Analysis of filling process of Ti6Al4V alloy melt poured in permanent mold during centrifugal casting process

Ti6Al4V hip joint was foundered and the filling process of the melt poured in permanent mould during the centrifugal casting process was analyzed and the mathematical model of the filling process was established. Furthermore, the mathematical model was validated with a wax model experiment. Calculating results show that the centrifugal field has an important influence on the filling process and the melt fills the mould with variational cross sectional area and inclined angle. The cross sectional area is in inverse proportion to the filling speed and its decreasing speed becomes fast with increasing rotating speed. The tangential value of the melt cross sectional free surface inclined angle is in direct proportion to the filling speed and the inclined angle increases with the filling length. Change curves of the cross sectional inclined angle and area were obtained by the wax model experiment when the rotating speeds were 60, 90 and 120 r/min respectively, which shows that the mathematical model is consistent with the experimental results. [

Correlation between Single Factor Material Constitutive Model Parameters and Temperature for Ti6Al4V Alloy

Accurate material constitutive model is considered highly necessary to perform finite element simulation and analysis.However,it is difficult to establish the material constitutive model because of uncertainty of mathematical relationship and constraint of existing experimental condition.At present,there exists considerable gap between finite element simulation result and actual cutting process.Particular emphases were put on investigating the correlation between ＂single factor＂ material constitutive model parameters and temperature for Ti6Al4V alloy,and also establishment of material constitutive model for this kind of material.Theoretical analyses based on dislocation theory and material functional relations showed that material model was deeply affected by variation temperature.By the least squares best fit to the available quasi-static and high-speed impact compression experiment data,material parameters at various temperatures were found.Experimental curves analyses and material parameters comparison showed that the ＂single factor＂ material constitutive model parameters were temperature dependent.Using the mathematical mapping between material parameters and temperature,＂single factor＂ material constitutive model of Ti6Al4V alloy was established,which was proven to be right by comparing with experimental measurements.This work makes clear that the ＂single factor＂ material constitutive model parameters of Ti6Al4V alloy are temperature dependent.At the same time,an accurate material constitutive model is established,which helps to optimize cutting process and control machining distortion for Ti6Al4V alloy aerospace parts.

Finite element simulation of real cavity closure in cast Ti6Al4V alloy during hot isostatic pressing

The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic pressing.The two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic pressing.Shrinkage cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP conditions.The two-dimensional morphology in the simulation results agrees well with the experimental results.This study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic pressing.In addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by simulation.It is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.

Characterization and Tribological Performance of Titanium Nitrides in Situ Grown on Ti6Al4V Alloy by Glow Discharge Plasma Nitriding

Titanium(Ti)nitrides were in situ grown on Ti6Al4V alloy(TA)using a glow discharge plasma nitriding(GDPN).The morphology,chemical composition,phase and mechanical property of the obtained nitrided TA were analyzed using a scanning electron microscope(SEM),energy dispersive spectroscope(EDS),X-ray diffraction(XRD),and nanoindentation tester,respectively.The tribological performances of un-nitrided and nitrided TAs were evaluated using a ball-on-plate wear tester,and the wear mechanism was also discussed in detail.The results show that the nitrided layer with the compound and diffusion layers is formed on the nitrided TA,which is composed of δ-TiN and a-Ti phases.The nanohardness and elastic modulus of nitrided TA are 6.05 and 143.13 GPa,respectively,higher than those of un-nitrided TA.The friction reduction and anti-wear performances of nitrided TA are better than those of un-nitrided TA,and the wear mechanism is primary abrasive wear,accompanying with adhesive wear,which is attributed to the formation of Ti nitrides with the high nanohardness and elastic modulus.

Corrosion Resistance of Molybdenum Nitride Modified Ti6Al4V Alloy in HCl Solution

The Mo-N surface modified layer on Ti6Al4V alloy was obtained by the plasma surface alloying technique. The structure and composition of the Mo-N modified Ti6Al4V alloy were investigated by X-ray diffraction （XRD） and glow discharge optical emission spectroscopy （GDOES）. The Mo-N modified layer contains Mo-N coating on subsurface and diffusion layers between the subsurface and substrate. The X- ray diffraction analysis of the Mo-N modified Ti6Al4V alloy reveals that the outmost surface of the Mo-N modified Ti6Al4V alloy is composed of phase Mo2N （fcc） and Mo2N （tetr）. The electrochemical corrosion performance of the Mo-N modified Ti6Al4V alloy in 0.5 mol/L HCl solution was investigated and compared with that of Ti6Al4V alloy. The chemical corrosion performance of the Mo-N modified Ti6Al4V alloy in boiling 37% HCl solution was investigated and compared with that of Ti6Al4V alloy. Results indicate that self-corroding electric potentials and corrosion-rate of the Mo-N modified Ti6Al4V alloy are higher than that of Ti6Al4V alloy in 0.5 mol/L HCl solution. The corrosion-rate of the Mo-N modified Ti6Al4V alloy is lower than that of Ti6Al4V alloy in boiling 37% HCl solution.

