Ti-23Al-17Nb合金双态组织的控制

研究Ti-23Al-17Nb(at%,下同)合金在不同热处理条件下形成的双态组织的微观细节特征及其形成规律,分析双态组织细节特征对力学性能的影响,探讨综合改善合金拉伸性能和高温持久性能的途径。结果表明,经α2+B2两相区温度变形的该合金,通过固溶处理/连续冷却和固溶快冷+时效两种方式的热处理均可形成双态组织。其中固溶快冷+时效方式可以实现O相板条数量、尺寸、分布及排列更有效的控制,时效温度的降低有助于板条的细化和混乱排列。在α2相等轴颗粒形貌及体积分数基本一致(约15%～20%)的情况下,O相板条体积分数的增加有利于合金高温持久性能的显著提高,但会造成合金室温拉伸延伸率的下降;O相板条的细化有利于合金室温和高温拉伸性能的同时改善,但使高温持久性能有所降低;通过1060℃固溶处理/油淬+850℃时效处理获得的双态组织具有强度、塑性和高温长时性能的最好匹配。     

Microstructure and tensile properties of orthorhombic Ti–Al–Nb–Ta alloys

Microstructure and tensile properties of orthorhombic Ti–Al–Nb–Ta alloys have been studied. In order to optimize ductility and strength of the orthorhombic alloys with the nominal compositions of Ti–22Al–23Nb–3Ta and Ti–22Al–20Nb–7Ta, various thermomechanical processing steps were implemented as part of the processing route. With a special heat treatment before rolling to obtain a fine and homogeneous rolled microstructure, the rolled microstructure resulted in a good combination of high tensile yield strength and good ductility of the alloys through available solution and age treatments. The duplex microstructure with equiaxed α₂/O particles and fine O phase laths in a B2 matrix, deforming in α₂+B2+O phase field and treating in O+B2 phase field, possesses the highest tensile properties. The R.T. yield strength and ductility of the Ti–22Al–20Nb–7Ta alloy are 1200 MPa, and 9.8% respectively. The yield strength and ductility values of 970 MPa and 14% were also maintained at elevated temperature (650°C).     

Microstructure control and high temperature properties of TiAl base alloys

An equiaxed fine grain structure, a γ grain structure with the precipitated ₂ laths, and a fully lamellar structure were obtained by the microstructure control using thermomechanical processing and heat treatment. The key to obtaining the equiaxed fine grain structure using isothermal forging is to decompose the lamellar structure and then produce the fine grain microstructure through dynamic recrystallization. TiAl base alloys consisting of fine equiaxed grains, in particular, Ti-39Al-9V consisting of the γ and B2 phases exhibited superplastic elongation of more than 600% at 1423 K. Creep rupture properties of TiAl binary alloys with various microstructures were studied in purified He in the temperature range from 1073 to 1373 K. Above 1173 K the precipitated ₂ phase improved the steady state creep rate and creep life. At 1023 K, the ₂ phase did not improve the creep rate, although the steady state creep rate decreased and the creep life increased as the γ grain size increased.     

Effect of microstructure on tensile properties and fracture behavior of intermetallic Ti2AlNb alloys

The tensile properties and fracture behaviors of Ti-22Al-27Nb and Ti-22Al-20Nb-7Ta alloys were investigated in the temperature range of 25-800℃ Three typical microstructures were obtained by ifferent thermomechanical processing techniques.The results indicate that the duplex microstructure has an optimum combination of tensile yield strength and ductility both at room and elevated temperatures.Adding Ta to Ti2AlNb alloy can improve the yield strength,especially at high temperature while retain a good ductility.The study on crack initiation and propagation in dedformed microstructure of Ti2AlNb alloys indicates that microstructure has ikmportant effect on the tensile fracture mechanism of the alloys.The cracks initiate within primary O/α2 grains along O/B2 boundaries or O phase laths in B2 matrix,and propagate along primary B2 grain boundaries for the duplex microstructure.The fracture mode is transgranular with ductile dimples for the duplex and the equiaxed microstructures,but intergranular for the lath microstructure.     

