TiAl有序合金研究现状及发展趋势

ＴｉＡｌ有序合金研究现状及发展趋势范晓明（长沙锅炉压力容器检验研究所）ＴｉＡｌ有序合金具有高的比强度和比模量，在高温时，这种合金依然可维持较高的强度和刚度，并具有良好的抗蠕变、抗氧化和抗氢脆的能力，是最具有潜力的轻质高温结构材料。作为新一代Ｘ－３０航...     

铌对Ti_3Al价电子结构及其脆性的影响

应用固体与分子经验电子理论计算了Ｔｉ３Ａｌ 及加入铌后各相的价电子结构， 并从均匀变形因子α、解理能Ｇｃ 及位错行为等方面分析了铌对Ｔｉ３Ａｌ 脆性的影响。铌使Ｔｉ３Ａｌ 合金的α及Ｇｃ 提高； 同时铌也减弱了ＴｉＴｉ 共价键， 增加了基面滑移， 从而导致Ｔｉ３Ａｌ 脆性有本质改善。     

铌对Ti3Al价电子结构及其脆性的影响

应用固体与分子经验电子理论计算了Ｔｉ３Ａｌ及加入铌后各相的价电子结构,并从均匀变形因子α,解理能Ｇｃ及位错行为等方面分析了铌对Ｔｉ３Ａｌ脆性的影响,铌使Ｔｉ３Ａｌ合金的α及Ｇｃ提高;同时氟也减弱了Ｔｉ－Ｔｉ共价键,增加了基面滑移,从而导致Ｔｉ３Ａｌ脆性有本质改善。     

Ti与Al反应合成TiAl基合金的过程和机理

采用扫描电子显微镜对反应热压１：１的Ｔｉ－Ａｌ混合粉所制备的ＴｉＡｌ基合金致密体量微结构和微区化学成分进行了观察和分析，根据Ａｌ元素的分布和各相存在的成分范围，发现Ｔｉ与Ａｌ反应过程中，首先在原Ｔｉ颗粒内部形成ＴｉＡｌ３，ＴｉＡｌ，Ｔｉ３Ａｌ和α－Ｔｉ四相，然后，反应在这四个固相间继续进行，随着Ａｌ元素的扩散和均匀化，已形成的ＴｉＡｌ３和α－Ｔｉ相进一步反主尖而消失掉，最终，显微组织由ＴｉＡｌ和Ｔ     

Al—TiB2自生复合材料的燃烧合成研究

研究了Ａｌ－ＴｉＢ２体系的燃烧合成过程，用粉末（Ａｌ，Ｔｉ，Ｂ）通过燃烧方法制备（Ａｌ－ＴｉＢ２）自生复合材料，采用ＤＴＡ，ＸＲＤ和ＳＥＭ技术对复合材料的形成和结果进行分析研究，得到如下结果，分别用８０％Ａｌ＋２０％（Ｔｉ＋２Ｂ）９０％Ａｌ＋１０％（Ｔｉ＋２Ｂ）原料粉末，通过燃烧合成可得到Ａｌ－ＴｉＢ２制备过程中产生少量ＴｉＡｌ３，Ａｌ基体与ＴｉＢ２结合紧密，无明显界面存在。     

Al－TiB_2自生复合材料的燃烧合成研究

研究了Ａｌ－ＴｉＢ＿２体系的燃烧合成过程。用粉末（Ａｌ、Ｔｉ、Ｂ）通过燃烧方法制备（Ａｌ－ＴｉＢ＿２）自生复合材料，采用ＤＴＡ、ＸＲＤ和ＳＥＭ技术对复合材料的形成和结果进行分析研究。得到如下结果：分别用８０％Ａｌ＋２０％（Ｔｉ＋２Ｂ）、９０％Ａｌ＋１０％（Ｔｉ＋２Ｂ）原料粉末，通过燃烧合成可得到Ａｌ－ＴｉＢ＿２，制备过程中产生少量ＴｉＡｌ＿３，Ａｌ基体与ＴｉＢ＿２结合紧密，无明显界面存在。     

