Passivation Behavior of Water-Quenched and Heat-Treated Ti–6Al–4V in Hank's Solution

Ti–6Al–4V is a prevalent material utilized in various industrial applications, and its microstructure modification commences with quenching, followed by diverse heat treatments. Although many works have concentrated on the mechanical properties of Ti–6Al–4V with tailored microstructures resulting from heat treatments, their corresponding corrosion behavior still lacks attention. In this study, the corrosion behavior of water-quenched Ti–6Al–4V that undergoes heat treatment between 700 and 850 °C in Hank's solution is investigated. Various electrochemical methods, such as open-circuit potential tests, potentiodynamic/potentiostatic polarization, electrochemical impedance spectroscopy, and Mott–Schottky tests, are jointly employed. The water-quenched Ti–6Al–4V displays a quick-cooling microstructure with a plentiful amount of martensite α/α′ phase. Heat treatment at 700 °C significantly alters the microstructures of the samples. Due to competitive factors, heat treatment at low temperatures results in uneven alloy composition, leading to poor uniformity of the passive film. At this phase, negative effects dominate, and the corrosion resistance of the samples deteriorates. When the heat-treatment temperature increases to 850 °C, the content of β phase, which possesses better corrosion resistance, increases and becomes dominant. Consequently, the corrosion resistance of the samples improves in Hank's solution.     

选区激光熔化Ti6Al4V合金的各向异性

采用金相分析和拉伸测试等方法,分析了激光熔化成形Ti6Al4V试样在不同沉积高度、不同方向截面的组织和性能。结果表明,平行于沉积方向的截面其组织类似柱状晶,具有较弱的织构特征;垂直于沉积方向的截面其组织为块状结构,具有较强的织构特征。选区激光熔化成形Ti6Al4V合金在沉积高度方向上的力学性能受柱状晶尺寸的影响,随着沉积高度的增大其抗拉强度和屈服强度先降低后升高而延伸率先提高后降低。织构和熔合不良等缺陷,使试样垂直于沉积方向上的强度和塑性都比平行于沉积方向的试样高。     

置氢Ti6Al4V合金的微观组织演变规律

为研究置氢Ti6Al4V合金的高温加工改性机理,从微观组织的角度对合金进行了对比分析.利用OM、SEM、XRD等研究了置氢对Ti6Al4V合金变形前后微观组织演变的影响.研究结果表明:氢的加入不仅使置氢Ti6Al4V合金中β相比例明显增大,而且改变了α相与β相之间的电势差,在氢含量为0.3%~0.5%两相颜色将发生互换,氢含量增加到0.50%以上时,合金中将出现面心立方结构的δ氢化物;随氢含量的增加,合金超塑拉伸变形后的组织由α+β两相等轴晶粒变为粗大的β晶粒,造成α与β界面的协调能力下降,并改变了合金的变形机制.     

Static coarsening behaviour of lamellar microstructure in selective laser melted Ti–6Al–4V

Static coarsening mechanism of selective laser melted (SLMed) Ti–6Al–4V with a lamellar microstructure was established at temperatures from 700 °C to 950 °C. Microstructure evolution revealed that high heat treatment temperature facilitated martensite decomposition and promoted lamellae growth. At each temperature, the growth rate decreased with increasing holding time. The static coarsening behaviour of SLMed Ti–6Al–4V can be interpreted by Lifshitz, Slyozov, and Wagner (LSW) theory. The coarsening coefficient were 0.33, 0.33–0.4, 0.4–0.5 for 700–800 °C, 900 °C and 950 °C, respectively. This indicated the coarsening mechanism was bulk diffusion at 700–800 °C, and a combination of bulk diffusion and interface reaction at 900 °C and 950 °C conditions.     

Microstructure and properties of Ti-6Al-4V fabricated by low-power pulsed laser directed energy deposition

Thin-wall structures of Ti-6Al-4V were fabricated by low-power pulsed laser directed energy deposition. During deposition, consistent with prior reports, columnar grains were observed which grew from the bottom toward the top of melt pool tail. This resulted in a microstructure mainly composed of long and thin prior epitaxial β columnar grains (average width ≈200 μm). A periodic pattern in epitaxial growth of grains was observed, which was shown to depend upon laser traverse direction. Utilizing this, a novel means was proposed to determine accurately the fusion boundary of each deposited layer by inspection of the periodic wave patterns. As a result it was applied to investigate the influence of thermal cycling on microstructure evolution. Results showed that acicular martensite, α' phase, and a small amount of Widmanstätten, α laths, gradually converted to elongated acicular α and a large fraction of Widmanstätten α laths under layer-wise thermal cycling. Tensile tests showed that the yield strength, ultimate tensile strength and elongation of Ti-6Al-4V thin wall in the build direction were 9.1%, 17.3% and 42% higher respectively than those typically observed in forged solids of the same alloy. It also showed the yield strength and ultimate tensile strength of the transverse tensile samples both were ˜13.3% higher than those from the build direction due to the strengthening effect of a large number of vertical β grain boundaries, but the elongation was 69.7% lower than that of the build direction due to the uneven grain deformation of β grains.     