Coordinately Improving the Wear and Fatigue Properties of Ti6Al4V Alloy by Designed CrZr-alloyed Layer

A CrZr-alloyed layer was prepared through a pre-zirconizing and subsequent chromizing treatment on a Ti6Al4V substrate.After the removal of the top Cr deposit and Ti4Cr layers,a（Cr,Zr）-Ti solidsolution layer was obtained.The microstructure,composition,microhardness and toughness of the（Cr,Zr）-Ti solid-solution layer were evaluated.The results showed that the pre-addition of Zr played an important role in inhibiting the precipitation of the soft Ti4Cr phase,which in turn allowed us to obtain a material characterized by a remarkable hardness.Wear and fatigue tests showed that the（Cr,Zr）-Ti solid-solution layer could coordinately improve the properties of the Ti6Al4V alloy.This was mainly due to the good match of hardness and toughness of the（Cr,Zr）-Ti solid-solution layer.In addition,the gradual change in composition and mechanical properties was conducive to the coordinated deformation between the（Cr,Zr）-Ti solid-solution layer and the Ti6Al4V substrate during fatigue tests.This reduced the stress concentration in correspondence of the interface between the two materials.

Adhesion Studies of Diamond-Like Carbon Films Deposited on Ti6Al4V Alloy after Carbonitriding

Diamond-like Carbon (DLC) coatings have attracted significant attention due to their low friction coefficient, high degree of hardness, chemical inertness, and high wear resistance as well as and their many possible uses in metallurgical, aeronautical, and biomedical applications. However, DLC has low adhesion strength to metallic substrates. Carbonitriding was performed before DLC deposition to improve this adherence. Different concentration of nitrogen in the gas mixture was used during the carbonitriding of Ti6Al4V alloy. DLC films were subsequently grown from methane using plasma enhanced chemical vapor deposition. The samples were characterized with Raman scattering spectroscopy, nanoindentation, and tribological tests. Films from 80.0% N2 had the best friction coefficient (0.07) and a critical load of ~22 N. In the scratching test, these films had adhesive failure and they completely detached from the substrate only in the end of the tests. SEM images show carbonitring promoted a significant increase in the surface defects (homogeneously distributed) but without the presence of microcracks. EDX analysis indicated that nitrogen element was diffused throughout the thickness of the samples. Hydrogen and carbon atoms from carbonitriding formed a diffusion-barrier layer that can be used as the first step for DLC deposition. This carbonitriding can also provide a carbide layer, which serves as the precursor for the nucleation and growth of DLC films.

Influence of Temperature on Nitrogen Ion Implantation of Ti6Al4V Alloy

in order to achieve increased layer thickness, and wearing resistance, enhanced ion implantation with nitrogen has been carried out at temperatures of 100, 200, 400, and 600℃ with a dose of 4x 1018 ions' cm-2. Using the Plasma Source ion Implantation (PSII) device, specimens of Ti6Al4V alloy were implanted at elevated temperatures, using the ion flux as the heating source. Auger Electron Spectroscopy (AES), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), micro-hardness measurements and pin-on-disk wearing tester were utilized to evaluate the surface property improvements. The thickness of the implanted layer increased by about an order of magnitude when the temperature was elevated from 100 to 600℃. Higher surface hardness and wearing resistance was also obtained in implantation under higher temperature. XRD image showed the presence of titanium nitrides on the implanted surface.

Influence of Component Size on the Corrosion Behavior of Ti6Al4V Alloy Fabricated by Electron Beam Powder Bed Fusion

The electrochemical behavior of Ti-6Al-4V with 1 mm and 16 mm thickness prepared by electron beam powder bed fusion(EB-PBF)was investigated in phosphate buffered saline.Electrochemical results showed that EB-PBF Ti-6Al-4V with a larger component size was more resistant to corrosion compared to the smaller component,because of less acicularαʹphase content and moreβphase content.As a non-equilibrium phase in the“high-energy state”,αʹphase has a greater susceptibility to corrode and reduces the corrosion resistance of the material,whileβphase improves corrosion resistance of titanium alloys.The results show that the phase composition has a more significant effect on the corrosion performance than the grain size.

