The behaviors of electrical resistivity vs temperature(ρ-T) of the molten p-type thermoelectric alloy Bi0.3Sb1.7Te3(at.%) were explored in heating and cooling processes. An obvious hump appeared on the ρ-T curve from 932 ℃ to 1,020 ℃ at the heating process, while the curve became smooth in the following cooling, which suggests an irreversible temperature-induced liquid-liquid structure transition(TI-LLST) occurred in the liquid alloy. Based on this judgment, solidification experiments were carried out to find out the effects of the different liquid states. It was verified that, for the melt experiencing the presumed TI-LLST, both the nucleation and growth undercooling degrees were elevated and the solidification time was remarkably prolonged. On the other hand, the configuration of Bi0.3Sb1.7Te3 phase was refined, and its preferential orientation was weakened.
TiC_x contained Al–Ti–C is a kind of grain refiner for Al alloys. In this work, the influence of C/Ti stoichiometry, i.e. the x value in TiC_x on grain refinement efficiency was investigated. TiC_x particles have been obtained in five Al–5Ti–m C(m = 0.1, 0.5, 0.8, 1, 1.25) master alloys and the x values were measured to be0.72, 0.75, 0.79, 0.81 and 0.8, respectively. It was found that the refinement performance of the master alloys had a close relationship with the x value of TiC_x . The Al–5Ti–m C alloy with lower-x TiC_x shows better refinement efficiency and anti-fading capability. It is supposed that TiC_x particles with lower x are more preferred to release Ti atoms during nucleating process and have a better Ti-absorbing capability.This contributes to the Ti-rich zone formation at TiC_x /melt interface, thus enhancing the refinement and anti-fading capability.
Huabing YangTong GaoHaichao WangJinfeng NieXiangfa Liu
A new method has been proposed to prepare Mg-Al-Si master alloys by utilizing scrap Al-Si-Fe alloys with higher Fe levels,which aims to segregate Fe from Al-Si-Fe alloys by Mg melt.The segregation behaviors,microstructure morphology and evolution mechanism of iron-rich phases in Mg-Al-Si alloy melts were studied,after Al-14Si-4Fe(wt%) alloys were added and dissolved completely.In the Mg-Al-Si alloys,iron has very little solubility and tends to combine with other elements to form intermetallic phases,which grow into a deposition layer due to the higher density.During the cooling and solidifying process of Mg-Al-Si melts,the needle-like Al5 SiFe phase in Al-14Si-4Fe alloy evolved into blocky Al_5Fe_2 and Al_(0.7)Fe_3Si_(0.3) phases.Besides,the Fe levels of the Mg-Al-Si master alloys were reduced to 0.017 wt%from nominal content of 0.164 wt%.Based on the above results,this work carried out a semi-quantitative phasecompositions analysis for the deposition layer by relative intensity ratio(RIR) method,and evolution mechanism of the iron-rich phases had also been discussed.This study has paved a new way to regenerate the scrap Al-Si-Fe alloys,which has a great significance of promoting the recycling of aluminum resources.
The structures and compositions of Ti and Zr rich phases in ternary Al-Ti-Zr and quaternary Al-Si-Ti-Zr systems were investigated by energy dispersive spectroscopy and X-ray diffraction.The additions of Ti and Zr were changed.It was found that Ti and Zr can replace each other in the Ti and Zr rich phases of Al-(Si-)Ti-Zr alloys.Compositions of the phases have been measured as a function of Ti and Zr additions.The content of Ti(Zr) in the phases increases with its addition in the alloys.Besides,the increase of Ti content can result in a decrease of lattice parameters.Microhardness of the phases in Al-18Si-xTi-/Zr alloys changes with composition evolution.Moreover,the microhardness is higher than that of the intermetallics of ternary Al-Si-Ti and Al-Si-Zr alloys,due to the distortion of crystal structure caused by the replacement of Ti and Zr.
The effect of compression on the crystallization behavior and corrosion resistance of Al(86)Ni9La5 amorphous ribbons was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning elec-tron microscopy (SEM) and electrochemistry test. The XRD and TEM results reveal that the compressed Al(86)Ni9La5 ribbons spun with the circumferential speed (R) of 29.3 m/s are in fully amorphous state; however, the compressed ribbons spun with R=14.7 m/s have crystalline phases embedded in the amorphous matrix. The SEM images indicate that after compression, the toughness of the ribbons increases. Electrochemical results show that the compression decreases the stability of the passive film of the Al(86)Ni9La5 amorphous ribbons, because of the compression-introduced free volume, shear bands and crystalline phases; meanwhile, with R=14.7 m/s, the compression-induced crystalline phases in the Al(86)Ni9La5 ribbons increase the corrosion potential.
The corrosion-induced crystallization of Al94 exNixGd6(x=6 and 10, in at.%) metallic glasses as well as phase separation, oxidation and cracking in good conductivity solution has been investigated by various techniques.The transmission electronic microscopy(TEM) result reveals that crystalline intermetallics and oxides present on the electrochemically thinned hole edge, and the phase separation occurs in the matrix of the as-spun ribbons with the circumferential speed Rcof 29.3 m/s. In addition, the bending and cracking of the samples occur after corrosion. The influence of Ni content on the phase separation, bending and cracking can be explained by the fact that the percolation of the backbone clusters in the amorphous alloy melts and glasses is enhanced by increasing the composition of Ni.
Yonggang WangYan LiuYingjie LiBang AnGuanghui CaoShifeng JinYimin SunWeimin Wang
