Titanium Alloy Parts Research Articles

Effect of heat treatment on the anisotropic machinability of additive manufactured titanium alloys in micro-milling

For titanium alloy parts prepared by selective laser melting (SLM), post-treatment operation is usually utilized to meet the needed surface accuracy and dimensional tolerances. However, the heat treatment process and anisotropy of different surfaces of SLMed titanium alloy can directly affect its machinability. In this study, the anisotropic machinability of SLMed TC4 before and after heat treatment was comprehensively compared by the milling force, surface quality, top-burr and work hardening. The results indicate that the milling force and work hardening degree of top surface of SLMed TC4 material are larger than those of side surface, and top surface the presents the better surface quality and smaller top-burr. It exhibits obvious anisotropic machinability in micro-milling. After heat treatment, the anisotropic machinability between different surfaces of SLMed TC4 materials were significantly reduced. The average surface roughness difference rate of top and side surfaces decreased from 10.08% to 2.79%, and the total average top-burr size difference rate decreased from 19.53% to 9.99%. The difference rate of milling force and work hardening degree of the top and side surfaces both showed a decreasing trend. This work demonstrates that the anisotropic machinability of SLMed TC4 material in micro-milling can be effectively mitigated by the heat treatment process.

Tribological Properties of Laser-Cladded NiCrBSi Coatings Undergoing Friction with Ti6Al4V Alloys

This work aims at reducing abrasion between titanium alloy parts, such as drive shafts and support pairs used in aviation. Three different NiCrBSi coatings, Ni40, Ni50, and Ni60, are prepared on surfaces of Ti6Al4V by laser cladding. The microstructural and mechanical properties of these coatings are analyzed by scanning electron microscope (SEM) and a microhardness tester. The tribological properties of the NiCrBSi coatings undergoing friction with Ti6Al4V are tested using a wear testing machine. The results show that the Vickers hardnesses of the Ni40, Ni50, and Ni60 coatings are 490 HV0.3, 609 HV0.3, and 708 HV0.3, respectively. For the above NiCrBSi coatings, more hard phases are produced with increases in the amounts of Cr in the powders, resulting in increases in the coatings’ hardnesses. The wear test results show that the NiCrBSi coatings could reduce the friction coefficients, which gradually decreased with increases in the coatings’ hardnesses. Both the coating-specific wear rates and the friction pair wear losses initially decreased and then increased. The Ni50 coating and the Ti6Al4V friction pair undergoing friction with the Ni50 coating showed the best wear performance, with a specific wear rate and wear loss of 0.51 × 10−7 mm3/(N·m) and 7.8 mg, respectively. The specific wear rates for Ni50 were only 8.4%, 35.4%, and 37.0% of the Ti6Al4V, Ni40, and Ni60, respectively. In addition, the friction pair wear loss was only 36.4%, 52.5%, and 55.3% of that while undergoing friction with Ti6Al4V, Ni40, and Ni60, respectively. The NiCrBSi coatings prepared on the surface of Ti6Al4V show excellent antifriction and wear resistance properties, providing a viable solution for the design of wear-resistant coatings on load-bearing and non-load-bearing titanium alloy parts.

Determining technological parameters for obtaining ta15 titanium alloy blanks with improved mechanical characteristics using the electron-beam 3D printing method

The object of this study is the process of electron beam 3D printing of articles made of TA15 titanium alloy powder. Peculiarities of the structure and properties formation of alloy blanks, obtained by this method have been described. Influence of process parameters (electron beam power and geometric scanning parameters) on the characteristics of the material were considered. Step of displacement of the beam trajectory changed from 0.1 to 0.25 mm with an interval of 0.05 mm. Specific energy of the electron beam varied from 20 to 70 J/mm3 for every trajectory displacement step. The macrostructure was examined visually while the microstructure was studied by optical microscopy. Mechanical properties were determined by uniaxial tension and impact bending tests. It was established that depending on the 3D printing parameters the macrostructure of most samples is dense but with unfavorable parameters non-fusions or shrinkage porosity defects may form. The microstructure of the dendritic type has an α´+β lamellar-acicular morphology, its dispersity and shape of α´–phase areas vary depending on the process parameters. A scanning step of 0.2 mm and a beam energy of 40 J/mm3 allows obtaining a dispersed microstructure in which there are no non-fusions and shrinkage micropores. The value of the Rm is 27 %, and the R0.2 is 24 % higher than that of the alloy obtained by the conventional technology of electron beam melting. The A5 is 3.2 times higher. However, impact toughness of the sample with dendrite unfavorable orientation to the direction of load applying may be lower compared to conventional technology. The results could be used for devising commercial technology of high strength titanium alloys parts produced by 3D printing

