Cyclic deformation behaviour of ferritic Fe-19Cr-4Ni-2Al alloy at elevated temperatures

Abstract

Cyclic stress response of ferritic Fe-19Cr-4Ni-2Al alloy was investigated under low cycle fatigue at elevated temperatures. The deformation microstructure developed was examined by transmission electron microscopy. The results showed that the alloy exhibited marked cyclic hardening at 773 K but continuous cyclic softening at 923 K. The cyclic hardening was considered to be associated with dynamic strain aging while the cyclic softening was interpreted in terms of the precipitate-dislocation interaction.     

Y，La改性Ni-10Cr-5Al合金的循环氧化行为研究

通过添加0.1%(质量分数)的单一稀土La和复合稀土Y-La,研究了两种含稀土的Ni-10Cr-5Al(质量分数,%)合金在1 100℃和1 200℃下的高温循环氧化行为。采用热重法并结合X射线衍射、扫描电子显微镜、能谱仪等,研究了合金的循环氧化动力学、氧化物的物相和组织成分等演变规律,分析了含稀土Ni-10Cr-5Al合金的氧化膜粘附性能在不同氧化温度下的差异及机制。结果表明,在1 100℃时,Ni-10Cr-5Al合金中添加0.1%(质量分数)的La或Y-La,不仅减少了氧化膜的厚度,而且因形成"钉扎"作用提高了氧化膜的粘附性,从而改善了合金的抗循环氧化性能。且复合添加Y-La的效果优于单一添加La的效果。但在1 200℃时,合金沿晶界的内氧化加快,反而恶化了合金的抗循环氧化性能。     

Oxidation Behaviour of Sputtered Ni-3Cr-20Al Alloy

1. IntroductionNi-base superalloys are the important materialsused at high temperature and greatly rely on the presence of Cr and/or Al to form a protective scale ofCrook or Allot. Therefore, the investigation of oxidation of the simple Ni-Cr-Al ternary alloys is beneficial to the understanding of oxidation patterns of complex Ni-base superalloys. Some works have been conducted on the Ni-Cr-Al alloys with normal grain sizeand the results indicated that different oxides couldbe formed accor…     

时效工艺对Fe-14Mn-5Si-8Cr-4Ni-0.2C合金形状记忆效应的影响

研究了时效工艺对Fe-14Mn-5Si-8Cr-4Ni-0.2C合金形状记忆效应和微观组织的影响，研究结果表明，变形后再时效对合金形状记忆效应的提高比不变形直接时效的显著得多，变形后时效将合金的形状回复率提高了190％，而直接时效只提高了83％，经SEM和TEM分析发现，同样时效时间下，与直接时效相比，变形后再时效一方面不仅减少了碳化物的析出数量，抑制了碳化物粒子的长大；另一方面还使第二相粒子主要在晶界上析出，而不是在晶内，正是这两方面的原因导致变形后时效对合金形状记忆效应的提高比不变形直接时效的高得多。     

Fe-18Mn-5Si-8Cr-5Ni-0.1N形状记忆合金组织和性能的研究

研究了Fe-18Mn-5Si8Cr-5Ni-0.1N形状记忆合金的形状记忆效应、回复应力、耐蚀性能.结果表明,在Fe-18Mn-5Si-8Cr-5Ni合金中加入0.1%的氮,对合金的形状记忆效应不利,但当预变形量小于4.5%时,降低幅度较小,在14%～18%左右.在变形量小于4.5%时,含氮合金加热时的回复应力高于未加氮的合金的回复应力;当变形量大于4.5%时,含氮合金的回复应力低于未加氮的合金的回复应力,两种合金的加热时最大回复应力的最大值相近(90 MPa左右).又由于氮具有强烈的固溶强化作用,大大强化了基体,使得合金在冷却过程中因回复应力导致的塑性变形量和二次相变量减小,从而导致合金冷却到室温的回复应力显著提高,当预变形量为6%时,含氮合金的室温回复应力最大,比未加氮的合金的最大室温回复应力高约21%.同时,氮的加入有利于提高合金的耐蚀性能.     

Effect of thermomechanical treatment on the phase transformation in Cu-44Ni-5Cr alloy

Cu-44Ni-5Cr alloy has been subjected to thermomechanical treatment which consisted of plastic deformation of as-quenched material by 50, 65 and 80% reduction in thickness followed by ageing in the interval of 500 to 650 °C for various durations of time. Progress in age-hardening was studied by means of hardness measurement and X-ray diffraction studies. The wavelength of composition modulation and strain amplitude were measured. It was found that age-hardening was a result of interaction between spinodal decomposition and recovery processes. Prior deformation was found to enhance the kinetics of both spinodal decomposition and coarsening. It was concluded that this resulted from increased vacancy concentration and increased coherency strain in the cold-worked material.     

Some aspects of electron beam welded and laser welded ferritic Fe-22Cr-3Mo-5Ni-0.3Ru alloy

Ferritic Fe-22Cr-3Mo-5Ni-0.3Ru alloy was welded by electron beam (EB) and laser techniques. Tensile tests, impact tests, oxalic acid etch, electrochemical potentiokinetic reactivation (EPR) and potential-time measurements were employed to investigate the mechanical properties, microstructural features and corrosion behaviour of the EB and laser welded metals. The oxalic acid etch tests revealed that the microstructure of the EB and laser welded metals consisted of columnar grains and cells, respectively. These structures were formed directly from the substrate by epitaxial solidification. Furthermore, the oxalic acid tests also showed that the EB and laser welded metals were immune to intergranular corrosion. Similar results were obtained by double loop EPR tests.     

