TC4 Alloy Research Articles

Effect of Preheating and Post-Heating on the Microstructures and Mechanical Properties of TC17-Ti2AlNb Joint with Electron Beam Welding.

To enhance welding quality and performance, preheating and post-heating are usually employed on high-temperature materials, concurrently with welding. This is a novel technique in vacuum chamber electron beam welding (EBW). TC17 and Ti2AlNb alloys are the hot topics in aero-engine parts, and the welding of dissimilar materials is also a broad prospect. To settle welding cracks of Ti2AlNb, EBW with preheating and post-heating was investigated on TC17 and Ti2AlNb dissimilar alloy, which improved the manufacturing technology on high-temperature materials. The dissimilar joint no longer had cracks after preheating, which exhibited excellent welding stability and metallurgical homogeneity, and preheating and annealing had an important effect on mechanical properties. The joint strength after 630 °C annealing is higher than that of TC17 alloy base metal (BM) and other annealing temperatures, reaching 1169 MPa at room temperature and 894 MPa at 450 °C tensile condition. The joint plasticity after 740 °C annealing is equivalent to TC17 BM. EBW with preheating improved the microstructure characteristics and enhanced the plasticity of Ti2AlNb alloy weld and dissimilar joint, which would contribute to the application of Ti2AlNb alloy and Ti2AlNb dissimilar parts.

Tribological behaviour of polytetrafluoroethylene containing plasma electrolytic oxidation coatings on TC4 alloy

Improving the tribological performance of titanium alloys is crucial to expanding their industrial applications. In this study, self-lubricating and wear-resistant coatings for TC4 alloy were achieved by combining plasma electrolytic oxidation (PEO) prepared using compounded electrolytes with incorporation of polytetrafluoroethylene (PTFE) as a solid lubricant. The investigation focused on the comprehensive effects of compounded electrolytes and PTFE on the microstructure and tribological behaviour of PEO coatings. After doping with PTFE, the coating prepared in electrolyte containing silicate, phosphate, and aluminate exhibited lowest wear rate (decreasing by 95.1%) and maximum hardness of 638.6 HV compared to other coatings. Additionally, the coefficient of friction (COF) significantly decreased from 0.8 to 0.16. This can be attributed to the strategy of depositing low-frictional discontinuous layers on hard PEO coatings.

Study on the tribological characteristics of surface triangular textured TC4 alloy prepared by SLM technology

Surface Triangular Textured TC4 Alloy specimens were prepared by 3D printing technology (SLM technology: selective laser fusion). Effects of wedge-shaped triangular textures with different texture area occupancy on hardness, friction and wear of the 3D printed TC4 alloy specimens were studied, in comparison with non- textured specimens. SFT -2 M pin-disc friction and wear testing machine was used to perform friction and wear experiments under 46 # mechanical oil lubrication conditions, and MH-500 Vickers hardness tester was used to measure hardness of the specimens. Scanning electron microscope (SEM), energy spectrometer (EDS), and electronic balance instrument were used to characterize the wear scar morphology, element content, wear amount, etc. of the specimens. Using the Fluent module in ANSYS Workbench software, we studied the mechanism for the reduction in the friction coefficient between friction pairs during the relative movement in lubricating oil. Results of the study show that the hardness of the 3D printing specimen is significantly greater than that of the non- textured one. In each group of experiments, the wedge triangular textured specimens showed better tribological properties, and the 3D printed specimen with an area occupancy of 22. 53 % exhibited the smallest average friction coefficient (0.17) and higher wear resistance than other specimens. The dynamic pressure effect due to the wedge triangle texture inside the lubricating oil film is the main reason for the reduced friction coefficient between the friction pairs.