Effect of Electrolytic Plasma Polishing on Surface Properties of Titanium Alloy

Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical titanium alloys remains to be investigated. This paper investigated the changes in surface roughness, surface morphology, microstructure, and chemical composition of Ti6Al4V alloy by EPPo and their effects on surface corrosion resistance, wettability, and residual stress. The results showed that Ra decreased from 0.3899 to 0.0577 μm after EPPo. The surface crystallinity was improved, and the average grain size increased from 251 nm to more than 800 nm. The oxidation behavior of EPPo leads to an increase in surface oxygen content and the formation of TiO2 and Al2O3 oxide layers. EPPo can significantly improve the corrosion resistance and wettability of titanium alloy in simulated body fluid and eliminate the residual stress on the sample surface. The surface properties are enhanced not only by the reduction in surface roughness but also by the formation of a denser oxide film on the surface, changes in the microstructure, an increase in surface free energy, and the annealing effect developed during EPPo. This study can provide guidance and references for applying EPPo to biomedical titanium alloy parts.

Boundary fluid constraints during electrochemical jet machining of large size emerging titanium alloy aerospace parts in gas–liquid flows: Experimental and numerical simulation

Large size titanium alloy parts are widely used in aerospace. However, they are difficult to manufacture using mechanical cutting technology because of severe tool wear. Electrochemical jet machining is a promising technology to achieve high efficiency, because it has high machining flexibility and no machining tool wear. However, reports on the macro electrochemical jet machining of large size titanium alloy parts are very scarce, because it is difficult to achieve effective constraint of the flow field in macro electrochemical jet machining. In addition, titanium alloy is very sensitive to fluctuation of the flow field, and a turbulent flow field would lead to serious stray corrosion. This paper reports a series of investigations of the electrochemical jet machining of titanium alloy parts. Based on the flow analysis and experiments, the machining flow field was effectively constrained. TB6 titanium alloy part with a perimeter of one meter was machined. The machined surface was smooth with no obvious machining defects. The machining process was particularly stable with no obvious spark discharge. The research provides a reference for the application of electrochemical jet machining technology to achieve large allowance material removal in the machining of large titanium alloy parts.

Finite Element Simulation and Microstructural Evolution Investigation in Hot Stamping Process of Ti6Al4V Alloy Sheets.

Titanium alloy hot stamping technology has a wide range of application prospects in the field of titanium alloy part processing due to its high production efficiency and low manufacturing cost. However, the challenges of forming titanium alloy parts with large depths and deformations have restricted its development. In this study, the hot stamping process of a Ti6Al4V alloy box-shaped part was investigated using ABAQUS 2020 software. The thermodynamic properties of a Ti6Al4V alloy sheet were explored at different temperatures (400 °C, 500 °C, 600 °C, 700 °C, 800 °C) and different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1). In addition, the influence law of hot stamping process parameters on the minimum thickness of the formed part was revealed through the analysis of response surface methodology (RSM), ultimately obtaining the optimal combination of process parameters for Ti6Al4V alloy hot stamping. The experimental results of the hot stamping process exhibited a favorable correlation with the simulated outcomes, confirming the accuracy of the numerical simulation. The study on the microstructure evolution of the formed parts showed that grain refinement strengthening occurred in the part with large deformation, and the formed box-shaped parts exhibited a uniform and fine microstructure overall, demonstrating high forming quality. The achievements of the work provide important guidance for the fabrication of titanium alloy parts with large depths and deformations used in heavy industrial production.

