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微等离子体氧化陶瓷膜对钛合金耐蚀性的影响

姚忠平 , 姜兆华 , 辛世刚 , 孙学通 , 张雪林 , 吴振东

中国腐蚀与防护学报

在偏铝酸钠溶液中,利用双向脉冲微等离子体氧化技术,在TC4钛合金表面原位生长复合氧化物陶瓷膜.分析表明,陶瓷膜由Al2TiO5、α-Al2O3和金红石型TiO2构成,其中Al2TiO5为主晶相,金红石型TiO2含量由膜外层向内层逐渐增多,而α-Al2O3含量由外向内逐渐减少;整个膜层分为致密层和疏松层两部分.陶瓷膜提高了钛合金的耐盐酸和硫酸腐蚀性能.微等离子体氧化陶瓷膜使得钛合金的耐点蚀性能明显提高,同时使TC4钛合金与LY12铝合金之间的电偶腐蚀得到改善.

关键词: 微等离子体氧化 , Ceramic coatings , Corrosion resistance , Titanium alloy

Effect of the Oxidation Time on Properties of Ceramic Coatings Produced on Ti-6Al-4V by Micro-Arc Oxidation

Zhaohua JIANG , Xuetong SUN , Yanping LI , Fuping WANG , Y , ong LÜ

材料科学技术(英文)

Ceramic coatings were prepared on Ti-6Al-4V alloy using ac micro-arc oxidation (MAO) in silicate-hypophosphate solution. Growth regularity and formation mechanism of ceramic coatings were discussed. It was found that during the first stage the growth rate of coatings toward the external surface was larger than that toward substrate and then the coating began to grow mainly towards Ti alloy. When the total coating thickness reaches a certain value, it would no longer increase. In addition, the variations of the composition and microstructure of ceramic coatings according to the depositing time were also investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM). The amount of rutile TiO2 gradually increased, whereas the amounts of the anatase TiO2 and amorphous phases first increased and then decreased slightly.

关键词: Titanium alloy , null , null , null

In vitro Biological E®ects of Ti2448 Alloy Modified by Micro-arc Oxidation and Alkali Heatment

Xue Han

材料科学技术(英文)

The purpose of this study was to test the hypothesis that the combination of micro-arc oxidation and alkali heatment (MAH) would improve the cytocompatibility of a newly designed Ti-24Nb-4Zr-8Sn alloy. In this study, commercially pure titanium (cp Ti) and Ti-24Nb-4Zr-8Sn were used. Surface modification of Ti-24Nb- 4Zr-8Sn by a two-step treatment of micro-arc oxidation (MAO) and alkali heatment was reported. Surface characterizations were performed by scanning electron microscopy (SEM), thin film X-ray diffraction (TF-XRD) and X-ray photoelectron spectroscopy (XPS). The MAH layer consisted of finer crystals and possessed a higher degree of crystallity and stability than the MAO layer. A biocompatibility study on treated and untreated Ti-24Nb-4Zr-8Sn in comparison with cp Ti was carried out to investigate the effect of the different surfaces on the bone integration property in vitro. The cellular assays revealed that the MAO and MAH layer favored the initial adhesion of MC3T3-E1 cells and that the growth rate of MC3T3-E1 cells on MAH layer was ignificantly
higher than that on the conventional MAO-treated layer after 3-day and 5-day incubation, demonstrating the greater potential of the hybrid treatment of micro-arc oxidation followed with alkali heatment as a novel surface modification method for implanting materials.

