cylinder-on-flat configuration. The tests were done in foetal bovine serum maintained at ambient temperature. Open circuit potential, dissipated energy and coefficient of friction were monitored throughout the experiments. The results show that the microstructures produced after zirconia additions were very different from those observed in pure Ti-6Al-4V. The presence of zirconia promoted the formation of globular zirconia-rich agglomerates throughout the matrix, leading to more improved fretting biocorrosion properties of Ti-6Al-4V

Effect of milling parameters on the dispersion characteristics of multi-walled carbon nanotubes in transition metal oxides

Abstract: In this research investigation on milling parameters to achieve uniform dispersion of multi-walled carbon nanotubes (MWCNTs) was conducted. High-energy ball milling (HEBM) technique was adopted to disperse 1 wt. % MWCNTs in titanium and manganese oxides with ball to powder ratio (BPR) of 10:1 at 6 and 9 hours milling times. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the as-received MWCNTs and admixed composite powders. The results indicated that HEBM was an effective route to disperse MWCNTs in transition metal oxides. In addition, the characteristics of admixed powders evidently showed that the increase of milling time effectively dispersed the MWCNTs in titanium and manganese oxide respectively, however deformation of sidewalls of MWCNTs was observed due to harsh milling conditions that resulted on non-sp2 defects in the MWCNTs

Structural integrity and dispersion characteristics of carbon nanotubes in titanium-based alloy

Abstract: Over the years, carbon nanotubes have attracted much attention in engineering materials research due to their outstanding and superlative properties. Owing to the demands for lightweight materials with excellent mechanical and thermal properties for diverse industrial applications encouraged the incorporation of carbon nanotubes into titanium alloys. However, there are various challenges associated with the incorporation of carbon nanotubes into titanium alloys which includes; uniform dispersion and retaining the structural integrity of carbon nanotubes after dispersion. Past works have emphasized the importance of homogeneous dispersion with less structural damage to the carbon nanotubes in the various metal matrix. Therefore, this research focused on dispersion of 0.5 wt. % multiwalled carbon nanotubes in Ti6Al4V using low energy ball milling and evaluating the dispersion characteristics and structural integrity of MWCNTs in Ti6Al4V after dispersion. Various characterization techniques such as high-resolution transmission electron microscopy, scanning electron microscopy, X-Ray diffraction and Raman spectroscopy were adopted to ascertain the microstructural evolution, morphology, interfacial reaction and structural integrity of the carbon nanotubes in the Ti6Al4V powders before and after dispersion. The results indicated homogeneous dispersion of carbon nanotubes with less structural damages which are confirmed from the (ID/IG) ratio of the Raman spectra and the TEM images

The Corrosion Behaviour of WC-Co-Ru Alloys in Aggressive Chloride Media

Hardmetals possess excellent wear resistance, making them suitable alloys in several industrial applications. Mine waters with both dissolved chloride and sulphate salts can be severely corrosive and can limit the application of hardmetal tools in the mining industry. Ru additions to these alloys can refine and improve selected mechanical properties, but its influence on the corrosion resistance is unknown. A series of WC-Co-Ru alloys was evaluated in different chloride containing media to investigate their corrosion resistance. Standard electrochemical corrosion tests, chronoamperometric measurements, and surface analyses with Raman spectroscopy were conducted. An increasing amount of Ru improves the corrosion resistance of all the alloys. The effect is not as dramatic as that observed with stainless steels containing Ru in corrosive media. In both corrosive media Ru decreased the cathodic Tafel constant and has a retarding influence on the cathodic part of the corrosion reaction. Raman analyses indicated the presence of tungsten oxide, hydrated tungsten oxide compounds, and CoO and Co3O4 formed on the alloy surfaces during the corrosion process

Effect of graphite addition on the tribological properties of pure titanium carbonitride prepared by spark plasma sintering

Abstract: Titanium carbonitride (TiCN) based cermet has received extensive attention as important components substantially utilized in cutting tools, milling operations and in sliding bearings. Recently, conventional WC-Co based hard alloys are being replaced with TiCN based cermets accompanied with the trend of high speed machining. These materials are considered potential candidate for a variety of tribological applications. In this study, the effects of graphite additions on titanium carbonitride (TiCN) based cermet were investigated. This involved consolidation of TiC0.7TiN0.3 composition of pure TiCN based cermet and/with 0.5, 1.0 and 1.5 wt % graphite using spark plasma sintering (SPS). The comparative studies on the tribological behaviours of the TiCN based cermets with graphite additions were performed using ball on disc set up at ambient temperature. Results show that the presence of different composition of graphite influences the microstructures of TiCN. In addition, a change in wear response of the sintered compacts was observed

Erosion-corrosion behaviour of dual phase medium carbon steel using a designed slurry pot

Abstract: A slurry pot has been designed, fabricated and evaluated for erosion-corrosion investigations. A variable voltage controller was used to vary the input voltage into the one-horse-power motor that controls the slurry pot. The actual speed of the slurry pot shaft was also calibrated using a non-contact digital tachometer. Voltages of 100 and 200 V resulted in rotational speeds of 1100 and 2100 rpm, respectively employed for the subsequent erosion-corrosion tests. Erosion-corrosion of a dual-phase carbon steel was investigated with the aid of the slurry pot in aerated 3.5 wt.% NaCl environments. The sample was normalised at 850 oC and then cooled in air to room temperature. Prior to the test, the normalised samples were heated to 700, 725, 750, 775, 800 and 825 oC, respectively and quenched in oil. Erosion-corrosion rates of between 0.027 to 1.26 g/cm2.hr at 1100 rpm and 0.57 to 1.9 g/cm2.hr at 2100 rpm were recorded. It was also observed that as hardness increased there was reduction in weight loss of the heat treated alloy