Enhancement of the Microstructure and Fatigue Crack Growth Performance of Additive Manufactured Titanium Alloy Parts by Laser-Assisted Ultrasonic Vibration Processing

Post-processing techniques can efficiently improve the surface quality, address microstructural defects, and optimize mechanical properties in additively manufactured parts. Surface severe plastic deformation processes such as ultrasonic nanocrystal surface modification (UNSM) integrated with localized laser heating were explored to enhance the surface properties, microstructure as well as the fatigue crack growth properties (FCG) in both directions of built. We successfully induced greater plasticity flow and achieved beneficial refinement of the surface grain structure by precisely controlling the heat and impact energies during surface treatment process. The LA-UNSM process, with the parameters utilized in this study considerably decreased the FCG rates of treated samples, when compared to samples without surface treatment. Improved fatigue crack growth properties along vertical and horizontal orientations after the post-process treatment were attributed to the induced-microstructural changes, improved surface quality, induced compressive residual stresses through gradient structure deformation layer that was prepared on the surface of the material. The fractographic analysis revealed that the cracks mostly originated from the pores in the as-produced state. This observation shows a clear correlation between the surface treatment performed and a substantial improvement in fatigue crack growth resistance.

Effect of process parameters on residual stresses in SLM-formed bionic porous titanium alloy structures

Bionic porous titanium alloy structures have demonstrated broad application prospects in the field of biomedicine, and selective laser melting (SLM) has become one of the main methods for preparing porous titanium alloy structures due to its high degree of forming freedom. Residual stress is a crucial indicator for evaluating the forming quality of SLM parts, thus its control methods have garnered significant attention. Therefore, it is important to understand the process parameters' influence on the generation and regulation of residual stresses in SLM-formed bionic porous titanium alloy parts. In this paper, finite elements and experiments are employed to research the relationship between process parameters and residual stresses in the SLM process, and a method for controlling residual stresses in the key sensitive areas is proposed. It is found that increasing the laser scanning speed is conducive to reducing the residual stress of the porous structure and alleviating the phenomenon of stress concentration. Appropriately increasing the laser power can reduce the residual stress in the Z direction of the porous structure, with the optimal range being from 200 W to 250 W. Using a medium laying powder thickness (0.03 mm∼0.04 mm) results in uniformly distributed residual stress on the surface of the porous structure, leading to the attainment of maximum residual compressive stress. Building upon this foundation, the experimental verification of forming quality established stability, while the derived parameter optimization method and forming mechanism offered theoretical support for process optimization in fabricating porous titanium alloy structures through SLM.

Study on Welding Deformation Correction of TC4 Titanium Alloy Panel Parts

Aiming at the problem that TC4 titanium alloy panel parts after welding have large internal residual stress and obvious panel deformation, which can’t meet the requirements of the parts, the viscoelastic plastic model of titanium alloy panel parts is established by finite element analysis, and the welding deformation-thermal alignment collaborative simulation environment is established by ANSYS, and the welding deformation and thermal alignment process are analyzed by numerical simulation. The law of shape correction when the correction temperature is 600 °C, 650 °C, 700 °C and the holding time is 3600s, 5400s and 7200s, respectively, and the calculation formula of springback rate is established to evaluate the effect of thermal shape correction, so as to optimize the heat treatment correction process. The results show that the correction temperature and holding time have obvious influence on the correction effect. When the correction temperature is 700 °C and holding time is 7200s, the correction effect is the best, and the springback rate is controlled below 25%, which meets the requirements of machining accuracy.

