Titanium Alloy Ti 6Al Research Articles

Analytical investigation of workpiece internal energy generation in peripheral milling of titanium alloy Ti–6Al–4V

Energy management is crucial to the cutting process where generation and conversion of various forms of energy is occurring. Reducing the energy that stored in the machined surface layer can significantly improve the quality of processing and dimensional stability of machined structures. To achieve this, an accurate energy conversion model is required. In the present study, energy generation and conversion process during peripheral milling titanium alloy Ti–6Al–4V are investigated. Analytical model of cutting energy that acted on the machined surface is first established. And then, energy criteria for machining-induced residual stress field are proposed, and the energy that stored in the machined surface layer is calculated on the basis of the measured residual stress. Finally, a Q-factor is proposed to relate cutting energy to workpiece internal energy. By experimental analysis, there is about 10.86% of the energy that acted on the machined surface converted to the workpiece internal energy. On the basis of the proposed energy conversion model, the influences of milling processing parameters on the machining-induced material internal energy are revealed. According to the research results, the increase in cutting speed, feed rate and radial depth of cut increase the machining-induced material internal energy, and it is the cutting speed and feed per tooth that turn out to be the chief reasons for energy conversion in peripheral milling.

Tool wear monitoring in milling of titanium alloy Ti–6Al–4 V under MQL conditions based on a new tool wear categorization method

Tool wear monitoring is crucial during machining of difficult-to-cut materials to save cost and improve efficiency. In this paper, a tool wear–monitoring strategy was proposed for milling of titanium alloy Ti–6Al–4 V under inner minimum quantity lubrication (MQL) conditions. Unlike the usual categorization method, tool wear was categorized into four states based on tool wear mechanism, tool wear rate, and tool life. Thus, more detailed information of tool could be predicted for tool wear monitoring. Cutting forces and acoustic emission were measured online as raw datasets. Statistical features were extracted from time and frequency domain, and mutual information (MI) was used for feature selection. Then, linear discriminant analysis (LDA) was adopted for dimensionality reduction and finding the optimal datasets for training. At last, ν-Support vector machine (ν-SVM) was applied for training and prediction. The proposed strategy had a prediction accuracy of 98.9%, which could be considered as valid and useful for tool wear monitoring.

Development of Microstructure and Texture of β Solution-Treated and Aged Metastable Beta Titanium Alloy Ti–5Al–3.5Mo–7.2V–3Cr

Present paper describes the development of microstructure and texture of metastable β titanium alloy Ti–5Al–3.5Mo–7.2V–3Cr in aged condition of β solution-treated and water-quenched (β ST WQ) samples. The β ST WQ samples were aged at different temperatures (550, 650, and 750 °C) and at different aging times (1, 2, and 4 h). The different morphologies of α phase precipitates have been observed during aging of the β ST WQ sample. These are grain boundary α, islands α, sub-boundary α, and uniform distribution of α within prior β grains. The size of the α phase precipitates increases, while volume fractions decrease with increase in aging temperature. The higher aging temperature has reflected the presence of precipitation-free zone (PFZ) within the surrounding area of prior β grain boundaries. The low and high temperatures aging have resulted in sharp {0001} || ND fiber and very weak texture in α phase, respectively. The hardness increases from β ST WQ to all aging temperatures due to precipitation hardening. The specimen aged at 550 °C has resulted in maximum hardness as a result of precipitation of fine α phase precipitates.

Investigation of Tool Wear and Chip Morphology in Dry Trochoidal Milling of Titanium Alloy Ti-6Al-4V.

Titanium alloys are widely used in the manufacture of aircraft and aeroengine components. However, tool wear is a serious concern in milling titanium alloys, which are known as hard-to-cut materials. Trochoidal milling is a promising technology for the high-efficiency machining of hard-to-cut materials. Aiming to realize green machining titanium alloy, this paper investigates the effects of undeformed chip thickness on tool wear and chip morphology in the dry trochoidal milling of titanium alloy Ti–6Al–4V. A tool wear model related to the radial depth of cut based on the volume of material removed (VMR) is established for trochoidal milling, and optimized cutting parameters in terms of cutting speed and axial depth of cut are selected to improve machining efficiency through reduced tool wear. The investigation enables the environmentally clean rough machining of Ti–6Al–4V.

Improvement of the fretting wear resistance of Ti6Al4V by application of hydrostatic ball burnishing.

