1,201,351 research outputs found
Wear resistant multilayer nanocomposite WC1−x/C coating on Ti–6Al–4V titanium alloy
No full textA significant improvement of tribological properties on Ti–6Al–4V has been achieved by developed in this study multilayer treatment method for the titanium alloys. This treatment consists of an intermediate 2 μm thick TiCxNy layer which has been deposited by the reactive arc evaporation onto a diffusion hardened material with interstitial O or N atoms by glow discharge plasma in the atmosphere of Ar+O2 or Ar+N2. Subsequently, an external 0.3 μm thin nanocomposite carbon-based WC1−x/C coating has been deposited by a reactive magnetron sputtering of graphite and tungsten targets. The morphology, microstructure, chemical and phase compositions of the substrate material after treatment and coating deposition have been investigated with use of AFM, SEM, EDX, XRD, 3D profilometry and followed by tribological investigation of wear and friction analysis. An increase of hardness in the diffusion treated near-surface zone of the Ti–6Al–4V substrate has been achieved. In addition, a good adhesion between the intermediate gradient TiCxNy coating and the Ti–6Al–4V substrate as well as with the external nanocomposite coating has been obtained. Significant increase in wear resistance of up to 94% when compared to uncoated Ti–6Al–4V was reported. The proposed multilayer system deposited on the Ti–6Al–4V substrate is a promising method to significantly increase wear resistance of titanium alloys
Influence of Yttrium on the Thermal Stability of Ti-Al-N Thin Films
No full textTi(1-x)Al(x)N coated tools are commonly used in high-speed machining, where the cutting edge of an end-mill or insert is exposed to temperatures up to 1100 degrees C. Here, we investigate the effect of Yttrium addition on the thermal stability of Ti(1-x)Al(x)N coatings. Reactive DC magnetron sputtering of powder metallurgically prepared Ti(0.50)Al(0.50), Ti(0.49)Al(0.49)Y(0.02), and Ti(0.46)Al(0.46)Y(0.08) targets result in the formation of single-phase cubic (c) Ti(0.45)Al(0.55)N, binary cubic/wurtzite c/w-Ti(0.41)Al(0.57)Y(0.02)N and singe-phase w-Ti(0.38)Al(0.54)Y(0.08)N coatings. Using pulsed DC reactive magnetron sputtering for the Ti(0.49)Al(0.49)Y(0.02) target allows preparing single-phase c-Ti(0.46)Al(0.52)Y(0.02)N coatings. By employing thermal analyses in combination with X-ray diffraction and transmission electron microscopy investigations of as deposited and annealed (in He atmosphere) samples, we revealed that Y effectively retards the decomposition of the Ti(1-x-y)Al(x)Y(y)N solid-solution to higher temperatures and promotes the precipitation of c-TiN, c-YN, and w-AlN. Due to their different microstructure and morphology already in the as deposited state, the hardness of the coatings decreases from similar to 35 to 22 GPa with increasing Y-content and increasing wurtzite phase fraction. Highest peak hardness of similar to 38 GPa is obtained for the Y-free c-Ti(0.45)Al(0.55)N coating after annealing at T(a) = 950 degrees C, due to spinodal decomposition. After annealing above 1000 degrees C the highest hardness is obtained for the 2 mol % YN containing c-Ti(0.46)Al(0.52)Y(0.02)N coating with similar to 29 and 28 GPa for T(a) = 1150 and 1200 degrees C, respectively
Fracture toughness characterization of thin Ti/SiC composites
No full textTitanium based alloys reinforced uniaxially with silicon carbide fibres (Ti/SiC)
are advanced and innovative materials for aerospace vehicles. To avoid
potential problems, these new materials should be extensively tested and
analyzed before application.
This research focuses on experimental fracture toughness study on 0.5 mm
thick Ti/SiC composite materials for aerospace applications. The fracture
toughness tests are mainly based on BS 7448 with some modifications for
transversely isotropic behaviour of the composite materials.
