Deformation of high β-phase fraction Zr–Nb alloys at room temperature

A series of in situ compression tests has been carried out at room temperature for three dual-phase Zr–Nb alloys with different Nb contents. Changes in the Nb content change the relative fraction of β-phase present in the alloy. The evolution of interphase and intergranular strain was monitored during deformation by neutron diffraction. Surprisingly the strength difference between the three alloys is caused principally by changes in the α-phase strength rather than being due to changes in the β-phase volume fraction; the yield strength of the Nb-rich β-phase is ～400 MPa and is almost unchanged in the three alloys. The strength of the α-phase significantly changed between alloys due to the combined effects of increasing oxygen content and decreasing grain size. The change in strengthening mechanisms in the α-phase is crystallographically anisotropic, e.g. more change was observed for prismatic slip than for pyramidal slip. As a result, the mechanical anisotropy of the α-phase decreases with increasing strength. Depending on the β/α strength ratio, the β-phase can be either weaker or stronger than the average material strength. A soft β-phase helps to produce compressive residual stresses in the α-phase, while a strong β-phase produces tensile residual stresses in α-phase. A combined finite-element method and elastoplastic self-consistent multiscale model is used to interpret the experimental results. Despite the inability to capture the rapid stress relaxation observed, the combined method is shown to be effective in interpreting the deformation behavior of these dual-phase Zr–Nb alloys. The results are relevant to the study of other two-phase alloys, particularly titanium-based alloys.     

Thermal stability and creep behavior of Ti–V–Cr burn-resistant alloys

The thermal stability and creep behavior of Ti–35V–15Cr (35V alloy) and Ti–25V–15Cr (25V alloy) burn-resistant titanium alloys are researched. The results show that post-exposure tensile properties deteriorated with the increase in exposure temperature (450–600 °C). The decrease in tensile properties of the 35V alloy results from the combination of surface oxidation and microstructural changes and the decrease in tensile properties of the 25V alloy results from surface oxidation. The main change of the microstructure during thermal exposure is the heterogeneous precipitation of α phase on β grain boundaries. Increased vanadium content in the alloy shows an adverse effect on alloys’ thermal stability. The creep resistance of the 35V alloy is little better that that of the 25V alloy. During creep exposure at 540 °C for 100 h, the heterogeneous precipitation of α phase on β grain boundaries in 35V alloy strengthens the grain boundary, leading to increases in the creep resistance, while the heterogeneous precipitation of α phase in grains and grain boundaries in the 25V alloy is rod-like, leading to decreases in the creep resistance.     

HYDROGEN EFFECT ON DEFORMATION BEHMIOR OF TITANIUM ALLOY AT HIGH TEMPERATURE

1.IntroductionContinuousfiberreinforcedtitaniummatrixcompositeshavepotentialapplicationatelevatedtemperature.Anewmethodhajsbeentriedbyoneofthepresentautho.s[1'21toalleviatethedeleteriousinterfacereactionbetweenthefiberandthematrix,whichislikelytooccurinthiscompositeduringfabrication.Previous.orb[llshowedthattitaniummatrixcompositecanachievefullconsolidationatrelativelylowtemperaturewiththeaidofhydrogenasatemporaryalloyingelement.Furtherstudyalongthisdirectionshouldbebasedonacomprehensiveunders…     

Direct evidence for competition between metastable ω and equilibrium α phases in aged β-type Ti alloys

Precipitation response of a recently developed b-type Ti–25Nb–2Mo–4Sn alloy(wt%) during aging was investigated in detail. Experimental results indicate that the metastable ω or equilibrium α phase can form alternatively even under the same aging condition, depending on the condition prior to the aging, i.e., solution treatment or severe cold rolling. This provides, for the first time, the direct evidence for the competition between ω and α in aged β-type Ti alloys. This peculiar aging response is found to be closely related to high-density dislocations and grain boundaries which suppress the formation of ω but favor the precipitation of fine a phase.     

