温度诱导的液-液结构转变对Sn-10%Sb合金凝固的影响

Sn-10%Sb合金在856~960℃可以发生温度诱导的液-液结构转变。研究了温度诱导液-液结构转变对Sn-10%Sb合金凝固行为及组织的影响。结果表明,合金熔体经历结构转变后,凝固时所需过冷度增大,并且凝固组织显著细化。

Functions and mechanism of modification elements in eutectic solidification of Al-Si alloys:A brief review

Being used more and more widely in engineering,AlSi alloys comprise about 80%of all kinds of aluminum alloys,which are the most widely utilized nonferrous alloys.Although most Al-Si alloys consist of multiple components,the eutectics in the structure accounts for 50%-90%of the sum volume of such alloys.Therefore,understanding the modification mechanism and function rules of the AlSi eutectic solidification is the technical key in controlling the structures and properties of such casting alloys.The present paper chiefly reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidification of Al-Si alloys.

Enhanced Thermoelectric and Mechanical Properties of n-type Bi2Te2.7Se0.3 Bulk Alloys by Electroless Plating with Cu

Bi2Te2.7Se0.3/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering in order to improve the thermoelectric and mechanical properties of n-type Bi-Te thermoelectric material. After electroless plating, with the increasing of Cu content, Seebeck coefficient keeps increasing and power factor enhances significantly. The highest power factor increases by three times and reaches 23.8 W·cm^-1·K^-2 at room temperature in Bi2Te2.7Se0.3 with 0.22 wt%Cu sample, which means electrical transport properties of Bi2Te2.7Se0.3/Cu samples have been improved.Meanwhile, the ZT values of Bi2Te2.7Se0.3/Cu samples can be enhanced at different temperature zone by adjusting the Cu content. Bi2Te2.7Se0.3 with 0.05 wt% Cu sample has the best thermoelectric properties in high temperature zone, and the ZT peak value increases from 0.35 to 0.85 at 623 K. When the Cu content increases to 0.15 wt%,the ZT peak value moves to the low temperature(373 K) and increases from 0.24 to 0.71. At the same time, the mechanical properties increases with the increasing of Cu content.

Temperature-induced liquid state change and its effects on solidification of thermoelectric alloy Bi_(0.3)Sb_(1.7)Te_3

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.

Effects of Electroless Plating with Cu Content on Thermoelectric and Mechanical Properties of p-type Bi0.5Sb1.5Te3 Bulk Alloys

Bi_（0.5）Sb_（1.5）Te_3/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering. After electroless plating, with increasing the Cu content, the electrical conductivity keeps enhancing significantly. The highest electrical conductivity reaches 3341 S/cm at room temperature in Bi0.5Sb1.5Te3 with 0.67 wt% Cu bulk sample. Moreover, the lowest lattice thermal conductivity reaches 0.32 W/m·K at 572.2 K in Bi0.5Sb1.5Te3 with 0.67 wt% Cu bulk sample, which is caused by the scattering of the rich-copper particles with different dimensions and massive grain boundaries. According to the results, the ZT values of all Bi0.5Sb1.5Te3/Cu bulk samples have improved in a high temperature range. In Bi0.5Sb1.5Te3 with 0.15 wt% Cu bulk sample, the highest ZT value at 573.4 K is 0.81. When the Cu content increases to 0.67 wt%, the highest ZT value reaches 0.85 at 622.2 K. Meanwhile, the microhardness increases with increasing the Cu content.

Influence of impact energy on work hardening ability of austenitic manganese steel and its mechanism

To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed under different impact energies. The work hardening mechanism was also analyzed. The results show that the best strain hardening effect could be received only when the impact energy reaches or exceeds the critical impact energy. The microstructural observations reveal that dislocations, stacking faults and twins increase with raising impact energy of the tested specimens. The hardening mechanism changes at different hardening degrees. It is mainly dislocation and slip hardening below the critical impact energy, but it changes to the twinning hardening mechanism when the impact energy is above the critical impact energy.

Low-frequency Internal Friction Behaviour of Zr55Al10Ni5Cu30 Metallic Glass with Different Quenching Temperatures

The correlation between the internal friction behaviour of Zr55 Al10 Ni5 Cu30 BMG samples and their quenching temperatures was investigated. It was found that, below the glass transition temperature, the activation energy decreased with increasing quenching temperature, but in the surpercooled liquid region the activation energy tended to be enhanced with a further increase in the quenching temperature. Besides, there were both anelastic and viscoelastic relaxation for the amorphous alloys. The anelastic behaviour would change into viscoelastic relaxation easily for the samples prepared at higher temperature.

The effect of melt overheating on the melt structure transition and solidified structures of Sn-Bi40 alloy

Evolution of the electrical resistivity of Sn-40wt%Bi melt with time under different overheating temperatures during isothermal experiments has been studied, and the relationship between different melt state, solidification behavior and solidified structure has also been investigated. The results show that the melt structure transition revealed by the abnormal change of resistivity would take place within a certain holding time just when the holding temperature is above a certain critical, and that the higher the temperature above the critical, the shorter the "incubation period" of the melt structure transition, and the faster the transition speed. The results of solidification experiments suggest that the melt structure transition caused by different holding time at the same temperature can lead to a higher so-lidification undercooling degree, finer grain size and change of microscopic pattern. Further exploration indicates that the solidification undercooling degree can come to a head when the melt is held at the specific temperature for a given time. The functionary mechanism of the phenomena above is also discussed briefly.