Ti6Al4V Alloy Samples Research Articles

Microstructures and mechanical properties of Ti6Al4V alloy fabricated by multi-laser beam selective laser melting

A self-developed four-laser beam selective laser melting (SLM) system was used to fabricate Ti6Al4V alloy samples in this study. The relative density, micro-hardness and mechanical properties of all isolated processing areas were compared under optimized processing parameters to ensure the consistency of this system. The samples built across overlap area show obvious raised platform due to the repeated laser scanning when relative hatch angle (θr) is 0°. This phenomenon can be greatly improved by adjusting θr to 90°. Microstructures and mechanical properties are not affected by the method of overlap conditions (θr and overlap width). Microstructures in overlap areas are dominated by columnar grains along the building direction and martensitic needles α′ inclined at about ±45° to the building direction, which are similar with those in isolated areas. Mechanical properties in overlap areas are also not inferior to those in isolated areas. The results prove the feasibility to fabricate large-scale components with a uniform microstructure and mechanical property by this SLM system.

Study of the impact of treatment modes on hardness, deformability and microstructure of VT6 (Ti-6Al-4V) and VV751P (Ni-15Co-10Cr) alloy samples after selective laser sintering

Selective laser sintering is an advanced method for obtaining sophisticated products and assembly permanent joints. This is particularly relevant for heat resistant alloys employed in aviation equipment. Heat treatment modes traditionally applied to the products are chosen in accordance with conditions of further product operation. In this paper there are given the results of experimental study of hardness, deformability and microstructure of samples after selective laser sintering of Ni-15Co-10Cr and Ti–6Al–4V alloy powders. It has been determined that Ni-15Co-10Cr alloy ageing increases the hardness and deformability of samples; these characteristics decrease if the ageing lasts for 9-19 hours. Annealing of Ti–6Al–4V alloy samples results in preserving original hardness. After complete annealing, the hardness of samples decreases from 32 … 33HRC to 24 … 26HRC. Microstructural studies showed that there are cracks between layers in the surface of Ti–6Al–4V alloy samples after sintering and not complete annealing. After full annealing, cracks' width and length decreased. Cracks in Ni-15Co-10Cr alloy samples' microstructure were not detected.

The Application of Direct Metal Laser Sintering (DMLS) of Titanium Alloy Powder in Fabricating Components of Aircraft Structures

This study presents detailed characteristics of the DMLS method as used for titanium alloy powder with reference to a possible intended use in aeronautics applications.In the present study test models were made, designed for trials in which the model material properties are to be determined and which specify the basic features of the RP/DMLS technique. In order to evaluate the ultimate use of the DMLS technique in fabricating titanium alloy parts, the following procedures were conducted: tensile and upsetting tests for Ti6Al4V alloy samples (a comparative analysis for DMLS models and models fabricated, respectively, from titanium sheet and bar was carried out), an SEM analysis of the microstructure of the fragments of the surface of polished and etched samples, a Vickers hardness test and an analysis of the accuracy of the reproduction of the shape and roughness of the model fabricated in the DMLS procedure. A detailed analysis of the DMLS method significantly supplements the existing body of knowledge on innovative rapid prototyping techniques [1–4], and the results allow us to specify a group of aircraft structure components which may be fabricated using this method. Excellent strength properties of DMLS models and the possibility of improving surface quality by mechanical working enable the fabrication of advanced aircraft structure components operated in target conditions (under load).

Residual Stress in SLM Ti6Al4V Alloy Specimens

Selective Laser Melting (SLM) presents a modern manufacturing process with an innovative technology which allows the production of full-density objects or fine-structured parts with complex geometry and inner structures. Stability and certification of the properties of SLM parts are important tasks for all producers and end-users. One of the drawbacks of this technology is high residual stress in as-made SLM objects. In this study X-ray diffraction technique was used for investigating the residual stress induced into SLM Ti6Al4V alloy samples. Principal stresses were estimated for the cut rectangular specimen. Two types of the cantilevers were produced and numerical simulation of the stress was performed. The bending of cut cantilevers was measured before and after heat treatment. Next series of the samples had rectangular shapes and different thicknesses from 1 to 46 layers. All as-manufactured specimens attached to the substrate showed the presence of tensile residual stresses near the top surface. Residual stress along the laser scanning direction had magnitudes twice that of the stress in the perpendicular direction. Conclusions regarding directions and values of stresses in SLM objects from Ti6Al4V powder are given.

