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

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

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

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

Comparative study of spark plasma sintering features on the densification of Ni-Cr binary alloys

Abstract: Spark plasma sintering (SPS) has been widely regarded as an advanced powder consolidation technique which helps in the development of array of engineering materials. Many have been reported in the literature about sintering parameters such as temperature, pressure, heating rate and holding time. However, little or no reports has been made on some of the intricate features such as process time(s), power SPS (KW), pressing speed (mm/min), and average pressing force (KN) on which sintering parameters are directly related to. This study aims to investigate the behaviour of spark plasma sintered Ni-17Cr binary alloys with emphasis on the densification, hardness value and spark plasma sintering features such as process time (s), power SPS (KW), pressing speed (mm/min), and the average pressing force (KN). Nickel and chromium powders were milled individually using High energy ball milling for durations of 5hr, 10 hr prior to mixing and subsequent sintering. The sintered 5 hr and 10 hr milled Ni-17Cr binary alloys attained relative densities of 98.72 % and 99.1 % respectively. The Microstructural morphology was examined using Scanning electron microscopy (SEM). The sintered 10 hr milled Ni-17Cr binary alloy revealed the higher hardness

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

Effect of CrC-Ni on the tribological behaviour of WC cemented carbide

Abstract. Tungsten carbide (WC) is extensively used in industrial processing as cutting tools, wear resistant components and drilling tools owing to the good combination of phenomenal properties. The binder phase of WC is usually cobalt (Co) as a result of good wetting behaviour and excellent solubility with regards to WC particles. However, degradation of WC-Co components when subjected to harsh environmental conditions often results in premature failures during application. In this study, the effect of CrC-Ni on the microstructure, mechanical and tribological properties of WC based cermet produced by spark plasma sintering was investigated. Sintered samples were then analysed and characterized by SEM and EDS. Macro hardness of the sintered compacts were evaluated using Rockwell hardness machine at 150kg load. Subsequently, comparative studies on the tribological behaviour of the experimental samples were performed using a reciprocating wear set up at 200°C. The area of the wear track cross-section was measured using optical profiler and the wear rate in terms of volume loss was calculated. Results showed improved mechanical and tribological properties on WC-20CrC-7Ni sample as compared to WC-Co cemented carbide sample

A correlation between nano and micro-hardness properties of TiN nanoparticles strengthened SAF 2205

Abstract : This work studied the correlation between Vickers and nano-hardness of SAF 2205 reinforced with TiN nanoparticles for the convenience of assessing its mechanical properties. Spark plasma sintering was used to fabricate the composites. Micro and nanoindentations were performed to determine micro and nanohardness values of the fabricated composite. Optical microscope was used to assess the microstructure. The microstructure revealed that the TiN dominated the ferrite/ferrite, ferrite/austenite and austenite/austenite grain boundaries. The micro and nanohardness at the TiN dominated grain boundaries were higher compared to the grain hardness. Hardness also increased considerably as the TiN nanoparticles increases. This is also owed to the strengthening effect played by TiN at the grain boundaries by disrupting dislocation motion in the composite. The determined Vickers hardness was plotted as a function of the corresponding nanohardness, a good linear relation was found between Vickers hardness and nanohardness. A linear relationship (HV = 215.15 + 15.03Hnano) was established which indicates that there is no difference in behavior for the Vickers hardness and nano- hardness

Spark plasma sintered Ti6Al4V-ZrO2 bio-composites: optimization of ball milling and turbula mixing of powders and their subsequent sintering parameters

Abstract: The use of Ti6Al4V as a biomaterial has been limited due to the dissociation of V and Al ions into the surrounding environment which can cause inflammations, cell damage and toxicity. To prohibit these undesirable challenges, the addition of ZrO2 into Ti6Al4V was proposed because ZrO2 is biocompatible, it has good wear and corrosion resistant properties, it has low affinity to bacterial colonization and it has high fracture toughness.The aim of this work is to determine the optimum powder synthesising parameters by Tubular mixer and ball mill for fabrication of sintered composites . Powder mixtures were prepared by 49 rpm,72 rpm and 74rpm for 2, 4 and 8 hours followed by spark plasma sintering at 1100 oC at heating rate of 100 oC/min for 10 min and pressure of 50 MPa.from the results obtained it was discovered that Tubular mixing of 90 Vol% Ti6Al4V and 10 Vol% ZrO2 at 72 rpm and ball milling of 90 Vol% Ti6Al4V and 10 Vol% ZrO2 at 74rpm speed have proved to produce homogeneous admixed powders, which can further produce fully dense SPS compacts with higher microhardness values

The role of graphite addition on spark plasma sintered titanium nitride

Abstract: tComposites of titanium nitride reinforced with graphite were synthesized using sparkplasma sintering at 2000◦C. The effects of graphite addition on the microstructure, relativedensity, and mechanical properties of TiN ceramics matrix were examined. The investiga-tion was performed on TiN powder with varying graphite content (1–5 wt.%) for 8 h using anenergy ball milling equipment. Results show that TiN without and with graphite (TiN + 1 wt.%graphite) sintered at 2000◦C recorded sintered relative density of 96.7% and 97% respec-tively. Additionally, TiN with 3 wt.% graphite had a relative density of 98%. However, theshrinkage of TiN + 3 wt.% graphite was observed to be the lowest compared to other com-posites at the same sintering conditions. Microstructural analysis indicates that the grainof titanium nitride in the composite was very fine and continuous. Subsequently, a bimodalparticle sizes were observed when 5 wt.% graphite was dispersed in TiN. The highest Vickersmicrohardness of 23.5 GPa and fracture toughness of 6.5 MPa m1/2were achieved with com-posites reinforced with 3 wt.% graphite at milling period of 8 h. The combination of TEM/EDSand HRTEM/FFT show a single pattern of diffraction and consistency in interplanar distanceobtained from X-ray diffractometry of the milled sample. There is a clear coherence interfacebetween the phases