Bian Xiufang

Pre-peak in the structure factor of liquid Al-Fe alloy

Based on the study of the positions and heights of the pre-peaks on the structure factors of liquid Al-Fe alloys, it is found that the heights are higher in the region on the phase diagram where nearly all the intermetallic compounds with higher melting temperature gather, and the highest at ; while the positions are smaller, and a minimum at . These results reveal the close relationship between the liquid structure and the Al-Fe alloy phase diagram. Two types of atomic configuration are constructed, and the origin of the pre-peaks is found to be the Fe-Fe correlation or the Al-Al correlation, or their mixture at different compositions.

Origin of the prepeak in the structure factors of liquid and amorphous Al-Fe-Ce alloys

Distinct prepeaks have been found in the structure factors of the liquid and amorphous Al-Fe-Ce alloys. The structural size of the chemical short-range order corresponding to the prepeak in the liquid alloy increases with decreasing temperature, and, after glass forming, the structural size is much bigger, and the amount of the structure corresponding to the prepeak increases with decreasing quenching temperature, but the structural unit size remains constant. The position of the prepeak shifts to smaller Q-values as the concentration of Ce increases. The addition of Ce can improve the interaction between atoms, so it is favourable to Al-based glass formability. The structural unit corresponding to the prepeak is an icosahedral quasicrystalline structure with Fe as the interstitial atom, and the prepeak is diffraction peak broadening caused by fairly fine (about 0.5-2.0 nm) icosahedral clusters.

Structural studies of clusters in melt of FeAl compound

By means of constant pressure molecular dynamics simulation technique, a series of simulations of the Fe50Al50 alloy have been carried out. The atoms interact via semi-empirical n-body noncentral potential. The pair correlation functions and the pair analysis technique is applied to reveal the cluster evolution in the process of quick solidification. By using the bond orientation order parameters, we have measured both local and extended orientation symmetries for computer-generated models of dense liquid and glass. A lot of polyhedra in liquid systems, e.g., icosahedra, are also obtained. In order to test the reliance of the computational results, corresponding x-ray diffraction experiments have been performed on the material.

Computation of liquid Cu70Ni30 alloy structure using EAM in rapid cooling and heating process

A series of simulations of the glass transition of Cu70Ni30 alloy have been carried out based on the molecular dynamics simulation technique under constant temperature and constant pressure. Atoms interact via semi-empirical many-body potential EAM. The pair correlation function, pair analysis technique and bond orientation order parameters are used to reveal the structural features of Cu70Ni30 alloy in a state of liquid, super cooled liquid and glass as well as structural evolution in the process of the rapid solidification. In the quick heating of the amorphous metal obtained by the quick cooling method, the ordering degree of the system is kept, to some extent, to the next stage.

Function of modification and refinement of rapidly solidified master alloy Al—Ti—Sr

The function of modification and refinement of a master alloy Al—Ti—Sr solidified at cooling rates of 10 K s-1 or less and 103 K s-1 or greater for a hypoeutectic Al–10 wt% Si alloy has been studied. The master alloy Al–Ti–Sr solidified at a cooling rate of 103 K s-1 or greater presents a more marked function of modification and refinement than that solidified at a cooling rate of 10 K s-1 or less, both under the casting condition of a sand mould and a permanent mould. The addition amount of the master alloy is reduced by rapid solidification technology, keeping the same degree of modification and refinement.

Molecular dynamics computation of the liquid structure of Fe50Al50 alloy

Abstract In this paper, a series of simulations of the Fe 50 Al 50 alloy have been carried out on the basis of the molecular dynamics simulation technique under constant-temperature, constant-pressure. The semi-empirical n-body non-central potential is used to describe the interaction between atoms. The three kinds of pair correlation functions and total pair correlation function are calculated to reveal the cluster evolution in the process of quick solidification. The pair analysis technique is adopted to check how the clusters in liquid metal change in the rapid cooling conditions. The four index parameters, i , j , l , m are used to distinguish the type of clusters in liquid. We measured both local and extended orientation symmetries for computer-generated models of dense liquid and glass by using the bond orientation order parameters. A lot of polyhedra in liquid systems such as icosahedron are obtained. In order to test reliance of the computation results, the corresponding experiments have also been performed on the material by the X-ray diffraction experiment.