快速凝固富钛Ti-V合金的微观组织和储氢性能

研究目的在于优化Ti0.8-0.9V0.2-0.1二元合金的相结构成分、微观组织和储氢性能。该合金主要用于从含有大量一氧化碳的高温气态混合物中吸收氢气。Ti0.8-0.9V0.2-0.1合金中的α-（HCP）和β-（BCC）相在纯氢气中基于氢化作用,形成单相FCC结构的氢化物,此过程与合金的化学成分无关。同步辐射X射线衍射的原位分析表明,在含有氢气和10%一氧化碳的混合气体中,只有β相转变成相应的氢化物。快速凝固（RS）处理细化了Ti0.8V0.2和Ti0.9V0.1合金的晶粒组织,而且,快速凝固处理增加了Ti0.9V0.1合金中的β相,其所占比例是普通熔铸条件下的两倍。扫描电子显微镜（SEM）分析表明,Ti0.9V0.1合金含有片状组织,层片的厚度约为300nm。热脱附谱（TDS）显示,微观组织的细化可以加快氢脱附的动力学过程。     

锆对铸造3104铝合金微观结构和力学性能的影响

研究了不同锆添加量的3104合金的析出组织和力学性能。结果表明,随着Zr含量的增加,合金晶粒尺寸减小,当Zr质量分数大于或等于0.25%时,合金晶粒最小(20μm)。同时,晶粒形状由羽毛状变为等轴状。此外,Zr还可以通过形成Si相和其它金属间化合物来改善合金中Si和Mn元素的分布。维氏硬度分析表明,Zr的加入会降低Al-Mn-Fe 3104合金的硬度。此外,根据拉伸试验结果,当Zr质量分数不高于0.25%时,随着Zr含量的增加,合金的抗拉伸强度和延伸率都有所提高。适当的Zr含量可以起到钉扎位错和阻碍滑移的作用,提高合金的强度和韧性。     

Characterization of deformation localization in cold-rolled metastable β-Ti–Nb–Ta–Zr alloy

The deformation-induced microstructural variation in the metastable β-type biomedical Ti–35Nb–5Ta–7Zr (wt.%) alloy subjected to multi-pass cold-rolling to 90% reduction has been investigated by a combination of X-ray diffraction, optical microscopy, conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) techniques. Multi-pass cold rolling for the Ti–35Nb–5Ta–7Zr alloy includes various localized deformation processes which can result in dislocation tangle, stress-induced ω-phase transformation and deformation-band formation. Deformation-induced amorphization caused by high-density defect accumulation in deformation bands has been identified. By means of TEM and HRTEM observations, distributional, morphological and structural features for deformation bands have been clearly revealed.     

稳定化热处理对Zn-10Al-2Cu-0.02Ti合金组织及蠕变行为的影响

采用扫描电子显微镜、透射电镜、电子探针以及X射线衍射物相分析等技术手段,对稳定化热处理前后Zn-10Al-2Cu-0.02Ti合金的显微组织进行观察,通过室温恒载荷拉伸、慢应变速率拉伸实验研究合金组织变化及其对合金室温蠕变行为的影响.结果表明:经过稳定化热处理((350℃,30 min,水冷)+(100℃,12h, 空冷)),后合金中的α+η层片状组织的减少,胞状和粒状组织增多;与挤压态合金相比,经过稳定化热处理后的Zn-10Al-2Cu-0.02Ti合金的抗蠕变性能显著提高,其稳态蠕变速率降低了96.9％.     

Mn含量对Mg-Zn-Mn变形镁合金显微组织和力学性能的影响

通过对3种不同Mn含量的Mg-6Zn-XMn变形镁合金的微观组织的观察及力学性能的测定,研究了Mn含量对Mg-Zn-Mn镁合金显微组织和力学性能的影响。结果表明：Mn元素以单质形式弥散地分布于Mg-Zn-Mn合金中,起到阻碍晶粒长大的作用,即随着Mn含量的增加,晶粒尺寸减小;Mn含量的变化对合金的屈服强度有一定的影响,即随着Mn含量的增加,屈服强度增加,其中挤压态增幅最大,双级时效次之,增幅分别是14%和5%;而Mn含量的变化对T6、T4+双级时效后合金的抗拉强度和延伸率的影响规律不明显,其中含0.68%Mn(质量分数, 下同)的合金整体性能较优,经双级时效后具有最高抗拉强度,达到360 MPa,伸长率为5.2%     

The influence of oxygen concentration and phase composition on the manufacturability and high-temperature strength of Ti–42Al–5Mn (at%) forged alloy

