V元素含量对钛合金中氢储备能力的影响

自制X值不同的Ti_(0.7)Zr_(0.3)(Cr_(1-x)V_x)_2合金,采用XRD和SEM对其成分及组织进行分析,同时利用Sieverts仪器测量结合贮氢量和贮氢密度数学计算模型,绘制合金的吸氢活化性能和压力-浓度-温度曲线。结果表明,Ti_(0.7)Zr_(0.3)(Cr_(1-x)V_x)_2合金为复杂的多相组织,由Laves相和不同晶格常数的bcc固溶相组成;合金具有较好的活化性能和抗氧化性能;随着V元素含量的增加,合金的贮氢含量增加,放氢含量减小。     

Ni—Fe奥氏体合金的氢脆及成分影响

研究了5种Ni-Fe奥氏体的氢致塑性损失和K_(IC)随成分的变化,发现当Fe含量为60%时,氢致塑性损失极小;Fe为50%时滞后断裂门槛值K_(IH)极小,根据不稳定氢化物含量,固溶氢含量以及位错结构随合金成分的变化解释氢致塑性损失和K_(IH)随成分的变化规律。     

预充氢马氏体时效钢的氢脆性能研究

目的研究预先存在于试样中的氢对材料力学性能的影响。方法对固溶态和三种时效态18Ni马氏体时效钢,采用双电解槽装置测量了其氢扩散系数,用热分析法获得了材料的氢扩散激活能。采用慢应变速率拉伸法评估了在预充氢后镀镉密封试样的力学性能,并由此评估它们的氢脆敏感性。结果固溶态试样的氢扩散系数最大,为1.40×10~(-8)_ cm~2/s;对时效态试样,当时效温度分别为465、490、530℃时,氢扩散系数分别为6.23×10~(-9)、5.52×10~(-9)、2.84×10~(-9) cm~2/s,即随时效温度升高,扩散系数降低。而扩散激活能正好相反,固溶态的最小,其他的依次逐渐升高。四种试样均显示出氢脆敏感性,且随着预充氢电流密度升高而增大。T465和T490的氢脆敏感性均大于58%,T530的氢脆敏感性小于40%。四种试样的断口形貌均表现为由中心起裂,向周围呈放射状扩展。中心起裂源处为典型的沿晶开裂,扩展区为准解理开裂。结论过时效态样品的抗氢脆性能最好。预先存在于试样中的氢在拉伸过程中向中心富集,造成中心沿晶开裂,与动态充氢拉伸断口相反。     

锆对Al—Li—Cu—Mg合金组织和力学性能的影响

本文研究了合金元素对Ａｌ－Ｌｉ－Ｃｕ－Ｍｇ合金组织和力学性能的影响。结果表明：锆可以显著地抑制合金的再结晶过程，细化合金的晶粒组织。为阻止固溶温度（５３０℃）下发生再结晶，锆含量至少为０．１０％。锆还可以加速时效过程，提高时效强化效果。最佳锆含量和固溶处理温度分别为０．１０～０．１６％和５３０℃，此时合金的强度和塑性匹配适宜。     

Effect of Hydrogen Content on Low-Cycle Fatigue Behavior of Zr-Sn-Nb Alloy

研究氢对NZ2新锆合金(Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr)低周疲劳行为的影响规律,采用4种不同氢含量(未渗氢,200,450,730μg/g)的板材试样进行室温和375℃下的低周疲劳试验.结果表明,在375℃下,循环变形时发现了动态应变时效现象,渗氢及氢含量的变化不会影响动态应变时效的发生;氢可以提高375℃下NZ2合金的低周疲劳寿命并且导致氢致循环软化.     