Serrated chip characteristics and formation mechanism in high-speed machining of selective laser melted Ti6Al4V alloys

Serrated chips,consisting of extremely uneven plastic deformation,are a prominent feature of high-speed machining of difficultto-machine materials.This paper focuses on the evolution of chip form,chip morphology features(chip free surface,tool-chip contact surface,and chip edge),and chip segment parameters in subsequent high-speed(vc=50 and 150 m min-1)machining of selective laser melted(SLMed)Ti6Al4V alloys,which are significantly different from conventional Ti6Al4V alloy in microstructure,mechanical properties and machinability.The effect of laser beam scanning schemes(0°,67.5°,and 90°),machined surfaces(top and front),and cutting speeds on serrated chip characteristics of SLMed Ti6Al4Valloys was investigated.Based on the Johnson-Cook constitutive model of SLMed Ti6Al4Valloys,an orthogonal cutting model was developed to better understand the effect of physical-mechanical properties on the shear localization,which dominates the formation mechanism of serrated chips in post-machining of SLMed Ti6Al4V alloy.The results showed that the critical cutting speed(CCS)for chip serration of SLMed Ti6Al4V alloy is lower than that for serrated chips of conventional Ti6Al4V alloy,and the serrated profile of SLMed Ti6Al4V chips was more regular and pronounced.Besides,due to anisotropic microstructure and mechanical properties of SLMed Ti6Al4Valloys,the serration degree of chips produced on the top surfaces of SLMed Ti6Al4Valloys is more prominent than that of chips generated on the front surfaces.In addition,because of the poor deformation coordination and high plastic flow stresses of needle-like martensiteα′,the plastic flow and grain distortion in the adiabatic shear band(ASB)of SLMed Ti6Al4V chips are significantly smaller than those in the ASB of conventional Ti6Al4V with equiaxed grains.

Effect of Fast Multiple Rotation Rolling on Microstructure and Properties of Ti6Al4V Alloy

Using fast multiple rotation rolling(FMRR),a nanostructure layer was fabricated on the surface of Ti6Al4V alloy.The microstructure of the surface layer was investigated using optical microscopy,transmission electron microscopy,scanning electron microscopy,and X-ray diffraction.The results indicated that a nanostructured layer,with an average grain size of 72—83 nm,was obtained in the top surface layer,when the FMRR duration was 15 min.And the average grain size further reduced to 24—37 nm when the treatment duration increased to 45 min.High density dislocations,twins,and stacking faults were observed in the top surface layer.The microhardness of FMRR specimen,compared with original specimen,was significantly increased.A uniform,continuous and thicker compound layer was obtained in the top surface of FMRR sample,and the diffusion speed of N atom in the top surface layer was accelerated.FMRR treatment provides corrosion improvement.

Effect of microstructure evolution of Ti6Al4V alloy on its cavitation erosion and corrosion resistance in artificial seawater

The investigate about the effect of the microstructure of Ti6Al4V alloy on its cavitation erosion and corrosion properties in marine can provide the key basis for the application.On the basis of as-received Ti6Al4V(TC4)alloy,FC-TC4 and AC-TC4 alloys were prepared by heat treatment with the cooling method of a furnace and atmospheric environment,respectively.Then the microstructure evolutions of three samples were scrutinized and the effect of microstructure on their cavitation erosion and corrosion resistance was explored.The results showed that more recrystallized grains formed as well as its content of α grains and high-angle grain boundaries increased in AC-TC4 alloy.To FC-TC4 alloy,there was obvious grain growth apart from recrystallization.Moreover,many nanotwins of Ti V and Ti Al_(3)were formed separately in FC-TC4 and AC-TC4 alloys due to the dislocation migration during heat treatment.The microstructure evolution led the hardness and elastic modulus of AC-TC4 alloy were the best,followed by FC-TC4 alloy,that of TC4 were the worst.Similarly,passivating ability of AC-TC4 alloy was the best among three samples because of its microstructure.Although cracks extended along the grain boundaries under the action of continual cavitation erosion,the passivation film formed by TiO_(2) and Al_(2)O_(3) would enhance their resistance to further corrosion and cavitation erosion in artificial seawater.