Influence of laser power on the corrosive behavior of laser metal deposited Ti6Al4V+Cu in artificially prepared sea water

Titanium alloy is an excellent corrosion resistance material due to its greater affinity with oxygen when exposed to an aggressive medium such as sea water. The protection against attack is due to the oxidizing fume formed into its surface. This paper reports the effect of laser power on the corrosive behavior of laser metal deposited Ti6Al4V alloy with 5 weight percent (wt. %) copper in freshly prepared artificial sea water. The open circuit potential, potentiodynamic polarization curves, and the scanning electron microscope (SEM) morphologies of the entire Ti6Al4V+5 Cu alloy samples had been investigated and reported. From the results obtained, it can be deduced that the laser power is inversely proportional to the corrosion rate. Sample PL3 deposited with a laser power of 1600 W exhibited the best corrosion rate of 0.0123 mm/year when exposed to sea water under aerated condition. The morphologies of the entire laser deposited samples of the scanning electron microscope (SEM) unveiled typical passivity due to the strong inter-atomic bonds between the α/β phases formed with the copper inclusion within the lattices of the titanium alloy.     

Microstructure and corrosion behaviour of additively manufactured Ti–6Al–4V with various post-heat treatments

This paper presents the results of an experimental investigation into the effects of solution treatment, age and stress relief on the corrosion behaviour of direct metal laser sintered Ti–6Al–4V. The evidence of microstructural change and phase evolution, as affected by heat-treatment temperature, was characterised through scanning electron microscopy and X-ray diffraction. The corrosion behaviour was evaluated electrochemically in Ringer's solution, at 37°C. It was determined that the non-equilibrium α’ phase, with a small amount of β nuclei, formed in the as-printed sample. Enhancement in the resistance of the passive oxide layer on the alloy was observed after solution treatment and age, as well as after high-temperature stress relief. The structure of the passive layer of the surface showed a heat-treatment temperature dependency.     

激光冲击处理对Ti6Al4V力学性能的影响

通过对钛合金Ti6Al4V的激光冲击处理,研究了激光冲击处理工艺对钛合金Ti6Al4V力学性能的影响.实验表明:激光冲击处理能有效提升Ti6Al4V的力学性能,在激光功率密度由1.15GW/cm2增加到2.31GW/cm2过程中,其冲击波峰值压力线性增加,表面最大残余压应力也相应增大,最高达-264MPa,表面硬化层的显微硬度高达510Hv,硬化层深度约为0.25mm,经过激光冲击处理后硬度相对于原始钛板提高了64%,随着激光能量的增加,冲击区域的抗拉强度极大增强,塑性降低.     

Effect of α-lath size on the mechanical properties of Ti–6Al–4V using core time hydrogen heat treatment

ABSTRACT

When hydrogen is dissolved, brittleness occurs in the material. However, in the case of titanium and titanium alloy, hydrogen can be temporarily dissolved and removed, thereby improving the mechanical properties of titanium and titanium alloy. In this study, Core time Hydrogen Heat treatment (CHH) applies to Ti–6Al–4V alloy to improve mechanical properties. CHH was performed at 800°C and 1000°C for 2?h. Thereafter, dehydrogenation was performed for 2 h at 700°C in vacuum atmosphere to remove residual hydrogen. After the CHH at 800°C, it was found that the α-lath size in the Ti–6Al–4V was narrowed; thereby increasing the Vickers hardness and tensile strength without decreasing in elongation.     

Corrosion behaviour of Ti6Al4V alloy in artificial saliva solution with fluoride content and low pH value

The corrosion resistance of the Ti6Al4V alloy in Carter–Brugirard artificial saliva (pH = 5.2), in saliva with sodium fluoride (NaF) addition (pH = 5.2) and in saliva with NaF and lactic acid (pH = 2.0) was evaluated. The open circuit potential of the alloy in all electrolytes was stable after approximately 2 h of immersion. Higher corrosion rate and lower polarization resistance were measured for the alloy immersed in fluoridated saliva, compared to genuine saliva, indicating that the addition of NaF lead to a worse corrosion resistance. In fluoridated and acidified saliva (pH = 2), the Ti6Al4V alloy exhibited the lowest corrosion resistance. The corroded surfaces are much rougher than those non‐corroded. A higher roughness was obtained for the alloy immersed in saliva with NaF and low pH, indicating that the corrosion process was more active in this electrolyte. Large precipitates of corrosion products and corrosive sites were found on the samples immersed in all electrolytes.     

