NiAl-31Cr-3Mo共晶合金的高温氧化行为

本文采用恒温氧化实验方法,在900 ～ 1150℃下测试了NiAl-31Cr-3Mo共晶合金的氧化性能,分析了合金的氧化动力学;SEM观测了合金表面以及横截面的形貌.研究表明,共晶合金表面在900～ 1100℃下形成了连续的Al2O3氧化膜,表现出一定的抗氧化性能;共晶合金表面在1150℃下未形成完整的Al2O3氧化膜...     

NiAl-28Cr-6Mo共晶合金的高温氧化行为

本文采用恒温氧化实验方法,在900～1150℃下测试了NiAl-28Cr-6Mo共晶合金的氧化性能,分析了合金的氧化动力学,SEM观测了合金表面以及横截面的形貌.研究表明,NiAl-28Cr-6Mo共晶合金在900～1100℃下合金表面生成了连续的Al2O3氧化膜,具有较好的抗氧化性能;900～1000℃氧化膜主要由θ...     

定向凝固NiAl-28Cr-5.8Mo-0.2Hf合金的高温拉伸蠕变行为

研究了定向凝固NiAl-28Cr-5.8Mo-0.2Hf合金的显微组织和在982－1100℃,50-124MPa应力下的高温蠕变行为，该合金是由NiAl相。Cr(Mo)相和少量Hf的固溶体相组成。蠕变测试结果表明：蠕变曲线是由较短的减速蠕变阶段和较长的加速蠕变阶段组成，且蠕变后的显微组织变化不大，蠕变变形机制是由位错攀移机制所控制。加强蠕变阶段蠕变速率的增加是由于裂纹的形成与扩展引起的。     

NiAl-30．9Cr-3Mo-0．1Dy合金的高温氧化行为

研究了NiAl-30．9Cr-3Mo-0．1Dy合金在1300K～1500K空气中的恒温氧化行为。结果表明：NiAl-30-9Cr-3Mo-0．1Dy合金的抗氧化性远优于NiAl-31Cr-3Mo合金：1500K的氧化动力学曲线基本遵循抛物线关系，在1350K～1450K的氧化动力学曲线符合立方抛物线关系，1300K的氧化动力学曲线则符合5次方关系。氧化过程中，合金的表面生成了连续致密的Al2O3氧化膜；稀土元素的活性作用以及Al2O3与基体合金之间的富Cr层的形成，提高了Al2O3的粘附能力。Dy的添加也减少了NiAl相上Al2O3的生成量，延缓了θ-Al2O3向α-Al2O3相的转变时间。     

定向凝固NiAl-28Cr-5Mo-1Hf合金的高温蠕变

研究了定向凝固NiAl-28Cr-5Mo-1Hf合金的显微组织和高温拉伸蠕变行为，该合金由NiAl相、Cr(Mo)相和少量聚集在NiAl和Cr(Mo)相界处的Ni2AlHf(Heusler)相组成，蠕变曲线表现为较短的减速蠕变阶段和较长的稳态蠕变阶段及较高的蠕变应变，且蠕变后显微组织的变化不大，该合金的蠕变由晶格自扩散引起的位错攀移所控制，蠕变断裂数据符合Monkman-Grant关系。     

两相共晶NiAl-9Mo合金的蠕变行为

研究了热等静压态的NiAl-9Mo合金在850-950℃和50-100 MPa下的蠕变行为.在试验应力和温度下,该合金蠕变曲线呈现出较短的减速阶段和较长的稳态蠕变阶段;其稳态蠕变速率可用幂指数蠕变方程来描述,应力指数值为4.75±0.25,表观激活能为 410.5±4.5kJ/mol.加速蠕变阶段蠕变速率的增加是由于裂纹的形成和扩展,且其断裂数据遵循Monkman-Grant规律.蠕变断口呈现出塑性断裂和沿晶蠕变断裂的混合特征,但后者比例较大,同一温度下随着应力的增大,沿晶断裂的比例呈现下降的趋势.     

定向凝固NiAl-32V亚共晶合金热稳定性研究

本文采用定向凝固技术制备NiAl-32V伪二元亚共晶合金,研究该合金在高温热处理后不同抽拉速率稳态区组织形貌,并分析其热稳定性及组织形貌变化规律。结果表明：该合金初生相组织在900℃(5~100h)组织热稳定性良好;NiAl相共晶层片均有粗化与球化现象,且热处理时间越久,粗化程度越大,球化现象越明显。不同温度(900℃、1000℃、1100℃)5h高温热处理后该合金初生相面积占比也略有变化,所有试样(抽拉速率V=6～150μm/s)NiAl共晶层片均有粗化与球化现象;随着热处理温度的增加,粗化和球化现象愈明显。     