Influence of dislocation structure on two-way shape memory effect in a CuZnAlMnNi alloy

Repeated rounds of “training-aging” treatment is a new technology to improve the two-way shape memory effect (TWSME) and the stability of Cu-based shape memory alloy (SMA), during which the influence of dislocation structure on TWSME has been studied by transmission electron microscopy (TEM). It is found that different dislocation structures produce a different influence on TWSME. Disorderly distributing dislocations promote the pseudo-stabilization of the parent phase, which decreases the amount of parent phase participating in the transformation and finally results in TWSME degradation during aging, but the stabilization can be eliminated through re-training. The stable dislocation arrays distributing orderly contribute to improving TWSME and obtaining stable TWSME. Compared with NiTi-based SMAs, Cu-based SMAs have many advantages, such as low cost, simple processing, excellent electric and thermal conductivity, which are favorable to their wide use. The application of Cu-based SMAs is generally associated with the TWSME achieved by thermomechanical training. It is known that dislocations will be produced when an SMA sample is subjected to training under applied stress. Many researchers have studied the effect of dislocations on TWSME [1–12], but there is controversy. Some of the researchers believed that the formation of preferential thermoelastic martensite was the origin of the TWSME, and that the preferential dislocations and retained martensite generated during training were favorable to the formation of preferential martensite variants [1–6]. The others regarded the dislocations introduced during the training process as the origin of the TWSME, and the arrays of dislocation and residual stress would favor the nucleation and growth of some preferential martensite variants, and thus resulted in TWSME [7–12]. In spite of a large amount of literature on Cu-based SMAs, the application of the alloys is much less than that of NiTi-based alloys, because of the instability of SME and transformation temperatures during practical applications [13]. The degradation of TWSME in Cubased SMAs during aging at different temperatures was associated with two mechanisms, first, with the annihilation of dislocations and next, with the precipitation of an α phase [11, 14, 15]. The degradation of TWSME during thermal cycling was reported to be caused by the increment of dislocation and martensite stabilization [16–18]. So far, the problem of the instability of Cu-based SMAs has not been solved satisfactorily. However, on the basis of repeated experiments, we found [19] that repeated rounds of “training-aging” treatment evidently improved the TWSME and the stability of Cubased SMAs. The stable shape recovery rate reached 99.7% or so after four rounds of “training-aging” treatment. We also found that different dislocation structures will produce a different influence on TWSME of a CuZnAlMnNi SMA, as will be reported below. The alloy used in this paper was prepared from 99.99% Cu, 99.95% Zn, 99.7% Al, 99.9% Mn and 99.5% Ni by melting using a graphite crucible in an induction furnace. The ingot was homogenized at 850 ◦C for 12 h and then hot-rolled into sheets with thickness about 1 mm. The strip samples cut from the sheets which were of the size of 200× 4× 1 mm, were solution-treated at 840 ◦C for 20 min, quenched into boiling water for 30 min and then cooled to ambient temperature in normal atmosphere. The transformation temperatures of the alloy with composition Cu-23.6Zn4.47Al-0.23Mn-0.17Ni (in mass %) were as follows: Ms= 20 ◦C, Mf= 1 ◦C, As= 27 ◦C, Af= 42 ◦C. The sample was uniformly fixed by bending up into a “U” shape on a mound with a diameter of 78 mm, and conducted thermal cycling between boiling water and 18 ◦C water. When the shape memory amount of the sample no longer changed with the number of training cycles, the first round of training was ended. The sample was then placed into boiling water for 8 h, and thus completed the first round of “training-aging” treatment. Subsequently, the as-aged sample was subjected to the second round of training until the stable shape memory amount was achieved again, and then the sample was placed, without any constraint, into boiling water for 8 h, which finished the second round of “trainingaging” treatment. The process, as above stated, was repeated. This repeated treatment process, conducting alternate training and aging, was called the “trainingaging” treatment. This is a new technology for improving the SME and its stability of Cu-based SMAs as reported in our previous paper [19]. The variation of dislocation structures during the treatment was observed on an H800 transmission electron microscope, and specimens were jet-polished with 33.3% nitric acid and 66.7% methanol solution. As can be seen from Fig. 1a there appear a large number of dislocations after the first round of training, because the training process itself is a thermal cycling process under applied stress during which the dislocations multiply with increase in the number of training cycles [18]. The dislocations which are distributing

An important factor powerfully influencing the Al-Ni-based alloys' glass-forming ability

In order to get better glass-forming abilities (GFAs), Ni atoms are partially replaced by Cu and Co atoms in Al84Ni12Zr4 alloys. Thermal analysis shows that the reduced crystallization temperature Trx has no direct correlation with the GFA of the alloys. However, it is notable that prepeaks have been found in the total structure factors of the amorphous Al84Ni(12−x)Zr4Cux and Al84Ni(12−x)Zr4Cox alloys. In addition, the results prove that the intensity of the prepeaks influences the GFA powerfully. The amorphous alloys with larger intensity of the prepeak show better GFA. The influence of prepeaks on the GFA can be explained by the atomic configuration difference among the liquid, crystal and glass states.

THE EFFECT OF MAGNESIUM ON THE ANTIMONY MODIFICATION OF AL-SI

In an investigation into the effect of effectof magnesium on the antimony modification of Al−11.8Si eutectic alloy, it was found that the finer-lamella eutectic silicon in Al−11.8Si modified with 0.2% antimony became a shorter, granulated rod form with a 0.2–0.6 percent increase in magnesium. The tensile strengthand elongation of the alloy increased by 8.5 percent and 69 percetn, respectively.