Jun Luo
,
Hong Yan
,
Nan Zheng
,
Rong-Shi Chen
金属学报(英文版)
doi:10.1007/s40195-016-0378-1
Four kinds of Mg alloys with different Zn and Ca concentration were selected to analyze the effect of Zn and Ca concentration on the microstructure and the mechanical properties of Mg-Zn-Ca alloys. It was found that Zn and Ca concentration has a great influence on the volume fraction, the morphology and the size of second phase. The Mg-1.95Zn-0.75Ca (wt%) alloy with the highest volume fraction, continuous network and largest size of Ca2Mg6Zn3 phase showed the lowest elongation to failure of about 7%, while the Mg-0.73Zn-0.12Ca (wt%) alloy with the lowest volume fraction and smallest size of Ca2Mg6Zn3 phase showed the highest elongation to failure of about 37%. It was suggested that uniform elongations of the Mg-Zn-Ca alloys were sensitive to the volume fraction of the Ca2Mg6Zn3 phases, especially the network Ca2Mg6Zn3 phases; post-uniform elongations were dependent on the size of the Ca2Mg6Zn3 phase, especially the size of network Ca2Mg6Zn3 phase. Reduction in Zn and Ca concentration was an effective way to improve the room-temperature ductility of weak textured Mg-Zn-Ca alloys.
关键词:
Mg-Zn-Ca
,
alloys
,
Ductility
,
Hot
,
rolling
,
Texture
,
Second
,
phase
Materials Letters
The coarsening of gamma' precipitate in Fe-Ni-Co based alloys with different contents of P (Mn) was investigated by TEM. For both experimental alloys, the growth kinetics of gamma' particles were in good accordance with the prediction of the Lifshitz-Wagner theory of diffusion-controlled coarsening with the exception of a little larger cut off value in the histograms of the gamma' precipitate. Compared with the usual alloy, the alloy with a lower content of P (Mn) showed that the gamma' particles exhibited a lower growth rate, and the density and size distribution of the precipitate were found to be more homogeneous.
关键词:
alloys
Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
The microstructural, tensile, and stress-rupture lives of conventionally and directionally solidified (DS) cast specimens of a nickel-based superalloy have been investigated using materials of normal commercial composition and two melts with additions of 22 and 30 ppm nitrogen. It was found that the ductility, tensile life, and stress-rupture life of the conventional castings dramatically decreased with the increase of nitrogen content, but, in the longitudinal direction of DS samples, these properties were independent of nitrogen within the contents studied. The transverse tensile rupture life of DS castings had no significant change with nitrogen, except for some decrease in elongation of the sample containing 30 ppm N. The stress-rupture life and elongation in the transverse direction of the DS samples were improved at the 22 ppm nitrogen level, which might be attributed to the dendrite refining. Increasing the nitrogen content resulted in a change in carbide morphology from that of a "Chinese script" to a blocky form and a change in microporosity formation, especially in the conventional castings. The increased nitrogen content resulted in a significant reduction in the volume fraction of eutectic microconstituents and the in dendrite refinement in DS samples, but nitrogen content did not affect the morphology of gamma' precipitates in the heat-treated alloys.
关键词:
alloys
材料科学技术（英文）
Positron annihilation behaviors have been studied in the single phase Nd2Fe14B magnet and the nanocomposite Nd2Fe14B/alpha -Fe magnet, prepared by melt spinning. The results showed that the number of vacancy-cluster at grain boundaries increases with increasing annealing temperature for the both types of magnets. The increase of this kind of defect can improve the coercivity of the single-phase magnet. Conversely, the increase of vacancy-cluster amount leads to decreasing of the coercivity for the nanocomposite magnet. It implies that the mechanism of dominant magnetic hardening for the two types of magnets is different, and the domain walls pinning mechanism in the single-phase magnet and the reversal magnetization nucleation mechanism in the nanocomposite magnet operate, respectively.
关键词:
alloys
Materials Letters
A new technique for specimen preparation of metal or ceramic powders for transmission electron microscopy (TEM) is presented. The powders were dispersed into ductile metal powders such as Al or Cu etc., which easily agglomerate to fragments or balls when submitted to ball milling. Specimens are then easily obtained from these agglomerates using conventional TEM specimen preparation methods. The procedure was shown to be a versatile means of obtaining accurate and representative specimens of powders for TEM.
关键词:
alloys
Journal of Materials Science
An investigation was carried out on the fabrication of carbon fibre-reinforced aluminium matrix composites with hybridization of particulates or whiskers of silicon carbide by pressure casting. A small amount of particulates or whiskers was uniformly distributed among carbon fibres and the preforms prepared from the treated fibres were directly infiltrated by molten aluminium under applied stress. It was found that the longitudinal tensile strengths of hybrid composites were greatly improved, although their fibre volume fractions were very low compared to those of conventional composites. With this hybridization method, it is also practical to tailor the fibre volume fraction of composites from 60 to 25 vol %, which is not possible in direct infiltration of fibre preforms by pressure casting. The results obtained lead to the conclusion that particulate or whisker additions act not directly as reinforcements but as promoters to improve the infiltration performances of fibre preforms, and consequently to increase the strength-transfer efficiency of carbon fibres. The addition of particulates or whiskers can also improve other properties of the composites, such as hardness and wear resistance.
关键词:
alloys
Journal of Applied Physics
Y2Fe14B0.5C0.5 has the same tetragonal structure as Y2Fe14B with space group P4(2)/mnm. Magnetic properties of the Y2Fe14B0.5C0.5 compound have been studied using an extraction magnetometer with a maximum field of 6 T, in the temperature range from 1.5 to 300 K. By means of fitting the hard magnetization curves, the magnetocrystalline anisotropy constants K1, K2, and K3 were determined. It was found that although the magnetocrystalline anisotropy field (mu-0H-a) increases abnormally with increasing temperature as in the case of Y2Fe14B, the dependence of anisotropy constants on temperature is quite different from that of Y2Fe14B. K1 and K3 decrease slightly with increasing temperature. K2 increases abnormally with increasing temperature, which contributes to the abnormal dependence of anisotropy field on temperature. In addition, the substitution of carbon for boron leads to a reduction of 3d-3d interaction and spontaneous magnetization. In contrast, uniaxial anisotropy is increased by the addition of carbon below room temperature.
关键词:
alloys
Philosophical Magazine Letters
The glass transition behaviour of the four metallic glasses La55Al25Ni20, Zn65Mg35, and Nd60Fe30Al10 and Zr30Y30Al15Ni25 has been studied by temperature-modulated differential scanning calorimetry (MDSC). It is clearly demonstrated that the glass transition can be separated from crystallization by MDSC. Two glass transitions have been observed for Zn65Mg35, Nd60Fe30Al10 and Zr30Y30Al15Ni25. Owing to the clearer observation of the glass transition, calculation of the reduced glass temperatures T-rg (glass transition temperature divided by the melting point) can now be made with greater confidence.
关键词:
alloys
Nanostructured Materials
This paper presents new results of an investigation of a commercial rapidly quenched Nd4.5Fe77B18.5 alloy that was studied previously. The enhanced remanence Jr = 13.2 KGs and high product energy (BH)max = 16.2 MGOe are shown to be due to ultrafine grain. The microstructure, consisting of no alpha-Fe that results in optimum magnetic properties, occurs in the amorphous Nd4.5Fe77B18.5 alloy after crystallization. The coexistence of Fe3B, Nd2Fe14B and residual amorphous phase play dominant roles in the achievement of the hard magnetic properties, and hence, the amorphous phase seems to act as an effective magnetic exchange-coupled medium.
关键词:
alloys