Effect of high pressure torsion process on the microhardness,microstructure and tribological property of Ti6Al4V alloy

In the present study,a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion(HPT)process under a pressure of 7.5 GPa up to 10 revolutions.Experimental results revealed that the microhardness of Ti6Al4V was increased remarkably by about~41%and saturated at about 432 Hv after the HPT process.A relatively uniform bulk nanostructured Ti6Al4V alloy with an average grain size of about52.7 nm was obtained eventually,and no obvious formation of metastableωphase was detected by XRD analysis.For the first time,the tribological properties of the HPT processed Ti6Al4V alloy were investigated by a ball-on-disc test at room temperature under a dry condition.It was found that HPT process had a great influence on the friction and wear behaviors of Ti6Al4V alloy.With increasing the number of HPT revolutions,both friction coefficient and specific wear rate were obviously decreased due to the reduction of abrasion and adhesion wears.After being deformed by 10 HPT revolutions,the friction coefficient was reduced from about 0.49 to 0.37,and the specific wear rate was reduced by about 48%.The observations in this study indicated that HPT processed Ti6Al4V alloys had good potential in structural applications owing to their greatly improved mechanical and tribological properties.

Analysis on the Wear Performances of Cemented Carbide Tools Containing Ti in the Coatings When Machining Ti⁃6Al⁃4V Alloys

Because of the high affinity of the same element Ti,cemented carbide tools containing Ti seem to be non⁃optimal in machining titanium alloys.However,in practice,cemented carbide tools containing Ti are still widely used in machining titanium alloys.Cutting experiments were conducted in order to systematically explain the contradictions between the practice and theory.The diffusion process between titanium alloys and the cemented carbide tools was analyzed by auger electron spectroscopy detecting the cutting regions.It was also analyzed by Ti/Co diffusion behavior simulated by molecular thermodynamics.The experimental results and the simulation results showed that the mutual diffusion of Ti/Co atoms was the major reason for the diffusion wear.The dissolution⁃diffusion wear was one of the main wear mechanisms for the cemented carbide tools containing Ti in the coatings.Moreover,four types of cemented carbide tools and two other types of cermet tools were used to machine the Ti⁃6Al⁃4V alloys at different cutting speeds to further verify the high affinity of cutting tools containing Ti in the substrate/coating.The verification experiments results showed that the cemented carbide tools containing Ti generally cannot be used for machining titanium alloys,but could show less affinity in the cutting regions with reasonable cutting conditions.

Composition and Structure of Ti-6Al-4V Alloy Plasma-based Ion Implanted with Nitrogen

The composition and structure of Ti 6Al 4V alloy plasma based ion implanted with nitrogen was investigated.The nitrogen depth distribution shows more antiballistic with distribution peak heightened with increased implantation time(dose),and more like a parabola at the low implantation pulse voltage.When implantation pulse voltage is increased,the implantation depth increased with the nitrogen distribution peak being deepened,widened and lowered somewhat.TiN,TiN+Ti 2N,or Ti 2N second phases were formed in the implanted layer.The relative percentage of nitrogen content in the form of TiN increases when going deeper into the implanted(TiN formed) layer.The increase of implantation pulse width and/or time is favourable for the formation of TiN rather than Ti 2N.It is unfavourable for formation of any nitrides when implantation pulse voltage is decreased to 30kV or less.Tiny crystalline particles (made mainly of Ti 2N and a smaller percentage of TiO 2 phases) of regular shapes such as triangle and tetragon, etc .(about 20 nm) are found distrbuted dispersively in the near surface region of samples implanted at the high implantation pulse voltage (75kV).

Growth kinetics of titanium boride layers on the surface of Ti6Al4V

Dual titanium boride layers consisting of continuous TiB2 top-layer and TiB whisker sub- layer were formed on the surface of Ti6Al4V alloy using powder-pack boriding technique. An iso-thickness diagram of the whole boride layer was fitted with the data of thickness of the coating, treatment time and process temperature using Sigma Plot10.0 software. Growth kinetics of the titanium boride layer were analyzed by measuring the extent of penetration of TiB2 and TiB whisker as a function of boriding time in the range of 5-20 h and boriding temperature in the range of 1000-1100 ℃. By the linear regression analysis of growth kinetics of titanium boride layer, the diffusivity K and average diffusion activation energy （Q） of boron atoms in Ti6Al4V alloy were calculated, respectively.