The objective of the research was to improve the fretting wear resistance of titanium alloy by hydrostatic ball burnishing. Ball burnishing is an economic surface finishing process for wide range of components. It is based on pressing and rolling a hydraulically floated ball along the surface of the component being treated, to plastically deform surface asperities. This process generates a deep field of compressive residual stresses (up to 1.0 mm) in the outer layers of the component. The compressive residual stresses and the high quality of the surface finish improve the wear resistance of the part. Experiments were made using ball-on-disc tribotester in oscillatory motion. 100Cr6 sphere co-acted with a disc made of titanium alloy Ti–6Al–4V. The friction force was monitored as a function of time during the test. Wear of disc was measured after the test using the non-contact 3D surface profiler. The optimal ball burnishing parameters have been determined after conducting the Taguchi L9 matrix experiment. During tests, normal load was kept constant at 50 N within the contact with frequency of 50 Hz and displacement amplitude of 0.02 mm. The results confirmed that hydrostatic ball burnishing had a significant influence on friction and wear.

Effect of the Beam Current during the Electron-Beam Melting of Titanium Alloy Ti–6Al–4V on the Structural Features and Phase Transitions in Gas-Phase Hydrogenation

The structure of the titanium alloy Ti–6Al–4V manufactured by electron-beam melting is shown to be represented by initial β-phase grains more than 40 μm in size; the internal volume of the grains is filled with α-phase precipitates in the form of plates. The average size of the α plates is 1.6, 2, and 5 μm at beam currents of 2, 2.5, and 3 mA, respectively. In situ X-ray diffractometry using synchrotron radiation shows that the phase transitions in the titanium alloy are divided into three main stages during hydrogenation to a concentration of 0.6 wt % at a temperature of 650°C and a pressure of 1 atm. An increase in the beam current from 2 to 3 mA does not significantly affect the phase composition of the alloy. During hydrogenation, the growth rate of the volume concentration of the β phase is lower at a higher beam current. This indicates a decrease in the rate of hydrogen absorption with increasing beam current, which is associated with an increase in the size of α plates.

Twinning and its effect on the evolution of acicular α in Ti–5Al–5Mo–5V–3Cr–1Zr

ABSTRACTNear β titanium alloy Ti–5Al–5Mo–5V–3Cr–1Zr with acicular α microstructure was hot compressed at 750°C/10−3 s−1. Twinning and its effect on the evolution of acicular α were investigated. Twinning is induced from the dislocations pile-up at α/β boundary. The twinning system is . During twinning, one type of pure shear displacement and three types of shuffle + shear mixed displacement are confirmed. The twinning dislocation can be expressed as (b, 4h0), , h0 is the interplanar distance of , , κ = c/a. Substructures form in acicular α through the migration of twin boundary, followed by meeting another neighbouring parallel twin and then causing the twins-merging. And the accumulation of the twinning displacement results in the bending of acicular α.

Characterization of Hot Workability for a Near Alpha Titanium Alloy by Integrating Processing Maps and Constitutive Relationship

Hot workability of near‐alpha titanium alloy Ti–6Al–3Nb–2Zr–1Mo with an initial duplex microstructure is evaluated through isothermal compressions in lower α + β phase field, upper α + β phase field, and β phase field. It is noteworthy that flow stress increases with increasing strain rates and decreasing temperatures. Based on Dynamic Material Model and Prasad's instability criterion, processing maps are established and subdivided into six characterization regions to ascertain deformation mechanisms connected with microstructure. The results show that super‐plasticity deformation (SPD) and dynamic recrystallization (DRX) of β phase can be achieved in the area with high power dissipation efficiency in α + β phase field and β phase field, thus making them being the optimum hot working domains. Besides, DRX of lamellar α, dynamic recovery (DRV) of equiaxed primary α (αp) as well as DRV of β phase occur in the remaining safe domains with increasing temperature. The microstructure in instability domains, where hot deformation should be kept away, is characterized by flow localization. Arrhenius‐type constitutive model incorporated with strain compensations is selected to describe the high‐temperature flow behavior of the test Ti‐alloy. The introduction of three detailed divisions with temperature ranges gives an accurate calculation for apparent activation energy.