Microstructure and intermediate-temperature mechanical properties of powder metallurgy Ti–6Al–4V alloy prepared by the prealloyed approach

The mechanical properties of powder metallurgy (P/M) Ti–6Al–4V alloys, produced from prealloyed powders by hot isostatic pressing, were evaluated over the intermediate temperature range of 300–500°C. A fully equiaxed or lamellar structure was observed depending on the processing temperature. Microstructural changes were attributed to the beta-transus temperature, predicted as 977°C. As the test temperature increased from 300 to 500°C, the strength of the Ti alloys decreased and their elongation increased, regardless of their initial microstructure. Over the entire temperature range tested, the strength and ductility of equiaxed phase morphologies were higher than those of the lamellar structure. In addition, finer equiaxed structures exhibited higher strength and lower ductility than coarser morphologies. These results were attributed to the initial microstructures of the P/M Ti–6Al–4V alloy samples, as confirmed by evaluating their fracture features.

Osseointegration improvement by plasma electrolytic oxidation of modified titanium alloys surfaces.

Titanium (Ti) is a material frequently used in orthopedic applications, due to its good mechanical properties and high corrosion resistance. However, formation of a non-adherent fibrous tissue between material and bone drastically could affect the osseointegration process and, therefore, the mechanical stability of the implant. Modifications of topography and configuration of the tissue/material interface is one of the mechanisms to improve that process by manipulating parameters such as morphology and roughness. There are different techniques that can be used to modify the titanium surface; plasma electrolytic oxidation (PEO) is one of those alternatives, which consists of obtaining porous anodic coatings by controlling parameters such as voltage, current, anodizing solution and time of the reaction. From all of the above factors, and based on previous studies that demonstrated that bone cells sense substrates features to grow new tissue, in this work commercially pure Ti (c.p Ti) and Ti6Al4V alloy samples were modified at their surface by PEO in different anodizing solutions composed of H2SO4 and H3PO4 mixtures. Treated surfaces were characterized and used as platforms to grow osteoblasts; subsequently, cell behavior parameters like adhesion, proliferation and differentiation were also studied. Although the results showed no significant differences in proliferation, differentiation and cell biological activity, overall results showed an important influence of topography of the modified surfaces compared with polished untreated surfaces. Finally, this study offers an alternative protocol to modify surfaces of Ti and their alloys in a controlled and reproducible way in which biocompatibility of the material is not compromised and osseointegration would be improved.

Solid particle erosion behaviour of Ti6Al4V alloy

The effects of particle impingement angle, impingement velocity and erodent particle size on the erosion rate and surface morphology of the Ti6Al4V alloy have been investigated comprehensively in order to evaluate solid particle erosion behaviour of Ti6Al4V alloy. Samples were eroded in a specially designed sandblasting system under various parameters using alumina (Al2O3) erodent particles. Surface morphology investigations were examined by scanning electron microscope using various analysis and modes (energy dispersive X-ray analysis, elemental mapping and compositional contrast). Ti6Al4V alloy showed ductile behaviour with a maximum erosion rate at 30° impingement angle. Erosion rate of Ti6Al4V alloy increased with increases in velocity and decreased with increases in erodent particle size. Scanning electron microscopy investigations of eroded surfaces of Ti6Al4V alloy samples reveal the dominant erosion mechanism such as microploughing, microcutting and plastic deformation. Embedded erodent particles on the surfaces of Ti6Al4V alloy nearly at all particle impingement angles and velocities were clearly detected.

Water Droplet and Cavitation Erosion Behavior of Laser-Treated Stainless Steel and Titanium Alloy: Their Similarities

This article deals with water droplet and cavitation erosion behavior of diode laser-treated X10CrNiMoV1222 stainless steel and Ti6Al4V alloy. After laser surface treatment, the water droplet and cavitation erosion resistance (WDER and CER) of these materials improved significantly. The main reason for the improvement is the increased surface hardness and formation of fine-grained microstructures after laser surface treatment. It is observed that there is a similarity in both the phenomena. The WDER and CER can be correlated with a single mechanical property based on modified ultimate resilience (MUR) provided the laser-treated layers are free from microcracks and interface defects. The CER and WDER behavior of HPDL-treated X10CrNiMoV1222 stainless steel and Ti6Al4V alloy samples using different test equipment as per ASTM G32-2003 and ASTM G73-1978, their correlation with MUR, and their damage mechanism compared on the basis of XRD analyses, optical and scanning electron micrographs are discussed and reported in this article.