定向凝固NiAl-28Cr-5.85Mo-0.15Hf合金的高温蠕变行为研究

研究了定向凝固NiAl-28Cr-5.85Mo-0.15Hf合金的微观组织和高温蠕变行为。结果表明合金是由NiAl枝晶轴和枝晶间区[NiAl和Cr(Mo)相的共晶]组成的。经过长期固溶时效处理NiAl/Cr(Mo)合金析出少量弥散分布的Huesler相,其余Hf以固溶体方式存在。合金拉伸蠕变曲线具有典型的三阶段特征,即较短的减速蠕变阶段和较长的第三蠕变阶段。合金应力指数n和蠕变激活能Q分别为3.36和245kJ/mol,该合金的蠕变变形是由位错攀移机制所控制的。     

NiAl微晶涂层对两种NiAl基共晶合金高温氧化性能的影响

研究了磁控溅NiAl微晶涂层对NiAl－28Cr-5Mo-1Hf和NiAl－33.5Cr-0.5Zr两种共晶合金在1000－1150℃静态空气中氧化性能的影响，添加Cr,Mo,Hf,Zr等元素使NiAl合金由单相转变为多相结构，高温氧化后表面分别形成抗氧化性能较差的Al2O3 CrO3 HfO2和Al2O3 Cr2O3 ZrO2复合氧化膜，并且发生严重的内氧化。施加NiAl微晶涂层后，高温下表面形成致密的单一氧化物Al2O3，抗氧化性能得到明显提高。     

共晶NiAl—9Mo合金的超塑性行为

研究了共晶 ＮｉＡｌ－９Ｍｏ合金的超塑性行为及其变形机制．该合金的微观组织由 ＮｉＡｌ以及 ＮｉＡｌ和α－Ｍｏ共晶体组成．在 １３２３－１３７３ Ｋ温度区间,以 ５.５５×１０－５－１．１１×１０－４ ｓ－１的应变速率拉伸变形时,表现出超塑性行为,最大延伸率达到 １８０％,应变速率敏感性指数达到 ０．５６．超塑性的变形机制为初生 ＮｉＡｌ基体的晶界滑动,断裂起源于超塑性变形过程中产生的孔洞．     

NiAl—28Cr—5Mo—1Hf合金的高温氧化行为研究

研究了NiAl-28Cr-5Mo-1Hf合金在1000－1200℃空气中氧化行为。X射线结构分析表明,氧化膜主要由α-Al2O3构成,并含有Cr2O3和少量HfO2。采用扫描电镜和能谱分析研究了氧化产物的微观组织及成分,并从合金组成探讨了NiAl-28Cr-5Mo-1Hf合金的氧化机制。     

High-temperature oxidation of directionally solidified Ni-Al-Cr3C2 eutectic

The isothermal oxidation behavior of a directionally solidified Ni-Al-Cr₃C₂ eutectic alloy in flowing air at 1100° C has been studied using various physical techniques. Initially, the alloy oxidizes relatively slowly as a protective - Al₂O₃ layer develops on its surface. However, this layer breaks down mechanically at temperature, enabling a more rapidly growing Cr₂O₃ -rich scale to develop, the carbide fibers supplying chromium for the oxidation process. The extent of oxidation is further increased by the development of substantial amounts of internal oxide in the alloy beneath this scale, with some preferential oxidation down the alloy-carbide fiber interfaces. The influence of carbide fiber orientation on the oxidation behavior is considered and discussed in relation to proposed oxidation mechanisms.     

The oxidation of a directionally solidified cobalt-tungsten eutectic alloy

A study of the oxidation of directionally solidified Co-W alloys were performed at 750, 900, and 1050°C. The study involved a comparison of the oxidation behavior of directionally solidified and as-cast alloys along with the oxidation behavior of the pure components. The study incorporated both thermogravimetric kinetic measurements and morphological studies of the oxides as a function of both temperature and time. Differences were noticed in both the oxidation rate and the oxide morphology and were attributed to differences in alloy microstructure. The directionally solidified Co-W alloy was found to be more spall resistant but also oxidized more rapidly than the conventionally as-cast alloy. Both alloys were more oxidation resistant than the pure components.     