Ti_3Al＋Nb在甲醇中沿相界的应力腐蚀SCIEI

研究了Ｔｉ－２４Ａｌ－ｌｌＮｂ合金中Ｔｉ３Ａｌ＋Ｎｂ金属间化合物在甲醇溶液中的应力腐蚀及室温氢致开裂的规律，探讨了组织结构的影响．结果表明，Ｔｉ３Ａｌ＋Ｎｂ在甲醇溶液中应力腐蚀敏感性很高，不向组织应力腐蚀断裂归一化门槛值为而ｋ（ＩＳＣＣ）／ＫＣ＝０．５３－０．６９；应力腐蚀裂纹止裂门槛值为Ｋ（ＩＳＣＣ）／Ｋ（ｌｉ）＝０．６１－０．７９．Ｔｉ３Ａｌ＋Ｎｂ在室温动态充氢时能发生氢致开裂，门槛值和应力腐蚀相近，但裂纹扩展速率或断裂时间比应力腐蚀要慢１－３个数量级．两者断口形貌也不相同．发现了相界应力腐蚀现象．对固溶后炉冷试样，当ＫＩ较低时，应力腐蚀裂纹优先沿α２／β相界形核和扩展，从而获得相界应力腐蚀断口．如固溶后空冷或ＫＩ较高，则不出现相界应力腐蚀．     

氢对锆合金模拟LOCA试验后残余塑性的影响

锆合金包壳在堆内吸氢,失水事故(LOCA)锆合金包壳会脆化,含氢包壳在事故进程或事故后续处理中更易破裂,造成放射性产物泄漏。文章对不同氢含量(0ppm、195ppm、310ppm、395ppm)锆合金模拟LOCA试验后残余塑性进行研究,探索了氢对锆合金模拟LOCA试验后残余塑性的影响机理。结果表明,随含氢量的提高,在模拟LOCA试验后锆合金残余塑性下降。氢的加入对锆合金显微组织结构影响较小,氢对锆合金微观组织结构的影响不是导致锆合金残余塑性降低原因。氢的存在导致锆合金模拟LOCA试验后残余塑性下降的原因之一是氢增加造成锆合金prior-β相中吸收氧含量提高,从而降低锆合金残余塑性,其次氢可能以饱和固溶或细小的氢化物脆性相方式存在于prior-β相中,也造成锆合金残余塑性下降。     

Zr-Nb合金的吸氢性能与相变行为

通过PCT(pressure-composition-temperature)吸氢性能实验研究了温度(700~900℃)和Nb含量(1%~30%,质量分数)对Zr-Nb合金吸氢性能的影响。结果表明,温度的变化对β-Zr相和δ氢化锆相的两相平衡有较大影响,β-Zr相较δ氢化锆相的高温稳定性更强。Nb的添加降低了体系与H结合的稳定性,随着Nb含量的增加,合金的最大吸氢量明显减少。相同温度条件下,β-Zr相和δ氢化锆相两相平台所对应的平衡氢分压随Nb含量增加而升高。Nb降低合金最大吸氢量的主要原因是高氢含量的δ相NbH2氢化物在低压下不能稳定存在。     

Zr元素含量对钛基钎料合金固溶强化的影响

利用EET理论分析Zr元素对钛基钎料合金的固溶强化效果,得出锆含量自45%~12%变化时,Ti-Zr-15Cu-10Ni(质量分数,%)钎料合金晶胞内最大共价电子数先保持不变、而后减小再增大.当锆含量为37.5%时,Zr元素对钛基钎料合金的固溶强化作用相对较大,采用此锆含量的钎料合金Ti-37.5Zr-15Cu-10Ni(质量分数,%)对Ti₃Al-Nb合金进行同质过渡液相扩散连接.在连接温度低于1000℃条件下,钎料合金的扩散能力主要受保温时间的影响;在较高连接温度下,钎料合金的扩散能力明显提高,可在短时保温条件下形成组织均匀、无析出物的连接界面.     

氢化物对锆4合金管材拉伸性能的影响

锆是一种强烈的氢化物形成元素。锆合金包套管在反应堆运行条件下,随着锆表面被水氧化的同时,也因下述反应:Zr+2H_2O——ZrO_2+2H_2↑产生了氢。其中一部分氢被锆合金包套管吸收。氢在锆合金中的固溶度很低,在350℃时,只有120ppm 左右,而在室温下几乎不固溶,以片状或针状氢化锆(ZrHx)形式     

A theoretical and experimental study of hydrides in zirconium alloys

A method developed for computing the critical length and thickness of hydride plates formed in delayed hydride cracking (DHC) in zirconium alloys is considered. The model is based on analyzing the distribution of tensile stresses in the plane of a sharp normal tensile crack. The characteristics of hydrides formed due to DHC in reactor tubes produced from alloy Zr-2.5% Nb are determined experimentally. The results of the computation agree well with experimental data. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 5–9, April, 2006.     

