显微组织对TA15合金高温拉伸性能的影响

研究了显微组织变化对TA15合金500℃高温拉伸性能的影响。结果表明:初生α相含量增加、α相方向性增强、次生α片变厚及β晶粒尺寸变粗大等显微组织的变化,可使TA15合金500℃高温抗拉强度降低,最大降幅达90MPa以上。研究表明,随初生α相含量增加,增多了晶界数量,而随温度升高晶界强度比晶粒强度下降快,导致高温抗拉强度随初生α相含量增加而降低。     

Designing high-strength titanium alloy using pseudo-spinodal mechanism through diffusion multiple experiment and CALPHAD calculation

This study used the pseudo-spinodal mechanism to obtain the ultrafine α phase for designing high-strength titanium alloy.Diffusion multiple experiments were designed to find the composition range of TM-xMo-yV alloy (TM: Ti-4.5Al-2Cr-2.5Nb-2Zr-1Sn) for obtaining ultrafine α phase.CALPHAD results confirm that when the alloy composition is located near the intersection of the α and β phase free energy curves,the alloy will undergo pseudo-spinodal transformation and obtain the ultrafine α phase.The designed TM-6Mo-3V alloy has a yield strength of 1411 MPa and an elongation of 6.5 ％.The strength of the alloy depends on the thickness,fraction of the α phase and the solid solution strengthening effect of the alloying elements.The deformation mechanism of the alloy is the dislocation slip of the α and β phases and the twin deformation of the α phase.The large number of α/β interfaces produced by the fine α phase is the main reason for limiting the ductility of the alloy.The use of the pseudo-spinodal mechanism combined with diffusion multiple experiments and CALPHAD is an effective method fordesigning high-strength titanium alloys.     

Morphology characteristics of α precipitates related to the crystal defects and the strain accommodation of variant selection in a metastable β titanium alloy

Profound and comprehensive investigations on the morphology characteristics of α precipitates are essential for the microstructural control of metastable β titanium alloys.At the very beginning of aging treatment,intragranular α precipitates with a dot-like morphology begin to generate nearby the dislo-cations,then those dot-like α precipitates with the same crystallographic orientation tend to connect with each other to develop a lath-like morphology.With the progress of aging treatment,the orientated lath-like α precipitates gradually combine with each other to form the V-shaped clusters or the triangular ones.The dislocations of{1(-1)0}β < 11 (-1)>β edge type are evidenced within the β grains,and it is found that variant selection ofα precipitates induced by the transformation strain and the interplay between α vari-ants and the dislocations are confirmed as the key factors for the formation of the V-shaped or triangular clusters.The results of this work could provide underlying knowledge on the morphology characteristics of intraguranular α precipitates related to the crystal defects and the strain accommodation of α variants in metastable β titanium alloys.     

两种组织TC11钛合金薄板弯曲疲劳性能的研究

本研究选取了具有（α＋β）等轴组织和α／β粗片层组织的TCll钛合金作为研究对象,采用研究了TCll合金薄板样品在恒总应变幅控制下的弯曲疲劳性能及其损伤行为,通过对疲劳开裂路径和断裂的观察与表征,探讨了疲劳损伤与组织结构间的关系。研究发现,恒总应变幅控制下的等轴组织TCll钛合金薄板的弯曲疲劳性能明显的高于粗片层组织合金。等轴组织合金的疲劳裂纹沿α相中的滑移带萌生并扩展,片层组织样品疲劳裂纹沿着α相或与片层垂直的方向扩展。     

Quantitative analysis of the microstructure of transitional region under multi-heat isothermal local loading forming of TA15 titanium alloy