TiAl反常屈服行为的位错钉扎机制

利用电子理论计算了ＴｉＡｌ的价电子结构和键能,并由此近似计算了ＴｉＡｌ的平面缺陷能。在此基础上,由能量计算结果结合激活能分析了ＴｉＡｌ反常屈服行为的位错钉扎机制。结果表明：ＴｉＡｌ的反常屈服行为是３ 种主位错钉扎机制交互作用引起的。同时,孪生交割钉扎位错机制也有很大作用。     

用SHS工艺合成TiAl,TiNi,Nial金属间化合物

用自蔓延高温合成技术的热爆模式制备了ＴｉＡｌ、ＴｉＮｉ和ＮｉＡｌ金属间化合物。研究了合成产物的形态及相组成，ＴｉＡｌ和ＮｉＡｌ系得到了铸态的组织，相组成为单一的ＴｉＮｉ相和ＮｉＡｌ相。ＴｉＡｌ系的产物形态为疏松的多孔体，由ＴｉＡｌ３、ＴｉＡｌ和Ｔｉ３Ａｌ三种相组成，获得的合成粉末颗粒尺寸比原料粉末小一个数量级。     

爆炸烧结粉末TiAlMn合金

研究了ＴｉＡｌＭｎ合金粉末的爆炸固结和高温烧结。该合金粉末是Ｔｉ一３０Ａｌ一２Ｍｎ（ｗｔ％）与Ｔｉ一３８Ａｌ一２Ｍｎ（ｗｔ％）金属间化合物粉末的混合物，利用进射电镜、扫描电镜、Ｘ射线衍射分析和光学显微镜分析了合金的微观组织和相特征。结果表明：爆炸固结和烧结后制备的ＴｉＡｌ合金的相对密度达９９．９０％，合金获得了细小的晶粒组织。经爆炸固结和在１１００℃下高温烧结，样品中Ｔｉ一３０Ａｌ一２Ｍｎ颗粒与Ｔｉ一３８Ａｌ一２Ｍｎ颗粒之间发生相互扩散，形成ＴｉＡｌ相。用高能球磨粉制备的ＴｉＡｌ合金具有比滚动球自粉制合金细的晶粒组织。     

Ti—Al—O—Cl四元系热力学平衡计算

在向ＴｉＣｌ４中加入一定的ＡｌＣｌ３以后，氯化法钛白工业中的氧化过程就变成了由Ｔｉ－Ａｌ－Ｏ－Ｃｌ四元系的热化学过程，应用ＳＯＬＧＡＳＭＩＸ和Ｈ－Ｓ－Ｃ计算化学软件对该四元系不同工艺条件下热化学平衡组分的计算结果表明，该四元系中，元素Ｔｉ，Ａｌ的氧化特性与体系的条件有着非常紧密的关系，即当体系的温度，ＴｉＣｌ４中ＡｌＣｌ３的数量，以及配氧系数变化时，Ｔｉ和Ａｌ的氧化特性同时也要发生相应的变化，特别     

Environmental effects on the room temperature ductility of polysynthetically twinned (PST) crystals of TiAl

Environmental effects on the room temperature ductility of polysnthetically twinned (PST) crystals of TiAl with two different lamellar orientations have been investigated through tensile tests conducted in four different atmospheres at strain rates in the range of 2.0 × 10⁻⁴ to 1.0 × 10⁻¹ s⁻¹. The tensile ductility of TiAl PST crystals is sensitive to test environment. It is higher when tested in vacuum or in dry air than in air or in hydrogen gas. Such environmental loss in ductility decreases with increasing strain rate. These results suggest that the environmental embrittlement of TiAl PST crystals can be interpreted in terms of hydrogen embrittlement. The fracture mode of TiAl PST crystals whose lamellar boundaries are inclined to the tensile axis also depends on test environment and strain rate. On the basis of the results obtained, the mechanism of the environmental embrittlement of TiAl PST crystals is discussed, with particular emphasis on the interaction of the lamellar boundaries with hydrogen atoms.     

