Y. X. Tian

Effect of Ho additions on the microstructure and mechanical properties of Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf alloys

Abstract The effect of Ho additions on the microstructure and compressive properties of the alloy Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf (at.%) was investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and by performing compression tests. The results show that Ho additions cause remarkable microstructural refinement. The addition of 0.1 at.% Ho to the alloy increases its strength and ductility. When the amount of Ho is increased to 0.2 at.%, the strength and ductility decreases. Ho addition inhibits the formation of the (Ti, Nb)5Si3 phase and the amount of the (Ti, Nb)5Si3 phase decreases, even disappears, with increasing Ho content. In addition, the fracture surfaces of Ho-free alloys deformed at room temperature in compression tests exhibit cleavage for both the (Nb, Ti) solid solution and the (Nb, Ti)5Si3 intermetallic compound, while limited local plastic strain of the (Nb, Ti) solid solution is observed in Ho-doped alloys. The effect and mechanism of strengthening and plastic deformation of Ho additions to the alloy was discussed in view of the microstructure.

Mathematic model analysis of Gaussian beam propagation through an arbitrary thickness random phase screen.

In order to research the statistical properties of Gaussian beam propagation through an arbitrary thickness random phase screen for adaptive optics and laser communication application in the laboratory, we establish mathematic models of statistical quantities, which are based on the Rytov method and the thin phase screen model, involved in the propagation process. And the analytic results are developed for an arbitrary thickness phase screen based on the Kolmogorov power spectrum. The comparison between the arbitrary thickness phase screen and the thin phase screen shows that it is more suitable for our results to describe the generalized case, especially the scintillation index.

Orientation relationship and interfacial structure between Nb solid solution precipitates and alpha-Nb(5)Si(3) intermetallics

The orientation relationship (OR) and the interfacial structure between Nb solid solution (Nbss) precipitates and alpha-Nb(5)Si(3) intermetallics have been investigated by transmission electron microscopy (TEM). The OR between Nbss and alpha-Nb(5)Si(3) was determined by selected-area electron diffraction analyses as (222)(Nb)//(002)(alpha) and [1 (1) over bar0](Nb)//[1 (1) over bar0](alpha) High-resolution TEM images of the Nbss/a-Nb5Si3 interface were presented. Steps existed at the interface that acted as centers of stress concentration and released the distortion of lattices to decrease the interfacial energy. In addition, the interfacial models were proposed based on the observed OR to describe the atomic matching of the interface. The distribution of alloying elements at the Nbss/alpha-Nb(5)Si(3) interface has also been investigated, and Hf was enriched at the interface to strengthen the grain boundary.

Microstructure and room temperature compressive properties of holmium doped DS NiAl-Cr(Mo)-Hf eutectic alloy

Abstract The microstructure and mechanical property of a eutectic Ni-33Al-28Cr-5.94Mo-0.05Hf-0.01Ho (holmium) alloy fabricated by using directional solidification under two withdrawal rates (3 mm min– 1 and 10 mm min– 1) are presented. It is shown that a promising as-cast microstructure is formed under the higher withdrawal rate, which can be characterized by the refinement of eutectic cells as well as eutectic lamellae between the NiAl and Cr(Mo) phases within the cells. As a positive response to this, superior room temperature mechanical properties with yield strength of 1153 MPa and compressive strain of 37 % are obtained. Based on these investigations, the mechanism responsible is discussed.

Microstructure and room temperature mechanical properties of Hf and Sn-doped Nb-20Ti-5Cr-3Al-18Si alloy

Abstract In this paper, the effects of Sn and Hf additions on microstructures and room temperature mechanical properties of Nb-20Ti-5Cr-3Al-18Si alloy were investigated. The Sn addition has no significant effect on the microstructure of the alloy. Sn is preferentially partitioned in (Nb, Ti)ss rather than (Nb, Ti)5Si3. The addition of Sn decreases the solubility of Cr in (Nb, Ti)ss. The addition of Hf causes coarsening of the eutectic structure of (Nb, Ti)ss and (Nb, Ti)5Si3 and the formation of the Hf-rich γ(Nb, Ti)5Si3 along phase boundaries. With the addition of Sn the strength of the alloy decreases, while its ductility increases slightly. The Hf addition simultaneously improves strength and ductility of the alloy. The relationships between composition, microstructure and properties are discussed.

Model-based restoration using light vein for range-gated imaging systems

The images captured by an airborne range-gated imaging system are degraded by many factors, such as light scattering, noise, defocus of the optical system, atmospheric disturbances, platform vibrations, and so on. The characteristics of low illumination, few details, and high noise make the state-of-the-art restoration method fail. In this paper, we present a restoration method especially for range-gated imaging systems. The degradation process is divided into two parts: the static part and the dynamic part. For the static part, we establish the physical model of the imaging system according to the laser transmission theory, and estimate the static point spread function (PSF). For the dynamic part, a so-called light vein feature extraction method is presented to estimate the fuzzy parameter of the atmospheric disturbance and platform movement, which make contributions to the dynamic PSF. Finally, combined with the static and dynamic PSF, an iterative updating framework is used to restore the image. Compared with the state-of-the-art methods, the proposed method can effectively suppress ringing artifacts and achieve better performance in a range-gated imaging system.

Elevated temperature compressive behavior of Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf alloy with minor Ho addition

Abstract The microstructure and elevated temperature compressive behavior of Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf alloys with and without 0.1 at.% Ho were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and compression tests. The results show that the addition of 0.1 at.% Ho to the matrix alloy significantly increases its elevated temperature strength at a higher strain rate, while the strengthening effect becomes weak at a lower strain rate. The elevated temperature compressive deformation behavior of the Ho-doped alloy can be adequately described by the power-law equation. The mechanism of Ho addition on elevated-temperature compressive behavior of the alloy is discussed in the paper.