Processing Of Titanium Alloys Research Articles

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

Electron beam melting (EBM), as one of metal additive manufacturing technologies, is considered to be an innovative industrial production technology. Based on the layer‐wise manufacturing technique, as‐produced parts can be fabricated on a powder bed using the 3D computational design method. Because the melting process takes place in a vacuum environment, EBM technology can produce parts with higher densities compared to selective laser melting (SLM), particularly when titanium alloy is used. The ability to produce higher quality parts using EBM technology is making EBM more competitive. After briefly introducing the EBM process and the processing factors involved, this paper reviews recent progress in the processing, microstructure, and properties of titanium alloys and their composites manufactured by EBM. The paper describes significant positive progress in EBM of all types of titanium in terms of solid bulk and porous structures including Ti–6Al–4V and Ti–24Nb–4Zr–8Sn, with a focus on manufacturing using EBM and the resultant unique microstructure and service properties (mechanical properties, fatigue behaviors, and corrosion resistance properties) of EBM‐produced titanium alloys.

Investigation on the temperature field under the action of the blunt tool edge for precision cutting of titanium alloys

According to the research of the generation and propagation of the cutting heat, and the two-dimensional cutting temperature model, the relationship between the blunt tool edge radius and cutting temperature was considered, then the average temperature cutting models of the shear plane, the rake face and the flank face were constructed with the consideration of the blunt tool edge during the cutting process of the titanium alloys. In addition, the temperature distribution near the blunt tool edge was studied during the cutting process of titanium alloys. The cutting temperature field models and the accuracy of the simulation analysis were in the same trend through the precision cutting experiment of titanium alloys. Most importantly, it can provide a reliable and theoretical basis for reasonable design of the blunt tool edge and the precise cutting of the titanium alloys accordingly.

Investigation on the milling performance of titanium alloy thin-walled part with air jet assistance

Cutter back-off and vibration are easily generated when machining of titanium alloy thin-walled parts due to its low rigidity, which has become the bottleneck for processing titanium alloy thin-walled parts. In order to investigate whether the impact force of air jet can reduce the part deformation and the vibration during machining process or not, experiments of milling Ti6Al4V alloy thin-walled part with and without air jet assistance were conducted. Vibration acceleration signals and cutting force signals in the milling process under the same cutting parameters are analyzed and compared. Also, vibration acceleration signals in frequency domain obtained by Fast Fourier Transform (FFT) are analyzed and compared. Furthermore, the impact force produced by air jet acting on the thin-walled part was collected separately before milling experiments and calculated according to the theory of hydromechanics to investigate its supporting effect. Finally, the experiment results show that air jet assistance can improve cutting stability and reduce cutting force, leading to better surface quality and reduced part deformation.

Research on Welding Process of Titanium Alloy

The welding organization and physical properties of the titanium alloy are analyzed; the welding defects and its causes of the titanium alloy are discussed. The welding processes of titanium alloy such as plasma arc welding, laser welding, diffusion welding and brazing welding are studied. Ten experiences about titanium alloy welding are summed up. Finally, the development direction of titanium alloy welding is pointed out.

Qualification of TA6V alloy cleaning processes using supercritical CO2 cleaning, from coupled SEM, XPS, and TPD analyses

Traditional industrial cleaning processes of titanium and titanium alloys use solvents which are potentially toxic and environmentally harmful. Carbon dioxide, which is nontoxic, nonflammable, recyclable, and available on a large scale, is a potential substitute for these solvents. Indeed, the zero surface tension of supercritical CO2 (SC-CO2) provides a significant advantage over liquid and aqueous solutions, and facilitates the access to small structures, while a high diffusion coefficient allows a fast rate of mass transfer. Moreover, its viscosity and density can be adjusted by tuning pressure and temperature. In this study, the performances of solvent-assisted SC-CO2 process are compared to traditional TA6V alloy cleaning processes. The efficiency of residual oil removal from a TA6V surface has been investigated by several techniques such as x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). While XPS gives a measure of the so-called relative atomic surface concentration of carbon, which is commonly used to characterize cleanliness of the surface in the nanometer range, both EPMA and SEM provide elementary analysis at μm3 range and are often associated with characterizing morphologies of protuberances. Temperature programmed desorption coupled to a quadrupole mass spectrometer has also been used to obtain qualitative information on the nature and the relative amounts of the species degassed from the polluted and cleaned material surfaces.

