Crystallization and decomposition of metastable phases in iron-base amorphous alloys

Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 23–24, March, 1990.     

应力对Al-Zn-Cu系平衡相的影响

采用99.999%分析纯的Al、Zn、Cu作原料,在外热式坩埚炉中熔制了5Cu40Zn55Al、15Cu20Zn65Al和3Cu17Zn80Al共3种合金,将其经过成分均匀化处理后,对包含亚稳相的3种合金分别进行球磨和手工锤击实验,采用X射线衍射仪分析合金平衡相组合.结果表明:合金通过球磨能得到窒温平衡相,而通过手工捶击则得不到室温平衡相;能否通过应力诱发相变快速获得室温合金平衡相组织与合金应力作用产生的变形机制有关;球磨能使合金内部发生大量变形,为合金向平衡相转变提供驱动力和原子扩散通道;而手工锤击主要是使合金发生以解理为主的脆性断裂,这种变形不能为亚稳相的转变提供必要的驱动力和原子扩散通道,从而得不到合金室温下的平衡相组成.     

镁合金微弧氧化陶瓷层显微缺陷与相组成及其耐蚀性

利用SEM，XRD及盐雾腐蚀等试验手段，研究了MB8镁合金微弧氧化陶瓷层生长过程中显微缺陷与相组成的变化规律及其对耐蚀性的影响。结果表明：微弧氧化初期，陶瓷层致密，几乎观察不到显微缺陷，随着处理时间的延长及陶瓷层的增厚，其外侧开始出现孔洞类缺陷，直至90％厚度范围布满相互交错的不规则孔洞；陶瓷层主要由MgO，MgSiO3，MgAl4O4和 非晶相组成，随着厚度的增加，陶瓷层中MgO的比例不断增加，而非晶相含量逐渐减少；短时间微弧氧化处理有利于制取艰非晶相为主的致密无缺陷的耐蚀陶瓷层。     

Self-accommodation of crystals of martensitic phases in titanium and zirconium based alloys

The orientation relationships between austenite and ???? and ???? martensite lattices in titanium and zirconium alloys is performed in view of the possibility of the formation of self-accommodating complexes, which is an important component of the shape memory effect. Different diffraction patterns calculated for various matrices of the orientation relationship were compared with the experimental patterns for Ti₄₅Zr₄₅Nb₁₀ alloy using a formula developed for the optimal expression of the orientation relationship for ????. The generalization and analysis of the literature data for titanium- and zirconium-based solid solutions performed using the developed algorithm lead us to conclusions regarding the tendency of ???? martensite in titanium-based solid solutions to self-accommodate, which occurred more strongly than that in zirconium-based alloys, and the best results in shape memory realization should be expected in Ti-Ta and Ti-Nb systems. Possible reasons for the absence of the shape memory effect for ???? martensite in titanium- and zirconium-based alloys, with regard to the necessary crystallographic conditions for the formation of self-accommodating processes are analyzed.     

Identification and analysis of intermetallic phases in overaged Zr-containing and Cr-containing Al-Zn-Mg-Cu alloys

This paper investigates the effect of alloying elements on the characteristics of intermetallic phases in Zr-containing and Cr-containing 7xxx Al-Zn-Mg-Cu alloys at overaged conditions. Four Al-Zn-Mg-Cu alloy plates with different alloying element contents were studied by optical microscopy based image analysis, differential scanning calorimetry, scanning electron microscopy combined with energy disperse X-ray spectroscopy and transmission electron microscopy. The grain structures, recrystallisation, intermetallic phases and precipitates in the selected alloys have been analyzed and the presence of coarse intermetallic phases has been interpreted using established phase diagrams. The different effects of Zr or Cr addition to the alloys have been compared. The experimental results showed that the recrystallised area fraction of Zr-containing alloys is less than that of Cr-containing alloys, being attributable to Zr reducing recrystallisation more effectively than Cr. The detected particles are mainly S phase, Al₇Cu₂Fe, as well as dispersoids of Al₃Zr for Zr-containing alloys and Cr-rich E phase for Cr-containing alloys. These coarse particles, especially the S phase which cannot be dissolved during solution treatment, are detrimental to the fracture toughness of the alloys.     

高速列车TC4钛合金焊接构架强度及寿命评估

采用电子束焊和氩弧焊方法制备的TC4钛合金接头,在4种温度条件下,测试了其焊缝、热影响区及母材的断裂韧性,并结合断口形貌、硬度分布及微观组织对比分析了断裂韧性测试结果. 结果表明,TC4钛合金TIG焊接头焊缝及热影响区的断裂韧性优于钛合金母材,CTOD值随温度下降而降低;相较之下,EBW焊接头焊缝断裂韧性值较母材更低,热影响区断裂韧性与母材较接近,温度变化对其CTOD值无显著影响. 钛合金TIG焊接头焊缝区域具有较低硬度值,其网篮状α相和较低比例的马氏体分布是其断裂韧性较高的根本原因;而钛合金EBW焊接头焊缝中针状马氏体的分布导致其局部硬度较高,并降低了断裂韧性.     

耐热镁合金及其研究进展

综述了耐热镁合金及其研究进展.介绍了Mg-Al、Mg-Zn、Mg-RE、Mg-Th、Mg-Ag合金系及镁基复合材料、快速凝固镁合金在耐热性能方面的发展;认为Mg-RE系合金由于其优良的耐热性能,可在我国大力发展,但碱土金属可部分代替昂贵的稀土元素.对这些合金来说,研究耐热相及结构对提高合金的高温强度和热稳定性是非常重要的.     

The ordering behavior of supersaturated metastable phases in β-Ti alloys

A phase resulting from quenching solution treated beta-Ti alloys has long been recognized as a metastable structure containing unusual phenomena, and is not well understood. Tweed structure consisting of the metastable phase was observed by transmission electron microscopy, and spot satellites inflicted by streaks were also observed in the lattice diffraction. The results of microstructural studies and diffraction pattern surveys have identified the metastable structure as the elastic strain zone caused by the supersaturation of solute atoms, which may be induced by the electron charge distribution and atomic bonding between solvent matrix and solute atoms, causing the tweed structure. This paper presents the main finding of a microstructural abnormality, and compares the results with ordering behavior such as premartensitic transformation, and reviews a new regularity generated in the metastable phase of the supersaturated state.     

Metastable phases of electron type in titanium alloys with 3d-metals

Conditions of formation and structural characteristics of metastable states forming due to changes in the concentration of alloying elements in titanium alloys with 3d-metals are considered. The states arising due to hardening from the range of solid solution and the states arising due to hardening from melt are studied. Growth in the concentration of alloying elements in all alloys of the type is accompanied by formation of a metastable ω-phase and an incommensurate ω-phase; in alloys of the Ti-Fe and Ti-Mn systems the formed phases also include icosahedral quasi-crystals and their approximants. Effects of various factors on the formation of metastable phases are discussed. An incommensurate ω-phase is considered as an example of specific nanocrystalline structure stabilized by electron interactions.     

Review of micro-scale and atomic-scale corrosion mechanisms of second phases in aluminum alloys

Localized corrosion of aluminum (Al) alloys, such as pitting corrosion, intergranular corrosion, and stress corrosion cracking is closely related to the micro-galvanic corrosion between the second phase and the Al matrix. Using high-resolution transmission electron microscopy and first principles calculations, the factors that affect corrosion mechanisms of the second phase in Al alloys at micro-scale and atomic-scale were examined, including the composition and structure of second phase, pH of the environment, stress and adsorption behavior of adsorbates (such as Cl⁻, H₂O, OH⁻ and O²⁻).