Effect of Ti3AlC2 particles on microstructure and tribological properties of micro-arc oxidation layer on TC4 alloy

TiO2 metal oxide layers rich in Ti3AlC2 phase was successfully prepared on TC4 alloy by micro-arc oxidation (PECC or ASD) process. Analysis of the material phases contained in the PECC layer by X-ray diffractometry; scanning electron microscopy and energy spectroscopy were used to analyses the pores and elemental distribution on the surface of the specimens; the cross-sectional thickness of PECC layers were measured by metallographic microscope; confocal microscopy was used to measure the surface roughness of the sample; High temperature wear resistance of PECC layers with different Ti3AlC2 concentration was compared by tribological wear testing. The results show: 1) The incorporation of Ti3AlC2 particles plays an obvious catalytic role in the growth of PECC layer and the thickness is up to 74.74 μm; 2) When the concentration of Ti3AlC2 gradually increases, the PECC layers fluctuates obviously, and the deposition sealing effect is remarkable; 3) When the concentration is 4-6 g/L, the alloy has the best wear resistance, volume wear is only 1.98×10-4 mm3 /N·m. Experiments have shown that surface modification of the alloy using the PECC process can further broaden the application of the alloy in the field of anti-wear

Fabrication of robust superhydrophobic surface on TC4 alloy by wire electrical discharge machining

Superhydrophobic metal surfaces have significant applications in various areas such as surface self-cleaning, resistance reduction, anti-corrosion, etc. However, inexpensive preparation methods for superhydrophobic surfaces with a good mechanical stability are still to be developed. In this study, microarray structures on TC4 alloy were readily fabricated using a wire electrical discharge machining technology. Following the treatment with a fluorinating reagent, the microarray surface exhibited excellent superhydrophobic properties, where the largest contact angle and the smallest sliding angle reached 159° and 3°, respectively. Influences of the dimensions of microarray structure on the TC4 alloy surface wettability were also investigated in this study. Experiments show that this superhydrophobic surface possesses favorable self-cleaning, good mechanical stability, and promising anti-corrosion properties. In addition, by controlling the dimensions of the microstructure a superhydrophobic surface with a gradient wettability was also fabricated, which exhibits the property of doing nondestructive transportation of liquids.

Microstructure and Wear Resistance of Grx-Ti-BN Composite Coating on TC4 by Argon Arc Cladding

The TC4 (Ti-6Al-4V) alloy has problems such as low material hardness, poor wear resistance, and abnormal sensitivity to adhesive wear and fretting wear. In this study, we used graphene-reinforced Ti/BN composite coatings prepared on the surface of the TC4 alloy by argon arc cladding technology. We explored the optimal content of graphene to improve its hardness and wear resistance. The physical phases and microstructures of the coatings were analyzed using an X-ray diffractometer, metallurgical microscope, and scanning electron microscope. Microhardness and wear properties of the cladding coating were measured by a Vickers hardness tester and a universal friction and wear tester. The incorporation of graphene resulted in a transformation of the reinforcing phase in the coating from TiN to Ti(N, C). The C element in the molten pool was substituted with the N element in an unending solid solution, resulting in the formation of Ti(N, C) through intermittent nucleation. As the amount of graphene in the molten pool increases, the concentration of carbon (C) also increases. This leads to the continuous growth of Ti(N, C) particles, resulting in a coarser coating structure and a decrease in coating performance. When the graphene content is 5 wt.%, the microstructure refinement of the coating is the most obvious, the microhardness is 900 HV0.2, which is 3 times higher than that of the matrix, and the wear rate is 4.9 × 10−5 mm3/(N·m), which is 4.9 times higher than that of the matrix. The wear mechanism of the coating is primarily abrasive wear with some slight adhesive wear.