Review of the initiation and arrest temperatures for delayed hydride cracking in zirconium alloys

Based on Kim's delayed hydride cracking (DHC) model, this study reanalyzes the critical temperatures for DHC initiation and arrest in zirconium alloys that had previously been investigated with Puls DHC model. In an unratcheting thermal cycle where DHC crack tip hydrides were dissolved fully at the peak temperature, the DHC initiation was suppressed, which required a supercooling or ΔT from the terminal solid solubility for dissolution (TSSD) temperatures. At a hydrogen concentration as 7 ppm H, the DHC initiation temperatures coincided with the TSSD, which is in conflict with Puls' DHC model. In a ratcheting thermal cycle, where the hydrides precipitated at the DHC crack tip were not fully dissolved, the DHC initiation was enhanced, so as to require a lesser ΔT, compared to that of the unratcheting thermal cycle. Therefore, the DHC initiation temperatures are concluded to depend upon at what temperatures the hydrides can nucleate in the zirconium matrix with the supersaturated hydrogen concentration. The DHC arrest temperatures were governed by the critical supersaturated hydrogen concentration or ΔC regardless of the thermal cycle treatment, providing further supportive evidence that Kim's DHC model is feasible.     

Driving force for delayed Hydride cracking of zirconium alloys

The effect of hydrogen concentration on the delayed hydride cracking velocity (DHCV) and the threshold stress intensity factor, K_IH of a Zr-2.5Nb tube were examined at test temperatures ranging from 100 to 280°C by subjecting compact tension specimens with a hydrogen concentration of 12 to 100 ppm H to an overtemperature cycle. The DHCV and K_IH increased and decreased, respectively, with an increase in the supersaturated hydrogen concentration over the terminal solid solubility for dissolution (TSSD) or ΔC. They then leveled off to constant values at ΔC in excess of the ΔC_max corresponding to a difference of the terminal solid solubility of the hydrogen on cool-down and on heat-up. Further, intentional introduction of an undercooling by 0 to 40°C at the test temperature decreased the DHCV of the Zr-2.5Nb tube, indicating that ΔC between the bulk region and the crack tip governs the DHCV. A new DHC model is proposed where the driving force for DHC is the difference in the hydrogen concentration between the bulk region and the crack tip by preferentially nucleating the hydrides only at the crack tip under an applied tensile stress, due to a hysteresis in the TSS of hydrogen on heat-up and on cool-down. A supplementary experiment was conducted to validate the feasibility of the proposed DHC model.     

Effects of electrochemical hydrogenation of Zr-based alloys with high glass-forming ability

Zr–(Ti)–Cu–Al–Ni metallic glasses exhibit a high thermal stability corresponding to a wide undercooled liquid region. Depending on their composition, the formation of metastable intermediate phases, e.g. a quasicrystalline phase is possible. The combination of early and late transition metals makes these alloys very interesting regarding their interaction with hydrogen. Amorphous Zr₅₅Cu₃₀Al₁₀Ni₅, Zr₆₅Cu_17.5Al_7.5Ni₁₀ and Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ ribbons were prepared by melt spinning and their microstructure and thermal behaviour was checked by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The cathodic reactivity of alloy samples at different microstructural states and after pre-etching in 1 vol.-% HF was investigated in 0.1 M NaOH by applying potentiodynamic polarisation techniques. Galvanostatically hydrogenated samples were characterised by XRD, DSC, TEM and thermal desorption analysis (TDA). For amorphous Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ samples an increase in electrochemical surface capacity by two orders of magnitude is observed after pre-etching. Compared to the quasicrystalline and crystalline alloy, the hydrogen reduction takes place at significantly lower overpotentials. Zr-based alloys cathodically absorb hydrogen up to H/M=1.65 while keeping the amorphous structure. Already small amounts of hydrogen cause a significant decrease of the thermal stability and changes in the crystallisation sequence. The hydrogen desorption is a two-stage process: (T<623 K) hydrogen desorption from high interstitial-site energy levels and (T>623 K) zirconium hydride formation and subsequent transformation under hydrogen effusion. Hydrogen suppresses the oxygen-triggered formation of metastable phases upon heating and supports primary copper segregation. At very high H/M ratios, severe zirconium hydride formation causes the crystallisation of new compounds.     