Evaluation of hydrogen embrittlement mechanisms

The incubation time which precedes the initiation of slow crack growth in the delayed failure of high-strength steel containing hydrogen was reversible with respect to the applied stress. The kinetics of the reversibility process indicated that it was controlled by the diffusion of hydrogen and had an activation energy of approximately 9000 cal per mole. Reversible hydrogen embrittlement studies were also conducted at liquid nitrogen temperatures where diffusional processes should not occur. The previously reported low temperature embrittlement behavior was confirmed indicating a basic interaction between hydrogen and the lattice. The experimental results could be satisfactorily explained by the lattice embrittlement theory proposed by Troiano.     

Effects of hydrogen on near-threshold crack propagation in niobium

The effects of hydrogen on near-threshold fatigue crack growth rate have been investigated in niobium at room temperature. Fatigue tests were performed on a hydrogen-free specimen as well as specimens containing hydrogen in solid solution and in the form of hydride. Specimens were tested using a tension-tension loading cycle at a frequency of 4 Hz and two load ratios of 0.05 and 0.4. The results show that the threshold stress-intensity factor ΔK_th decreases with the addition of hydrogen and reaches a minimum at a hydrogen concentration approximately equal to the solubility limit of hydrogen in niobium. As the hydrogen concentration exceeds the solubility limit, ΔK_th increases with the increase of the amount of hydrogen dissolved in the specimen. Analysis of this behavior suggests that stress-induced hydride cannot be responsible for the embrittlement of niobium with hydrogen, and dislocation-hydrogen interaction plays an important role in the embrittlement process. SEM metallography studies also confirm the importance of dislocation in the embrittlement of niobium by hydrogen.     

Studies of Evaluation of Hydrogen Embrittlement Property of High-Strength Steels with Consideration of the Effect of Atmospheric Corrosion

Hydrogen embrittlement of high-strength steels was investigated by using slow strain rate test (SSRT) of circumferentially notched round bar specimens after hydrogen precharging. On top of that, cyclic corrosion tests (CCT) and outdoor exposure tests were conducted prior to SSRT to take into account the effect of hydrogen uptake under atmospheric corrosion for the evaluation of the susceptibility of high-strength steels. Our studies of hydrogen embrittle properties of high-strength steels with 1100 to 1500 MPa of tensile strength and a prototype ultrahigh-strength steel with 1760 MPa containing hydrogen traps using those methods are reviewed in this article. A power law relationship between notch tensile strength of hydrogen-precharged specimens and diffusible hydrogen content has been found. It has also been found that the local stress and the local hydrogen concentration are controlling factors of fracture. The results obtained by using SSRT after CCT and outdoor exposure test were in good agreement with the hydrogen embrittlement fracture property obtained by means of long-term exposure tests of bolts made of the high-strength steels.     

Hydrogen-enhanced cracking of superalloys

Internal hydrogen embrittlement was studied in two nickel-base superalloys (IN718 and IN625) and one iron-base superalloy (A286). Subcritical crack growth (SCG) measurements were made on uniformly precharged specimens containing up to 50 weight parts per million (wt ppm) hydrogen, and the behavior was correlated with metallographic observations. For intermediate hydrogen concentrations, three-stage SCG ratevs stress intensity behavior was observed in IN718 and IN625 but not in A286. For all alloys, the threshold stress intensity decreased with increasing hydrogen concentration. Cracking in the nickel alloys was transgranular, and there was a transition from dimpled to faceted failure as the hydrogen concentration increased. Failure in A286 was mainly by intergranular microvoid coalescence at high hydrogen concentrations. Enhanced localization of plasticity and void pressurization due to hydrogen are proposed to explain the observed hydrogen embrittlement of these alloys. The effects of hydrogen on the stacking fault energy, trapping sites, microstructure, and cracking ahead of the main crack front are discussed with reference to the above alloys and their hydrogen embrittlement. Formerly Research Assistant, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign     