Microstructure characterization and nano & micro hardness of tri-modal microstructure of titanium alloy under different hot working conditions

In this work, the dependences of tri-modal microstructure parameters and corresponding nano & micro hardness on through-process processing parameters were quantitatively studied during the three-step thermo-mechanical processing of TA15 titanium alloy. It is found that the processing parameters of first step, especially for the deformation temperature and strain rate, mainly affect primary equiaxed α (αp) through the α→β phase transformation and the competition between dynamic recovery and dynamic recrystallization. The second processing step primarily affects the content and thickness of lamellar α (αl). In the third processing step, compared with low-temperature aging, normal annealing provides sufficient driving force for αl and secondary lamellar α (αs) growing, which leads to thicker αl and αs. As for the nano & micro hardness, in one sample undergoing different process, transformed β matrix (βt) is always harder than αl and αs due to the interfacial-strengthening effect. In addition, with increasing strain rate of the first step, αp becomes harder due to the constantly enhanced work hardening effect while the hardness of βt varies little because of the competition between interfacial strengthening and distribution disorder degree. However, the nano hardness of αl decreases firstly and then increases with strain rate, which presents the same trend with the micro hardness of integrated hardness at different processing conditions.

High-temperature behaviors of grain boundary in titanium alloy: Modeling and application to microcrack prediction

Grain boundary (GB) deformation usually occurs during the high-temperature deformation process of titanium alloy, which may result in microcrack initiation and propagation. GB exhibits the characteristics of viscosity softening and rate sensitivity in its deformation, which lead to flow softening, enhanced plasticity and rate sensitive damage of the alloy. In view of the fact that it is extremely hard to directly observe GB deformation in experiments, a cohesive zone model (CZM) of GB has been proposed by taking into account the aforementioned characteristics. The CZM model is then combined with an actual-microstructure-based crystal plasticity finite element model (CPFEM) to include the effect of grain morphology, grain orientation and α and β phases of titanium alloy. The model is applied to study the microcrack initiation and propagation of a near-α titanium alloy. The predicted microcrack initiation and propagation were verified by experimental observations, which proves the reliability of the proposed model. Then, the model is applied to study the fracture rule of GBs, the effects of grain morphology, misorientation and property on the fracture of GBs. The results show that (a) the α-α GBs tend to be the most difficult one to deform, while the β-β GBs are the easiest one; (b) grain morphology affects microcrack initiation and propagation most. The α-β GBs decohesion at triple junctions is the dominant type for crack initiation, then the crack propagates mainly along the straight GBs vertical to tensile axis; (c) the critical strength of GB reaches the minimum at the case that the grains misorientation falls into 45–60°.

Tool life enhancement in dry diamond turning of titanium alloys using an eddy current damping and a magnetic field for sustainable manufacturing