In situ study of hydride precipitation kinetics and re-orientation in Zircaloy using synchrotron radiation

The orientation and distribution of hydrides formed in zirconium alloy nuclear fuel cladding can strongly influence material behavior and in particular resistance to crack growth. The hydride microstructure and hydride platelet orientation (whether in-plane or radial relative to the cladding tubes) are crucial to determining cladding failure limits during mechanical testing. Hydride formation is normally studied by post-facto metallography, performed at room temperature and in the absence of applied stress. This study uses synchrotron radiation to observe in situ the kinetics of hydride dissolution and precipitation in previously hydrided Zircaloy samples. The experiments allow the direct observation of hydride dissolution, re-precipitation, and re-orientation, during heating and cooling under load. The solubility limits and the hydride-matrix orientation relationship determined from in situ experiments were in good agreement with previous post-facto examinations of bulk materials. The present measurements performed under stress and at temperature showed a characteristic diffraction signature of reoriented hydrides. The results suggest a threshold stress for hydride re-orientation between 75 and 80 MPa for the microstructure/texture studied. These results are discussed in light of existing knowledge.     

The Nickel-Rich Region of the Ni-Ge Phase Diagram

We present new results on the phase boundaries separating the single and the 2-phase regions of the Ni-rich Ni-Ge phase diagram. The accuracy of the boundary between the 2-phase Ni(Ge) + Ni₃Ge and single-phase Ni₃Ge region is reinforced by the addition of new data obtained from dissolution experiments. This boundary is consistent with the results of a recent thermodynamic model at temperatures lower than ~840 °C, but is leaner in Ge content at higher temperatures. Additional data on the equilibrium solubility of Ge in Ni (Ni₃Ge solvus) reinforces the accuracy of the phase boundary to temperatures as low as 700 °C; these data are not new, but are not included in the most recent assessments. The recent thermodynamic model of the Ni₃Ge solvus is in remarkably good agreement with the experimental results. The composition dependence of the ferromagnetic Curie temperature, T _c, is also re-evaluated by the addition of data not previously included in recent assessments. The dependency of T _c on Ge content is essentially linear to concentrations of ~13% Ge, which exceeds the solubility of Ge in Ni-Ge alloys. Empirical equations relating equilibrium compositions and temperatures of the phase boundaries and the composition dependence of T _c are presented.     

Electrochemical hydriding performance of Mg–TM–Mm (TM=transition metals,Mm=mischmetal) alloys for hydrogen storage

Eighteen as-cast binary Mg–Ni, Mg–Mm and ternary Mg–Ni–Mm and Mg–Ni–TM (TM=transition metals (Cu, Zn, Mn and Co); Mm = mischmetal containing Ce, La, Nd and Pr) alloys were hydrided by an electrochemical process to determine the alloys with the most potential for electrochemical hydrogen storage. The alloys were hydrided in a 6 mol/L KOH solution at 80 °C for 480 min and at 100 A/m². To assess the electrochemical hydriding performance of alloys, maximum hydrogen concentrations, hydrogen penetration depths and total mass of absorbed hydrogen in the alloys were measured by glow discharge spectrometry. In addition, the structures and phase compositions of the alloys both before and after hydriding were studied by optical and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. It was determined that the highest total amount of hydrogen was absorbed by the Mg–25Ni–12Mm and Mg–26Ni (mass fraction, %) alloys. The maximum hydrogen concentrations in the Mg–25Ni–12Mm and Mg–26Ni alloys were 1.0% and 1.6%, respectively. The main hydriding product was the binary MgH₂ hydride, and the ternary Mg₂NiH₄ hydride was also detected in the Mg–25Ni–12Mm alloy. The electrochemical hydriding parameters achieved are discussed in relation to the structures of alloys, alloying elements and hydriding mechanisms.     