焊后热处理对异种合金摩擦焊件组织与性能的影响

用金相观察、SEM分析和拉伸试验等方法研究不同的焊后热处理制度对异种合金(Ti2AlNb/TC11)线性摩擦焊接件显微组织与力学性能的影响。结果表明:仅进行时效热处理时,随着保温时间的延长或热处理温度的提高,焊缝两侧热影响区条状α/O相析出量不断增加,焊接接头强度也相应得到提高;固溶及时效热处理后,TC11合金侧热影响区在晶界上析出大量粗条状α相,Ti2AlNb合金侧热影响区晶界主要由条状O相构成,焊接接头强度超出母材TC11合金的强度。     

Microstructure,creep, and tensile behavior of a Ti–21Al–29Nb(at.%) orthorhombic+B2 alloy

The creep and tensile deformation behavior of a Ti–21Al–29Nb (at.%) alloy were studied. Monolithic sheet materials were produced through conventional thermomechanical processing techniques. Heat treatments at all temperatures above 1050 °C, followed by water quenching, resulted in fully-B2 microstructures. Below 1050 °C, either equiaxed or Widmanstätten O-phase precipitated within the B2 grains. RT elongation-to-failure values of less than 2% were recorded for aged microstructures containing 72–78 volume percent O phase. Tensile-creep experiments were conducted in the temperature range 650–710 °C and stress range 48–250 MPa. The measured creep exponents and activation energies suggested that the creep mechanisms were dependent on stress and microstructure. Microstructural effects on the tensile properties and creep behavior are discussed and the data was compared to that for other Ti₂AlNb-based alloys.     

Electrochemical Hydrogen Storage Characteristics of the as-Cast and Annealed La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0~0.4) Electrode Alloys

研究了Mg-3.8Zn-2.2Ca-xSn(x=0,0.5,1,2,质量分数%)镁合金的铸态组织、抗拉性能和蠕变性能。结果发现:在含Sn合金中会形成CaMgSn相,并且随着Sn含量从0.46%增加到1.88%(质量分数),合金中CaMgSn相的数量增加。同时,合金中Ca2Mg6Zn3相的形貌从最初的连续和/或半连续网状转变为半连续和/或断续状。此外,含Sn合金的晶粒被明显细化,其中含0.90%Sn合金的晶粒最细。与三元合金相比,含0.46%和0.90%Sn合金的抗拉性能和蠕变性能改善明显,而含1.88%Sn合金的屈服强度和蠕变性能虽然得到改善,但其抗拉强度和延伸率减小。在含0.46%、0.90%和1.88%Sn的3个合金中,含0.90%Sn的合金显示了优化的抗拉性能和蠕变性能。     

The microstructure, tensile properties, and creep behavior of as-cast Mg–(1–10)%Sn alloys

The microstructure, tensile properties, and creep behavior of Mg–(1–10)wt%Sn alloys were studied in this paper. The microstructure of as-cast Mg–Sn alloys consisted of dendrite -Mg and second Mg₂Sn phases and the secondary dendrite arm spacing (DAS) of the -Mg phase was decreased with the increase of tin content. The micro-hardness of the alloys increased when tin content rises, while the greatest tensile and elongation were exhibited by Mg–5 wt%Sn. The indentation creep experiments were conducted at 150 °C for applied loads of 30 kg, it suggested that the indentation creep resistance of Mg–Sn alloys could be obviously improved with the increase of tin content, and Mg–10%Sn alloy had better indentation creep resistance than that of AE42.     

Microstructure,tensile properties and compressive creep resistance of Mg-(5-8.5)%Sn-2%La alloys

The microstructure,tensile properties and compressive creep resistance of permanent-mould cast Mg-(5-8.5)%Sn-2%La (mass fraction) alloys were investigated.The results show that Mg-(5-8.5)%Sn-2%La alloys are all composed ofα-Mg phase, Mg_2Sn and Mg-La-Sn compounds.Compared with those of Mg-5%Sn binary alloy,the grain size and the content of Mg_2Sn compound in Mg-5%Sn-2%La alloy are decreased.With the increase of Sn content in Mg-(5-8.5)%Sn-2%La alloys,the content of Mg_2Sn compound increases,while that of...     

Dynamic stress–strain properties of Ti–Al–V titanium alloys with various element contents

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI,Ti–5Al–3V ELI,commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared.These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary a phase.Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s-1.The results show that Ti–6Al–4V alloy with equiaxed primary a(ap)volume fraction of 45 vol%or 67 vol%exhibits good dynamic properties with high dynamic strength and absorbed energy,as well as an acceptable dynamic plasticity.However,all the Ti53ELI specimens and Ti64ELI specimens with ap of 65 vol%were not fractured at a strain rate of4,000 s-1.It appears that the undamaged specimens still have load-bearing capability.Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al,V,Fe,and O increase,while dynamic strain is not sensitive to the composition in the appropriate range.The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.