Peripheral milling-induced residual stress and its effect on tensile–tensile fatigue life of aeronautic titanium alloy Ti–6Al–4V

ABSTRACTThe special application environment puts forward the higher requirement of reliability of parts made from titanium alloy Ti–6Al–4V, which is closely related to the machining-induced residual stress. For the fact of the non-linear distribution of residual stress beneath the machined surface, distribution of peripheral milling-induced residual stress and its effect on fatigue performance of titanium alloy Ti–6Al–4V are still confusing. In the present study, residual stress profile induced by peripheral milling of Ti–6Al–4V is first studied. And then, energy criteria are proposed to characterise the whole state of the residual stress field. Finally, the effects of residual stress profile and surface energy on tensile–tensile fatigue performance of titanium alloy Ti–6Al–4V are discussed. The conclusions were drawn that the variation trend of surface residual stress (σr,Sur), maximum compressive residual stress (σC,ax), location (hr0) and response depth (hry) of residual stress profile with cutting parameters showed a similar pattern for both measure directions those parallel (σ1) and perpendicular (σ3) to the cutting direction. Cutting speed and feed rate have a main effect on surface residual stress, and the depth of cut has little effect on all the four key factors of residual stress profile. With the increase of cutting speed and feed rate, machining-induced surface energy tends to become larger. But increasing the depth of cut caused the strain energy stored in unit time to decrease. Furthermore, the effect of depth of cut on surface energy was weakened when the value of cutting depth becomes larger. Both the surface compressive residual stress and the maximum compressive residual stress are beneficial for prolonging the fatigue life, while large value of machining-induced surface energy leads to a decrease of fatigue life. Analysis of variance result shows that maximum residual compressive stress has a greater impact on fatigue life than other residual stress factors.

Increased Systemic Malondialdehyde Levels and Decreased Mo/Co, Co/Fe2+ Ratios in Patients with Long-Term Dental Titanium Implants and Amalgams.

Introduction: the biological safety of dental biomaterials has been questioned in human studies. Material and Methods: Several heavy metals/oligoelements were compared by Inductive Coupled Mass Spectrometry (ICP-MS) in hair samples from 130 patients (n = 54 patients with long-term titanium dental implants and amalgams (A + I group), 51 patients with long-term dental amalgam alone (A group), as well as controls (n = 25: without dental materials) of similar age. All patients (except controls) had had titanium dental implants and/or dental amalgams for at least 10 years (average: 17). We evaluated whether A + I patients could present higher systemic malondialdehyde levels (MDA) as compared to the A group. Results: The A + I group have lower molybdenum levels (A + I) and reduced Mo/Co and Mo/Fe2+ ratios, which could predispose them to oxidative stress by raising MDA levels as compared to the A group alone; our findings suggest that higher Co levels could enhance oxidative stress in the A + I group. However, there were no differences on metals from titanium alloy (Ti-6Al), Cr from crowns or Hg2+, Sn, Zn2+, Cu2+ levels between the A + I and A groups. Conclusion: patients with long-term dental titanium and amalgams have systemic oxidative stress due to rising MDA levels and lower Mo/Co and Mo/Fe2+ ratios than those with amalgams alone.

Microstructure and property of laser additive manufactured alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si after aged at different temperatures

The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures. In this study, the influence of aging temperatures (600, 700 and 800 °C) on microstructure and mechanical properties of titanium alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si was investigated. The results indicate that after solid solution treatment at 970 °C followed by water quenching, the alloy mainly consists of coarsening lamellar α phase in martensite α′ matrix. Aging at 600 °C will not change the size of primary lamellar α phase but lead to huge amount of secondary α phases (αs) generating with very fine microstructure. By increasing the aging temperature, the number of αs decreases but with coarsened microstructures. When aged at 800 °C, the width of the αs phase reaches 350 nm, almost 7 times wider than that aged at 600 °C. The changing size of αs obviously influences the property of the alloy. The fine αs leads to high strength and microhardness but low plasticity, and specimen aged at 700 °C with suitable αs size has the best comprehensive properties.

Biological activity of the implant for internal fixation.

Early treatment of bone fractures was performed using implants, which are often used in the form of plates of various types, which are fixed on the bone surface (extracellular fixation) and nails that are located in the medullary canal (intracerebral fixation). The goal of this study was to investigate the features of osseointegration of implants for internal fixation (intramedullary or extramedullary) with various bioactive coating techniques. During experimental study on 20 mongrel dogs, the implant model in the form of 1.0-mm plate made of titanium alloy (Ti6Al 4V) was placed in the medullary canal (first series) or under the periosteum (second series): the plates had bioactive coating (hydroxyapatite) produced using the technology of magnetron sputtering (six animals), plasma electrolytic oxidation or microarc oxidation technology (PEO; eight animals), and composite technology (six dogs). Anatomic and histological studies have shown that the process of active osseointegration of porous implants with bioactive coating begins after 7days: at first, granulation tissue - and then fibrous connective tissue - is formed; after 14days, the osteogenic substrate can be found, and after 28days, the entire implant area is covered by the lamellar bone tissue, which creates single implant-bone block. The most active formation of bone tissue is observed around implants with bioactive coating produced using the last two technologies. Low traumatic placement of porous implants with bioactive coating in the medullary canal or subperiosteally provides the stimulation of reparative osteogenesis and rapid (especially with PEO technique) osseointegration of the implant.