Titanium alloys are widely applied in the aerospace, automobile, and biomedical industries for manufacturing precise components because of their excellent material properties. However, titanium alloys are regarded as difficult to cut materials due to their low thermal conductivity, the resulting serious tool wear and poor surface integrity inevitably lead to high machining cost and energy consumption. On the other hand, uses of fluid lubricant in machining processes of titanium alloys are sizable in order to provide an effective cooling media to dissipate high cutting heat generated in machining. Although the use of lubricant has been discouraged because of the drew damages to the environment and health, dry machining of titanium alloys is not practical currently as high friction force and cutting temperature induced from the dry machining environment which further accelerate and worsen tool life. Therefore, the environmental concerns cover a feasibility of dry machining of titanium alloys; In this study, a novel machining technology, a magnetic field was applied in dry single point diamond turning (SPDT) of titanium alloys to enhance diamond tool life, which aims to overcome the machining difficulties of dry machining. An eddy current damping effect reduces the machining vibration of rotating workpiece and a magnetic field enhances the thermal conductivity of tool/workpiece interface in SPDT, which help to relieve the problematic sources of tool damage in dry machining process. Under the influence of magnetic field, experimental results showed an improvement of surface integrity of machined surface, reductions of adhesive wear, flank wear and built up edge of tool as well as the machining vibration in dry SPDT. The proposed machining technology minimizes the environmental damage of wet machining, uplifting tool life and surface quality of machined components simultaneously, it offers a feasibility of environmental friendly dry SPDT of titanium alloys in practical applications, providing sustainable manufacturing for high precise products.

Wpływ drgań ultradźwiękowych na siłę i chropowatość powierzchni w procesie szlifowania stopu tytanu Ti6Al4V

The paper presents the preliminary experimental study results in grinding process of Ti6Al4V titanium alloy. The aim of this study was to determine, through grinding force components and surface roughness analysis, what effect on this process has assisting it with workpiece ultrasonic oscillations.

The estimation of machining results and efficiency of the abrasive electro-discharge grinding process of Ti6Al4V titanium alloy using the high-frequency acoustic emission and force signals

The paper presents the results obtained for abrasive electro-discharge grinding (AEDG) of Ti6Al4V titanium alloy with the use of super hard grinding wheels of cubic boron nitride with a metal bond. The experimental investigations were focused on process monitoring for sharp and worn grinding wheels. For the evaluation of the grinding process, the grinding force amplitude and a few descriptors of the high-frequency stress waves were investigated in both time and frequency domains. The results show that during the AEDG, specific elastic waves are generated. Since these waves have characteristic amplitudes, frequencies, and other different descriptors dependent on the current grinding wheel cutting ability and discharge parameters, they can be applied to estimate a statistically significant regression function. For each measurement signal, a few statistical features are calculated and used as input for data selection and classification procedures. Registration and classification of forces and acoustic emission signals can be used to analyse the abrasive electro-discharge grinding process and allow for the determination of the machining results and the lifespan of super hard grinding wheels.

Micro milling of titanium alloy Ti-6Al-4V: 3-D finite element modeling for prediction of chip flow and burr formation

Cutting process of titanium alloy Ti-6Al-4V is considered difficult due to chemical affinity between tool and work material, adhesion, built-up edge and burr formation, and tool wear resulting in loss of productivity. Three dimensional (3-D) chip flow together with local field variables such as temperature, elastic/plastic strain, strain-rate and velocity in the shear zones during micro milling process can be predicted using continuum-mechanics based 3-D Finite Element (FE) modelling and simulation of elastic/viscoplastic work material deformations. This paper provides much needed process insight for chip flow, built-up edge and burr formation by using modeling work with experimental validation. Scanning electron microscopic (SEM) observation of the 3-D chip morphology and burrs demonstrate ductile fractured surfaces together with localized instability and failure behaviors. FE simulations are utilized to investigate the effects of micro milling operation i.e. up and down milling and tool edge radius on 3-D chip flow, built-up edge, and 3-D burr formation. Simulated results are compared with measurements of chip morphology, shape, and dimensions together with tool edge condition of built-up edge and chip adhesion yielding to good agreements.