In this paper, an analogue experiment was carried out to study the effect of processing parameters including deformation temperature, deformation degree, cooling mode and loading pass on the microstructure of transitional region under isothermal local loading forming of TA15 titanium alloy. The volume fraction, grain size and aspect ratio of primary α phase of transitional region were quantitatively characterized. It is found that deformation temperature and deformation degree also have interaction on the microstructure evolution of transitional region under isothermal local loading forming. At a certain deformation degree, primary α grain size increases first and then decreases with increasing temperature. However, primary α grain size varies little with deformation degree at higher temperature (in upper two phase region) but increases firstly and then decreases with deformation degree at lower temperature (in lower two phase region). Primary α aspect ratio increases with deformation degree at lower temperature but varies little at higher temperature. The morphology of transformed structure in β matrix is greatly influenced by deformation temperature and less influenced by deformation degree under air-cooling. The precipitated Widmanstatten α phase in β matrix is in lamellar form and arranges in colonies under air-cooling, but it is in thinner acicular form and distributes disorderly under water quenching. Loading pass has little influence on the morphology of microstructure.     

固溶时效处理对TM60合金组织和力学性能的影响

通过对8型钛合金TM60进行不同制度的固溶时效处理,研究了各制度下其显微组织、相结构和力学性能的变化。研究结果表明：α相的含量和体积分数对合金性能有较大影响,固溶处理温度选择在700℃,时效处理温度应选择在400℃~450℃,β型钛合金TM60具有最佳的强塑性。     

Evidence of FCC titanium hydride formation in β titanium alloy: An X-ray diffraction study

This study has shown a complete phase transformation from the bcc β phase Ti-30 wt% Mo alloy to the fcc δ phase titanium hydride by thermal hydrogenation treatment. This fcc δ hydride has a lattice parameter of 0.4444 (± 0.0001) nm and acomposition of TiH_1.96 and it is very brittle. It appears that the types of hydride formed depend on the phase regime where thermal hydrogenation takes place, i.e., the fcc δ hydride forms from the β phase regime, the fct (c/a > 1) γ hydride forms from the α phase regime, and a mixture of both hydrides forms from the α + β phase regime.     

Microstructural Evolution of Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd Titanium Alloy with Carbon Additions

The effect of carbon addition on microstructural evolution was studied in a near-α titanium alloy(Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd). It was found that flake and ribbon titanium carbides with a NaCl crystal structure formed in the as-cast alloys with carbon additions of over 0.17 wt pct. Flake carbide particles are the product of eutectic transformation and precipitate from the high-temperature β phase. The ribbon carbide particles are primary phases formed prior to the nucleation of any metallic phases. The as-cast alloys with carbide precipitation after heat-treatment atβt-30℃ followed by water quenching showed the spheroidization of α lamellae and partial dissolution of carbide particles. After annealing at βt 15℃, carbide particles are mostly distributed at the grain boundary and spheroidized through mixed grain boundary plus bulk diffusions.     

钛合金双片层组织对性能的影响

研究了通过热处理制度调整,在合金α片层之间形成细小的条状次生α相,形成一种新型的钛合金显微组织——双片层组织.通过对比等轴组织、双态组织、片层组织和双片层组织的性能,结果表明,在合金的强度和塑性不损失的条件下,双片层组织进一步提高了裂纹在合金中的扩展阻抗,使得合金的断裂韧性得到改善,疲劳裂纹扩展速率得到降低.双片层组织...     

变形量对TC25钛合金饼坯组织和力学性能的影响

将Ф240 mm TC25钛合金坯料在T_β+25℃温度下保温一段时间后锻制成饼坯,研究20%、40%和60%三种典型变形量对饼坯的组织和拉伸力学性能的影响。结果表明,三种变形量的饼坯显微组织均由多个平直的束状α相互相交错形成网篮组织;随着变形量的增加,平直的束状α相减少,α相方向性减弱,长条α相尺寸减小;同时,随着变形量的增加,拉伸强度增强。     

Effect of alloying element modification on superplastic deformation properties of Ti–4Mo–4Al–2Sn–0·5Si (IMI550)