Investigation and optimization of heat treatment process on tensile behaviour of Ti6Al4V alloy

This article examines the microstructure and tensile strength of annealed Ti6Al4V alloy at different temperatures and times. Taguchi based L9 (3²) design was used for the experimental design matrix and optimization of the tensile strength of heat treated samples. The optimum parameter combination was at the temperature of 950 °C and soaking time of 1 hour. ANOVA results show that temperature is the most influencing parameter and a regression equation of degree two was developed to predict tensile strength. Results of the microstructure show lamellar structure development within the samples heat-treated at 1000 °C.     

Effect of Vacuum Heat Treatment on the Microstructure and Tribological Property of Ti–6Al–4V Alloy with Cu Coating

The effect of vacuum heat treatment on the interface microstructure and tribological property of Cu-coated Ti – 6Al – 4V alloy is investigated herein. After the vacuum heat treatment process, a diffusion layer is formed at the interface between the Cu coating and the Ti – 6Al – 4V substrate. The formed intermetallic compounds at the interface between the Ti – 6Al – 4V substrate and Cu coating are CuTi₂, CuTi, Cu₄Ti₃, and β-Cu₄Ti. The activation energy of intermetallic compound growth in the diffusion zone of Cu-coated Ti – 6Al – 4V is 126.0 kJ mol⁻¹, and the pre-exponential factor is 0.1 m² s⁻¹. The tribological properties of the Cu-coated Ti – 6Al – 4V alloy are best when subjected to diffusion treatment at 700 °C for 300 min, with weight loss reduced by 58.2% compared to the Ti – 6Al – 4V alloy. The wear resistance of the Ti – 6Al – 4V alloy can be enhanced by Cu coating and vacuum diffusion heat treatment, and the formation of the Cu – Ti intermetallic compound contributes to this improvement. These findings offer new insights for further advancements in the tribological properties of titanium alloys.     

Improved Tribocorrosion Properties of Ti6Al4V Alloy by Anodic Plasma Electrolytic Oxidation

Ti6Al4V alloy has good corrosion resistance due to the formation of the passive oxide films on the surface of Ti6Al4V alloy. However, Ti6Al4V alloy has poor tribocorrosion resistance in the seawater environment. Herein the present work, plasma electrolytic oxidation (PEO) with the electrolyte of glycerol and sodium borate is used to generate PEO coatings on the surface of Ti6Al4V alloy to improve its tribocorrosion properties. The microstructure and tribocorrosion properties of PEO coatings are investigated by using scanning electron microscopy, X-ray diffraction, and tribometer, respectively. The growth kinetics and the tribocorrosion mechanisms of PEO coatings are discussed in detail. It is shown in the results that PEO coatings deposited on the surface of Ti6Al4V alloy are composed of rutile and anatase phases. The surface hardness and thickness of PEO coatings are enhanced with the increase of the voltage and time. The wear rate of Ti6Al4V alloy with PEO coatings is significantly reduced in artificial seawater.     

Effects of scan line spacing on pore characteristics and mechanical properties of porous Ti6Al4V implants fabricated by selective laser melting

The use of porous structures is gaining popularity in biomedical implant manufacture fields due to its ability to promote increased osseointegration and cell proliferation. Selective laser melting (SLM) is a metal additive manufacturing (MAM) technique capable of producing the porous structure. Adjusting the parameter of scan line spacing is a simple and fast way to gain porous structures in SLM process. By using the medical alloy of Ti6Al4V, we systematically study the influence of the scan line spacing on pore characteristics and mechanical properties of porous implant for the first time. The scanning electron microscope (SEM) results show that the porous Ti6Al4V implants with interconnected pore sizes which ranges from 250 to 450 μm is appropriate for compact bone. The compression strength and modulus of the porous Ti6Al4V implants decrease with the increase of the scan line spacing, and two equations by fitting the data have been established to predict their compression properties. The compressive deformation of the porous Ti6Al4V implants presented an adiabatic shear band (ASB) fracture, which is similar to dense Ti6Al4V owing to the dense thin wall structures. The ability to create both high porosity and strong mechanical properties implants opens a new avenue for fabricating porous implants which is used for load-bearing bone defect repair and regeneration.     