Flow behavior and processing map for hot deformation of ATI425 titanium alloy

Flow behavior and processing map play important roles in the hot deformation process of titanium alloys. In this research, compression Gleeble tests have been carried out to investigate the stress–strain relationship at temperatures ranging from 700 to 1000°C and strain rates ranging from 0.001 to 1s−1 for ATI 425 titanium alloy. Arrhenius type constitutive equation was obtained to describe the compressive flow behavior with modification of additional deformation dead zone, friction model, temperature model and strain rate. The introduction of novel calculation method for α value in Arrhenius equation gives more accurate fitting than traditional one. Processing maps were drawn based on the distribution of dissipator co-content, and optimized deformation temperature and strain rate range obtained. It is proven to be accurate and effective through the experimental results. The microstructure analysis shows that more dynamic recrystallization can be achieved in the area with larger η value on the processing map.

Research on tool wearing on milling of TC21 titanium alloy

Titanium alloys are used in aircraft widely, but the efficiency is a problem for machining titanium alloy. In this paper, the cutting experiment of TC21 titanium alloy was studied. Cutting parameters and test methods for TC21 titanium alloy were designed. The wear behavior of TC21 titanium alloy was studied based on analysis of orthogonal test results. It provides a group of cutting parameters for TC21 titanium alloy processing.

Ultra-fine grained microstructure of metastable beta Ti-15Mo alloy and its effects on the phase transformations

Processing of metastable titanium alloys by severe plastic deformation provides an opportunity to achieve exceptional grain refinement, to enhance the strength and to affect phase transformations occurring during thermal treatment. The main aim of this study is to investigate the microstructure of ultra-fine grained (UFG) material and effect of microstructural changes on phase transformations in metastable β-Ti alloy Ti-15Mo.Metastable β-Ti alloys are currently the most studied Ti-based materials with prospective use in medicine. Ti-15Mo alloy after solution treatment contains metastable β-phase. Metastable ω-phase and stable α-phase particles are formed upon annealing,.Solution treated Ti-15Mo alloy was deformed by high pressure torsion (HPT) at room temperature. Severely deformed structure after HPT with grain size of ~200 nm was studied by transmission electron microscopy. In-situ electrical resistance measurements showed significant changes in undergoing phase transformations when compared to coarse-grained (CG) material. Scanning electron microscopy revealed heterogeneous precipitation of α-particles at grain boundaries (GB). Due to the high density of GBs in UFG structure, these precipitates are very fine and equiaxed.The study demonstrates that SPD is capable of enhancing mechanical properties due to grain refinement and via affecting precipitation processes in metastable β-Ti alloys.

티타늄 합금의 나노유체 극미량 윤활 밀링 공정 열특성에 관한 수치 해석 연구

This paper presents a numerical study on the thermal characteristics of a milling process of titanium alloy with nanofluid minimum-quantity lubrication (MQL). The computational fluid dynamics (CFD) approach is introduced for establishing the numerical model for the nanofluid MQL milling process, and estimated temperatures for pure MQL and for nanofluid MQL using both hexagonal boron nitride (hBN) and nanodiamond particles are compared with the temperatures measured by thermocouples in the titanium alloy workpiece. The estimated workpiece temperatures are similar to experimental ones, and the model is validated.

Powder Metallurgy Strategies to Improve Properties and Processing of Titanium Alloys: A Review

Powder metallurgy (PM) is an attractive technology for manufacturing net‐shape titanium‐based components. However, it is challenging to make PM titanium products competitive in terms of mechanical properties. This article gives an overview of the current challenges in PM titanium and the best strategies to overcome them by alloying. By adding suitable alloying elements the properties of PM titanium components can be enhanced. The use of sintering aids helps to control the typical residual porosity of PM titanium alloys. Furthermore, controlling microstructure by alloying offers the possibility to go for high performance applications. Moreover, ductility is improved by adding elements that scavenge oxygen. A favorable selection of alloying elements offers a practical and competitive approach to meet the mechanical requirements in future PM titanium applications.