Dip Coating of Nano Hydroxyapatite on Titanium Alloy with Plasma Assistedγ-Alumina Buffer Layer:A Novel Coating Approach

This paper reported a novel coating approach to deposit a （HA） film on Ti6Al4V alloy with Al2O3 buffer layer for thin, crack free and nano-structured hydroxyapatite biomedical implants. The Al2O3 buffer layer was deposited by plasma spraying while the HA top layer was applied by dip coating technique. The X-ray diffraction （XRD） and Raman reflections of alumina buffer layer showed α- to γ-Al2O3 phase transformation; and the fractographic analysis of the sample revealed the formation of columnar grains in well melted splats. The bonding strength between Al2O3 coating and Ti6Al4V substrate was estimated to be about 40 MPa. The presence of dip coated HA layer was confirmed using XRD, scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDX） analysis. The SEM images exhibited that HA top layer enveloped homogenously the troughs and crests of the underneath rough （Ra = 2.91 μm） Al2O3 surface. It is believed that the novel coating approach adopted might render the implant suitable for rapid cement-less fixation as well as biocompatible for longer periods.

Insights into in-situ TiB/dual-phase Ti alloy interface and its high load-bearing capacity

To better understand the strengthening mechanism of in-situ formed TiB reinforcements in dual-phase Ti6 Al4 V alloy,the interface characters and properties ofα-Ti/β-Ti/TiB system were thoroughly investigated with the combined use of high-resolution transmission electron microscopy(HRTEM),abinitio calculations,and indentation tests.The ab-initio calculations suggest that the highly coherent(100)_(TiB)/(121)_(β-Ti)phase boundary(PB)has fairly low interface energy of 0.082 J/m^(2)with an exceptionally high adhesion strength of 6.04 J/m^(2),owing to the formation of strong interfacial Ti–B ionic bonds.The semi-coherent(201)_(TiB)/(0001)_(α-Ti)interface shows a relatively higher interface energy of 1.442 J/m^(2)but still with a fairly high adhesion strength of 4.95 J/m^(2).With the obtained interfacial energetics,thermodynamics analyses were further carried out to explore the nucleation mechanism ofα-Ti in TiB reinforced Ti6Al4V composite.Superior to the heterogeneous nucleation at TiB/β-Ti interface,the homogeneous nucleation ofα-Ti within theβ-Ti phase can be more energy-preferred,due to its lower nucleation energy barrier and critical radius.Further indentation tests under various loads of different modes confirmed a remarkably enhanced load-bearing capacity of dual-phase Ti6Al4V alloys,under the critical significance of the strong interfacial bonding achieved by reinforcements of in-situ formed TiB.

On Ti6Al4V Microsegregation in Electron Beam Additive Manufacturing with Multiphase-Field Simulation Coupled with Thermodynamic Data

Electron beam additive manufacturing is an effective method for the fabrication of complex metallic components.With rapid solidification,the characteristics of microsegregation within the interdendritic region are interesting and important for the subsequent phase transformation and final mechanical properties.However,in view of the microsecond lifetime and the small length scale of the molten pool,experimentally investigating microsegregation is challenging,even with electron probe micro-analysis.In this study,a multiphase-field model coupled with the real thermodynamic data of Ti6Al4V alloy was successfully developed and applied to simulate the rapid solidification of columnarβgrains via electron beam additive manufacturing.The thermal gradient(G)and cooling rate(R)were obtained from a 3D powder-scale multiphysics simulation and provided as inputs to a multiphase-field model.The eff ects of the electron beam process parameters and thermal conditions on the columnarβgrains were investigated.Liquid films and droplets were observed to have solute enrichment in the intercellular region.The size of the liquid film increased at a lower scanning speed and energy power.Increasing the scanning speed and energy power refined the columnarβgrains and decreased the liquid film size.The extent of microsegregation considerably increased at lower energy power,whereas the change in scanning speed had little eff ect on the microsegregation.The results also indicate that solute vanadium results in significant solute trapping and microsegregation during the rapid solidification of the Ti6Al4V alloy.

Fine equiaxed β grains and superior tensile property in Ti-6Al-4V alloy deposited by coaxial electron beam wire feeding additive manufacturing

Coarse columnar β grains result in anisotropic mechanical properties in Ti alloys deposited by additive manufacturing. This study reports that Ti-6Al-4V alloy fabricated by coaxial electron beam wire feeding additive manufacturing presents a weak anisotropy, high strength and ductility. The superior tensile property arises from a microstructure with fine equiaxed β grains(EGβ), discontinuous grain boundary α phase and short intragranular α lamellae. A large region of fine EGβ arises from a special combination of the temperature gradient and solidification rate, and attractive α morphology is caused by solid phase transformations during interpass thermal cycling and post heat treatments.