Comparison of equivalent ball milling processes on Fe70Zr30 and Fe70Nb30

Abstract

Dynamical analysis of the movement of a single ball in a planetary ball mill yields a cubic law with the frequency of the mill for the power released during the process. This fact has been explored for two binary compositions: Fe 70 Zr 30 and Fe 70 Nb 30 using two different milling frequencies. The experimental techniques used, in general, support the predictions of the equivalent milling time model. However, some deviations appear which could be ascribed to differences in the temperature inside the vial during milling. Journal of Alloys and Compounds, 536S1 (2012) and approximately the same amount of sample ~0.2 g was extracted in argon atmosphere for each composition. This process was done six times and, in the following, they will be named as milling steps from 1 to 6 (4, 8, 12, 16, 20 and 24 h milling at 360 rpm and 8, 16, 24, 32, 40 and 48 h milling at 286 rpm, respectively). At the first milling step no powder could be recover for the Zr alloy but the starting material stuck on the ball and vial surfaces forming a shiny layer.Samples were analyzed using differential scanning calorimetry (DSC) in a PerkinElmer DSC7; X-ray diffraction (XRD) using Cu-K wavelength, scanning electron microscopy (SEM) in a Jeol JSM-6460 LV and Mössbauer spectrometry (MS) in a transmission geometry using a 57 Co(Rh) source. Values of the hyperfine parameters were obtained by fitting with NORMOS program [6]. The isomer shift, IS, was quoted relative to the Mössbauer spectrum of an -Fe foil at room temperature. 3Results and discussion Figure 1 shows the XRD patterns of several samples. The amorphous phase of the asmilled samples is evidenced by a broad amorphous halo. Figure 2 shows the DSC scans at 40 K/min of the different studied samples. All the features observed in the curves are irreversible as they disappear in a second scan, which was used as the corresponding baseline. A general agreement can be found for the two samples of each composition obtained at the same milling step. This is especially clear concerning the broad exothermic peak ascribed to the release of the energy stored during milling (structural and strain relaxation phenomena at low temperatures and grain growth and crystallization phenomena at high temperatures). For allJournal of Alloys and Compounds, 536S1 (2012) 9-12 http://dx.doi.org/10.1016/j.jallcom.2011.11.084 the samples, a deviation from the baseline occurs about 400 K which coincides with a slight decrease of the mass of the sample observed by thermomagnetic gravimetry, TG (both experiments, DSC and TG were performed under argon flow). Thus this feature should be ascribed to some gas desorption from the powders.However, concerning endothermic processes some differences arise between the two set of experiments performed at different frequencies and depending on the studied composition. For Nb alloy, there is an endothermic peak about 625 K which appears only for the samples milled at 360 rpm. Similar endothermic peaks were found in FeGeNb powders being ascribed to solving intermetallic(...

Enhancement of the magnetic refrigerant capacity in partially amorphous Fe70Zr30 powders obtained by mechanical alloying

“…The M(T) curve at m 0 H ¼ 0.05 T is shown in Fig. 4 T Int C ¼ 355 K, in agreement with the magnetic contribution with HF<20 T detected after room temperature Mössbauer experiments [13]. However, these peaks are not sharp but very broad, which can be ascribed to a distribution of transition temperatures in both phases.…”

“…Recent studies [13] performed at room temperature on mechanically alloyed Fe 70 Zr 30 composition (starting from pure powders) showed a weak magnetic phase at room temperature embedded in a paramagnetic amorphous phase. The aim of the present work is to show that the presence of this magnetic phase with a Curie temperature w100 K above that of the amorphous matrix is the responsible for a clear enhancement of RC.…”

Role of starting phase of boron on the mechanical alloying of FeNbB composition

“…In figure 10a we can see the evolution of the crystalline volume fraction as a function of the milling time for boron [13,14,15]. In figure 10 we can see that the use of commercial amorphous or crystalline boron to prepare the starting mixture can lead to different results.…”

Fe-X-B-Cu (X = Nb, NiZr) Alloys Produced by Mechanical Alloying: Influence of Milling Device

“…This approach has been previously applied in FeNb and FeZr alloys [35]. In our study, the cycles ratio in the P7 is 1 (Ω = Ω o = 600 rpm).…”

“…On the other hand, it is possible to calculate an equivalent milling time between different mills [34,35]. The calculation of this equivalent time is based on the assumption that the power transferred per unit of mass (P/m) is directly proportional to the time so that in two different devices the powder achieves the same final microstructure.…”