Junling Gao

Size effects on the compressive deformation behaviour of a brittle Fe-based bulk metallic glass

The mechanical behaviour of brittle Fe-based bulk metallic glass (BMG) samples with different diameters and aspect ratios (ARs) has been investigated. For samples with an AR of 2, the fracture strength increases with a decrease in the sample diameter which can be well-explained by the Weibull analysis with a Weibull modulus of 34. For samples with a fixed diameter of 2 mm, a transition between three deformation modes, i.e. fragmentation, distensile cracking and confined shearing was observed as the AR was decreased. When the AR is below 0.19, large friction between the platen and specimen end suppresses the distensile cracking and prompts shear deformation, resulting in multiple shear bands and large compressive plasticity. Our analysis indicates that the deformation mode of brittle BMGs strongly depends on the applied stress conditions and can exhibit ductile characteristics under constraints. The present findings are important for engineering applications of brittle BMGs in which various geometries will be used.

Formation, Crystallization Behavior, and Soft Magnetic Properties of FeCSiBP Bulk Metallic Glass Fabricated Using Industrial Raw Materials

Formation of pseudo-binary Fe-C-Si-B-P bulk metallic glasses (BMGs) with good glass-forming ability (GFA) and soft magnetic properties prepared using industrial pig-iron and P-Fe alloys as raw materials was investigated. It was found that the GFA could be enhanced by tuning the content of carbon, and fully glassy rods with a maximum diameter of 2xa0mm were obtained in the Fe77.3C5.9Si3.3B4.8P8.7 alloy. The crystallization behavior and its effects on the soft magnetic properties of the Fe77.3C5.9Si3.3B4.8P8.7 alloy were analyzed. The superior magnetic properties, coupled with large GFA and low cost of raw materials, make the current Fe-based BMGs promising for potential applications in electric industries.

Effects of Cooling Rates on Glass Formation and Magnetic Behavior for the Fe73.0C7.0Si3.3B5.0P8.7Mo3.0 Bulk Metallic Glass

In this paper, effects of cooling rates on glass formation and magnetic behavior of the Fe73.0C7.0Si3.3B5.0P8.7Mo3.0 (at. pct) alloy were investigated via different purging gases (i.e., helium and argon) during suction casting. X-ray diffraction patterns and transmission electron microscopy characterization confirmed that the maximum attainable diameter for glass formation is increased from 5 to 7xa0mm with the helium as the purging gas, relative to the argon. Meanwhile, the coercivity value (Hc) of the sample cast in helium is almost 5 times larger than that fabricated in argon, although the magnetization saturation in these two alloys is similar. Our pair distribution function analysis, density, and positron annihilation lifetime spectroscopy measurements indicated that the sample cast in helium possesses more free volume; however, the difference between them is insubstantial. Further, experimental results revealed that the residual stress in the samples cast under helium is much larger than that in those prepared in Argon, which could be responsible for the abrupt change in the coercivity.

Thermoelectric Properties of Mn1+xTe-Based Compounds Densified Using High-Pressure Sintering

In this paper, powder metallurgy technology combined with high-pressure sintering (HPS) were used to fabricate Mn1+xTe (xxa0=xa0−0.02, 0, 0.04) alloys at 743xa0K. The products of synthesis were identified by x-ray diffraction; microstructures were examined by field-emission scanning electron microscopy (FE-SEM); the electrical conductivity and the Seebeck coefficient were measured in the temperature range of 300–800xa0K. The results show that all HPS samples consisted of nanoparticles. Mn1+xTe (xxa0=xa0−0.02, 0, 0.04) thermoelectric materials with a high Seebeck coefficient and low electrical conductivity have potential to warrant further study in the future. The peak figure of the merit, ZT, reaches 0.59 for Mn0.98Te at 773xa0K.

Thermoelectric performance of n-type (PbTe) 1− x (CoTe) x composite prepared by high pressure sintering method

Composites of nominal composition (PbTe)1−x(CoTe)x (xu2009=u20090–0.18) were fabricated by high pressure (6xa0GPa) sintering (773xa0K) method. The thermoelectric performances were investigated in the temperature range of 293–773xa0K. The experimental results show that CoTe utilized as the secondary phase can remarkably enhance the TE properties of PbTe, of which the highest ZT value reaches 0.88xa0at 473xa0K when xu2009=u20090.14. The enhancement of TE performance owes much to its high electric conductivity of CoTe. Meanwhile, the high pressure sintering (HPS) samples consist of nanoparticle, which significantly enhances the boundary scattering on carriers, decreases thermal conductivity, and increases Seebeck coefficient. All the results indicate that HPS method and the addition of CoTe-composite are effective methods to enhance the thermoelectric performance of PbTe as a potential TE material.

Recent advances in inorganic material thermoelectrics

Thermoelectrics is a research area that focuses on the development of high-performance materials for direct thermal and electrical energy conversion in power generation and solid-state cooling. Ever since Ioffes inference in 1950s that heavily doped semiconductors make the best thermoelectrics, inorganic semiconductors and semimetals have remained the cornerstone of high-performance thermoelectric materials. In this article, we review the recent advances in inorganic material thermoelectrics with special emphases on: (i) the complementary local-global view of material and the roles of configurational entropy and Fermi surface complexity in material screening; (ii) the emerging schemes of resonant bonding, dynamic disorder, “gap” engineering, pudding-mold-shaped bands in material performance enhancement; (iii) a list of promising bulk materials, such as host–guest structures, half-Heusler compounds, silicides, Zintl phases, and incommensurate structures; and (iv) state-of-the-art materials synthesis and fabrication techniques. These advances will facilitate the development of next-generation bulk thermoelectric materials.