Titanium Alloy Ti6Al4V Research Articles

Mechanical Surface Treatment of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering Using Laser Cavitation

Additive manufactured (AM) metals are attractive materials for medical implants, as their geometries are directly produced from computer-aided design (CAD)/computer-aided manufacturing (CAM) data. However, the fatigue properties of AM metals are weak compared with bulk metals, which is an obstacle to the practical applications of AM metals. To improve the fatigue properties of AM metals, we developed a mechanical surface treatment using laser cavitation. When we irradiate a pulsed laser to a metallic surface in water, laser ablation is generated, and a bubble that behaves like a cavitation is produced. The bubble is referred to as a “laser cavitation”. In the surface treatment using laser cavitation, we use the plastic deformation caused by the impact force at the bubble collapse and pulsed laser energy that produces local melting at the same time. Thus, the mechanical surface treatment using laser cavitation is a type of surface mechanical alloying. In this study, to demonstrate the improvement in the fatigue properties of AM metals, we treated titanium alloy Ti6Al4V, which was manufactured by direct metal laser sintering (DMLS), with laser cavitation, and we evaluated the surface morphology, roughness, residual stress, hardness, and finally tested it using a torsion fatigue test. Unmelted particles on the DMLS surface, which cause fatigue cracks, were melted and resolidified using laser cavitation, resulting in a reduction of the maximum heights of roughness (Rz) of about 75% and the arithmetical mean roughness (Ra) of about 84% of the non-peened one. Although tensile residual stresses of about 80–180 MPa were generated on the as-built surface, compressive residual stresses of about −80 MPa were introduced by laser cavitation. Furthermore, laser cavitation formed Ti4O5 oxide film, which increased the surface hardness by about 106%. Finally, we performed torsional fatigue tests and revealed that laser cavitation extended the fatigue life from 19,791 cycles to 36,288 cycles at an applied shear stress (τa) at 460 MPa, which is effective in suppressing crack initiation.

Tailoring microstructure of additively manufactured Ti6Al4V titanium alloy using hybrid additive manufacturing technology

An innovative hybrid additive manufacturing (HAM) technology combining laser shock peening without coating (LSPwC) and laser powder bed fusion (LPBF) has been proposed to tailor the microstructure of additively manufactured Ti6Al4V titanium alloys. Herein, we investigated the characteristics and evolution of interfacial microstructures between adjacent LPBF layers using electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). The experimental results demonstrated that the martensitic laths in the LSPwC-treated region changed to equiaxed ultrafine grains under alternating mechanical and thermal effects. Moreover, the LSPwC-induced shock wave caused a transformation in the interface bonding behavior at the interface between the adjacent LPBF layers from the transitivity mechanism to the impregnation mechanism. Based on these results, the LSPwC-induced microstructural evolution mechanism at the interface between adjacent LPBF layers is related to LSPwC pre-activated high-density dislocations and nano twins that promote recrystallization during LPBF new layers and the formation of ultrafine equiaxed grain interlayers. Consequently, compared with the LPBF specimen, the HAM specimen indicated a high ultimate tensile strength of ∼1303 MPa and an excellent elongation of ∼12.7 %.

Bonded and additively manufactured crack retarders: A comparative study of damage tolerance properties

Fatigue crack grows faster in the integral structure than in the riveted structure. This study compares the bonded, cold-sprayed and ultrasonically consolidated crack retarders to increase the fatigue life of integral airframe structure. The 2024-T351 aluminum M(T) specimen reinforced with crack retarders made of AISI 301 and 316L steels, Ti–6Al–4V titanium alloy and unidirectional CFRP laminate are evaluated in terms of fatigue life, delamination resistance and weight efficiency. Specimens were subjected to constant amplitude loading up to the final failure. A substantial decrease in fatigue crack growth rate was achieved using the ultrasonically consolidated AISI 301 crack retarder.

Effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints

Abstract The main objective of this investigation is to study the effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints. The dissimilar joints of Ti6Al4V titanium alloy and AISI 304 steel were developed using the different levels of bonding time (30, 45, 60, 75 and 90 min) in a vacuum chamber at a bonding temperature of 900 °C and compressive pressure of 14 MPa. The microstructure of joints was analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). The elemental analysis of joint interface was studied using the SEM energy dispersive spectroscopy (EDS). The evolution of intermetallic compounds at the joint interface was analyzed using X-ray diffraction (XRD). The ram tensile tests and lap shear tests were performed to assess the bonding strength and lap shear strength of dissimilar joints. Results showed that the dissimilar joints of Ti6Al4V alloy–AISI 304 steel developed using the diffusion bonding time of 75 min showed higher lap shear strength of 151 MPa and bonding strength of 244 MPa due to the better coalescence of the joining surfaces and evolution of optimum width of diffusion region having minimum embrittlement effects.

Microstructure transformed by heat treatment to improve fatigue property of laser solid formed Ti6Al4V titanium alloy

Additive manufacturing (AM) can manufacture near-net-shape metal parts with complex geometries, but their fatigue performance limits wide application. In this work, the heat treatment was optimized to change microstructure to improve fatigue performance of laser solid formed Ti6Al4V alloys. After heat treatment at 800 °C for 4 h, the distribution of α plate transformed from colony to basket-weave, and the fatigue limit increased from 203 MPa to 225 MPa at a stress ratio of 0.1. The results showed that the basket-weave structure affected the original texture of the colony and changed the fatigue crack propagation path. This effectively improved the fatigue life to expand the application potential of additive manufacturing parts.

Electrochemical deposition of a hydroxyapatite layer onto the surface of porous additively manufactured Ti6Al4V scaffolds

Successful acceptance of biomaterials by a patient's body significantly depends on an interaction between the surface and the biological components of the host environment. In the case of orthopedic scaffolds, surface treatment may improve their osseointegration. This study deals with the electrochemical deposition of ceramic hydroxyapatite (HAp) coatings onto additively manufactured titanium specimens with a porous structure. The specimens of three different types (pore sizes of 200, 400, and 600 μm) were modeled using CAD software and fabricated using the Ti6Al4V titanium alloy. HAp coatings were electrochemically deposited onto the surface of un-annealed specimens using four different experimental conditions. Based on the results and optimization of the conditions with the un-annealed specimens, ideal conditions were selected for the coating of the annealed specimens. The nature of the ceramic layer on un-annealed and annealed samples was compared. Surface morphology and distribution of ceramic coatings on the surface of the specimens were compared and evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). The un-annealed specimens exhibited more compact surfaces and larger deposits of nanocrystalline HAp when compared to the annealed specimens. The results indicate that electrochemical deposition is a suitable method for the production of a ceramic coating layer onto the surface of porous titanium specimens with promising potential for clinical applications.

High-entropy TiAlCuFeNiV electrospark coating on titanium alloy Ti6Al4V

High-entropy TiAlCuFeNiV coatings were prepared on titanium alloy Ti6Al4V by electrospark deposition with a non-localized electrode using an equimolar anode mixture consisting of granules of pure metals and alloys. During the ESD process, the electrical erosion of granules made of different metals proceeded with different intensities, which determined the ratio of metals in the coating. The thickness of the coatings was in the range from 20 to 24.7 μm. According to the data of X-ray phase analysis, the structure of the coatings is represented by a solid solution with a body-centered cubic (bcc) lattice and CuTi3, FeTi, Al65Cu20Fe15, and Ni35Al30Ti35 intermetallic compounds, and the proportion of intermetallic compounds increased with increasing pulse duration during ESD. Coatings were tested for oxidation resistance at a temperature of 900 °C and corrosion resistance by impedance spectroscopy and potentiodynamic polarization in a 3.5 % NaCl solution, as well as microhardness, friction coefficient and wear of coated samples with depending on the discharge pulses duration.

Enhancing useful flow of cutting fluid and thermal performance in surface grinding via segmented wheel

Cutting temperature is reported to be a serious concern while grinding aerospace materials such as titanium alloy Ti6Al4V, which is having very low thermal conductivity. Segmented wheels designed with active abrasive regions and passive non-cutting slots have been proposed as a potential solution for thermal management in the grinding zone. Reduced accumulation of heat due to intermittency in cutting and enhanced dissipation through passive slots could exhibit improved temperature control even at dry grinding conditions. As the number of segments increased, the grinding force was significantly reduced for Ti6Al4V. Under the wet cutting condition, the segmented wheel could facilitate a more effective flow of cutting fluid into the passive slots, which is referred to as useful flow. However, there was a trade-off set by the number of segments, where an eight-segmented wheel showed superior thermal performance in comparison with the 32-segmented wheel. The reasoning of the same in terms of useful flow patterns and boundary layer thickness has been attempted in this paper.

