Zr-2.5Nb合金的织构演变

锆基合金在反应堆环境中具有低的中子吸收截面、高机械性能、低辐照蠕变性能和高腐蚀抗力,常被用做压水堆材料.如Zr-2.5Nb合金被用做印度220 MW和250 MW压水堆的压力管.     

The Mechanism of kIH in Delayed Hydride Cracking of Zr-2.5wt% Nb at 150 ℃

This work studies the KIH mechanism of delayed hydride cracking (DHC) in Zr-2.5wt% Nb alloys. A modified experimental method was developed, in which specimens are fatigued between consecutive experiments, and a constant load instead of a decreasing load is used in each experiment. The hydride clusters formed and fractured at the crack tip during different experiments are thus separated and studied individually. A new R-curve phenomenon that characterizes the resistance to DHC was observed. KIH is thus more rigorously defined. Based on the measurement of the critical hydride cluster length at different K1, the threshold phenomenon of KIH is explained.     

Relationship between microstructure and mechanical properties in Nb–V microalloyed TRIP steel

Nb–V additions clearly affected the precipitation state, respective phase transformations and final microstructure, and in turn, resulting mechanical properties of an intercritically annealed transformation induced plasticity sheet steel. As the precipitation hardening played a limited role in the overall strengthening, the grain refinement was the prevailing strengthening mechanism associated with the addition of the Nb–V microalloying to a basic TRIP780 composition. In addition to this, the microstructural changes, resulting from the addition of microalloying, lowered the stability of retained austenite, which decreased the elongation of the steel. Nevertheless, using this microalloying concept, an exceptional product of R_mxA₈₀ exceeding 16?000 MPa % could be achieved.     

A Comparative in vitro Study on Biomedical Zr-2.5X(X=Nb,Sn) Alloys

Nb and Sn are major alloying elements in Zr alloys.In this study,the microstructure,mechanical properties,corrosion behavior,cytocompatibility and magnetic resonance imaging(MRI) compatibility of Zr-2.5X(X = Nb,Sn) alloys for biomedical application are comparatively investigated.It is found that Zr—2.5Nb alloy has a duplex structure of α and β phase and Zr—2.5Sn alloy is composed of 7.phase.Both separate addition of Nb and Sn can strengthen Zr but Nb is more effective in strengthening Zr than Sn.The studied Zr—2.5X(X = Nb,Sn) alloys show improved corrosion resistance compared to pure Zr as indicted by the decreased corrosion current density.The alloying addition of Nb enhances the pitting resistance of Zr,whereas the addition of Sn decreases the pitting resistance of Zr.The extracts of Zr—2.5X alloys produce no significant deleterious effect on fibroblast cells(L-929) and osteoblast-like cells(MG 63),indicating good in vitro cytocompatibility.The Zr—2.5X(X = Nb,Sn) alloys show decreased magnetic susceptibility compared to pure Zr and their magnetic susceptibility is far lower than that of pure Ti and Ti—6AI—4V alloy.Based on these facts,Zr-2.5Nb alloy is more suitable for implant material than Zr-2.5Sn alloy.Sn is not suitable as individual alloying addition for Zr because Sn addition decreases the pitting resistance in physiological solution.     

The athermal α → ω transformation in Zr-2 at% Nb alloy

The athermal transformation in Zr-2 at.% Nb alloy has been investigated by transmission electron microscopy. Analysis of the selected-area diffraction pattern has shown that the orientation relationships between the omega and the parent-phase in quenched Zr-2 at.% Nb alloy are the same as have been previously observed for the reaction in pure zirconium. Thus it was deduced that the direct transition has taken place in the alloy during cooling. The-originated -particles were visualized using the dark-field technique. The formation of the athermal omega in the-region of-stabilized Zr-Nb alloy is discussed in terms of the relative positions of the free energy equilibrium curvesT ₀ ,T ₀ ,T ₀ and the correspondingM _s ,M _s andT _s start curves. It is concluded that the omega phase can occur over a much wider range of alloy compositions than is usually recognized on the basis of transformation data.     

Effects of Nb content in Ti–Ni–Nb brazing alloys on the microstructure and mechanical properties of Ti–22Al–25Nb alloy brazed joints

Vacuum brazing was successfully used to join Ti–22Al–25Nb alloy using Ti–Ni–Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti–Ni–Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, ?3, and Ti2 Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached359 MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180?C for 20 min, and it was321, 308 and 256 MPa at 500, 650 and 800?C, respectively. Cracks primarily initiated and propagated in ?3compounds, and partially traversed B2+O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2+O region, which was favorable for the mechanical properties of the brazed joint.     

Evolution of microstructure,texture and grain boundary character in a severely cold rolled Ti + Nb IF steel

Severe cold rolling (up to 99.5% reduction) of a Ti + Nb IF steel has been found to produce nano-sized to ultrafine grains. The γ fibre intensity increases with the level of cold deformation. The fraction of high angle grain boundaries increases with increasing rolling reduction and then levels off at the highest deformation level. The coincidence site lattice boundary fraction increases continuously with increase in the amount of cold rolling.     