Surface Properties of the Ta and Ag Dual-Ion-Implanted Ti6Al4V Alloy

First, Ti6Al4V alloy samples were modified by tantalum ion implantation at a dose of 1.5×1017ions/cm2, and then silver ion at a dose of 1×1017ions/cm2. Glancing angle X-ray diffraction analysis was used to characterize the phase composition of un-implanted Ti6Al4V alloy and Ta+Ag dual-ion-implanted Ti6Al4V alloy samples. X-ray photoelectron spectroscopy analysis was used to investigate the chemical states of the elements on the Ta+Ag dual-ion-implanted Ti6Al4V alloy sample’s surface. The results show that small amounts of Ta and Ag were present in their elementary forms, along with TiO2, Ta2O5, and TaOx.

Surface modification of Ti–6Al–4V alloy using an oxygen glow-discharge plasma to suppress the elution of toxic elements into physiological environment

We present the application of a plasma-oxidation technique for modifying a the corrosion resistance of a Ti–6Al–4V bio-implant material in a physiological environment. The corrosion resistance of a plasma-oxidized Ti–6Al–4V alloy sample was evaluated by immersing the sample in a lactic acid solution and determining the amounts of eluted elements in the immersion-test solution. The amounts of toxic elements, aluminum and vanadium, eluted from the plasma-oxidized sample were compared with those from the thermally oxidized sample to demonstrate the corrosion resistance of the plasma-oxidized surface to be greatly improved. To elucidate the reasons for this improvement in corrosion resistance, the oxide layers formed on the Ti–6Al–4V alloy were characterized by X-ray photoelectron spectroscopy, which revealed that Al and V oxides were enriched at the outermost surface of the thermally oxidized sample, whereas they were less segregated at the outermost surface of the plasma-oxidized sample. Based on the atomic fractions of elements at the outermost surface of the oxide layers after the immersion test, it was deduced that the elution occurred mainly at the outermost surface of the oxide layer. Therefore, it can be deduced that the characteristic surface composition of the plasma-oxidized sample, with reduced fractions of toxic elements, played an important role in suppressing the elution of toxic elements.

Characterization of Ti and Ti6Al4V Surfaces After Mechanical and Chemical Treatments: A Rational Approach to the Design of Biomedical Devices

At present, titanium-based biomaterials for the production of prosthetic devices have achieved a satisfactory quality level; current research aims at improving their surgical dependability and biomechanical performances. In this contest, a crucial aspect is represented by the osseointegration process, which implies the secure association of endosseous devices with the surrounding biological tissue. Osseointegration is largely controlled by surface characteristics with regard to both chemical composition and morphological properties. Therefore, the design of such devices might be guided by the characterization of surface morphology produced by mechanical and chemical treatments. This paper illustrates the results obtained by the application of a set of treatments on titanium (Ti2) and Ti6Al4V alloy (Ti5) samples. Mechanical treatments mainly affect the dimension of larger defects, acting on a macrometric scale and inducing specific patterns; chemical treatments (i.e., acid attack at room or higher temperature) can dissolve surface material altering defect dimensions on a micrometric scale. This study may represent a useful tool for the rational design of implant surface characteristics.

Quasi-static torsional deformation behavior of porous Ti6Al4V alloy

Laser processed Ti6Al4V alloy samples with total porosities of 0%, 10% and 20% have been subjected to torsional loading to determine mechanical properties and to understand the deformation behavior. The torsional yield strength and modulus of porous Ti alloy samples was found to be in the range of 185–332 MPa and 5.7–11 GPa, respectively. With an increase in the porosity both the strength and the modulus decreased, and at 20% porosity the torsional modulus of Ti6Al4V alloy was found to be very close to that of human cortical bone. Further, the experiments revealed clear strain hardening and ductile deformation in all the samples, which suggests that the inherent brittleness associated solid-state sintered porous materials can be completely eliminated via laser processing for load bearing metal implant applications.

Influence of surface roughness on consecutively hydrogen absorption cycles in Ti–6Al–4V alloy

In the present work the influence of roughness of the material surface with hydrogen absorption in Ti–6Al–4V alloy during four hydrogenated cycles is studied. The Ti–6Al–4V alloy samples were hydrogenated during several cycles at 650 °C for two hours, in 50% hydrogen and 50% argon atmospheres, 1 atm pressure and a flux of 50 cm 3/min each one. The hydrogen concentrations are measured using Elastic Recoil Detection Analysis technique; meanwhile the roughness is measured using an Atomic Force Microscope. X-ray Diffraction analysis shows changes in crystal orientation due to hydrogen absorption. The hydrogen capacity of the Ti–6Al–4V alloy is observed to be directly correlated to the surface quality of the sample during the first hydrogenation cycles, but in the fourth cycle, the hydrogen absorption is almost equal for all the samples independently of their surface roughness.