Биосовместимость Ti – Al интерметаллидных покрытий на титановом сплаве Ti6Al4V

Titanium alloy Ti6Al4V is the most common metal material in orthopaedics. However, it is characterized by high elasticity and bioinertness, which makes it difficult to osseointegrate on its surface and leads to aseptic loosening of the implant, has insufficient corrosion resistance and high wear, leading to the accumulation of metal ions and wear particles in the body of patients. To eliminate these shortcomings, a Ti – Al coating was prepared by electrospark processing of the Ti6Al4V alloy in an equimolar mixture of titanium and aluminum granules. The prepared TiAl coating consists of intermetallic phases: Ti3Al, TiAl, TiAl2, and TiAl3, which have higher tribological properties. Thus, the average value of the friction coefficient of the sample with a TiAl coating was 12% lower, and the reduced wear was 2.36 times less than the original Ti6Al4V alloy one in a simulating body fluid. In addition, the deposition of a TiAl coating on the Ti6Al4V alloy makes it possible to increase the corrosion resistance of its surface. Biomedical studies have shown that the deposition of a TiAl coating on a Ti6Al4V alloy increases the resistance of erythrocytes to the hemolytic agent action. Improving the biological activity of the alloy surface during ESA deposition of TiAl coating leads to normal growth of fibroblasts on it without signs of cytotoxity. Treatment of samples with adhered cell culture by a solution of trypsin-Versen led to a reduction in the density of cells in the coating by 42 %, while in the alloy by 60 %. This indicates a better fibroblast attachment to the surface of the Ti-Al coating, compared to the Ti6Al4V alloy.

A physics-based constitutive model for machining simulation of Ti-6Al-4V titanium alloy

Today, simulation of cutting processes still relies, in most cases, on the phenomenological representation of flow stress properties of workpiece materials. This investigation presents a physics-based (dislocation-based) constitutive model to simulate the flow stress properties of Ti6Al4V titanium alloy at elevated temperatures and a large range of strain rates. The Split Hopkinson Pressure Bar (SHPB) data and inverse modelling of orthogonal cutting tests are combined using a novel approach to obtain flow stress properties and to calibrate the damage and friction models. The applicability of the presented model for cutting simulation is critically discussed.

Optimization of TIG Welding Parameters for Ti-6Al-4V Titanium Alloy using the Taguchi Design of Experiment

This paper presents the effect of tungsten inert gas welding parameters (i.e. welding current, welding speed and filler wire speed) on weld bead geometry, notch tensile strength (NTS) and weld bead hardness of 2.0 mm thick annealed Ti6Al4V titanium alloy sheet welded in a square butt joint configuration using Taguchi L9 (33) three level - three factor matrix. Taguchi’s signal to noise ratios was calculated to obtain optimum welding parameters for Vickers hardness at weld area, Notch tensile strength (NTS), Front bead width (FBW) and Front reinforcement height (FRH). Analysis of Variance (ANOVA) was conducted to find statistically significant and insignificant factors with respect to each response. It was noted that welding speed has significant effect on weld hardness, notch tensile strength, front bead width and height. Optimum parameters for hardness were found to be 120A current, 400 mm / min welding speed and 250mm/min filler wire speed. Confirmation test using the optimal levels of welding parameters was also conducted in order to compare predicted results with values obtained through experimentation.

Study on In-Situ Tool Wear Detection during Micro End Milling Based on Machine Vision.

Most in situ tool wear monitoring methods during micro end milling rely on signals captured from the machining process to evaluate tool wear behavior; accurate positioning in the tool wear region and direct measurement of the level of wear are difficult to achieve. In this paper, an in situ monitoring system based on machine vision is designed and established to monitor tool wear behavior in micro end milling of titanium alloy Ti6Al4V. Meanwhile, types of tool wear zones during micro end milling are discussed and analyzed to obtain indicators for evaluating wear behavior. Aiming to measure such indicators, this study proposes image processing algorithms. Furthermore, the accuracy and reliability of these algorithms are verified by processing the template image of tool wear gathered during the experiment. Finally, a micro end milling experiment is performed with the verified micro end milling tool and the main wear type of the tool is understood via in-situ tool wear detection. Analyzing the measurement results of evaluation indicators of wear behavior shows the relationship between the level of wear and varying cutting time; it also gives the main influencing reasons that cause the change in each wear evaluation indicator.