The hydrogen embrittlement of Fe-Ni martensites

Iron alloys containing 20 and 30 pct Ni and 3 to 4 cu cm H per 100 g metal have been subjected to slow strain-rate tensile tests in a study of hydrogen embrittlement. In the lower nickel massive martensite alloy, embrittlement is manifest as the cracking of prior austenite grain boundaries and is severe at room temperature but less marked at -196°C; while in the higher nickel acicular martensite alloy, the embrittlement observed at 20°C does not occur at —196°C. Hydrogen embrittlement in these materials is believed to be the result of high hydrogen contents in the vicinity of the prior austenite grain boundaries combined with stress concentrations caused by boundary perturbations which result from the impact of the martensite shears. During deformation, microcracks form and propagate in the prior austenite grain boundaries, probably assisted by internal hydrogen pressure and the lowering of crack surface energy by hydrogen adsorption. The temperature dependence and the effect of the type of martensite on the embrittlement can be explained by their effects on the hydrogen content and stress concentrations at prior austenite grain boundaries during deformation.     

A model for the initiation of hydrogen embrittlement cracking at notches in gaseous hydrogen environments

A model for the initiation of hydrogen embrittlement cracking in gaseous hydrogen environments is presented. The model is based on the stress-induced diffusion of hydrogen atoms to the regions of high triaxial stress ahead of a plastically strained notch. The influence of yield stress and notch geometry on the apparent threshold stress intensity for embrittlement are considered and derived analytically. The time dependence for crack initiation for apparent stress intensities above the threshold is derived from a simple diffusion model. The results of the model are in agreement with reported hydrogen embrittlement phenomena.     

Resistance of low-carbon nitrogen-bearing stainless steel to hydrogen embrittlement and slow failure

The resistance of and low-carbon stainless steel, containing nitrogen and silicon, to hydrogen embrittlement and slow failure is investigated, in a corrosive medium with hydrogen saturation. The resistance is relatively high.     

溶解氧变化对阴极极化下10Ni5CrMo钢氢脆敏感性的影响

摘要：为研究溶解氧质量浓度对10Ni5CrMo钢在阴极极化条件下氢脆敏感性影响规律，对10Ni5CrMo钢进行了阴极极化下的电化学交流阻抗谱测试﹑并采用慢应变速率拉伸实验和断口分析方法研究了海水中溶解氧质量浓度变化和不同阴极极化下10Ni5CrMo钢的氢脆敏感性。结果表明：溶解氧质量浓度变化对10Ni5CrMo钢强度几乎没有影响；同一溶解氧质量浓度下，随极化电位负移，断裂时间、伸长率、断面收缩率明显降低，氢脆系数增加，氢脆敏感性显著提高，极化电位达到-1000mV时，氢脆系数已超过安全区允许的最高值25%，进入危险区；同一极化电位下，随着海水中溶解氧质量浓度减少，材料塑性变差，断裂时间、伸长率和断面收缩率不断降低，氢脆系数增加，氢脆敏感性提高。     

The role of dislocations during transport of hydrogen in hydrogen embrittlement of iron

In order to assess the role of hydrogen transport in hydrogen embrittlement, one of the kinetic aspects of hydrogen embrittlement, the strain rate dependence, was analyzed in terms of hydrogen transport. The results have been analyzed in terms of a new model which takes into account atomic and macroscopic diffusion in describing dislocation-hydrogen interactions. It was found that the strong strain rate dependence of hydrogen embrittlement can be explained by a dynamic trapping effect, which is associated with an increase in the population of dislocations during deformation.