The influence of oxygen concentration and the phase composition on various properties of Ti–42Al–5Mn (at%) forged alloy was evaluated, with the objective of expanding the utilization of this material. As a result, it was established that reduced oxygen concentration and increased β-phase fraction are effective for increased manufacturability (hot forgeability and machinability), and that increased oxygen concentration, reduced β-phase fraction, and increased lamellar structure fraction are effective for increased high-temperature strength. Accordingly, it is difficult to achieve optimization of all characteristics simultaneously. Nevertheless, at a high oxygen concentration of 0.16 wt% obtained via ceramic crucible melting, relatively favorable levels of all properties can exist simultaneously.     

大晶粒FeAl合金超塑性变形的显微组织演变和变形激活能

本文对大晶粒ＦｅＡｌ金属间化合物塑性变形的微观组织演变进行了研究，并测定了其超塑性变形激活能，显微组织分析表明，合金的超塑性变形是一个晶粒变形，内部形成亚晶界，进而亚晶界向晶界转换，从而使晶粒得以细化的过程，Ｆｅ－３６．５Ａｌ，Ｆｅ－３６．５Ａｌ－１Ｔｉ和Ｆｅ－３６．５Ａｌ－２Ｔｉ合金变形激活能的测定值分别为３７０，２９０和２６０ｋＪ．ｍｏｌ＾－１大大低于其他的ＦｅＡｌ基合金蠕变激活能，表明超塑性     

亚稳态β钛合金的成分设计、变形机制与力学性能研究进展

本文介绍了当前孪晶塑性/相变塑性(TWIP/TRIP)钛合金的研究现状和设计方法,统计了TWIP/TRIP钛合金中发生{332}<113>、{112}<111>双孪晶钛合金β相的晶粒尺寸、屈服强度和加工硬化率。讨论了Bo-Md图在多组元钛合金设计上的应用和局限性,特别是析出不同二次相(α相与ω相)对基体β相稳定性的影响。从基体β相稳定性、析出相、β相晶粒尺寸和晶体学取向三方面归纳了亚稳态β钛合金TWIP/TRIP变形机制的影响因素,并对其中存在的一些问题和不足进行了分析,简要总结了双孪晶机制对钛合金力学性能的影响。通过综述最新的研究进展及相关问题,对未来高强韧钛合金的发展提出新见解。     

Shape memory properties of Ti–Nb–Mo biomedical alloys

Mo is added to Ti–Nb alloys in order to enhance their superelasticity. The shape memory properties of Ti–(12–28)Nb–(0–4)Mo alloys are investigated in this paper. The Ti–27Nb, Ti–24Nb–1Mo, Ti–21Nb–2Mo and Ti–18Nb–3Mo alloys exhibit the most stable superelasticity with a narrow stress hysteresis among Ti–Nb–Mo alloys with Mo contents of 0, 1, 2 and 3 at.%, respectively. The ternary alloys reveal better superelasticity due to a higher critical stress for slip deformation and a larger transformation strain. A Ti–15Nb–4Mo alloy heat-treated at 973 K undergoes (2 1 1)〈1 1 1〉-type twinning during tensile testing. Twinning is suppressed in the alloy heat-treated at 923 K due to the precipitation of the α phase, allowing the alloy to deform via a martensitic transformation process. The Ti–15Nb–4Mo alloy exhibits stable superelasticity with a critical stress for slip deformation of 582 MPa and a total recovery strain of 3.5%.     

Effects of ultrasonic treatment on the formation of iron-containing intermetallic compounds in Al-12%Si-2%Fe alloys

In general, the iron impurity is detrimental to the mechanical properties of Al–Si alloys. The α-phase and β-phase are the most important and common iron-containing intermetallic compounds (IMCs) in Al–Si alloys. During conventional casting, the acicular β-phase is stable, and considered to be harmful. In this paper, the Al-12%Si-2%Fe alloy was treated by power ultrasound and solidified under different cooling conditions. The effects of ultrasonic treatment (UST) and cooling rate on morphology and composition of IMCs were investigated. The results showed that UST can change the morphology and composition of iron-containing IMCs and promote the formation of metastable α-phase. When the ultrasound was applied at 720 °C, the amount of starlike α-phase increases and the acicular β-phase decreases with increasing applied time of UST. In addition, the polygonal α-phase is formed and substitutes for the β-phase when quenching after UST for 60 s and 120 s, suggesting that the formation of β-phase can be suppressed under this condition. For the case of UST at 610 °C which the β-phase has been nucleated, the β-phase transforms from an acicular shape to the rod-like morphology, indicating that the cavitation-induced fracture of β-phase.     