Electrochemical and Tribological Behavior of Surface-Treated Titanium Alloy Ti–6Al–4V

To enhance its low wear resistance, a surface treatment of ion nitriding was performed for Ti–6Al–4V titanium alloy. Structural characteristics of specimens were revealed by optical and scanning electron microscopy, and tribological behavior was evaluated using ball-on-disk tribometer by application of two different charges 5 N and 10 N. Electrochemical methods of potentiodynamic polarization curves and electrochemical impedance spectroscopy were used to evaluate the effect of this thermochemical treatment on the corrosion resistance of the studied alloy. Results showed that microhardness of nitrided Ti–6Al–4V represents a value greater with four, five times than that of the untreated alloy. The coefficient of friction was also optimized for the two charges applied. SEM analysis of the worn surfaces indicates that the wear of treated Ti–6Al–4V stills just superficial. However, electrochemical tests show that corrosion resistance of titanium alloy deteriorates after plasma nitriding.

Prediction of Tool-Chip Interface Temperature in Cryogenic Machining of Ti–6Al–4V: Analytical Modeling and Sensitivity Analysis

Abstract The goal of this work is to predict the tool-chip interface temperature during cryogenic machining and determine the effectiveness of this cooling strategy. Knowledge of the tool-chip interface temperature is needed to conduct process planning: choosing a tool cooling geometry, cutting speed, and cryogen flow rate as well as predicting tool life and achievable material removal rate. A detailed explanation of the analytical heat transfer model is presented, which is a modified form of Loewen and Shaw's orthogonal cutting model, where a thermal resistance network is applied to represent the heat transfer mechanisms in, and out of, the cutting tool. An in-depth discussion of the temperature rise at the tool-chip interface during orthogonal machining of titanium alloy Ti–6Al–4V is presented. The effect of cutting speed, cryogen flow rate and quality, and cooling strategy are explored. The model is used to compare the effect of internal cryogenic cooling with external flood cooling using a water-based metalworking fluid or liquid nitrogen. A sensitivity analysis of the model is conducted and ranks the relative importance of various design parameters. The thermal conductivity of the cutting insert has the greatest influence on the predicted interface temperature. The low boiling temperature and phase change are what make internal cooling of a cutting insert with liquid nitrogen effective at reducing the tool-chip interface temperature. If the heat flowing into the tool, from the tool-chip interface, does not exceed the available latent heat in the cryogen, then this method is more effective than external flood cooling.

Experimental Investigation on machining of Titanium Alloy (Ti 6Al 4V) and Optimization of its Parameters using ANN

Engineering industries continuously face challenges in maintaining a consistently high product quality in terms of dimensional accuracy and surface finish, sustaining a high production rate, and economical processing of materials by minimizing cutting tool wear, rejections and rework. In this study, turning of Titanium alloy (Ti-6Al-4V) has been taken up for optimizing the material removal rate and surface finish, the reason being its wide application in aerospace industry. Cutting speed, feed rate and depth of cut were assigned as the input variables. Design of experiments based on Taguchi technique and L27 orthogonal array was employed to analyze the experimental data and the predicted values. Analysis of variance was used for identify the input parameter exerting maximum influence on surface finish and MRR. It was observed that the experimental results are in good agreement with the predicted values from DOE and multilayered feed forward Artificial Neural Network employed to predict process responses. The optimal values of the input and output parameters are tabulated. DOI: http://dx.doi.org/10.5755/j01.mech.24.4.20251

Globularisation of α Lamellae in Titanium Alloy: Effect of Strain, Strain Path and Starting Microstructure

To gain in-depth understating on the globularisation of α lamellae in titanium alloys, a systematic study has been carried out to evaluate the effect of strain and strain path on the microstructural evolution of titanium alloy Ti–6Al–4V with two different starting microstructures viz., water quenched martensitic and air cooled lamellar microstructure. Ti–6A1–4V was subjected to similar amounts of strain using uniaxial (monotonic) and multi-axial (non-monotonic) deformation. A vis-a-vis comparison of the microstructures obtained after deformation revealed that the material with fine α lamellae exhibits better globularisation kinetics irrespective of the mode of deformation. Further alteration of the strain path (multi-axial or non-monotonic) in the material before achieving critical percentage of deformation results in reduced globularisation. Beyond this critical amount of deformation, the results obtained for both monotonic and non-monotonic deformation are comparable. However, multi-axial or non-monotonic deformation results in better homogeneity in terms of microstructural evolution.