Influence of porosity on mechanical properties and in vivo response of Ti6Al4V implants

Metallic biomaterials are widely used to restore the lost structure and functions of human bone. Due to the large number of joint replacements, there is a growing demand for new and improved orthopedic implants. More specifically, there is a need for novel load-bearing metallic implants with low effective modulus matching that of bone in order to reduce stress shielding and consequently increase the in vivo lifespan of the implant. In this study, we have fabricated porous Ti6Al4V alloy structures, using laser engineered net shaping (LENS™), to demonstrate that advanced manufacturing techniques such as LENS™ can be used to fabricate low-modulus, tailored porosity implants with a wide variety of metals/alloys, where the porosity can be designed in areas based on the patient’s need to enhance biological fixation and achieve long-term in vivo stability. The effective modulus of Ti6Al4V alloy structures has been tailored between 7 and 60 GPa and porous Ti alloy structures containing 23–32 vol.% porosity showed modulus equivalent to human cortical bone. In vivo behavior of porous Ti6Al4V alloy samples in male Sprague–Dawley rats for 16 weeks demonstrated a significant increase in calcium within the implants, indicating excellent biological tissue ingrowth through interconnected porosity. In vivo results also showed that total amount of porosity plays an important role in tissue ingrowth.

Evaluation of surface-modified Ti–6Al–4V alloy by combination of plasma-carburizing and deep-rolling

Plasma surface diffusion processes such as plasma-carburizing and nitriding have been used to improve tribological properties of titanium and its alloys. However, the improvement of fatigue strength by these processes has not been successful due to brittleness introduced in the high-hardness surface layer and the disappearance of compressive residual stress and grain growth by heating. In this work, a Ti–6Al–4V alloy sample was plasma-carburized at a relatively low temperature to improve wear resistance, and then, deep-rolled to induce compressive residual stress. Scanning electron microscopy, optical microscopy, laser scanning microscopy, surface roughness tester, X-ray diffractometer, and micro-hardness tester were used to characterize the modified surface layer. The residual stress and work hardening state was analyzed by X-ray diffraction techniques. The effect of deep-rolling on fatigue strength and wear resistance of plasma-carburized Ti–6Al–4V alloy was also investigated. The fatigue properties and wear resistance of Ti–6Al–4V alloy modified by a combination of low-temperature plasma-carburizing and deep-rolling were significantly improved in comparison with those of the unmodified Ti–6Al–4V alloy.

Measurement of the reversible hydrogen storage capacity of milligram Ti–6Al–4V alloy samples with temperature programmed desorption and volumetric techniques

We report the results of a study using temperature programmed desorption (TPD) and a volumetric sorption technique to measure the hydrogen storage capacity of the Ti–6Al–4V alloy. Samples of various sizes and surface treatments were studied to obtain a statistically meaningful value for the maximum hydrogen storage capacity, as well as to understand the effect of sample size, sample oxidation, and hydrogen charging conditions on the measured capacity. We find a maximum reversible hydrogen storage capacity of ∼3.76 wt% with hydrogen exposures near ambient temperature and pressure. This value is higher than any reported in the literature previously, possibly due to the utilization of very small particles and rapid hydrogen exposures, which allow for equilibration times of approximately 1 h. Comparison of a variety of samples indicates that the measured hydrogen capacity is affected by surface oxidation. Samples generated in a strongly oxidizing environment exhibit decreased hydrogen uptake. The implications of these results are discussed with regards to previously reported capacity values in the literature.

Saddle field fast atom beam source: A new low pressure plasma nitriding method for a alloy Ti–6Al–4V

Ti and its alloys (Ti–6Al–4V) have been used in different engineering applications due to their several outstanding properties. Nevertheless, their use in practical applications is limited in many cases due to their poor tribological property. Researches are ongoing on surface modification of Ti based materials by different plasma and ion based techniques to overcome this problem. However, the conventional plasma nitriding techniques have several problems such as formation of an arc, increased possibility of surface contamination due to a comparatively higher operating pressure, production of a very thin nitrided layer after a long processing time, etc. In this present work, the possibility of a new low-pressure plasma nitriding process using a Plasma Enhanced Chemical Vapor Deposition (PECVD) based saddle field fast atom beam source on a Ti–6Al–4V alloy sample is investigated. Plasma nitriding was carried out at 900 °C and at a pressure 0.1 Pa for 8 h by using a beam current 0.5 A. Optical Microscopy investigation of the cross-section of the nitrided sample revealed a compound nitrided layer (thickness approximately 16 μm) followed by a diffusion layer. X-Ray Diffraction (XRD) analysis confirmed the presence of a TiN phase in the nitrided layers. A roughly three fold higher hardness value (1578 HV 0.015) in the top nitriding layer was observed by Vickers microhardness testing compared to hardness value of untreated sample (568 HV 0.015),with a gradually decreasing hardness in the core material. The results show that this is a promising method for low pressure plasma nitriding of Ti alloy within a short processing time compared to the conventional nitriding process.