纤维尺寸和界面形态对定向凝固NiAl-Mo共晶合金电化学腐蚀性能的影响

由于凝固组织对腐蚀有着重要的影响,本文主要目地获取最优组织形态和电化学参数生产钼纳米丝。研究表明NiAl-Mo共晶合金定向凝固下,组织由基体NiAl相和纤维Mo相共生耦合生长。随着抽拉速率从10 μm/s增大到40 μm/s时,纤维尺寸从800 nm减小到300 nm,界面形态也从平界面变化成胞界面。同时在0.1 M HCl电解液下测量其极化曲线,发现凝固速率为20 μm/s时耐腐蚀性能最好。对于NiAl-Mo共晶合金,影响电化学腐蚀性能不仅仅是纤维尺寸,而且还取决于界面形貌。为了更进一步研究界面形态对腐蚀的影响,本文设计了跃迁变速实验,实验表明定向凝固组织形貌会随着变速比的增大从平界面变成胞界面最后变成枝界面,然而最后的纤维尺寸和变速比无关,和恒速抽拉相同。极化曲线表明平界面有着最好的耐腐蚀性能。     

High-temperature oxidation of directionally solidified Ni-Cr-Nb-AI (γ/γ′-δ) eutectic alloys

The oxidation of Ni-23.1Nb-4.4Al and Ni-19.7Nb-6 Cr-2.5Al alloys in air at temperatures in the range 870–1100°C has been studied for times up to 168 hr, in the as-cast, slowly cooled, and directionally solidified forms. The oxidation rate decreases with increasing temperature for the ternary alloy, and this appears to be due to the increasing tendency to establish a continuous Al₂O₃ layer at the metal surface, although at no temperature in this range is a complete layer established. At the lowest temperature the -Ni₃Nb lamellae are preferentially oxidized, with fingers of oxide extending into the metal, but at 900°C and above a continuous single-phase 8-free layer is established at the metal surface very early in the oxidation. The oxidation rate of the quaternary alloy increases with increasing temperature. At the lower temperatures a continuous Al₂O₃ layer is established at the metal surface, but at the highest temperature the aluminum oxidizes internally and a continuous layer is not established, internal oxidation penetrating down the lamellae. It appears that niobium, like chromium, is able to promote the formation of external Al₂O₃ layers; if this fact is accepted, the beneficial role of chromium in these alloys is difficult to explain.     

定向凝固过共晶Nb-Si基合金的组织优化

采用液态金属冷却定向凝固炉制备Nb-16Si-24Ti-10Cr-2A1．2Hf合金,凝固速率分别为1．2、6、18、36、50mm／min,随后对定向凝固速率为50mm／min的合金进行（1400℃,10h）,（1450℃,10h）和（1500℃,10h）的热处理。研究了定向凝固速率和热处理温度对合金微观组织的影响。结果表明：合金的定向凝固组织主要由沿着试棒轴向生长的初生Nb5Si3相和耦合生长的Nbss／Nb5Si3共晶胞组成,在共晶胞边缘,有少量的Cr2Nb存在。横截面上共晶胞边界明显,随着凝固速率的增加,定向凝固组织明显细化,Nbss／Nb;Si,共晶胞形貌也发生变化。合金经过热处理,Nbss连成基体,部分CrENb相熔解,微观成分偏析减小。经过（1450℃,10h1热处理,实现了对过共晶Nb—Si基合金的组织优化。     

The influence of yttrium additions on the oxidation resistance of a directionally solidified Ni-Al-Cr3C2 eutectic alloy

Isothermal oxidation of a directionally solidified Ni-Al-Cr₃C₂ eutectic alloy results in development of an external -Al₃O₃-rich scale. However, this scale breaks down after relatively short times at temperature and a less protective Cr₂O₃-rich scale is formed, together with substantial internal oxide in the alloy. In an attempt to maintain the external -Al₂O₃-rich scale and prevent damaging subscale oxidation, modified yttrium-containing directionally solidified alloys have been developed. The oxidation resistance of these alloys at 1000 and 1100°C in flowing air has been investigated and found to be considerably better than that of the corresponding yttrium-free alloy. At both temperatures an external -Al₂O₃-rich scale is produced and is retained for much longer periods than on the yttrium-free alloys during isothermal and thermal cycling oxidation. Some scale breakdown does occur during thermal cycling at 1100°C, but -Al₂O₃ is able to re-form as the surface oxide. However, although external -Al₂O₃-rich scales are retained for long periods on these alloys, some oxide penetration into the alloy beneath these scales does occur where coarse carbide fibers intersect the alloy surface. This is associated with relatively poor scale integrity at these intersections.     

定向凝固NiAl-Fe-Nb金属间化合物的显微组织和类超塑性行为

研究了定向凝固Ni 2 0Al 2 7Fe 3Nb金属间化合物的显微组织和高温拉伸条件下的变形行为。结果表明 ,该合金的显微组织由枝晶 β NiAl相和枝晶间γ/γ′相组成。在 95 0～ 110 0℃之间以 5 .2× 10 -4～ 1.0 4× 10 -2s-1的初始应变速率拉伸变形时 ,该合金表现出类似超塑性的变形行为 ,应变速率敏感指数m在 0 .2 1～ 0 .4 5之间。在 10 5 0℃以 5 .2× 10 -3 s-1的初始应变速率拉伸时 ,获得最大延伸率 2 6 0 % ,m =0 .2 9。通过显微组织观察 ,对这种具有类似超塑性变形行为的机理进行了初步的讨论