Effects of annealing temperature and cooling rate on microstructures of a novel titanium alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si manufactured by laser additive manufacturing

The microstructure changes of Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si alloy manufactured by laser additive manufacturing (LAM) are systematically investigated with statistical analysis of primary α phase (αp) and secondary α phase (αs) under different annealing conditions. Results indicate that, with the increase in holding temperature, the content of αp lamellas decreases with the increasing αs content, maintaining the total α phases concentration stabilized. The width of αp lamellas and the nominal specific surface area of α phase both exhibit positive correlation with the temperature, while the increment of αp and the widths of αs lamellas show an increase–decrease tendency. Besides, with the decrease in cooling rate, the total content of α and the width of αp lamellas increase, while the nominal specific surface area of α phase shows no significant change. The results indicate that, in the annealing process, the holding temperature determines the surplus and growth interfaces of αp lamellas, and the cooling rate influences the nucleation quantity of αs in unit time. During the cooling stage, the αp lamellas grow initially, and then, the nucleation and crab-like structure growth occur followed by those of the αs lamellas. The time intervals among them are influenced by cooling rate. The mechanism of microstructure formation of the LAMed titanium alloy during annealing stage was discussed, which would guide for the heat treatment method to achieve required microstructure.

Microstructure evolution and mechanical characterization of friction stir welded titanium alloy Ti–6Al–4V using lanthanated tungsten tool

Friction stir welding (FSW) exhibits significant advantages to join titanium and its alloys compared to other welding methods. FSW of 3 mm thick titanium alloy Ti–6Al–4V sheets was carried out using a lanthanated tungsten alloy tool. The traverse speed was varied from 40 mm/min to 200 mm/min in steps of 80 mm/min by keeping other parameters constant. The microstructure evolution was observed using optical and scanning electron microscopy. Advanced characterization techniques such as electron backscatter diffraction and transmission electron microscopy were applied to observe the evolved microstructure in detail. The micrographs revealed a recrystallized structure in all the joints. The joint at 40 mm/min showed a fully developed lamellar structure. An increase in the β phase was observed at HAZ while TMAZ showed a distorted structure. The increase in traverse speed caused a reduction in average grain size. No tool wear debris was observed in the stir zone while a worm hole defect was noticed at 200 mm/min. Ti–6Al–4V hardened after FSW due to grain refinement and an increase in dislocation density. The joint strength was closer to the strength of the base metal and the joints failed outside the joint area except at 200 mm/min.

Tribological Performance of Titanium Alloy Ti–6Al–4V via CVD–diamond Coatings

In the present study, HFCVD nanocrystalline, microcrystalline and boron-doped nanocrystalline diamond coatings have been deposited on titanium alloy. The effect of boron doping on coefficient of friction and residual stresses of diamond coatings have been studied. The tribological characteristics of the aforementioned three coatings on Ti–6Al–4V substrates were studied using ball on disc micro-tribometer, the thickness of the coatings being 3 μm. The coated Ti–6Al–4V discs were slid against alumina (Al2O3) balls with normal load ranging from 1 to 10 N. The boron-doped NCD coated sample disc was found to possess the lowest average coefficient of friction ~ 0.0804 while the undoped NCD and MCD coated sample discs were found to possess the average coefficients of friction of ~ 0.143 and ~ 0.283, respectively. Raman spectroscopy studies revealed that the residual stresses in boron-doped nanocrystalline coatings were tensile in nature, while the residual stresses in undoped NCD and MCD were found to be of compressive nature.

A study on keyhole evolution and weld ripple formation in dissimilar welding under pulsed laser

ABSTRACTA three-transient multiphase model is developed to study the dissimilar metal welding of pure niobium plate to titanium alloy Ti–6Al–4V sheet under pulsed laser. The physical process of dissimilar metal welding involves melting, resolidification, mass transfer, self-consistent keyhole, and weld bead formation. The major physical factors, such as recoil pressure induced by vapourisation, surface tension, heat transfer, fluid flow, Marangoni shear stress, buoyancy force, and their coupling are considered. The results show that the keyhole mainly occurs on the Ti–6Al–4V side due to the differences in physical properties of the materials. The effects of pulse overlapping factor on the weld bead are studied. It is found that the pulsed laser has a significant influence on the weld bead formation. The mixing of materials mostly occurred in the upper part of the molten pool. The simulated weld bead profile and the phase distribution agree well with the experimental results.