On the correlation between Nd:YAG laser-induced wettability characteristics modification and osteoblast cell bioactivity on a titanium alloy

The factors responsible for modifications to the wettability characteristics of a titanium (Ti6Al4V) alloy bio-metal following Nd:YAG laser treatment and the effects thereof on the response of osteoblast cells were considered in this work. It was found that interaction of the Nd:YAG laser beam with the Ti6Al4V alloy resulted in the wettability characteristics of the bio-metal improving. Such improvements in the wettability characteristics of the Ti6Al4V alloy were found to be due to: an increase in the surface roughness; and increase in the surface oxygen content and an increase in the polar component of the surface energy. From the cell response tests it was determined that the osteoblast cell adhesion and proliferation on the Nd:YAG laser treated Ti6Al4V alloy samples was considerably greater than on the untreated samples. By isolating the effects of surface roughness it was possible to confirm or refute the existence of a correlation between wettability characteristics and osteoblast cell bioactivity for the Nd:YAG laser treated Ti6Al4V alloy. The findings indicated that the aspects of wettability characteristics: surface oxygen content and polar component of the surface energy play an important role in promoting cell proliferation, particularly when surface roughness was simultaneously increased. Thus it was possible to conclude that the wettability characteristics of the Nd:YAG laser treated Ti6Al4V alloy were correlated to osteoblast cell bioactivity.

Effects of surface treatment of Ti–6Al–4V titanium alloy on biocompatibility in cultured human umbilical vein endothelial cells

Among the titanium alloys employed as implant materials, the Ti–6Al–4V alloy is still widely used. Ti–6Al–4V titanium alloy samples, in untreated state and subjected to treatments in air by furnace or glow-discharge processes, were put in contact with human umbilical vein endothelial cells (HUVEC) in order to evaluate their effects on biocompatibility. In HUVEC kept for 48 h in the presence of the three sample types neither cell proliferation nor protein content nor lactate dehydrogenase release in the culture medium are affected, while apoptosis is induced after 48- and 96-h contact of the cells with the untreated sample type, and after 96-h contact with the plasma treated one, the furnace treated sample type being ineffective. The expression of two adhesion molecules, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) was also studied. The incubation of HUVEC with the three sample types for 48 or 96 h induces a significant increase in ICAM-1 protein levels, in comparison with control cells, while VCAM-1 expression is not detectable. In the same way, TNF-α release in the culture medium, assayed after 48- and 96-h contact of the cells with the three sample types, is significantly higher, in comparison with control, even if the highest values are registered in the presence of the untreated samples. Taken together, these data indicate that, although Ti–6Al–4V alloy samples, and in particular the treated ones, show a good biocompatibility, attention must be given to the first signs of inflammation.

Plasma surface modification of Ti and TiAlV alloy

AbstractSurface modification of commercially pure Ti and of Ti6Al4V alloy samples was performed by plasma immersion ion implantation with 25 kV energy. Plasma was generated by RF discharge in air, in nitrogen, or in a mixture of nitrogen and methane. Treatment in air plasma produced an oxide layer on the surface without appreciable incorporation of nitrogen, as detected by XPS. Significant surface enrichment of aluminium was measured after air plasma treatment of Ti6Al4V, but no such segregation was observed after nitrogen plasma treatment. These effects are interpreted by involvement of thermodynamic driving forces. Development of rutile and a sub‐stoichiometric oxide were identified on Ti while no crystalline phases could be evaluated on the Ti6Al4V upon oxidation. The cubic TiN phase was found after nitrogen PIII treatment on both Ti and Ti6Al4V. Nanomechanical tests showed a significant increase in the hardness for Ti6Al4V after oxidizing PIII treatment in air. Considerable change in hardness could not be measured, however, after nitriding PIII treatments. Copyright © 2004 John Wiley & Sons, Ltd.