Microstructure and Impact Toughness of Laser-Arc Hybrid Welded Joint of Medium-Thick TC4 Titanium Alloy

This study delves into the impact toughness of medium-thick (12 mm thick) titanium alloy joints crafted through a multi-layer, multi-pass welding technique that blends laser-arc (MIG) hybrid welding technology. Microstructural scrutiny, employing optical microscopy, SEM and TEM, unveils a consistent composition across weld passes, with prevailing α/α′ phases interspersed with some β phase, resulting in basket-weave structures primarily dominated by acicular α′ martensite. However, upper regions exhibit Widmanstatten microstructures, potentially undermining joint toughness. Hardness testing indicates higher values in cosmetic layers (~420 HV) compared to backing layers and bending tests manifest superior toughness in lower joint regions, attributed to smaller grain sizes induced by repetitive welding thermal cycles. Impact toughness assessment unveils diminished values in the weld metal (WM) compared to the heat-affected zone (HAZ) and base material (BM), amounting to 91.3% of the base metal’s absorption energy. This decrement is ascribed to heightened porosity in upper regions and variations in grain size and phase composition due to multi-layer, multi-pass welding. Microstructural analysis proximal to failure sites suggests one mechanism wherein crack propagation is impeded by the β phase at acute crack angles. In essence, this study not only underscores the practicality of laser-MIG hybrid welding for medium-thick TC4 alloy plates but also underscores the reliability of joint mechanical properties.

Effects of TiC particles on tribological and corrosion resistance of PEO coating on TC4 alloy

To improve wear resistance and corrosion behavior of TC4 alloy, plasma electrolytic oxidation (PEO) was performed in a TiC particle containing electrolyte. Results show that increasing PEO current density is conducive to improving the coating thickness, promoting incorporation of TiC particles, and enhancing wear resistance of the coating. While increasing TiC content in electrolyte reduces PEO coating thickness. Under the optimized condition, where the electrolyte has 2 g L−1 TiC and PEO current density is 5 A dm−2, the derived PEO coating exhibits both high wear resistance and corrosion resistance. Moreover, it is shown that the incorporated TiC particles are more likely to become components in the inner layer of the derived MAO coating.

Microstructural and wear resistance evolution of Alx(TiVZr)100−x lightweight high-entropy alloys

To solve the problem of high density of wear-resistant high-entropy alloys (HEAs), three Alx(TiVZr)100−x HEAs（Al25, Al30 and Al35）were researched. Results indivocated that the Alx(TiVZr)100−x HEAs consisted of solid solution phases and Al1(Zr,Ti,V)1 precipitates with content of 1.91%/Al25, 3.82%/Al30 and 4.85%/Al35. As the matrix hardness of Al25, Al30 and Al35 was approximately 1.60 times of TC4 alloy. Aside, the micro-cutting behaviour was weakened by the Al1(Zr,Ti,V)1 precipitates for their high hardness and the semi-coherent relationship with the matrix. Therefore, the relative wear resistance of Al25, Al30 and Al35 to TC4 was 2.10, 2.94 and 3.42, respectively. More notably, the enhancement of wear resistance of AlTiVZr alloys induced by Al1(Zr,Ti,V)1 precipitates was considerably greater than that by the matrix hardness.

Hot deformation behavior and microstructure evolution of TC11 dual-phase titanium alloy

Thermomechanical processing is one of the major steps in the fabrication of structural components used in various engineering applications. The thermomechanical coupling effect of temperature and strain rate has a significant impact on the stress-strain thermal deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloy. Here, the hot deformation behavior of TC11 dual-phase alloy has been comprehensively investigated by the hot compression tests with deformation temperatures ranging from 870 °C to 960 °C and strain rates of 0.01 s−1 to 1 s−1. Based on the flow stress curves and Arrhenius-type constitutive equation, a strain compensated Arrhenius model for TC11 alloy was successfully developed, achieving rapid and accurate prediction of high-temperature flow stress. By studying the deformed microstructure characteristics of materials under various deformation conditions, the role of deformation temperatures and strain rates was fully discussed in microstructure evolution, including the primary α phase (αp) and lamellar (αs). The thin-long lamellar shape αs can be obtained at a higher strain rate and deformation temperature. The predominance of single-peaked stress features in most flow curves, along with EBSD characterization results, indicates that continuous dynamic recrystallization (DRX) is the primary softening mechanism under different deformation conditions. This work supports the rapid prediction of flow stress and the relationship between process parameters and microstructural evolution to expedite the design optimization of plastic deformation process parameters and the development of advanced TC11 titanium alloy with targeted microstructures.