By loading on specimens in the direction perpendicular to the fibre axis, three
critical values of fracture toughness parameters characterizing fracture
resistance of material, plane strain fracture toughness [Plane strain fracture toughness
}, critical crack tip
opening displacement [Critical crack tip opening displacement
] and critical J-integral [Critical at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
]are measured for two
kinds of titanium alloy specimens and three kinds of Ti/SiC composites
specimens.
The values of [Provisional value of Plane strain fracture toughness
] obtained from the fracture toughness tests are not valid [Plane strain fracture toughness
]
for these materials, since the thickness of specimens is insufficient to satisfy the
minimum thickness criterion; however, the results could be used as particular
critical fracture toughness parameter for 0.5 mm thick structures of the materials.
The valid values of [Critical J at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
] and [Critical crack tip opening displacement
] could be used as fracture toughness
parameters for all thickness of structures of the materials. The results also show
that: fracture toughness of the titanium alloys decreases dramatically after being
unidirectional reinforced with SiC fibre, which is mainly triggered by poor
fibre/matrix bonding condition. Moreover, Ti-Al3-V2.5 reinforced with 25%
volume fraction SiC fibre performs better than the other two composites in
fracture resistance
Interfacial microstructure and shear strength of Ti-6Al-4V/TiAl laminate composite sheet fabricated by hot packed rolling
No full textA two layer Ti-6Al-4V(wt%)/Ti-43Al-9V-Y(at%) laminate composite sheet with a uniform interfacial microstructure and no discernible defects at the interfaces has been prepared by hot-pack rolling, and its interfacial microstructure and shear strength were characterized. Characterization of the interfacial microstructure shows that there was an interfacial region of uniform thickness of about 250 μm which consisted of two layers: Layer I on the TiAl side which was 80 μm thick and Layer II on the Ti-6Al-4V side which was 170 μm thick. The microstructure of Layer I consisted of massive γ phases, needlelike γ phases and B2 phase matrix, while the microstructure of Layer II consisted of α₂ phase. The microstructure of the interfacial region is the result of the interdiffusion of Ti element from Ti-6Al-4V alloy layer into the TiAl alloy layer and Al element from the TiAl alloy layer into the Ti-6Al-4V alloy layer. The shear strength measurement demonstrated that the bonding strength between the TiAl alloy and Ti-6Al-4V alloy layers in the laminate composite sheet was very high. This means that the quality of the interfacial bonding between the two layers achieved by the multi-path rolling is high, and the interface between the layers is very effective in transferring loading, causing significantly improved toughness and plasticity of the TiAl/Ti-6Al-4V laminate composite sheet
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Controlling the interstitial element concentration in Ti-6Al-4V using calciothermic reduction
No full textThe production of Ti-6Al-4V components via powder metallurgy routes is looked upon as an efficient production method that reduces wastage, but leaves finished products with high interstitial oxygen concentrations that do not meet industrial standards. The ability to control the interstitial oxygen concentration in Ti-6Al-4V powder metallurgy would improve the viability of near net shape processing for the production of industrial components. One process that has demonstrated the ability to remove oxygen from titanium alloys is calciothermic reduction, which is a reduction process originally developed to reduce titanium dioxide to commercial purity titanium using a molten flux of calcium and calcium chloride. The aim of this thesis is to examine whether calciothermic reduction can be used to control the interstitial concentration of oxygen and nitrogen in powder metallurgy Ti-6Al-4V and understand the reaction mechanisms that enable this process to work. By understanding these mechanisms, the process can then be optimised to improve the properties of powder metallurgy Ti-6Al-4V components, and provide a basis to extend this to other alloy systems.
Calciothermic reduction was demonstrated to be effective at reducing the interstitial oxygen concentration in powder metallurgy Ti-6Al-4V to acceptable industrial standards (< 2,000 wt .ppm). The optimisation of the process required the balance of thermodynamics and kinetics to be controlled; thermodynamics was important to ensuring the reaction would begin, with the kinetics becoming more important during the reduction process because the removal of interstitial oxygen concentration relied upon a diffusion based mechanism.