The influence of the hole-generation process on fatigue response of open-hole and assembled titanium samples

The holes required for a bolted connection can be produced in several ways. The defects around the hole and the hole surface finish influence the fatigue life of the produced part. Abrasive waterjet cutting is compared with conventional drilling to assess these influences on titanium alloy parts. Open-hole tensile tests show a preferential fatigue behavior for conventionally drilled samples because of the lower roughness. The originality of this work focuses on linking the surface texture and damage to the life expectancy of the open-hole samples and determining the failure steps/modes of the assembled samples. A model is proposed to track the crack progression that offers adequate life estimations for open-hole samples. Single-shear assembly bearing tests show no difference between the drilling processes, and failure is obtained by secondary bending for both drilling methods.

INCREASING THE WEAR RESISTANCE OF TITANIUM ALLOYS BY DEPOSITION OF A MODIFYING COATING (Zr,Nb)N

The possibility of increasing the wear resistance of titanium alloy parts by depositing a zirconium-niobium-nitrogen [(Zr,Nb)N] coating with an adhesive Zr,Nb sublayer on their surfaces was investigated. Given that the Vickers hardness of this coating is HV = 2336 ± 115, and the value of the critical fracture load during the scratch test is L<sub>C2</sub> = 14 N, which is noticeably lower compared to nitride coatings deposited on a carbide or ceramic substrate, the (Zr,Nb)N coating provides a noticeable increase in wear resistance. The wear rate of the uncoated sample was 2.5 times higher compared to the (Zr,Nb) N-coated sample. Coating deposition allows simultaneously reducing the friction coefficient (from 0.45 for an uncoated sample to 0.33 for a coated sample) and increasing the wear resistance.

Effect of cooling rate on the phase transformation and post strength of Ti-6Al-4V under hot forming conditions: experiments and modelling

A systematic experimental and numerical study of the cooling rate effects on the post-formed strength and microstructure evolutions of a dual phase Ti-6Al-4V alloy under hot forming conditions was performed in this study. A series of cooling treatment tests were designed to achieve typical cooling scenarios in current hot forming processes, i.e. air cooling, water quenching and die quenching. The post-treated mechanical properties and phase volume fractions were characterized and quantified. The results show that higher temperatures and higher cooling rate would facilitate the β phase transformation and martensite transformation of α′ phases, leading to the higher yield strength in the formed part. Based on the macro- and micro- properties relations and observed data, a unified model for the hot forming and cooling of Ti-6Al-4V was proposed and calibrated, enabling the accurate prediction of both the macro-strength and microstructures under different cooling conditions of the material. The proposed model was further implemented into FE simulation for practical forming process simulations. A typical hot gas forming process of a rectangular cross-sectioned titanium alloy hollow tubular part was investigated. Experiments of hot gas forming with different cooling conditions, i.e. forming temperatures and cooling rates, were carried out and used to validate the established material model and simulation model. Good prediction accuracy was obtained under all the tested conditions, with the maximum prediction errors of 5.55% for macro-strength and of 9.79% for average grain size. The results and the model developed in this paper provides an effective way to facilitate the process designs and optimization for hot forming titanium alloy parts in various applications.

Cyclic softening behavior of TC17 titanium alloy fabricated by laser directly energy deposition

In aero-engines, cyclic softening can cause premature fracture of components, which is regarded as a challenge for the security of titanium alloy parts in service. In this work, the cyclic deformation behavior of LDEDed and β-forging TC17 titanium alloys with different morphology of α phase was explored, cyclic softening mechanism was investigated by using transmission electron microscopy (TEM) observation of dislocation morphology. The experimental results demonstrate that cyclic softening occurs when the total strain range increases to 2.0 %. The LDEDed specimen has a smaller stress amplitude and a larger plastic strain during cyclic softening than wrought specimen. In the softened deformation microstructure of LDEDed specimen, the size of αp decreases with the increase of strain, but the size and shape of αp and αs in wrought specimen do not change much. The main dislocation forms that dominate the cyclic softening in the α phase and the β matrix are slip bands and dislocation tangles, respectively, and the slip band in the α phase cannot pass through the secondary phase in the β matrix for slip transfer. Under the same strain, the lower dislocation density in the LDEDed microstructure is due to the larger directional back stress produced by the forward loading, which causes the dislocation rearrangement and annihilation under the reverse loading.