Shape Memory Effect of As-aged Fe-14Mn-5Si-8Cr-4Ni-0.2C Alloy

1. IntroductionFe-Mn-St-Cr-Ni shape memory alloys exhibit notonly a good shape memory effect (SME), but alsoa good corrosion resistance[1'21, compared with FeMn-St alloys. Furthermore, it can be used in manufacturing pipe couplings because of its high phasetransformation temperature and great thermal hysteresis. But the recovery strain in these alloys is stilllow, which limits their application in pipe couplings.Therefore, to increase the recovery strain is key totheir practical applica,ti…     

Anelastic spectroscopy in Ti-13V-11Cr-3Al alloy

Titanium alloys display low density, high mechanical strength and good corrosion resistance, being ideal structural materials for aerospace engineering. In this paper, the effects of nitrogen on the anelastic properties of the bcc alloy Ti-13V-11Cr-3Al were investigated. The results show an asymmetric thermally activated relaxation structure in the high-temperature region. This relaxation structure was decomposed, and relaxation processes due to stress-induced ordering of nitrogen atoms around the metallic matrix and substitutional solutes were identified.     

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.     

时效温度对Ti-5Mo-5V-6Cr-3Al热轧管材组织性能的影响

通过扫描电镜(SEM)和X射线衍射分析(XRD)等手段对新型Ti5563合金热轧态管材经固溶时效和时效处理后的组织及物相含量进行了分析,比较了不同热处理后合金的力学性能,研究了时效温度对材料组织和力学性能的影响。结果表明:直接时效处理是提高Ti5563合金热轧态管材综合性能较为有效的方法;在520~660℃时效处理时,温度越低,α析出相越多,尺寸越小,分布越弥散,合金强度越大;随着温度增加,α析出相减少且尺寸变大,强化作用减弱,合金的塑性增加。     

固溶温度对Ti-5Mo-5V-2Cr-3Al钛合金棒材组织和性能的影响规律

研究了固溶温度对Ti-5Mo-5V-2Cr-3Al钛合金棒材显微组织和力学性能的影响。结果表明,钛合金固溶处理温度在相变点以下,空冷后,显微组织由β相、初生α相以及次生α相组成。随着固溶温度的升高,显微组织中β相晶粒尺寸增大,晶界α相厚度减小,产生有序化现象,而次生α相数量和尺寸减小,使合金的强度降低,塑性升高,但固溶处理温度为800℃时,网状晶界α相使塑性迅速下降;当固溶处理温度在相变点以上,Ti-5Mo-5V-2Cr-3Al钛合金重新形核并长大,随着固溶温度的升高,β相晶粒尺寸增大,初生α相数量减少,强度和塑性都下降,过冷β相晶粒发生应力诱发马氏体现象。     

轴尖用Ni-40Cr-3.5Al-1.0Nb-B合金的性能和组织

介绍了高硬度轴尖用Ni-40Cr-3.5Al-1.0Nb-B合金的性能,研究了该合金加工工艺、热处理工艺对硬度的影响,分析了合金的相组织和时效强化机理.     

Ti-6Cr-5Mo-5V-4Al合金热加工性能研究

目的 基于应变速率敏感系数、温度敏感系数,研究Ti-6Cr-5Mo-5V-4Al(Ti-6554)合金的热加工性能。方法 通过Gleeble-3500热模拟实验机,在温度为953~1 043 K、应变速率为0.001~10 s^?1时,对Ti-6Cr-5Mo-5V-4Al合金进行高温压缩实验。建立不同应变下的应变速率敏感系数图、温度敏感系数图,分析不同变形条件下的微观组织。结果 随着应变速率的增加,应变速率敏感系数逐渐下降,而低温度敏感系数区域主要集中在低应变速率区域。基于微观组织表征,发现变形过程中存在明显的动态相变和动态再结晶过程。结论 确定Ti-6554合金的合理加工条件为953~964 K、0.001 s^?1和1 037~1 043 K、0.001 s^?1。     

Effect of plasma on nitriding of Fe-18Cr-9Ni alloy

The plasma nitriding behaviour of Fe-18Cr-9Ni alloy was compared with gas nitriding. The alloy was nitrided under the following conditions: specimen temperature: 823 K, nitriding time: mainly 108 ks, total pressure: 0.4–0.7 kPa, mixture ratio of N₂ and H₂∶ 0.25, discharge voltage: 350–450 V, current: 0.8–1.1 A. Formation of a surface layer of iron nitrides was not observed. Formation of a homogeneous internal nitriding layer, consisting of small precipitates of CrN and the γ-phase matrix, was, however, noted. The lattice constant at the specimen surface was smaller than that at greater depth. This may have been because the sputtering effect decreased the dissolved nitrogen content at the specimen surface. The sputtering of iron nitrides at the specimen surface by the plasma was experimentally confirmed through γ′-Fe₄N formation on Si beside an alloy specimen. The characteristics of the plasma nitriding mentioned above are discussed in relation to the sputtering.