Correlations between the grain size [or the diffracting particle size (DPS)] and the magnetic properties of mechanically milled Fe–ZrO2 nanocomposite powders are reported. Nanocomposite powders with iron volume fractions below, near, and above the percolation value were annealed at temperatures between 573 and 1083 K and investigated. The composite as-milled powders exhibited enhanced coercivities (≳300 Oe) compared to similar mechanically milled iron powders. The iron diffracting particle size (grain size) as a function of annealing temperature showed two regimes. The first regime, corresponding to temperatures at and below 773 K, consisted of enhanced coercivities and remanence ratios with a relatively stable iron diffracting particle size of ∼25 nm. In the second temperature regime, above 773 K, the DPS increased, but remained well below the value for pure iron. Concomitant with this increase, large reductions in the coercivities were observed in the second regime.
Nanocomposite structures composed of ferromagnetic particles dispersed in a matrix are systems in which the magnetic properties can be tailored by varying the size and spacing of the ferromagnetic particles. Nanocompo$i~es of SmCos in a non-magnetic Nb0.dk8.67 matrix exhibit a wide variety of magnetic properties. SmCos powder is premilled prior to mechanical alloying. The premilliing results in a maximum coercivity of 16 kOe after 2 hours of milling, and an enhanced remanence ratio. Both features may be due to exchange anisotropy and/or exchange coupling between hard and soft ferromagnetic phases. The nanocomposite samples show that, when the SmCos particulates are small enough, the primary effect of alloying is to disperse them throughout the matrix with no further refinement of size.
The mechanical alloying process continually deforms, cold welds, and breaks apart metal powder particles. During the process of mechanical alloying elemental crystalline powders can produce an amorphous alloyed powder. Consolidation of these powders by powder metallurgy techniques can produce amorphous bulk metals.
Two Alloys 62.24 Zr-10.89 Ti-9.71 Ni-13.14 Cu-4.02 B and 64.84 Zr-11.35 Ti-11.12 Nt-13.69 Cu weight percent were mechanically alloyed for 45 hours by a SPEX 800 high energy ball-mill. The changes in structure were monitored by X-ray diffraction after every 5 hours of milling. Both powder compositions became amorphous after 15 hours of milling. New compounds began to form during milling to 35 hours. Milling for longer times produced no further structure changes. The milled samples were annealed at 950°C for 1 hour which produced a complex set of crystalline materials. The crystalline phases containing boron have larger lattice parameters and less tendency for grain growth.
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