One-step in situ preparation of Zr(Ti)-MOFs on titanium alloys at a low temperature of 80 °C and atmospheric pressure

Preparing metal-organic frameworks (MOFs) film in situ on the surface of the Ti-6Al-4V (TC4) titanium alloy is challenging owing to the dense and stable surface TiO2 passive film. In this study, titanium-doped zirconium-based MOFs (Zr(Ti)-MOFs) film was constructed in situ on the TC4 alloy in one step at a low temperature and atmospheric pressure, with ZrCl4 as the source of Zr metal ions. ZrCl4 attacked and dissolved the TiO2 film to form Zr-O-Ti bonds on the surface of TC4 to provide nucleation sites for further reactions. At the same time, Zr4+ and dissolved Ti4+ combined in solution to form Ti containing Zr-O cluster nodes, which aggregated and grafted to the Zr-O-Ti bonds on the substrate surface, and reacted with organic ligands (terephthalic acid) to form Zr(Ti)-MOFs film. The Ti4+ dissolved from the TC4 participate in the Zr-MOFs formation, thereby changing the high temperature and high-pressure conditions required for the traditional preparation of Zr-MOFs (UiO-66). The in situ preparation of Zr(Ti)-MOFs on TC4 was achieved at 80 °C under atmospheric pressure conditions. This study elucidated the growth mechanism of Zr(Ti)-MOFs on the TC4 surface, providing a reference for the design and In-situ preparation of multifunctional MOFs on the TC4 titanium alloy.

Effect of surface strengthening by ultrasonic shot peening on TC17 alloy

This paper investigates the effects of ultrasonic shot peening (USP) on surface morphology, microstructure, and residual stress field distribution of TC17 alloy under different process parameters. The aim is to reveal the surface strengthening mechanism of TC17 alloy caused by USP. The results suggest that the use of the 2.5 mm projectile diameter leads to an increase in surface roughness, plastic deformation, and a deeper grain refinement layer compared to the 1.5 mm projectile diameter. Additionally, it results in a greater depth of the compressive residual stress layer and maximum compressive residual stress. The crack initiation sites under two projectile diameters are located below the compressive residual stress layer. The USP treatment introduces compressive residual stress on the surface, inhibiting the initiation of surface cracks, and the deeper compressive residual stress layer offsets the early fatigue failure caused by higher roughness.

Surface Roughness of Interior Fine Flow Channels in Selective Laser Melted Ti-6Al-4V Alloy Components.

A challenge remains in achieving adequate surface roughness of SLM fabricated interior channels, which is crucial for fuel delivery in the space industry. This study investigated the surface roughness of interior fine flow channels (1 mm diameter) embedded in SLM fabricated TC4 alloy space components. A machine learning approach identified layer thickness as a significant factor affecting interior channel surface roughness, with an importance score of 1.184, followed by scan speed and laser power with scores of 0.758 and 0.512, respectively. The roughness resulted from thin layer thickness of 20 µm, predominantly formed through powder adherence, while from thicker layer of 50 µm, the roughness was mainly due to the stair step effect. Slow scan speeds increased melt pools solidification time at roof overhangs, causing molten metal to sag under gravity. Higher laser power increased melt pools temperature and led to dross formation at roof overhangs. Smaller hatch spaces increased roughness due to overlapping of melt tracks, while larger hatch spaces reduced surface roughness but led to decreased part density. The surface roughness was recorded at 34 µm for roof areas and 26.15 µm for floor areas. These findings contribute to potential adoption of TC4 alloy components in the space industry.

