Papers by Keyword: Ti6Al4V Alloy

Abstract: Titanium alloy Ti6Al4V was oxidation annealed in the beta-phase region (1050 °C/3 hours + WQ) in a furnace under a non-protective atmosphere. The above treatment caused the formation of an alpha-case layer on the surface. The above layer, because of its high hardness and strength, has a significant effect on the surface properties of the alloy. However, undesirable effects include the formation of cracks in this layer and a change in the mechanism of initiation and propagation of fatigue cracks. Based on the above findings, it is also very complicated to predict the fatigue life of Ti alloys processed in this way because of the presence of cracks in the alpha-case layer and the varying thickness of this layer. From the fractography and microstructural point of view, the initiation of fatigue cracks in the heat-treated alloy is realized by transcrystalline cleavage and the formation of pronounced fracture facets as a consequence of surface cracks in the alpha-case layer. Fatigue crack propagation (in the alpha-case layer region) is realized along the interface of the alpha-phase needles and the beta-phase primer grain without the significant presence of so-called fatigue striations.

Abstract: The two-phase titanium alloy Ti6Al4V (often referred to as GRADE 5 or Ti64) is currently probably the most widely used type of Ti alloy. It is characterized by an excellent combination of strength - toughness - chemical stability. However, at temperatures above 500 - 800 °C it is prone to the diffusion of oxygen into surface layers, where the increased oxygen content creates the so-called “alpha-case” layer. The formation of this layer is associated with a reduction mainly in the deformation characteristics of the alloy. The paper focuses on the metallographic analysis of the "alpha-case" layer after annealing at 1050 °C with a holding time of 3 hours and cooling at different cooling rates (500 °C/s, 1 °C/s and 0.08 °C/s). Microstructure changes were observed by light microscopy using polarized light – PL, dark field – DF and phases were identified by SEM methods. The influence of changes in the microstructure on the mechanical properties was determined by measuring the microhardness HV0.2 /10 (STN EN ISO 6507) with Zwick / Roell ZHµ and measuring the resistance to impact stress KU (Charpy system STN EN 10045-1). Based on the microhardness measurement, an increase in the microhardness of the surface layers was observed at all cooling rates and at the same time, a decrease in the impact resistance was observed compared to the initial state.

Abstract: Electrospark treatment of a titanium alloy Ti6Al4V in a mixture of granules allows the formation of intermetallic Ti-Al coatings. The coating structure is penetrated by a network of cracks with a thickness of 0.46 to 1.19 microns and a specific area of 1.5 to 3.4%. A change in the ratio of Ti to Al in the mixture of granules does not lead to a monotonic change in the thickness and number of cracks. A decrease in the pulse duration from 200 to 20 μs leads to a slight decrease in the thickness of cracks and significantly increases their total area from 2.1 to 3.4%. An increase in the discharge pulse repetition rate can significantly increase the thickness of cracks in Ti-Al electrospark coatings.

Abstract: The investigation of the corrosion resistance of Ti6Al4V alloy components produced by additive technology is still lacking in the literature. This paper aims to study the electrochemical behaviour of Ti6Al4V components fabricated by laser powder-bed fusion additive manufacturing process. The metallographic analysis was carried out by an optical microscope. The electrochemical behaviour has been evaluated in 3.5 wt. % of natural aerated NaCl aqueous solution by potentiodynamic polarization test. The results have been compared to a conventionally manufactured Ti6Al4V component. The typical martensitic structure has been shown by the additive manufactured sample. As expected, the metallographic analysis revealed a martensitic microstructure. The electrochemical tests carried out on the surface of the as-received additive manufactured specimen showed an influence of its morphology on the values of passive current density, higher than that recorded for the conventionally manufactured sample, used as the control. After mechanical polishing, the electrochemical tests were repeated on the "bulk" of the samples. The open circuit potential values were higher than the value recorded for the conventionally manufactured sample. The conditions of the additive process affect the corrosion resistance of the components due to the roughness of the surface and to the microstructure created.

