Effect of Mechanical Milling and Cold Pressing on Co Powder

Abstract

Cold pressing (CP) of the amorphous-like Co powder suppressed most of the XRD peaks, in particular the peak along (100) plane. The DSC curve of unmilled CP Co powder has shown a distinct sharp exothermic peak at615C°. Upon annealing at700C°, only the FCC phase with lattice parameter of 3.51 Å was detected by XRD. Our results implied that the exotherm at615C°corresponds to compaction-pressure-assisted HCP to FCC first-order phase transition. The XRD analysis of 30 h milled powder revealed for the first time the FCC phase witha=3.80 Å. However, due to presence of (100) and (210) peaks, this phase is thought to be FCT with lattice parametersa=b=3.80andc=3.07 Å. Consequently, the high-energy milling carried out in the current work induced for the first time HCP to FCT transition in Co. Upon CP of milled powder, the lattice parameterashrunk from 3.80 to 3.75 Å. However, during annealing of the CP milled Co powder at750C°, the FCT to FCC transition occurred, yielding the FCC phase witha=3.51 Å.

Cold-pressing and vacuum arc melting of γ-TiAl based alloys

“…It has been shown in this current study that incorporating uniaxial cold pressing for particle bonding with the precursor metallic powder, made the fabrication of the c-TiAl based alloys successfull via vacuum arc melting with minimum Al-vaporization. It has been noted that cold pressing of powder can influence the properties of elemental prior to melting [27].…”

Matrix Structure Evolution and Nanoreinforcement Distribution in Mechanically Milled and Spark Plasma Sintered Al-SiC Nanocomposites

“…On the one hand, the use of powder metallurgy processing techniques such as ball milling, mechanical milling/alloying [ 12 ] resulted in the synthesis of nanocomposite powders [ 13 ] with uniform distribution of the nano-size reinforcement. Moreover, it enabled the production of nanostructured matrices such as copper [ 14 , 15 , 16 ], nickel [ 15 ], tungsten [ 17 ], cobalt [ 18 ], magnesium [ 19 ], Al-Mg [ 20 ], and aluminum [ 21 , 22 ]. On the other hand, the use of novel consolidation techniques such as spark plasma sintering (SPS) [ 7 , 23 ], also known as field assisted sintering (FAST), permitted sintering nanocomposites to full density with preserved nanostructure features of the matrix because of the high heating rates, short sintering cycles, and low sintering temperatures associated with the process [ 24 , 25 , 26 , 27 ].…”

CONFIGURATION OF Co PHASE AND MAGNETORESISTANCE PROPERTIES IN HIGH ENERGYMILLED Co-CGRANULAR COMPOUNDS

“…Co secara alamiah memiliki struktur alotropi, yakni fasa Hexagonal Closed Packed (HCP) pada suhu ruang dan fasa Face Centered Cubic (FCC) pada suhu T 695 K. Namun demikian fasa Co-FCC dapat juga diketemukan pada suhu ruang ketika Co memiliki ukuran kristalit yang sangat halus. Fasa Co-HCP berubah menjadi Co-FCC dengan proses penggerusan menggunakan Milling energi tinggi [6,7]. Pada studi ini sifat magnetoresistance pada paduan komposit Co-C granular yang dibuat dengan komposisi Co:C adalah 36:64.…”