Effect of Al2O3 nanoparticles additions on wear resistance of plasma electrolytic oxidation coatings on TC4 alloys

To enhance the tribological properties of TC4 alloy, the plasma electrolytic oxidation (PEO) method was utilized to prepare the coating incorporated various contents of Al2O3 nanoparticles (0, 3, 6, 9, 12 and 15 g/L) on TC4 alloy. The phase composition, chemical compositions, elemental distribution and microstructure of the coatings were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray computer tomography (XCT). The results revealed that the introduction of Al2O3 nanoparticles into the electrolyte promoted the formation of Al2TiO5 phase in the PEO coatings, and most of the nanoparticles were embedded into the coatings which reduced porosity of the coatings, but increased surface roughness. Also, the increase in the addition of Al2O3 nanoparticles enhanced the microhardness of the PEO coatings due to the formation of Al2TiO5. The tribological behavior of the PEO coatings was improved significantly owing to the high microhardness and porous structure of the coatings. The primary wear mechanism of the coating with 12 g/L Al2O3 nanoparticles was abrasive wear as this coating formed a lubrication zone during the wear process. Besides, the friction coefficient and wear loss mass of the PEO coating prepared with 12 g/L Al2O3 nanoparticles additive exhibited the excellent wear resistance compared to its counterparts.

Achieving excellent fatigue crack growth resistance and tensile strength combination in multilayered TC4/TB8 structures

Here we report a multilayered TC4/TB8 titanium alloy structure fabricated by diffusion bonding that can produce an excellent property combination. Its fatigue crack growth (FCG) life increases by 6.2 times and 2.6 times compared to TB8 plate and TC4 plate, respectively. Meanwhile, the tensile ultimate strength reaches 1128 MPa, which is near high strength of TB8 alloy. The delamination at bonded interfaces and crack deflection within layers induced by different mechanical responses of both TC4 and TB8 alloys promote the FCG life improvement of multilayered TC4/TB8 structures. Besides, multilayered structures can obtain sufficient strength due to well-bonded joints and high-strength TB8 layers. The influence of dissimilar layers and interlayer cracking on the distribution of stress and strain fields at the crack tip was simulated using the Abaqus software.

Strength and ductility improvement of the axial gradient microstructure TC21 titanium alloys manufactured by electropulsing plus step-quenching treatment

In order to reduce the weak area caused by traditional connection method and improve the structural efficiency of aircraft, the design concept of an integral component with dual microstructure is proposed. The electropulsing treatment (EPT) was used to produce an axial gradient microstructure (AGM) in TC21 titanium alloy, followed by the step-quenching treatment (SQT) to tailor the precipitation behavior of the α phase. Results demonstrate that the AGM produced by the combination of EPT and SQT achieves a simultaneous enhancement in both strength and plasticity of the alloy. Compared to EPT alone, the SQT results in the dissolution of the bimodal microstructure region with small-sized α phase, and an increased density of secondary α phase precipitation in both the transition and lamellar microstructure regions. During room temperature tensile deformation, coordinated distribution of deformation occurs sequentially in various regions, the 101̅0112̅0type of prismatic slip and deformation nanotwins exist in the equiaxed and lamellar α phase, respectively. Moreover, the deformation gradually declines from the bimodal region to the lamellar region, leading to the fracture of AGM in the bimodal region and an overall augmentation of the strength and plasticity of TC21 alloy. Hence, the results of this paper can provide research basis for the strength and plasticity improvement and deformation damage mechanism of high strength and toughness titanium alloy.