Abstract: Barrier layer was prepared by Micro-arc oxidation(MAO) technique in silicate solution, and cathodic plasma electrolytic deposition (CPED) technique was used to fabricate Al₂O₃ ceramic coatings on Ti6Al4V alloy in Al(NO₃)₃(30g/L) and ethanol-aqueous solutions. Surface morphology and elemental of the coatings were investigated by scanning electron microscope (SEM) and energy disperse spectroscopy (EDS). Reaction phenomena were recorded and products of reactions were analyzed by infrared absorption spectrum KBr compression method. Furthermore, mechanisms of different electrolytes were evaluated.

Abstract: The paper presents the simulated 3D Finite Element Model (FEM) while grinding the Ti6Al4V alloy using a single abrasive wheel. Grinding simulation was carried out using a Lagrangian finite element based machining model to predict the tangential cutting force, temperature distribution at grinding zone and the effective stress and strain. All simulations were performed according to the cutting conditions designed, using the plane up-grinding. The work piece was considered as typical materials to machine difficulty. As the cutting speed is increased from 15 m/min to 33 m/min at higher feed rate, a maximum value of 750 MPa stress and higher temperature localization to an extent of 900°C at grinding zone were observed.

Abstract: Growth of long fatigue cracks in Ti6Al4V alloy manufactured by direct metal laser sintering (DMLS) was investigated. Two DMLS systems, EOSINT M270 and EOSINT M290, with different process parameters were used for production of CT specimens having three different orientations of crack propagation with respect to the DMLS build direction. The as-built specimens were stress relieved at 740 °C. The fatigue crack growth curve and the threshold values of the stress intensity factor for crack propagation were experimentally determined. It has been found that the chosen DMLS processing parameters and the used stress relieving procedure results in material exhibiting isotropic crack growth behavior, i.e. the crack growth was found to be independent of the DMLS build direction. The fatigue crack growth rates and the threshold values for the crack growth were compared with published results characterizing the as-built material and material after different post processing heat treatments.

Abstract: Direct Metal Laser Sintering (DMLS) is additive manufacturing (AM) process that can produce near net shape parts from metal powders such as titanium alloys. DMLS is a layer by layer additive manufacturing technique based on high power fiber laser that creates solid layers from loose powder material and joins them in an additive manner. The specific DMLS process conditions, lead to a specific and complex microstructure and to mechanical properties that show a degree of directionality. It was found that microstructural characteristics are related to the building process parameters. The aim of this work is to evaluate the fatigue performance of the Ti6Al4V alloy depending on the process parameters, building orientations and post-process heat treatment.

Abstract: Nanocrystalline surface layer about 10~15μm thick was fabricated on the surface of Ti6Al4V sheet by means of the surface mechanical attrition treatment (SMAT). The average grain size was about 10nm and the grain characteristic presented equiaxed morphology. The nanocrystalline surface layer could be perfectly maintained below 550°C in the following thermal stability analysis. Neutral salt mixture was about 21% NaCl, 31% BaCl₂ and 48% CaCl₂ and additionally 5% Na₂CO₃ of total was utilized. After carburizing process, a continuous charcoal grey carburized layer was composed of TiC and carbon supersaturated solid solution, the hardening layer was about 10~15μm thick. The hardness of the outermost surface reached 1000HV, which was much higher than its coarse-grained counterpart in the same carburizing condition. The experimental result indicated that the carburizing kinetics was obviously enhanced by nanocrystalline surface layer assistance. Furthermore, the neutral molten salt-bath carburizing was verified that it could be performed in a relatively low temperature of 650°C.

Abstract: The paper presents results of influence of modified artificial plasma on corrosion resistance of Ti6Al4V ELI alloy. The samples were subjected to grinding, anodic oxidation and steam sterilization. After 28-day exposure to Ringer’s solution as well as Tas - SBF and R - SBF fluids, studies of electrochemical impedance spectroscopy, corrosion resistance and the amount of metal ions released into the solutions were carried out. The obtained results were compared to the results obtained for the samples in the initial state. It was found that the highest reactivity in contact with the Ti6Al4V ELI alloy was observed for the Tas - SBF containing TRIS whereas the lowest reactivity was observed for the Ringer's solution. The obtained results indicate the possible use of the modified physiological solutions, in order to carry out a more rigorous test of corrosion resistance of metal materials.