Abstract

The superplastic deformation properties of a commercial titanium alloy, IMI550 (Ti–4Mo–4Al–2Sn–0·5Si, wt-%) are compared with a specially melted ‘modified’ alloy in which 1 wt-%Mo (slow diffusing element) is replaced with 1 wt-%Fe (fast diffusing element) on the basis that the diffusional properties of the β phase, to which these alloying elements segregate, is a significant factor in determining the overall flow properties. It is shown that the superplastic deformation properties of both alloys in the temperature range 800–850°C develop with strain as the initial heterogeneous α + β structure develops into uniform duplex equiaxed microstructures. Thereafter, the modified alloy exhibits enhanced superplastic properties (reduced flow stresses in the strain rate range 5 × 10^-5–5 × 10^-3 s^-1). The results are analysed quantitatively on the basis of the Ashby and Verrall model applied to the α and β phases combined according to the isostress model for two phase deformation which accounts for the interaction of the α and β phases.     

固溶冷却速率对全片层亚稳β钛合金α相形貌的影响EI北大核心CSCD

采用Gleeble热模拟压缩试验机、显微硬度计、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等研究固溶冷却速率对TB17钛合金力学性能和条状α形貌的影响。结果表明:具有网篮组织的TB17钛合金经两相区固溶后,当固溶冷却速率为200℃/min时,合金显微硬度为250HV,随着固溶冷却速率的降低,钛合金显微硬度逐渐增加,当固溶冷却速率降低到1℃/min(炉冷)时,显微硬度增加到320HV。在连续冷却过程中会发生β→α相变,在β基体上析出次生α相,同时条状α相会转变为“叉状”结构;随着固溶冷却速率的降低,“叉状”结构逐渐变粗长大,当固溶冷却速率为40℃/min时,“叉状”结构的宽度约为14 nm,当固溶冷却速率为10℃/min时,“叉状”结构的宽度约为100 nm,当固溶冷却速率为1℃/min(炉冷)时,“叉状”结构的宽度约为300 nm;而当固溶冷却速率大于10℃/min时,条状α相侧面和端面包裹着斜方马氏体α″相,马氏体相的存在促进了α相转变和“叉状”结构的形成。当固溶冷却速率逐渐降低至1℃/min左右相当于炉冷速率时,“叉状”结构变粗,条状α相端面和侧面的斜方马氏体相消失,发生α″→α相变。     

Effect of prior β processing steps on microstructural refinement during thermomechanical processing of a two phase (α + β) titanium alloy

Abstract

Microstructural evolution in Ti - 6.8Al - 3.2Mo - 1.8Zr - 0.3Si alloy during a newly designed thermomechanical schedule has been systematically studied with the aim of obtaining a suitable microstructure for superplastic forming. The schedule involves prior processing in the β phase field and subsequent rolling in the (α + β) phase field. In all experiments the starting material was thermally or thermomechanically treated in the β phase field and subsequently quenched in order to produce a martensitic structure. The morphology of the primary α in material for hot rolling could be substantially altered from that obtained with the conventional (α + β) processing schedule of two phase titanium alloys. Prior β processed microstructure, (α + β) rolling temperature, and deformation were found to influence the α phase morphology in the alloy. The effect of subsequent annealing in the (α + β) phase field on microstructural stability has been examined. The results show that the proposed thermomechanical processing schedule provides a relatively wide temperature - strain 'processing window' in β and (α + β) phase fields over which a fine grain (< 5 μm) equiaxed α structure can be obtained in Ti - 6.8Al - 3.2Mo - 1.8Zr - 0.3Si alloy.     

