In this paper, the Al Mg B14 and Al Mg B14–Ti B2 composites were synthesized by means of mechanical alloying and the field-activated and pressure-assisted synthesis process. The effect of temperature and pressure on the purity and property of products was discussed. The results show that the process of preparing Al Mg B14 bulk materials is optimized as follows: synthesis temperature1,400–1,500 °C, heating rate 100 °C min-1, axial pressure60 MPa, heat preservation 8–10 min, optimum starting powders' ratio Al: Mg: B = 0.1915:0.1363:0.6722, and adding excessive 3 wt% Al. The abrasion resistance of Al Mg B14 composites with varying amounts of Ti B2 was studied using single-point diamond scratch tests with loads ranging from 10 to 100 N in 10 N increments. The scratch width increases almost linearly with the applied load and decreases with Ti B2 proportion increasing up to 70 wt%.With its advantages of fast heating, short reaction time,energy conservation, and high purity, this method offers a new way to synthesize Al Mg B14 and Al Mg B14–Ti B2 composites.
Rare-earth elements（Re） Sc and Y doped Mg2Si thermoelectric materials were made via a field-activated and pressure-assisted synthesis（FAPAS） method at 1023-1073 K,50 MPa for 15 min.The samples created using this method have uniform and compact structures.The average grain size was about 1.5-2μm,the micro-content of Re did not change the matrix morphology.The sample with 2500 ppm Sc obtained the best Seebeck coefficient absolute value,about 1.93 times of that belonging to non-doped Mg2Si at about 408 K.The electric conductivity of the sample doped with 2000 ppm Y becomes 1.69 times of that of pure Mg2Si at 468 K,while the former had a better comprehensive electrical performance.Their thermal conductivity was reduced to 70%and 84% of that of non-doped Mg2Si.Thus,the figure of merit and ZT of these two samples were enhanced visibly,which were 3.3 and 2.4 times of the non-doped samples at 408 K and 468 K,respectively.The maximal ZT belonging to samples doped with 2500 ppm Sc went up to 0.42 at about 498 K,higher than 0.40 of sample doped with 2000 ppm Y at 528 K and 0.25 of non-doped Mg2Si at 678 K,and the samples doped with Sc seemed to get the best thermoelectric performances at lower temperature.
Mechanical alloying (MA) and field-activated, pressure-assisted synthesis (FAPAS) were used for the in situ synthesis and densification of ultra-hard, super-abrasive AlMgB14 metallic ceramic, performed at 1500℃ under a pressure of 60 MPa with the elemental constituents of aluminum, magnesium, and boron. The microstructure and components of synthesized metallic ceramic were observed and determined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that the main components of the samples were AlMgB14 with a few MgAl2O4·MgAl2O4 was derived from the contamination of the preliminary powders and the milling process. The average hardness of the samples that provided the results was 26.1 GPa. The average density of the samples was 2.62 g/cm-3 , which is 98% of its theoretical density. The sample of AlMgB14-TiB2 composite with 30 wt% TiB2 had a hardness of 29.5 GPa, which is consistent with that of AlMgB14-TiB2 composite with 30 wt% TiB2 prepared by mechanical alloying/hot uniaxial pressing. Thus, a new approach was developed using the mechanical alloying and FAPAS process to synthesize AlMgB14 with fast heating, high efficiency, energy saving, and high yield.