关键词: Titanium alloy

Hot deformation behavior of a near alpha titanium alloy with/without thermal hydrogen processing

Qing WANG

金属学报(英文版)

The true stress-true strain curves of Ti-6Al-2Zr-1Mo-1V alloy with hydrogen were obtained by hot compression test. The microstructures of the alloy before and after thermo-compression were observed. The apparent activation energies of deformation were calculated for the alloy with and without hydrogen. The behavior and mechanism of deformation for hydrogenated Ti-6Al-2Zr-1Mo-1V alloy at high temperature were analyzed. The relationship between hydrogenation time and hydrogen content at 800 ℃  can be expressed as the equation: CH(t)=1.2-1.2exp(-t/120). The true stress-true strain curves of hot compression for Ti-6Al-2Zr-1Mo-1V alloy with hydrogen first move down and then move up as hydrogen content increases. Appropriate hydrogen content can reduce the peak of flow stress to minimal value. The apparent activation energies of deformation of the alloy with 0.47% hydrogen content and without hydrogen were calculated as 140 kJ•mol-1 and 390,kJ•mol-1, respectively, at 800   ℃ and at strain rate 8.3×10-4 s-1. The apparent activation energy of deformation increases when the strain rate enhances from 8.3×10-4 s-1 to 8.31×0-2 s-1.

关键词: Titanium alloy , hydrogenising treatment , compression at high temperature , apparent activation energy of deformation , microstructure.

Superplasticity of Ti2448 Alloy with Nanostructured Grains

M.J. Xiao

材料科学技术(英文)

Ti-24Nb-4Zr-8Sn, abbreviated as Ti2448 from its chemical composition in weight percent, is a multifunctional β type titanium alloy with body centered cubic (bcc) crystal structure, and its highly localized plastic deformation behavior contributes significantly to grain refinement during conventional cold processing. In the paper, the nanostructured (NS) alloy with grain size less than 50 nm produced by cold rolling has been used to investigate its superplastic deformation behavior by uniaxial tensile tests at initial strain rates of 1.5×10-2, 1.5×10-3 and 1.6×10-4 s-1 and temperatures of 600, 650 and 700°C. The results show that, in comparison with the coarse-grained alloy with size of 50 ¹m, the NS alloy has better superplasticity with elongation up to ~275% and ultimate strength of 50-100 MPa. Strain rate sensitivity (m) of the NS alloy is 0.21, 0.30 and 0.29 for 600, 650 and 700°C, respectively. These results demonstrate that grain refinement is a valid way to enhance the superplasticity of Ti2448 alloy.

关键词: Titanium alloy

Effects of Current Density on Microstructure of Titania Coatings by Micro-arc Oxidation

Yue Yang

材料科学技术(英文)

In the present study, titania coatings were prepared under different current density conditions in micro-arc oxidation (MAO) process on titanium alloy in NaAlO2 solution. The aim of this work was to study the effects of current density on the microstructure of titania coatings. The morphology and phase composition of the coatings were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectra. The thickness and surface roughness of the coatings were characterized by confocal laser Scanning Microscopy (CLSM). The results showed that the coatings were composed of crystalline anatase and rutile phases of TiO2, and contain a network of evenly distributed small pores. It has also shown that an
increase in current density leads to an increase in rutile content.

关键词: Titanium alloy

Experimental Investigation and Numerical Simulation of the Grain Size Evolution during Isothermal Forging of a TC6 Alloy

Miaoquan LI , Shankun XUE , Aiming XIONG , Shenghui CHEN

材料科学技术(英文)

Hot compression was conducted at a Thermecmaster-Z simulator, at deformation temperatures of 800~1040℃, with strain rates of 0.001~50 s-1 and height reduction of 50%. Grain size of the prior α phase was measured with a Leica LABOR-LUX12MFS/ST microscope to which QUANTIMET 500 software for image analysis for quantitative metallography was linked. According to the present experimental data, a constitutive relationship for a TC6 alloy and a model for grain size of the prior α phase were established based on the Arrhenius' equation and the Yada's equation, respectively. By finite element (FE) simulation, deformation distribution was determined for isothermal forging of a TC6 aerofoil blade at temperatures of 860~940℃ and hammer velocities of 9~3000.0 mm/min. Meanwhile, the grain size of the prior α phase is simulated during isothermal forging of the TC6 aerofoil blade, by combining FE outputs with the present grain size model. The present results illustrate the grain size and its distribution in the prior α phase during the isothermal forging of the TC6 aerofoil blade. The simulated results show that the height reduction, deformation temperature, and hammer velocity have significant effects on distribution of the equivalent strain and the grain size of the prior α phase.