Thermal diffusivity of submicro- and nanocrystalline Zr–2.5% Nb and Zr–50% Nb alloys at high temperatures

Measurement data are given for the thermal diffusivity of Zr–2.5% Nb and Zr–50% Nb alloys both with the usual polycrystalline structure and with submicro- and nanocrystalline structures at high temperatures, which were determined in the automated mode using the dynamic technique of plane temperature waves.     

Evaluation of emcocel® 50 and emcocel® 90, a new excipient in direct compression

Abstract

The tabletting properties of a new microcrystalline cellulose product, Emcocel® 50 and Emcocel® 90 were evaluated and compared with the tabletting properties of Avicel® PH 101. The evaluation of placebo tablets, of the dilution potential, of formulations with active compounds as Aspirin, Phenobarbital and a spraydried extract in high concentrations showed that Emcocel® has comparative tabletting properties in regard of Avicel® PH 101.     

Manganese dependence of microstructure and mechanical properties in Fe–Mn alloy

Two Fe–Mn alloys with relatively low Mn content were designed. The microstructure characteristics and resultant mechanical properties were investigated in detail by means of electron back-scattered diffraction, transmission electron microscopy and X-ray diffraction. The results show that the formation of α′-martensite is effectively suppressed and the yield strength and total elongation are significantly enhanced by increasing Mn content from 12 to 13 mass%. A great amount of α′-martensite can effectively enhance strain hardening rate, but they deteriorate ductility. The austenite grain is always divided by multiple-variant ?-martensite plate. In addition, the prior austenite grain boundaries and austenite/?-martensite interfaces can act as obstacle to suppress the growth of ?-martensite plates.     

Effect of in situ phases on microstructure and properties in Al–Bi immiscible alloy

Al–Bi immiscible alloy is of particular interest as potential self-lubricating wear materials with a homogeneous distribution of minority phase. However, it is difficult to obtain a homogeneous microstructure by conventional casting methods due to liquid phase separation of Al–Bi immiscible alloy. We have developed a new strategy to restrain liquid phase separation and improve the properties of Al–Bi immiscible alloy by in situ phases. The in situ AlB₂ phase acts as heterogeneous nucleation site to accelerate the nucleation and slow down the velocity of the Bi-rich droplet, resulting in a significant size reduction and a homogeneous microstructure of Al–Bi immiscible alloy. The self-lubricating wear resistance of Al–Bi immiscible alloy can be further enhanced by in situ Al₂Cuphase.     

Metal and Metal Oxide Nanoparticles in Chemiresistors: Does the Nanoscale Matter?

Sensor technology is one of the most important key technologies of the future with a constantly increasing number of applications, both in the industrial and in the private sectors. More and more gas sensors are used for the control of technical processes, in environment monitoring, healthcare, and automobiles. Consequently, the development of fast and sensitive gas sensors with small cross sensitivity is the subject of intense research, propelled by strategies based on nanoscience and -technology. Established systems can be improved and novel sensor concepts based on bottom-up approaches show that the sensor properties can be controlled by molecular design. This Review highlights the recent developments and reflects the impact of nanoscience on sensor technology.     

Influence of oxygen content on microstructure and mechanical properties of Ti–Nb–Ta–Zr alloy

The influence of oxygen content on microstructure and mechanical properties of Ti–22.5Nb–0.7Ta–2Zr (at.%) alloy was investigated in this work. According to experiments, the grains were refined apparently when the oxygen content was between 1.5% and 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased with increasing oxygen content. But at the content of 1.0%, the elongation was nearly the same to that of the original alloy (about 16%). The elastic modulus remained comparatively low (<65 GPa) when the content was lower than 1.5%, and then increased dramatically. Therefore, there existed the best oxygen content-1.0%, at which fine grains were obtained, as well as UTS of 750 MPa, elongation of 16% and elastic modulus of 65 GPa. The Ti–22.5Nb–0.7Ta–2Zr–1.0O alloy maintained typical ductile fracture characteristics of beta titanium alloy, and had a little superelasticity.     

Effect of heat treatment on microstructure and mechanical properties of Cr–Ni–Mo–Nb steel

Abstract

The microstructure and mechanical properties of a medium carbon Cr–Ni–Mo–Nb steel in quenched and tempered conditions were investigated using transmission electron microscopy (TEM), X-ray analysis, and tensile and impact tests. Results showed that increasing austenitisation temperature gave rise to an increase in the tensile strength due to more complete dissolution of primary carbides during austenitisation at high temperatures. The austenite grains were fine when the austenitisation temperature was <1373 K owing to the pinning effect of undissolved Nb(C,N) particles. A tensile strength of 1600 MPa was kept at tempering temperatures up to 848 K, while the peak impact toughness was attained at 913 K tempering, as a result of the replacement of coarse Fe rich M₃C carbides by fine Mo rich M₂C carbides. Austenitisation at 1323 K followed by 913 K tempering could result in a combination of high strength and good toughness for the Cr–Ni–Mo–Nb steel.