Obtaining strength and ductility synergy for directed energy deposited Ti17 alloys by machine learning

Recently, obtaining a balance of tensile strength and ductility in direct energy deposited (DED) titanium alloy components has been a major concern, which obstructs their further application. Herein, machine learning (ML) methods were applied to find the optimal process window of DEDed titanium alloy parts from a wide range of possible depositing process variables. Four algorithms were used for ML model training and tensile property prediction of DEDed titanium alloy. The results showed that the prediction ability of the XGBoost model was the best. The optimized ‘laser power’-‘scanning rate’ process window produced DEDed titanium alloy specimens with an ultimate tensile strength (UTS) of 1050 MPa and an elongation (E) of 12.5 %. It was demonstrated that ML methods could promote the discovery of the optimal process window, leading to an outstanding synergy of tensile strength and ductility.

Effect of cyclic heat treatment on microstructure and tensile property of a laser powder-bed fusion-manufactured Ti–6Al–2Zr–1Mo–1V alloy

Laser powder-bed fusion (L-PBF) is increasingly being employed to fabricate titanium components for aerospace applications. However, L-PBF fabricated titanium alloy parts typically exhibit high strength but low ductility because of fine α′ martensite. Post-heat treatment is essential to compose α′ into stable α, thereby achieving improved ductility. In this study, we put forward a novel post-heat treatment, i.e., a cyclic treatment that included multiple cycles of low-to-high and high-to-low temperature annealing, to improve the ductility of an L-PBF fabricated Ti–6Al–2Zr–1Mo–1V (TA15) alloy. Its effect on the microstructures and tensile properties was investigated. The results showed that the as-fabricated TA15 alloy exhibited fine martensite, leading to high strength (i.e., an ultimate tensile strength of 1168 MPa) and low ductility (i.e., an elongation of 7.1 %). Conventional post-heat treatments introduced lamellar α+β structures and resulted in improved ductility of 9–13.9 % and reduced strength of 896–1070 MPa. The cyclic multistep treatment created trimodal structures of α-laths, equiaxed α, and thin film β. Especially, it contributed to the formation of up to 57 % equiaxed α grains compared to less than 5 % in the conventional treatments, leading to the enhanced ductility. This specific structure displayed superior properties, an ultimate tensile strength of ∼900 MPa, and elongation of ∼16 %, which are comparable to the TA15 alloy wrought counterparts. The optimized strength and ductility also demonstrated the potential of cyclic multistep treatment to enhance the performance of other additive manufactured titanium alloys.

Improvement of microstructure and mechanical properties of TC4 titanium alloy GTAW based wire arc additive manufacturing by using interpass milling

TC4 titanium alloy wire arc additive manufacturing (WAAM) is easy to produce coarse columnar β grain structure which affects mechanical properties. So in this paper, an innovative process of interpass milling assisted TC4 titanium alloy gas tungsten arc welding (GTAW) WAAM is proposed. The controlling interpass milling depth is used to improve the microstructure and mechanical properties of TC4 titanium alloy parts during the GTAW-WAAM. The results showed that the coarse columnar β grains and fine α phase were observed in the non-interpass milling part. When the interpass milling assistance GTAW-WAAM was employed, the coarse columnar β grains transformed into short columnar and equiaxed grains. With the increased of interpass milling depth, the average size of α phase was gradually refined to 13.5 μm below. The highest average microhardness in the top, middle and bottom areas obtained by using the interpass milling depth of 300 μm were 369 HV0.2, 371 HV0.2 and 371 HV0.2 respectively, which was increased by 32 HV0.2, 28 HV0.2 and 26 HV0.2 compared with non-interpass milling respectively. The horizontal and vertical ultimate tensile strength first increases and then decreases with the increase of interpass milling depth, reaching its maximum at a milling depth of 300 μm. The highest tensile strength of the horizontal and vertical directions obtained by using the interpass milling depth of 300 μm were 1022 MPa and 1042 MPa. The level of the ultimate tensile strength is related to the combined proportion of total average β grain size and total average < 15 μm α phase size, and the proportion of both is balanced and maximized to obtain the maximum ultimate tensile strength. The interpass milling depth of 300 μm satisfies both conditions, so its maximum horizontal and vertical ultimate tensile strength is achieved. Fracture type of tensile specimen was ductile fracture due to observing a lot of dimples on the fracture morphology. The above conclusions show that interpass milling is an aided process to effectively improve the microstructure and mechanical properties of TC4 titanium alloy GTAW wire arc additive manufacturing thin-walled parts, which has high research significance and practical value.

