Özge Balcı

Effects of milling parameters on the microstructural and thermal properties of nanocrystalline lanthanum hexaboride powders

This study reports the effects of some milling parameters (duration, ball-to-powder weight ratio (BPR), process control agent (PCA)) on the fabrication of nanocrystalline LaB6 powders via a combined process of mechanochemical synthesis (MCS) and acid leaching, starting from La2O3-B2O3-Mg powder blends. MCS was carried out in a high-energy ball mill (SPEX™ 8000D Mixer/Mill, at 1200xa0rpm) using hardened steel vial and balls under Ar atmosphere. As-synthesized products were leached out with 4xa0M HCl from unwanted MgO phase and probable Fe impurities. When a BPR of 18:1 was used, 5xa0h of MCS and leaching yielded LaB6 powders with an average particle size of 100xa0nm, containing a very small amount of FeB49 phase. Pure LaB6 powders were obtained with an average particle size of 53xa0nm after 12xa0h of MCS of the 0.5xa0wt% PCA added La2O3-B2O3-Mg powder blends with a BPR of 10:1 and after leaching.

Powder Metallurgy of Al-Based Composites Reinforced with Fe-Based Glassy Particles: Effect of Microstructural Modification

ABSTRACT Al metal matrix composites reinforced with high volume fraction of Fe50.1Co35.1Nb7.7B4.3Si2.8 glassy particles were fabricated by mechanical milling followed by hot pressing. Elemental Al powders blended with 60 vol.% of glassy particles were mechanically milled for 1, 5, 10, 15, and 20u2009h, respectively. Selected samples were sintered by uniaxial hot pressing under Ar atmosphere. The changes in the microstructure along with their mechanical properties were investigated. Structural and microstructural characterization followed by microhardness and compression test results of the bulk composite material is reported. The use of high volume fraction of Fe-based glassy particles as reinforcement led to significant hardening of the Al matrix while leading to a remarkable combination of high strength and plasticity.

Synthesis of bulk nanocrystalline HfB2 from HfCl4-NaBH4-Mg ternary system

AbstractThis study reports on the synthesis and consolidation of pure HfB2 powders starting from HfCl4–NaBH4–Mg blends via autoclave processing, annealing and purification followed by pressureless sintering (PS, with 2xa0wt% Co aid) or spark plasma sintering (SPS).n During autoclave reactions conducted at 500xa0°C for 12xa0h under autogenic pressure, excess amounts of NaBH4 were utilized to investigate its effects on the reaction products and mechanism. A subsequent washing (with distilled water), annealing (at 750, 1000 and 1700xa0°C) and acid leaching (HCl) were applied on the as-synthesized products. Pure HfB2 powders with an average particle size of 145xa0nm were obtained after autoclave synthesis in the presence of 200xa0wt% excess NaBH4, washing, annealing at 1000xa0°C for 3xa0h and 6xa0M HCl leaching. SPS sample has higher relative density and microhardness values (94.18% and 20.99 GPa, respectively) than those of PS sample (90.14% and 14.85 GPa). Relative wear resistance was improved considerably (8.2 times) by employing SPS technique.n