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Ti-45Al-8.5Nb-W-Mo-Y合金的组织转变 总被引:4,自引:1,他引:3
研究了Ti-45Al-8.5Nb-W-Mo-Y合金的相结构。该合金铸态组织大部分由α2 γ片层域团组成,同时含有少量的B2 ω相。经过1200℃,2h处理后,B2相全部转变成ω相。合金经过70%-80%热变形后,组织由等轴γ晶粒,残余高温B2 ω相,少量的变形片层域团α2 γ片层组成。变形组织再经过1280℃,2h的热处理,其中高温相大幅度减少,同时α2板条增加。挤压态组织由变曲的片层及少量的等轴γ晶粒组成。循环热处理技术细化组织。 相似文献
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The lower ambient temperature fatigue life and higher fatigue data scatter of Ti-6 wt % Al-4 wt % V castings relative to wrought material, were investigated by analysing the nature of the crack initiation sites. Initiation mechanisms were characterized by precision sectioning the fracture surfaces at the crack nucleation locations. The combined effect of internal casting defects and a microstructure containing large colonies of similarly orientated -platelets was found to be responsible for the low smooth fatigue life. The large scatter in the fatigue data was attributed to the variety of casting defects in the material and their large size distribution. Most failures that were examined initiated from defects close to the specimen surface possibly due to some bending moment in the axial cyclic loading. The free dendrite arms in the large shrinkage pores were shown to contain -platelets in a colony arrangement. The shortest fatigue life associated with this type of defect was attributed to the notch effect of the dendrite arm interstices. 相似文献
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《Scripta Metallurgica》1989,23(10):1685-1690
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Baoxian Su Liangshun Luo Binbin Wang Yanqing Su Liang Wang Robert O.Ritchie Enyu Guo Ting Li Huimin Yang Haiguang Huang Jingjie Guo Hengzhi Fu 《材料科学技术学报》2021,62(3):234-248
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. 相似文献
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The kinetics of clustering and reversion of G-P zones in an Al-1.3 at. % Ag alloy have been investigated by resistivity measurements, with special attention to the initial parts of reversion. From an analysis of clustering kinetics, vacancy formation, solute migration and solute-vacancy binding energies have been deduced to be 0.70, 0.53 and 0.10 eV respectively.The activation energy for reversion, which is identified as the activation energy for solute atom diffusion, is found to vary from 0.98 to 1.46 eV with increasing reversion time. This is attributed to variations in the vacancy concentration in equilibrium with small dislocation loops. 相似文献
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K. Le Biavant S. Pommier C. Prioul 《Fatigue & Fracture of Engineering Materials & Structures》2002,25(6):527-545
ABSTRACT Fatigue crack initiation was studied in a bimodal TA6V titanium alloy. A ghost structure inherited from the forging process, the scale of which is roughly 100 times the apparent grain size, was found to govern the initiation process. In these macrograins, that we have labelled macrozones, most of the primary alpha grains (αp ) are found to display the same crystallographic orientation. Fatigue cracks are initiated on the basal plane or, if basal slip is difficult, on the prismatic plane. Thus in macrozones, where basal or prismatic slip is easy, numerous neighbouring tiny cracks appear over the whole macrozone, which have the size of the primary αp grains. In these macrozones the contribution of crack coalescence to crack growth is consequently very significant. On the contrary, if basal and prismatic slips are both difficult in the macrozone, no crack can be found in the corresponding macrozone. The crack initiation process is thus highly heterogeneous at the scale of the macrozone. Furthermore, this microstructure is found to induce a large scatter in the fatigue life of notched samples. 相似文献
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Ti-4.4Al-3.8Mo合金的亚稳相变及其对硬度的影响 总被引:2,自引:0,他引:2
对锻态 Ti-4Al-3.8Mo合金分别进行了β单相区和α β两相区(相变点之下45℃)淬火处理,研究了亚稳相变对硬度的影响.结果表明,β单相区淬火处理的样品硬度比α β两相区处理的样品高约10%.β单相区淬火后的相组成为全α'马氏体,自910℃的α β两相区淬火后的相组成为等轴初生α相 α'马氏体 α"马氏体.硬度出现差异的主要原因是后者中存在硬度较低的初生α相和α"马氏体.本文修正了Ti-β稳定元素二元系亚稳相图(示意图),指出在α α'和α α"相区之间存在α α' α"相区,并使用修正后的相图解释了Ti-4.4Al-3.8Mo合金的相组成与硬度的关系. 相似文献
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Fatigue crack propagation in SiC continuous fibre-reinforced Ti-6Al-4V alloy metal-matrix composites
《Composites》1993,24(3):229-234
Fatigue crack growth from a through-thickness cut notch has been studied at ambient temperature in a Ti-6Al-4V alloy matrix reinforced with Sigma (SiC) fibres. All tests have been carried out in three-point bending, and localized dominant cracks have been produced in all cases. In these composites such dominant cracks often grow off-axis, and marked effects of stress ratio on crack growth rates have been measured. At low stress ratio, the composites exhibit outstanding crack growth resistance. It has been possible to observe fatigue striations within the matrix alloy and these observations allow local crack growth rates (and hence local effective stress intensity ranges) to be determined. The implications of such studies for defect tolerance and usable stress ranges for these composites have been considered. 相似文献
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S.Z. Zhang Z.W. Song J.C. Han C.J. Zhang P. Lin D.D. Zhu F.T. Kong Y.Y. Chen 《材料科学技术学报》2018,34(7):1196-1204