Effect of Oxygen Content on Microstructure and Mechanical Properties of Additive Manufactured Ti-6Al-4V

Titanium alloys are used in many fields including military, aerospace, and biomedical because of their excellent specific strength, corrosion resistance, and biocompatibility. Recently, much research has been focused on addressing the disadvantages of conventional manufacturing methods, including reducing material and energy waste when manufacturing titanium alloy parts by additive manufacturing methods. However, due to rapid cooling, during the additive manufacturing process the material develops acicular and lamellar microstructures, and despite high strength, those features are detrimental to ductility and toughness, as compared with conventionally manufactured alloys. As a result, numerous studies have sought to obtain an equiaxed microstructure through heat treatment. However, the developed heat treatment processes are quite complex, and involve several heat treatment cycles, making such processes economically unfavorable. To overcome these limitations we suggest a different approach to obtaining an equiaxed structure in 3D-printed titanium alloy, by controlling the oxygen level. The present study analyzed the globularization behavior of Direct Energy Deposited (DED) Ti-6Al-4V alloy as a function of oxygen content and a simple heat treatment. The microstructure was globularized through oxygen level control and furnace cooling to compensate the disadvantages in the mechanical properties of additive manufactured alloys.

Machinability improvement of titanium alloys in ultra-precision machining with micro-structured surface

Titanium alloys get wider applications in different areas due to its excellent mechanical properties. However, poor thermal conductivity and low elastic module of titanium alloy induce high tool wear and make it being one of hard-to-machine materials; especially the segmented chip formation accelerates the diamond tool wear in ultra-precision machining (UPM) of precision parts. This study applies micro-structured surface to improve machinability of titanium alloys in UPM by reducing the chip segmentation induced cutting forces fluctuations. Finite element (FE) model is built to study chip formation mechanism and characterize geometries of segmented chips in orthogonal diamond cutting of Ti6Al4V alloy with the aims at the design of micro-structures array. Turning experiments are conducted to compare cutting force, surface roughness, and tool wear for diamond turning of Ti6Al4V alloy on smooth surface and micro-structured surface. The results show that the FE simulated saw chips agree well with the measured ones. Moreover, the micro-structured surface helps to decrease cutting force, reduce diamond tool wear, and improve surface quality for UPM of titanium alloy. Especially, the new method fabricates micro-grooves array on the machined surface in half-finishing process of UPM without the need of any material pre-processing and extra manufacturing equipment, which can also provide the guidance for efficient and sustainable UPM of titanium alloys parts with high surface quality.

Prospects Of Use And Processing Of Titanium Blanks Obtained By xBeam 3D Metal Printing Technology

The article presents the new range of additive technologies called xBeam 3D metal printing that allows the production of titanium alloy parts for the medicine, aeronautical and automotive industries. The new technology opens up essential challenges, such as identifying and analysing the optimal finishing machining strategies for this type of part. The article analyses the production and machining of TI6Al4V produced by Wire Arc. The research focuses on implementing optimal cutting modes to obtain the required surface quality. This article provides a better understanding of the machining of titanium blanks using this technology. The optimistic results make this method the best alternative to traditional casting technologies and powder metallurgy.

Simulation and analysis of hot cylindrical flow forming process of titanium alloy

The spinning process of cylindrical titanium alloy parts was studied using a three-dimensional model and finite element simulation. The forming conditions and stress changes under different spinning process parameters have been analyzed. Based on the numerical simulation test, the blank’s state in the processing process is analyzed and predicted, providing a process reference for the spinning trial.