时效处理对稀土钪微合金化钛合金组织与性能的影响

为提高钛合金在高温下的服役寿命,开展了稀土钪微合金化钛合金材料高温蠕变试验研究。将Ti64-0.25Si-xSc(x=0,0.3)合金在950 ℃×0.5 h,AC固溶后,分别在不同的温度和时间下时效,对合金的维氏硬度和高温抗蠕变性能进行测试,将蠕变曲线按时间硬化蠕变模型ε=Aσⁿt^m拟合,借助OM、TEM表征分析合金的微观组织演变。结果表明,合金在510 ℃下时效6 h的蠕变性能最为优异,加入稀土钪可以抑制晶粒的长大,改变晶粒的取向,促进网篮组织的形成,在合金中形成的Sc₂O₃可以净化基体,对提高钛合金的高温抗蠕变性能有着明显的作用。合金微观结构中存在大量的位错相互作用,堆积缠绕,合金的蠕变机制主要是位错的滑移。     

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。     

MICROSTRUCTURE AND PROPERTIES OF Mn-CONTAINING TiAI ALLOYS

The microstructure of Ti-33wt-％ Al-(1.6-4.5)wt-％ Mn alloys are composed ofγ+α_2 phases,but the volume of x_2-phase is a little.Mn alloying decreases the latticeparameters a and c of γ-phase and the c/a ratio becomes nearly to one,because the atomicradius of Mn is less than the atomic radius of Ti or Al.Mn alloying promotes the formation oftwins in γ-phase and increases the ability of plastic deformation of TiAl alloys at room tem-perature.     

显微组织对TA11钛合金棒材力学性能的影响

通过对TA11钛合金不同组织状态的棒材进行组织、性能检测分析,研究了初生α相含量和尺寸对TA11钛合金室温拉伸性能、热稳定性能、蠕变性能的影响。研究结果表明,初生α相含量对TA11钛合金的拉伸性能影响较小,但对合金的抗蠕变性能影响明显:初生α相含量在50%~90%范围内时,合金的室温拉伸性能、热稳定性能随初生α相含量的增加变化不明显,抗蠕变性能随初生α相含量的增加而提高;初生α相尺寸对TA11钛合金的拉伸性能、蠕变性能具有一定的影响,随着组织粗大程度的增加,拉伸强度降低,抗蠕变性能提高。     

A COMPLEX DEFORMATION MECHANISM FOR SUPERPLASTIC DEFORMATION OF Mg ALLOY

本文选用大晶粒和微细晶粒两种镁合金,利用现代测试手段进行超塑性变形机制的研究.结果表明,在超塑性变形条件下,两种合金都显示以晶界滑动为主的,由扩散蠕变和位错滑移所协调的复合变形机制.作者提出一个包括三种变形机制在内的复合机制模型.在超塑性变形中,下层金属晶粒通过晶界滑动不断涌现到试样表面横向晶界发生宽化及空洞的地方,从而不断增加沿拉伸轴方向上的晶粒数.这是试样在拉伸变形中获得非常大的伸长量的原因.     

Corrosion behaviour of AZ91D and AM50 magnesium alloys with Nd and Gd additions in humid environments

AM50 and AZ91D alloys modified with rare earths (RE) were evaluated under atmospheric conditions. Nd and Gd additions resulted in formation of Al₂RE and Al–Mn–RE compounds and reduction of the fraction of β-phase. According to surface potential maps, RE-containing intermetallics were more noble than the β-phase, but less than Al–Mn inclusions. As a result, the action of micro-galvanic couples depended on the added amount of RE and the initial alloy microstructure. Nd or Gd additions improved the corrosion resistance of the AM50 alloy by up to 43%, but had no significant effect on the corrosion resistance of the AZ91D alloy.