Evaluation of the mechanism that underpins the removal of oxygen via calciothermic reduction, was assessed using a FIB-SIMS based technique. This method of analysis was developed during this research and demonstrated to be effective at quantifying interstitial oxygen concentrations in titanium alloy, which was used to confirm the formation of oxygen concentration gradients from titanium alloy bulk to the surface during calciothermic reduction.
Further investigation of the reduction process indicated that calciothermic reduction could facilitate the nitriding of Ti-6Al-4V in a sealed air environment, forming a wear resistant surface layer in a novel process referred to as “Calciothermic Assisted Immersion Nitriding” (CAIN). The nitriding process produced a consistent TiCxNyOZ surface layer where the chemical composition of the layer developed in a three stage reaction involving the inward diffusion of interstitial carbon and nitrogen, whilst oxygen was removed from the surface. This surface layer improved the tribological properties of the Ti-6Al-4V samples by changing the wear mechanism from adhesive to abrasive, which resulted in an increased wear resistance, which was comparable to a commercial produced, physical vapour deposition TiCN coating.Open Acces
Influence of oxidation treatment on the corrosion behaviour of Ti-6AI-4V alloy
No full textTitanium-6Al-4V is a greatly desired alloy due to its attractive properties and exceptional corrosion resistance. Surface modifications such as thermal oxidation (TO) and oxygen boost diffusion hardening (OBDH) improve the tribological properties and wear resistance of Ti-6Al-4V. However, surface modification influences the corrosion behaviour of the metal. Therefore, the aim of this research project is to characterize how surface modifications influence the electrochemical behaviour of Ti-6Al-4V
Analysis on turning Ti-6Al-4V with different cooling methods
No full textThe aim of this paper is to optimize the machining of Ti-6Al-4V alloy, by studying the chip formation, roughness and tool wear for different cooling conditions. The results were compared between cooling methods, minimal quantity of fluid (MQF) and flooding, and also without fluid for the tool H13A. The turning of Ti-6Al-4V has shown good results on roughness (0, 8μm) and tool life, which was 11% lower with MQF than with the flooding method. The tool wear causes variation of the shear angle, which promotes strength hardening of the chip. As a result, the machined surface could be damaged. The use of the cutting fluid helps to save the cutting edge and could reduce the strength hardening. Nevertheless, it could also facilitate the formation of built-up edge. The nucleation of alpha lamellar colonies can occur due to a combination of deformation rates and temperature, mainly when the flooding is used, but it's not conclusive. The lamellar colonies were also found with the MQF in some regions, however, this structure did not show hardness variation compared to equiaxial. For all this reasons, the machining parameters might be carefully chosen.Department of Materials and Technology Univ. Estadual Paulista UNESP, Guaratinguetá/SP, 12516-410Department of Materials and Technology Univ. Estadual Paulista UNESP, Guaratinguetá/SP, 12516-41
Analysis on turning Ti-6Al-4V with different cooling methods
No full textThe aim of this paper is to optimize the machining of Ti-6Al-4V alloy, by studying the chip formation, roughness and tool wear for different cooling conditions. The results were compared between cooling methods, minimal quantity of fluid (MQF) and flooding, and also without fluid for the tool H13A. The turning of Ti-6Al-4V has shown good results on roughness (0, 8μm) and tool life, which was 11% lower with MQF than with the flooding method. The tool wear causes variation of the shear angle, which promotes strength hardening of the chip. As a result, the machined surface could be damaged. The use of the cutting fluid helps to save the cutting edge and could reduce the strength hardening. Nevertheless, it could also facilitate the formation of built-up edge. The nucleation of alpha lamellar colonies can occur due to a combination of deformation rates and temperature, mainly when the flooding is used, but it's not conclusive. The lamellar colonies were also found with the MQF in some regions, however, this structure did not show hardness variation compared to equiaxial. For all this reasons, the machining parameters might be carefully chosen
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