Study of high temperature mechanical behavior of the thermally oxidized Ti‐6Al‐4V alloy

The influence of oxidation of a Ti‐6Al‐4V alloy at 800 °C on its tensile properties at 600 °C has been studied. Specimens of this alloy were oxidized at 800 °C for 0.5, 1, 5, 10, 20 and 40 h. Tensile tests at 600 °C were carried out and the fracture surfaces were also examined. Oxidation of the specimens resulted in the formation of an oxide layer that spalled and another oxide layer that adhered to the substrate. Oxide formation increased with increase in duration of oxidation. In this investigation, density curves of the oxide layer as a function of duration of oxidation at 800 °C were used to identify a parabolic oxide growth law. The results of this study revealed coherence between the experimental data and calculations based on the Pilling‐Bedworth law. The mechanical strength of the Ti‐6Al‐4V alloy did not vary significantly with oxidation, but reduction in cross sectional area with increase in oxide layer thickness, as well as the slope of the stress‐strain curve decreased beyond the ultimate tensile strength. Fracture of the tensile tested specimens was predominantly ductile with microcavities. At certain regions of the oxide layer, brittle fracture with radial cracks was observed indicating intergranular fracture.     

Microstructure and mechanical properties of as-built and heat-treated electron beam melted Ti–6Al–4V

This paper investigates the effect of post-deposition heat treatment on porosity, microstructure, and mechanical properties of Ti–6Al–4V produced via an Electron Beam Melting process. Samples were studied in the conditions of as-built and heat treated at 920°C and 1030°C. The as-built samples were characterised by columnar β grains consists of α+β microstructure with Widmanstätten and colony morphologies were found. Heat treatment resulted in increased α lath width. The yield strength and ultimate tensile strength was greater in the as-built condition than wrought material. Porosity re-growth occurred after heat treatment but it did not affect the tensile properties. Greater ductility after heat treatment was attributed to the larger α lath width which increases effective slip length.     

Investigation of joining Al–C–Ti cermets and Ti6Al4V by combustion synthesis

The paper has addressed a route for the welding of titanium alloy (Ti6Al4V) and Al–C–Ti powders by the combustion synthesis (CS) method. Al–C–Ti powders were compressed in the titanium alloy pipes with relative densities of 65%, and then the powder compact was sintered by two reaction mode at the same time as the annulus of titanium alloy and the synthesized product were joined. The paper has studied the effects of reaction mode and Al content in starting powders on the structure and property of the welded joints. And it has also discussed the microstructure of welded joints by laser-induced combustion synthesis (LCS). The mechanical properties of the welding seam have been also tested. The results show that LCS welding has realized fusion welding and the welding seam has good mechanical properties. Furthermore, SEM analysis has indicated that nano-size grains of TiC were formed in the joint layer.     

Ti6Al4V合金激光原位制备TiN枝晶增强梯度复合表面层

利用连续波2kW Nd-YAG激光在Ti6Al4V合金表面原位制备TiN枝晶增强梯度金属基复合材料表面层，并研究了该表面层的显微组织和磨损性能。结果表明：该表面层沿激光熔化深度具有明显的梯度结构，表面层与Ti6Al4V基体之间呈现良好的冶金结合，Ti6Al4V的表面硬度及耐磨性得到了显著增强．     

Influence of Cu addition on the structures and properties of Ti15SnxCu alloys

In this study, Ti15SnxCu alloys were synthesised using an argon-arc melting and casting method. The as-cast alloy ingot was heat-treated for 2?h at 1000°C and then quenched in water to investigate the effects of heat treatment on the microstructure and corrosion behaviour of the Ti15SnxCu alloys. In comparison to the heat-treated Ti15Sn alloy, the average size of cellular grains (d_G), the lamellar length (λ_L), and the lamellar thickness (λ_T) in heat-treated Ti15Sn2Cu alloy were refined by approximately 36, 30, and 36%, respectively. The corrosion behaviour of heat-treated Ti15SnxCu alloys was made nobler by adding 2?wt-% Cu content. The precipitation of large amounts of nobler (Ti, Sn)₂Cu nanoparticles hindered grain growth, improved the UTS, 0.2YS, microhardness and good corrosion resistance.     

钛合金表面激光熔覆Ni基梯度涂层的研究

为了改善Ti6Al4V钛合金表面耐磨性能和抗高温氧化性能,采用CO2激光在Ti6Al4V钛合金表面进行激光熔覆Ni基梯度涂层试验.利用扫描电镜和显微硬度计等手段分析了熔覆层组织,测试了基体和熔覆层的显微硬度.结果表明,采用适当的工艺参数,可以在钛合金表面获得连续、均匀、无裂纹和气孔的熔覆层.熔覆层组织由树枝晶和晶间共晶组织构成,并与基体形成牢固的冶金结合.由基体到表面,显微硬度过渡平稳,呈明显梯度渐变特征.