Coarse Grain Growth Research Articles

Effect of sodium addition on structural and magnetic properties of solid state processed SrFe12−xAlxO19 (x ≤ 4)

Aluminum-substituted M-type strontium hexaferrite (SrM-Al, SrFe12−xAlxO19, 0 ≤ x ≤ 4) with uniform microstructure and excellent magnetic properties was synthesized by conventional ceramic processing based on solid state reaction. Coercive field was highly enhanced by heavy doping with Al3+ although magnetization was significantly reduced. However, formation of coarse microstructure and poor development of Hc with low level doping of Al3+ disturbed practical application. To promote phase formation and to suppress growth of coarse grains which were induced by incorporation of Al3+ ions, SrM-Al ceramics was processed with NaOH. Such Na-assisted processing of SrM-Al reduced formation of non-magnetic phases and assisted development of uniform fine grains. In addition, the large residual strain by Al3+ doping was partially relieved by the same approach. As a result, saturation magnetization of SrFe12−xAlxO19 was remarkably enhanced and the BHmax of randomly oriented hard magnetic ceramics was improved to 1.23MGOe by concomitant addition of Na and Al ions.

Effects of Extrusion Process on Microstructure of Aluminum Profiles with Different Wall Thickness Sections

The material undergoes the different deformation stage and the changing history of strain-rate and temperature affects the microstructure evolution during extrusion process. To understand the effect of extrusion process on microstructure evolution, the microstructures of aluminum profile with different wall thickness sections are compared and the variety of strain-rate and temperature are analyzed. The result show that the larger increasing gradient of strain-rate leads to the incomplete recrystallization process in thin wall section during the pocket die stage. The coarse grains are developed by second recrystallization because of the violent strain-rate changes, which is caused by the entrance of bearing-land. The lasting time of high strain-rate and temperature decided the growth of coarse grains, which is affected by bearing-land length.

Study on growth of coarse grains of diamond with high quality under HPHT

The growth of coarse grains of diamond was observed with graphite as carbon source and Fe80Ni20 alloy powder as catalyst at HPHT in a China-type SPD 6×1670T cubic high-pressure apparatus with highly exact control system. To synthesize coarse grains of diamond crystal with high quality, advanced indirect heat assembly, powder catalyst technology and catalyst with optimal granularity were used. Especially the nucleation of diamond and the growth rate were strictly controlled by the optimized synthesis craft. At last, diamond crystals (about 0.85 mm) in the perfect hex-octahedron shape were successfully synthesized at ∼5.4 GPa and ∼1360. in 60 min. The characteristic of crystal growth with powder catalyst technology under HPHT was discussed. The results and techniques might be useful for production of coarse grains of diamond.