Chunxiang Cui

Growth of ZnO nanowires in aqueous solution by a dissolution-growth mechanism

A novel methodology based on the dissolution-growth mechanism was developed to prepare ZnO nanowire films. The film morphology and structure were investigated by using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction analysis methods. The results show that the ZnO nanowires are single crystalline c-oriented wurtzite. The ZnO rod crystals were eroded to provide the growth primitive of ZnO nanowires, which formed on top of the rod crystals when the erosion reaction got the equilibrium. The length of the resultant nanowires is rather large because the successive erosion of the rod crystals maintains the low concentration of Zn2O(OH)2n-2 in the aqueous solution.

The formation mechanism and interface structure characterization of in situ AlN/Al composites

The fabrication of AlN/Al composites through nitrogen-bearing gas (NH3) bubbling method into Al melts or Al–Mg melts was once experimentally and analytically studied. The experimental results show that Mg addition greatly enhanced the nitridation rate and volume fraction of AlN. However, a detailed characterization of these changes is still incomplete. This paper presents results of an extensive experimental study and theoretical analysis carried out to investigate the profound effect of the formation of AlN with Mg addition. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy were used to characterize the microstructure. The edge-to-edge matching crystallographic model which applied to the three common crystal structures (body-centered cubic, face-centered cubic, and hexagonal close packed) was used to analyze and investigate this notable phenomenon. The calculation and analysis of theoretical model manifested that AlN is formed by the direct interfacing of pure Al or Al–Mg and NH3 with active nitrogen, instead of forming into the precursor Mg3N2 first and then the precursor transformed to AlN.

Microstructure of Al-5Ti-1B-1RE nanoribbon and its refining efficiency on as-cast A356 alloys

Abstract The novel Al-5Ti-1B-1RE nanoribbons were synthesized by melt-spinning. The microstructure showed that the Al-5Ti-1B-1RE nanoribbon consisted of granular-like TiB2 and core-shell-like TiAl3/Ti2Al20Ce. The Al-5Ti-1B-1RE nanoribbon could give rise to the excellent refining effect on as-cast A356 alloys. The refining efficiency and formation mechanism of Al-5Ti-1B-1RE nanoribbons were investigated. In accordance with the experimental results, it could be seen that the Al-5Ti-1B-1RE nanoribbon could maintain the refining effect after 60 min of holding. Additionally, owing to the addition of Al-5Ti-1B-1RE nanoribbon, the mechanical properties of A356 alloys could be enhanced significantly.

Preparation of nanocrystal modificator and its modification mechanism

Abstract In order to increase the modifying effect, the Cu-P master alloy was rapidly solidified with melt-spin method, and the nano-sized ribbon was gained at 105–106 °C/s. Subsequently, ZL109 alloy was modified by nanocrystal and massive Cu-P master alloy, respectively, with molten metal casting method. The results show that the microscopic structure of ZL109 alloy modified by nanocrystal Cu-P master alloy is better than that modified by massive Cu-P master alloy, the original crystal silicon and eutectic silicon are refined more effectively and the mechanical properties are increased evidently: the tensile-strength is increased by 25%, the elongation is increased by 32.26% and the hardness is increased by 17.2%. Therefore, the melt-spin treatment is a feasible method to improve the modifying effect of Cu-P master alloy.

Fabrication of the Ti5Si3/Ti composite inoculants and its refining mechanism on pure titanium

The in situ Ti5Si3/Ti inoculants were successfully prepared by vacuum arc-melting and melt-spinning method. An efficient route by adding a small quantity of Ti5Si3/Ti inoculants to Ti melt has been first proposed to modify the coarse grains of as cast microstructure of pure titanium in this paper. It was found that the microstructure of ribbon inoculants was cellular structure that composed of Ti5Si3 and α-Ti phases. The grain refining effect of the inoculants was significantly improved with the adding ratio range from 0.2% to 0.5% in weight. With the increase of addition amount of inoculants on Ti melt, the tensile strength, yield strength and microhardness of pure titanium are significantly improved except elongation. The excellent grain refining effect can be attributed to the heterogeneous nucleation of the titanium grain on the precipitated Ti5Si3 phases in the Si-rich regions and the constitutional supercooling of Si in the Si-poverty regions. It is suggested that the in situ Ti5Si3/Ti inoculants is a promising inoculants for titanium alloys.