关键词: Titanium alloy , null , null , null , null

Surface Microcracks and Relief Caused by Lamella Sliding during High Temperature Tension of Titanium Alloy with Lamella Structure

Feng XU

材料科学技术(英文)

Lateral surface near the fracture of tensile sample was examined by scanning electron microscopy (SEM) before and after oxide film removing. The relationship between surface morphology and microstructure was established. The results show that the microcracks are caused by brittleness rupture of surface oxide films due to α lamellas sliding along α lamella boundaries. And the sliding of aligned α lamellas bring not only microcrack formation but also the raise of colony relative to prior sample surface. A slip model, which depicts the relationship between surface morphology and microstructure, was brought forward to analyze the observation.

关键词: Titanium alloy , null , null

A New Aging Treatment Way for Near α High Temperature Titanium Alloys

Na Peng

材料科学技术(英文)

Two near α titanium alloys Ti-5.6Al-4.8Sn-2.0Zr-1Mo-0.35Si (1#) and Ti-6.0Al-4.8Sn-2.0Zr-1Mo-0.35Si (2#) were solution-treated in the upper α+β phase fields and the duplex mixture microstructures consisting of the less volume fraction primary phase ( αp) and the transformed phase (βt) were obtained. The aging treatments were carried out at 700℃ for 1# alloy and 760℃ for 2# alloy under varied terms, respectively. It guaranteed 2 ordered phase to precipitate only in p but not in t for the two alloys. The slower precipitation and growth of the α2 ordered phase and silicide was observed in 1# alloy in comparison with that in 2# alloy. The mechanical properties including tensile strength and ductility, the creep and lasting properties at the temperature of 600℃ were investigated. Prolonging aging time did not predominantly change the tensile strength and ductility for the two alloys. The 600℃/100h thermal exposure caused a notable decrease of tensile ductility in 2# alloy though no distinct decrease could be observed in 1# alloy after the thermal exposure. The lasting property of 1# alloy was increased with prolonging aging time and finally equal to or even better than that of 2# alloy. Nevertheless, No evident increase emerged in 2# alloy with prolonging aging time. Similarly, the creep property of 1 # alloy monotonously increased with increasing aging time and finally equal to or even better than that of 2# alloy. No evident increase could be observed for 2# alloy. It can be deduced that the overgrowth of α2 ordered phase and silicide is unable to enhance hot strength properties but causes an unacceptable damage to tensile ductility. The optimum equilibrium of the comprehensive properties depending on the proper control of α2 ordered phase and silicide can be achieved by selecting aging temperature and time.

关键词: Titanium alloy , null , null

3D Finite Element Numerical Simulation of Residual Stresses on Electron Beam Welded BT20 Plates

Lixing HUO , Furong CHEN , Yufeng ZHANG , Li ZHANG , Fangjun LIU , Gang CHEN

材料科学技术(英文)

A three-dimensional finite-element model (FEM) used for calculating electron beam (EB) welding temperature and stresses fields of thin plates of BT20 titanium has been developed in which the nonlinear thermophysical and thermo-mechanical properties of the material has been considered. The welding temperature field, the distributions of residual stresses in as-welded (AW) and electron beam local post-weld heat treatment (EBLPWHT) conditions have been successfully simulated. The results show that: (1) In the weld center, the maximum magnitude of residual tensile stresses of BT20 thin plates of Ti alloy is equal to 60%~70% of its yield strength δs. (2) The residual tensile stresses in weld center can be even decreased after EBLPWHT and the longitudinal tensile stresses are decreased about 50% compared to joints in AW conditions. (3) The numerical calculating results of residual stresses by using FEM are basically in agreement with the experimental results. Combined with numerical calculating results, the effects of electron beam welding and EBLPWHT on the distribution of welding residual stresses in thin plates of BT20 have been analyzed in detail.

关键词: Electron beam local heat treatment , null , null , null

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