Force enhanced wire laser additive manufacturing of aluminum and titanium alloys

Brittle intermetallic compound formation is typically difficult to avoid during fusion joining of dissimilar metals. In this paper, a new approach called force enhanced wire laser additive manufacturing is proposed to join aluminum and titanium alloys. Ti6Al4V titanium alloy single track was additively fabricated on AA7075 plate successfully, through two liquid pools of the wire and the substrate, separated by a buckled unmelted part of the wire, leading to a mechanically interlocked interface. The effects of manufacturing parameters including laser power, wire feeding speed, scanning speed and initial contact force between wire and substrate on the surface morphology, internal interface microstructure and formation of intermetallic compounds were investigated through high-speed camera, spectrometer, laser topography, optical imaging, SEM imaging, XRD characterizations along with numerical simulations at different scales. And the maximum tensile strength reached 380 MPa in the tensile test. The experimental and numerical results indicate that the thermal modulation approach can effectively control the formation of brittle compounds between titanium and aluminum alloys and that the initial contact force ensures a good bond between the two metals.

Electric discharge drilling of blind holes in titanium alloy Ti6Al4V

PurposeThis experimental study aims to deal with the improvement of process performance of electric discharge drilling (EDD) for fabricating true blind holes in titanium alloy Ti6Al4V. Micro EDD was performed on Ti6Al4V and blind holes were drilled into the workpiece.Design/methodology/approachThe effects of input parameters (i.e. voltage, capacitance and spindle speed) on responses (i.e. material removal rate, tool wear rate and surface roughness [SR]) were evaluated through response surface methodology. The data was analyzed using analysis of variance and multi-optimization was performed for the optimized set of parameters. The optimized process parameters were then used to drill deeper blind holes.FindingsBlind holes have few characteristics such as SR, taper angle and corner radius. The value of corner radius reflects the quality of the hole produced as well as the amount of tool roundness. The optimized process parameters suggested by the current experimental study lower down the response values (i.e. SR, taper angle and corner radius). The process is found very effective in producing finished blind holes.Originality/valueThis experimental study establishes EDD as a feasible process for the fabrication of truly blind holes in Ti6Al4V.

Laser Welding of Ti6Al4V Titanium Alloy in Air and a Water Medium.

Ti6Al4V titanium alloys are widely used in a variety of scientific and industrial fields. Laser beam welding is one of the most effective techniques for the joining of titanium plates. The main objective of this study was to investigate the influence of the most important laser parameters on welding performance of titanium alloy in two different physical environments such as air and water (i.e., serum) media. Specifically, the laser beam welding of 2 mm thick Ti6Al4V samples was applied using an Nd:YAG laser in open-air welding using argon as a shielding gas, and in wet welding using a serum environment. The deepest penetration was achieved at -3 mm focal position with 11 J of laser energy in both investigated media (i.e., air and serum). The maximum hardness (1130 HV) was achieved for the focal position of -4 mm in serum medium while it was 795 HV for a focal position of -5 mm in air medium. The minimum (1200 μm and 800 μm) and maximum (1960 μm and 1900 μm) weld widths were observed for air and serum medium, respectively. After the welding process, martensite, massif martensite, and transformed martensite were observed in the microstructure of Ti6Al4V. To the best of our knowledge, the underwater wet welding of titanium alloy was carried out and reported for the first time in this study.

Study of the Tribological Properties of HVOF-Sprayed Ni-Based Coatings on Ti6Al4V Titanium Alloys