Special interlayer pause strategy for controlling grain morphology and tensile property anisotropy of TC11 alloys fabricated by directed energy deposition technology

Directed energy deposition (DED)-built titanium alloys have long suffered from the anisotropic mechanical properties induced by the long columnar prior β grains growing along the building direction, which restricts their applications. In this work, a special interlayer pause (SIP) strategy is designed to reduce the tensile property anisotropy by adjusting the grain morphology. The grain morphologies, microstructure, crystallographic texture, tensile properties and their anisotropy of DEDed TC11 titanium alloys were systematically investigated. The results show that the SIP strategy promotes the columnar-to-equiaxed transition of grain morphology, reduces grain sizes, and weakens the crystallographic textures. The microstructure of SIP samples consists of superfine basketweave and lamellar α laths and residual β phases. The average length of α laths increases with the SIP layer number. In addition, the maintained superfine α phases contribute to an ultrahigh yield strength of ∼1200 MPa of the SIP samples. The yield strength of the horizontal direction gradually decreases and that of the vertical direction increases with increasing the SIP layer number, resulting in a lowered strength anisotropy of less than 2%. When adopting an optimal SIP strategy, the as-deposited TC11 alloy exhibits a relatively small ductility anisotropy.

Effect of environmental media on the growth rate of fatigue crack in TC4 titanium alloy: Seawater and air

The fatigue crack growth rate of TC4 alloy in seawater is significantly faster than that in air. In order to analyze the behind reasons, the crack propagation path are investigated by scanning electron microscopy in conjunction with electron backscattering diffraction. The results indicates that the complex ionic environment in seawater can diminish the resistance of the fatigue crack growth. Especially, the damage of the α/β interphase induced by hydrogen embrittlement and Cl- in the seawater accelerate the fatigue crack propagation along the phase interface, although the presence of α/β interphase can reduce the crack propagation rate in air.

Enhancement of fatigue properties of selective laser melting fabricated TC4 alloy by multiple shot peening treatments

This study investigated the impact of multiple shot peening (SP) treatments on the surface morphology, microstructure, residual stress and fatigue performance of TC4 alloy manufactured by selective laser melting (SLM). The multiple SP treatments were conducted sequentially using cast steel beads, ceramic beads and glass beads at different peening intensities. In comparison to the conventional single SP process, multiple SP treatments reduced surface roughness and stress concentration coefficient while further increasing the residual compressive stress on the alloy surface. SP significantly enhanced the fatigue life of the alloy by 6.4 to 9.6 times, with a more pronounced improvement observed with multiple SP. Fatigue fracture analysis revealed that the untreated alloy showed multiple fatigue sources which all located on the surface, with surface printing defects acting as potential sites for crack initiation. After SP treatments, all fatigue cracks were initiated beneath the surface. The improved fatigue performance of SLM-formed TC4 alloy could be mainly attributed to the SP-induced surface microstructure refinement and residual compressive stresses. Furthermore, results indicated that, for subsurface crack initiation, the initial cracks primarily stemmed from the fracture of α/α' martensite in the primary β columnar grains.

Enhancing PEO coating on TC6 alloy through in-situ synthesis of MoSe2—Towards more efficient wear-reducing lubrication and wear resistance

Plasma electrolytic oxidation (PEO) has demonstrated significant enhancements in the mechanical properties and corrosion resistance of titanium alloys. Despite these advantages, the presence of micropores and microcracks in the coating can still detrimentally impact tribological properties. This paper introduces a novel approach involving the in-situ growth of a surface structure. The resulting interface structure exhibits outstanding tribological properties under a load of 3 N and a speed of 1.5 cm/s. In contrast to prior studies, improvements are made to the electrical parameters and electrolyte formula of Plasma electrolytic oxidation, facilitating the in-situ growth of MoSe2. This results in the formation of a lubricating layer and a robust TiO2 ceramic coating with excellent adhesion. A systematic analysis of friction, wear characteristics, reveals that MoSe2 in situ grow on the surface of the PEO coating, within micropores, microcracks, and crater structures after hydrothermal treatment. This process significantly enhances the microporous structure of the coating, with the MoSe2 film forming a dense and uniform interlocking layer with the PEO lower layer. Dry friction test experiments demonstrate a 33.7% reduction in friction coefficient and a 29% decrease in wear rate compared to the PEO sample, indicating the synergistic effect between the MoSe2 film and the PEO coating.