In order to understand the effect of Mo alloying on the microstructural evolution of TiAl alloy, the as-cast microstructure, heat treated microstructure characteristic, and hot compression microstructure evolution of Ti-44 A1 alloy have been studied in this work. The as-cast microstructure morphology changes from(γ+α_2)lamellar colony and β/β_0+γ mixture structure to β/β_0 phase matrix widmannstatten structure,when Mo content increases from 2 at.% to 6 at.%. Affected by the relationship between β phase and αphase, the angles between the lamellar orientation and the block β/β_0 phase are roughly at 0°, 45° and90°. Comparing with heat treatment microstructure, the hot compression microstructure contains lessβ/β_0 phase, however, the β/β_0 phase containing 2 Mo alloy and 3 Mo alloy hot compressed at 1275 ℃ has the inverse tendency. In addition,(α_2 +γ) colony is decomposed by the discontinuous transformation. 相似文献
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《Materials Science & Technology》2013,29(6):503-510
AbstractThe fatigue crack growth resistance of α–β titanium alloys can be altered by microstructural modification. During welding, the fusion zone microstructure depends on cooling rate. In the present work, the alloy Ti-6Al-4V was welded over a range of heat inputs, using electron beam and gas tungsten arc welding. The weld microstructure varied from predominantly martensitic under rapid cooling conditions to a mixture of martensite and diffusional products on slower cooling. Post-weld heat treatment resulted in a basketweave α–β aggregate that coarsened with temperature and time. In all welded and heat treated conditions, the fusion zone exhibited a fatigue crack growth resistance superior to that of the base material, which was in part attributed to the lamellar microstructure of the fusion zone. Welding residual stresses also played a beneficial role in the as welded condition. Post-weld heat treatment eliminated the advantage resulting from the welding stresses but not that as a result of microstructure. 相似文献
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Xu Zhensong Wang Huaming Tang Haibo Cheng Xu Zhu Yanyan 《Journal of Materials Science》2022,57(26):12540-12555
Journal of Materials Science - The intrinsic directional positive thermal gradient of additive manufacturing usually leads to columnar grains crossing several layers and corresponding anisotropy in... 相似文献
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Baoxian Su Binbin Wang Liangshun Luo Liang Wang Yanqing Su Fuxin Wang Yanjin Xu Baoshuai Han Haiguang Huang Jingjie Guo Hengzhi Fu 《材料科学技术学报》2021,74(15):143-154
Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6Al-3Nb-2Zr-1 Mo (Ti80) alloy in hydrochloric acid (HCI) ranging from 1.37 to 7 M,and temperature ranging from 25 to 55 ℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCI concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCI at 25 ℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCI solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25 ℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCI concentration at which Ti80 alloy can maintain passivation at 25 ℃ can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxed α phase is more susceptible to corrosion compared to intergranular β3 phase due to a lower content of Nb,Mo,and Zr in the former. 相似文献
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The morphology and kinetics of the precipitation of the alpha phase produced by two different heat treatment routes, namely, (a) direct isothermal decomposition and (b)-quenching and subsequent ageing, were studied. In isothermally decomposed samples the (supersaturated) + transformation was seen to occur mainly through the discontinuous growth of the transformed zone consisting of groups of parallel side plates from the grain boundary regions towards the interior of the grain. Unlike for the case of a regular discontinuous precipitation, here the transformed regions are not separated from the untransformed by an incoherent interface and the growing-plates do obey a fixed orientation relationship with the grain from which they are evolved. The theory of cellular reaction has been applied to explain the growth rate of the duplex ( + ) region. The overall reaction kinetics were analysed on the basis of the Johnson-Mehl formulation and were found to be consistent with that of a discontinuous precipitation reaction, where grain boundary nucleation sites were saturated at an early stage of the transformation. The structure of the-quenched samples showed a uniform distribution of athermal omega particles which acted as precursors to the-precipitates. As a consequence, the reaction rate was greatly enhanced and-precipitation in the quenched and aged samples was seen to occur continuously in the entire body of the grain. 相似文献
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Ti-4Al-2V is a new type of alpha titanium alloy that suitable for the application in high-temperature and high-pressure water/steam
environment. Ti-4Al-2V can be used in marine engineering, nuclear power industry. In this paper the surface characterization
of the Ti-4Al-2V implanted with 75 keV nitrogen with fluences of 3 × 1017 and 8 × 1017 N+/cm2 is investigated by glancing-incidence XRD, XPS and microhardness. The results show that new phase TiN are formed after N implantation in the surface region. The nitrogen implantation increases the surface hardness up to 340 and 260% for fluence
of 8 × 1017 and 3 × 1017 N+/cm2, respectively. The enhancement of hardness is related to the formation of TiN and irradiation induced hardness. 相似文献