Ti5Si3/β-Ti nano-core–shell structure toughened glassy Ti alloy matrix biocomposites

In the experiment, Ti75Zr11Si9Fe5 and Ti66Zr11Si15Fe5Mo3 ingots were prepared by vacuum arc-melting furnace. Both Ti alloy ribbons of 3–5 mm in width and about 80 μm in thickness were made from bulk samples by an as-quenched technique under an argon atmosphere. Both melt-spun glassy ribbons exhibit large supercooled liquid regions, high reduced glass transition temperatures, and good thermal stabilities. For both alloys, the stable phases after heating are a Ti glassy matrix and in situ nano-Ti5Si3 particles encircled by nano shell of β-Ti. After the Ti5Si3/β-Ti nano-core–shell structure was in situ formed, in situ Ti5Si3/β-Ti nano-core–shell structure toughened glassy Ti alloy matrix composites were prepared. For the Ti66Zr11Si15Fe5Mo3 ribbons, its high strength is attributed to both Mo solution strengthening and nano core–shell Ti5Si3/β-Ti toughening and dispersion strengthening. Observations and analysis on microstructure and fracture morphology of melt-spun glassy ribbons indicated that multi-slip bands were formed during the tensile test.

Effects of the nanostructured Fe-V-Nb modificators on the microstructure and mechanical properties of Si-Mn steel

The nanostructured Fe-V-Nb master alloy was prepared in vacuum rapid quenching furnace and then was added in the steel melts as modificators before casting. Next, the effects of the nanostructured Fe-V-Nb modificators on the microstructure and mechanical properties of the steel were studied. The results show that the grain size of the steel has been effectively refined, which is mainly because the dispersed nanoscale particles can produce more nucleation sites during the solidification of the liquid steel. Tensile properties and fracture morphology reveal that the yield strength and toughness of the steel modified by nanostructured Fe-V-Nb modificators are better than that of the microalloyed steel. TEM analysis shows that vanadium and niobium in the modificators exist in the form of (V, Nb) C which effectively increases the nucleation rate and leads to better mechanical properties of the steel.

Study of Structure and Magnetic Properties of SmCo10 Alloy Prepared by Different Methods

In this paper, the phase compositions, microstructures, atomic structures, and magnetic properties of Co-rich SmCo10 alloys prepared by arc-melting, annealing, and melt-spinning were studied. It was found that as-cast alloy is composed of Th2Zn17-type Sm2Co17 matrix with an average grain size of ∼45  m accompanied by lamellar eutecticum (consisting of α-Co and Th2Zn17-type Sm2Co17) distributed at grain boundaries. The annealed alloy has the same phase composition and phase distribution as the as-cast alloy except that the average grain size decreases to ∼35  m, and the eutecticum has more homogeneous distribution on the matrix. Simultaneously, the atomic structure of Sm2Co17 is unchanged with only a decrease in structural disorder after annealing. The as-spun ribbons are composed of ∼95.5 vol.% TbCu7-type Sm2Co17 and the rest α-Co. The short rod-shaped α-Co grains are intermittently distributed at the grain boundaries of equiaxed Sm2Co17 grains. The as-spun ribbons show a higher coercivity, and the annealed alloy shows maximum magnetization. The structural parameters were calculated by Extended X-ray Absorption Fine Structure (EXAFS), and the relationship between structure and magnetic properties was discussed in detail.

Effects of adding different types of carbon on the structure and magnetic properties of SmCo6.9Hf0.1 alloy

Abstract In this paper, SmCo 6.9 Hf 0.1 as-cast alloys and ribbons with the addition of either graphite (C) or carbon nanotubes (CNTs) were prepared by arc melting and melt-spinning, respectively. The effects of adding carbon on the structure and magnetic properties SmCo 6.9 Hf 0.1 were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), magnetic force microscopy (MFM) and vibrating sample magnetometer (VSM). It was found that the microstructure and magnetic structure of SmCo 6.9 Hf 0.1 ribbons were changed obviously due to the introduction of C or CNTs, although their crystal structure was characterized as the same Sm(Co,Hf) 7 single phase, no matter carbon was added or not. As a result, the magnetic properties of carbon-contained ribbons were enhanced in a certain degree. This was considered to be related to the refined equiaxed grains, small domain size and the pinning effect of C or CNTs-rich regions. The magnetic properties of SmCo 6.9 Hf 0.1 (CNTs) 0.05 ribbons reached H c =12.5 kOe, M r =57.0 emu/g and M r / M 2 T =0.788.

Carbon fibers coated with graphene reinforced TiAl alloy composite with high strength and toughness

To meet the more rigorous requirement in aerospace industry, recent studies on strengthening and toughening TiAl alloys mostly focus on high Nb addition, which inevitably bring in an increasing of density. In this study, a carbon fibers coated with graphene reinforced TiAl alloy composite was fabricated by powder metallurgy, melt spun and vacuum melting. This composite got remarkable mechanical properties combined with a prominent density reduction. In contrast with pure TiAl ingots, this sample exhibits an average fracture strain from 16% up to 26.27%, and an average strength from 1801 MPa up to 2312 MPa. Thus, we can achieve a new method to fabricate this low-density, good mechanical performance TiAl composite which could bring in more opportunities for application in aerospace industry.