Grain morphology and texture evolution of TC21 titanium alloy during annealing with different time

A homogeneous equiaxed‐structure TC21 titanium alloy is hot rolled and annealed for different time ranging from 1 h to 6 h. The grain morphology and texture evolution of α and β phases during annealing are mainly investigated using the electron back‐scattered diffraction characterization. In the early annealing stage, the α grain mainly maintains the elongated morphology generated in the rolling. With increasing annealing time, more and more elongated α grains become equiaxed due to enhanced static recrystallization and boundary splitting. Differently, the β grain exhibits a fully equiaxed morphology all the time due to the sufficient static recrystallization, and get a coarsening with increasing annealing time. The α phase exhibits a (0001) basal texture in the early annealing stage, and then forms a TD‐split texture with increasing annealing time. The β phase exhibits the {001}<110> texture at every annealing time. Based on the analysis about the texture of different grain sizes, the effects of recrystallization nucleation and oriented growth on texture evolution are discussed. It suggests that TD‐split texture in α phase is originated from both the recrystallization nucleation and oriented growth. The formation of {001}<110> texture in β phase is mainly originated from the oriented growth.     

Annealed microstructure dependent corrosion behavior of Ti-6Al-3Nb-2Zr-1 Mo alloy

Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^-6A/cm²)and high polarization impedance(10⁶Ω·cm²)in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO₂to aqueous Ti³⁺),active dissolution of substrate Ti to aqueous Ti³⁺and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.     

TC18钛合金热压参数对流动应力与显微组织的影响

通过在700~950℃和应变速率0.001~50s-1条件下的热模拟实验,系统研究了TC18钛合金应变速率、变形温度对变形抗力和显微组织的影响。结果表明:提高变形温度或降低应变速率,可显著降低TC18合金变形过程中的真应力,与单相区相比,两相区变形抗力对温度的变化更为敏感。在α+β区变形时,α相和β相都参与变形,球状初生α沿形变方向略有拉长,β相沿金属流动方向形成纤维组织;β相变点以上温度变形时,β相沿金属流动方向呈纤维状分布,在950℃可以观察到再结晶的等轴β晶粒。     

Mechanism and kinetics of carbide dissolution in near alpha Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd titanium alloy

The present work evaluates the influence of bulk carbon content and aging temperature on the stability of carbide in near alpha Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd titanium alloy. The carbide particles were formed during heat treatment in the β phase field and preserved by water quenching. Subsequent aging treatments at 750–850 °C caused partial dissolution of these precipitates, as a result of the peritectoid reaction between the β phase and carbide. The models based on interface reaction controlled dissolution, via uniform atomic detachment, dislocation mechanism or vacancy flow, yielded experimental predictions comparable to the observed dissolution kinetics. Furnace cooling after heat treatment in the β phase field dissolved carbide particles completely, and the microstructure changed from acicular-like or block α to equiaxed α with increase of carbon content.     

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.     

The Study on Quench Transformation in Ti-10V-2Fe-3Al Alloy

The quench transfomation in a Ti-10V-2Fe-3Alnear B-titanium alloy was studied by meansof X-ray diffraction, transmission electronmicroscopy, and optical micyoscopy. The quenchingtemperatures were above and below the β transustemperature. The phase constitutions of specimensquenched from various solution temperatureswere identified and the phase morphologies wereexamined. In addition, the relationship betweenphase lattice parameters and quenching tempera-tures was given for α, β and α ~(11) phases. Thisalloy has a tendency of precipitation of athermalω phase and formation of stress induced α~(11) mar-tensite from β phase during quenching. Quenchedfrom the temperatures above the β transus tem-perature, the alloy mainly consists of β phase,a small amount of α~(11) martensite and athemalω phase aye also present in the alloy. Afterquenching from the temperatures below the βtransus temperature, the α phase appeaysin the alloy in addition to the phases mentionedabove.     

Ti700sr高温钛合金TIG焊接接头组织及性能研究

采用TIG焊接方法对Ti700sr高温钛合金板材进行了焊接,研究了接头的组织形貌、硬度分布及力学性能.结果表明,Ti700sr高温钛合金板材焊接后的接头成形良好,焊缝区组织由粗大的柱状晶及细长的针状α相构成,热影响区组织由细针状α和残余β相构成,热影响区析出相得到有效控制,相边界上无明显硅化物析出;焊接热影响区的硬度相...