Solidification of Bcc/T1/T2 three-phase microstructure in Mo–Nb–Si–B alloys

The three-phase, (Mo,Nb)_ss/(Mo,Nb)₅Si₃/(Mo,Nb)₅SiB₂, Bcc/T₁/T₂ microstructures that develop in Mo–Nb–Si–B alloys have been examined in arc cast and directionally solidified samples to identify the phase sequencing during solidification. A Mo-32.6Nb-19.5Si-4.7B (at.%) alloy was directionally solidified using an optical floating zone (OFZ) furnace in a flowing Ar gas atmosphere at a constant growth rate of 10 mm/h. The microstructure of the directionally solidified alloy is characterized by an elongated T₂ phase surrounded by bcc and T₁ phases with an interwoven morphology From the evaluation of the microstructures in arc cast ingots of several alloys at a constant 32.6 at%Nb composition, the path of the liquidus valleys with decreasing temperature has been determined to intersect at a common point that establishes the solidification reaction as a eutectic. The incorporation of the experimental results into a computational thermodynamic analysis provides insight on the partitioning of components within each phase during solidification.     

Structure and hydrogen absorbing properties of ScCrMn alloy

The crystal structures of ScCrMn alloy and its hydride are determined by XRD Rietveld analysis and TEM examination. The ScCrMn alloy exhibits a rarely ideal close-packed C14 type hexagonal Laves phase structure with lattice parameters a = 5.064(1), c = 8.263(2) Å, deviating from the ANOE dependent rule on Laves phase structure. The hydrogenation of the alloy to ScCrMnH_3.9 results in significant lattice expansion of 27%, but does not alter the matrix lattice structure. The XRD pattern of the hydride also shows close-packed structure with little line broadening, comparable to that of the alloy, indicating a high degree of crystallinity, where the hydrogen atoms are homogeneously distributed in evenly distributed interstitials with minimal defects. The alloy demonstrates extremely easy activation property. The alloy can be activated at a low pressure of 0.46 kPa and exhibit very fast absorption rate at sub-atmosphere at room temperature. The hydrogenation thermodynamics of the alloy are evaluated by P-C-T measurements at different temperatures. At hydrogen concentration H/M = 0.66 corresponding to a defined room temperature plateau pressure, the relative partial molar enthalpy ΔH and entropy ΔS derived by Van’t Hoff equation are −63 kJ/mol and −111 J/mol K, respectively. These results manifest that the hydride stability of the ScCrMn alloy is comparable to those of the hydrogen isotope storage alloys of ZrCo and ZrTi_0.2V_1.8, and would be superior on relevant applications. The DSC-TG measurements of the hydride reveal that the total release of hydrogen can basically be achieved at 653 K, accompanied by an oxidation reaction with residual oxygen to form water vapor. The results indicate that the alloy is an effective catalyst for the dissociation of hydrogen and combination of oxygen.     

Ti55合金电子束焊缝氢致延迟裂纹的扩展机理

钛合金广泛应用于军事航空领域 ,但是一些钛合金在焊接条件下 ,焊缝会产生氢致延迟裂纹 ,其致裂机理尚不十分清楚。通过充氢CT(Compacttension)试件的恒载拉伸试验 ,研究了氢浓度对Ti5 5合金电子束焊缝裂纹尖端应力强度因子门槛值Kth及裂纹扩展速率da/dt的影响规律 ,分析了氢致延迟裂纹扩展的机理。结果表明 ,氢在Ti5 5合金焊缝中的固溶度约为 79× 10 -4%。当充氢浓度C0 低于 79× 10 -4%时 ,随着焊缝氢浓度C0 的增大 ,裂纹开始扩展的应力强度因子门槛值Kth迅速减小 ,而裂纹扩展速率da/dt随着C0 的增大而增大 ;C0 为 79× 10 -4%时 ,Kth为最小值并呈恒值特征。裂纹尖端应力场诱导氢原子扩散导致氢化物TiH2 析出是Ti5 5合金电子束焊缝氢致延迟裂纹扩展的主要机制