Chips Morphology Analysis under Graphene Oxide Suspension with Tungsten Carbide Tool in Drilling Ti-6Al-4V

Recently, titanium alloys have been widely used in industry owing to their excellent physical and mechanical properties. However, the severe cutting conditions such as abrasion, adhesion and high temperature accelerate the rate of chip formation and strongly affect the quality of machined surface. This paper investigates that the effect of the conventional coolant (CC) and graphene oxide suspended (GO) on the drilling process of titanium alloy Ti-6Al-4V using tungsten carbide tools. Here are two main chip formation could be found that zigzag chips and spiral chips. Through the analysis of chip morphology, it was found that under graphene oxide suspended fluid. It can be found that using conventional coolant would form the zigzag chips, while it formed spiral chips when graphene oxide suspended fluid applied. In addition, by analysing the chip free surfaces, the chip lamella stuck and chip flaw happened when conventional fluid used. While the back surfaces could be found that less chip stuck and crack occurred when graphene oxide suspended coolant applied. Finally, chip thickness were investigated that thinner chip thickness was found when graphene oxide suspended fluid used.

Study on the Tribological Properties of Porous Titanium Sliding against Tungsten Carbide YG6

In the metal cutting process, the friction and wear behavior between the cutting tool and machined surface is the most important factor that affects the surface quality and the service life of the cutter. The irregular pore structure of porous titanium alloy has changed its mechanical properties and the processing technology. The friction and wear mechanism of the cutting tool and the machined surface is greatly different from the traditional dense metal processing because of the crumbling at the edges, tearing phenomenon and the pore agglomeration effect of chips. In this paper, the tribological characteristics and the wear mechanism of friction pair which was formed by porous titanium alloy material and hard alloy cutter were studied from cutting force, cutting speed and temperature in micro-cutting condition, and the influence of porosity on the wear rate and friction coefficient was analyzed. Results show that the main factor which influences the friction coefficient and wear rate is the porosity. The wear mechanisms of porous titanium materials were abrasive and oxidation wear while the wear mechanism of tungsten carbide YG6 was abrasive wear. The friction coefficient and wear rate of the relatively stable state are beneficial to improve the surface quality and tool life. As a result, in the micro-cutting process of porous titanium alloys, the best choice of machining parameters for different porosity materials are as follows: the load is about 8 N, the sliding speed is about 400 r/min and the temperature is about 300 °C.

Experimental characterization on micro-end milling of titanium alloy using nanofluid minimum quantity lubrication with chilly gas

The objective of this research is to experimentally characterize the micro-end-milling process of titanium alloy (Ti-6Al-4V) using both nanofluid minimum quantity lubrication (MQL) and chilly gas. A series of micro-end-milling experiments are conducted by considering nanodiamond particles for nanofluid MQL. In the case of chilly gas cooling, the chilly CO2 gas having the temperature of −25 °C is provided. During the experiments, the milling forces, coefficients of friction, surface roughness and tool wear are analysed according to types of nanofluids and their weight concentrations. Overall, the experimental results show that the nanofluid MQL with chilly CO2 gas cooling is effective for reducing milling forces, coefficients of friction, tool wear and surface roughness. It is also demonstrated that the lower concentration (0.1 wt.%) of nanodiamond nanofluid is more effective to reduce the milling force, coefficient of friction and tool wear. On the other hand, it is found that the higher concentration (1.0 wt.%) is more advantageous for reducing the surface roughness.

Processing and properties of Titanium alloy based materials with tailored porosity and composition

This paper deals with powder processing of Ti6Al4V titanium alloy based materials with tailored porosity and composition. Ti6Al4V powder was mixed either with salt particles acting as space holder, so as to provide two-scale porosity, or with hard TiN particles that significantly modified the microstructure of the material and increased its hardness. Finally an original three-layer component was produced. Sample microstructure was observed by SEM and micro-tomography with special interest in pore size and shape, inclusion distribution and connectivity. Compression tests provided elastic modulus and yield stress as functions of density. These materials are representative of bone implants subjected to complex biological and mechanical conditions. These results thus open avenues for processing personalized implants by powder metallurgy.