In aviation, the relative sliding between titanium alloy components causes varying degrees of wear. This work aimed at reducing abrasion between titanium alloy parts and improving their service life. Three different Ni-based coatings, WC-10Ni, Ni45, and NiCr coatings, are sprayed on the surface of Ti6Al4V alloy by HVOF. Test results of the mechanical and tribological properties of such coatings show that the hardness of the Ni45 and NiCr coatings are 673 HV0.1 and 438 HV0.1, respectively, which are lower than that of the WC-10Ni coating. When subjected to a high load, the Ni45 and NiCr coatings suffer a cracking of flat particle interfaces due to the low hardness, which lowers the fracture toughness more than that of the WC-10Ni coating. The specific wear rates of the coatings gradually decrease with the increase in the coating hardness and fracture toughness. However, the cutting of Ti6Al4V by the WC-10Ni coating and the adhesion of the NiCr coating to Ti6Al4V result in severe wear loss of the Ti6Al4V friction pair. The moderately hard Ni45 coating has a weaker cutting and adhesion effect on Ti6Al4V than the WC-10Ni and NiCr coatings, respectively, and the Ti6Al4V friction pair has the lowest wear loss. This study is a viable scheme for the design of wear-resistant coatings on titanium alloy surfaces and for improving the tribological properties between titanium alloy components.

Properties of Cold Sprayed Titanium and Titanium Alloy Coatings after Laser Surface Treatment.

Additive manufacturing (AM) has seen remarkable development in recent years due to relatively high efficiency of the process. Cold spraying (CS) is a particular method of AM, in which titanium and titanium alloy powders are used. CS is a very competitive technology enabling the deposition of coatings, repairing machine parts, and manufacturing new components. For specific applications, the surface of cold-sprayed materials may require further processing. This paper reports an attempt to employ laser surface treatment (LST) of cold-sprayed coatings on an aluminium alloy substrate. The influence of laser beam interaction time on the coatings' properties was analysed. The microstructure was investigated and observed employing scanning electron microscopy (SEM). To evaluate residual stress after CS and LST, the sin2ψ technique was used. Investigations were also performed on Vickers hardness, contact angle, and surface roughness. Significant changes in the surface morphology of the coatings and elevated residual stress levels dependent on the laser beam interaction time were observed. Increased Vickers hardness was recorded for titanium alloy Ti6Al4V. LST also led to increased surface hydrophilicity of the modified materials Ti and Ti6Al4V.

Influence of heat accumulation on the distribution uniformity of microstructure and mechanical properties of laser additive manufacturing joint of 80 mm thick Ti6Al4V titanium alloy plates

Laser additive manufacturing (LAM) with directed energy deposition (DED) as the predominant foundation is an efficient and flexible joining technology that makes the fabrication of components with large thicknesses and complex structures possible. Heat accumulation phenomena caused by successive layer deposition strongly affect the microstructure and properties of components created with LAM. This study presents the conditions for component joining of constant process parameters and laser power gradient reduction process parameters to compare and investigate the influence of heat accumulation on the uniformity of mechanical properties and microstructure. The effects of the thermal cycle curve in different zones during LAM on the microstructure and mechanical properties of the top, middle and bottom of the deposition zone (DZ) under various parameters were investigated through finite element simulation and experiment. Results indicated that the cooling speed at the top of the DZ is slow and the heat accumulation effect is high. The aspect ratio of the α phase at the top of the deposition zone is high and high heat accumulation deteriorates mechanical properties. The heat accumulation effect is weakened when the gradient process parameters are used for joining. The content and size of the α phase at different joint heights are further homogenized. The tensile strength difference at various positions decreases and is higher than the tensile strength of the joint under constant parameters. This study promotes the LAM technology and provides a control reference for heat accumulation and microstructure regulation of large-thickness Ti6Al4V titanium alloy joints fabricated by LAM.

Modeling of Laser Shock Processing Technology Using an Artificial Neural Network to Determine the Mechanical Properties of the Ti–6Al–4V Titanium Alloy

Modeling of Laser Shock Processing Technology Using an Artificial Neural Network to Determine the Mechanical Properties of the Ti–6Al–4V Titanium Alloy

Optimization of Titanium Alloy Drilling to Minimize the Secondary Burr after Deburring Process.

The formation of burrs on the edges of machined surfaces is one of the inherent problems during machining. The burrs are formed both on the tool entry surface and exit surfaces. The paper proposes a modification of the drill involving an additional cutting insert located in the shank part. This innovative solution allowed the drill and deburring insert to be integrated, enabling both processes to be performed within one machining operation. The impact of the selected insert geometry and deburring process parameters on the size of burrs was determined during the experimental studies. Using the proposed deburring process for the Ti6Al4V titanium alloy, with appropriately chosen tool geometry and cutting parameters, reduces the secondary burr height by more than 90% compared to the original value.