Formation and Properties of Amorphous and Nanocrystalline Phases in Mechanically Alloyed Fe-Based Multicomponent Alloys
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determined using the well-known Scherrer formula. Due to wear debris of the milling tools, chemical analysis of the milled powders revealed a slight increase of the Fe content (< 0.8 at.% Fe) compared to the nominal composition of the alloys. Thermal analysis was done in a PerkinElmer DSC 7 and TMA 7 at heating rates of 10 and 40 K/min. RESULTS AND DISCUSSION
Figure 1 shows x-ray diffraction patterns for
Fe 72 (A15 PIIC 6 B 4 )1 +2/26
after different milling
times as a typical example. With increasing processing time a decrease of the crystalline Fe and Al diffraction peaks and the formation of a broad diffuse diffraction intensity corresponding to an amorphous phase can be seen. In addition, a broadening of the bcc Fe lines due to a decreasing grain size and an increase in atomic-level strain is observed. In contrast to singlephase amorphous ribbons produced by rapid quenching [3, 4], mechanical alloying of elemental powders reveals an additional nanoscale bcc Fe-rich phase after 130 h of milling. For the initially quaternary Fe 7 9P1 IC 6B 4 alloy and a substitution of Fe by 5 at.% Al (Fe74A15 PI 1C6 B4 ) and 2 at.% Ga (Fe72Al 5PJ 1C6B4Ga 2) the formation of an amorphous/nanocrystalline phase mixture is
obtained (Fig. 2). Figure 3 shows x-ray diffraction patterns for
Fe74 -x(Al5Pi 1C 6 B4 )1 1+x26
with
different composition. This change in composition was chosen to maintain a fixed A15 PIIC 6B4 ratio. Starting with Fe 74A15PI IC6B4 a change of the Fe content in Fe 74_x(Al 5 PH C 6B 4)i+x/26 (x = 2, 4, 5, 6) also leads to an amorphous/nanocrystalline phase mixture after a milling time of 130 h for all compositions. Using the well-known Scherrer formula, the average grain size was estimated from the full-width at half maximum (FWHM) of the Fe reflections after correction for instrumental broadening. For all samples investigated a grain size of 10 ± 2 nm was found.
C6
--3
*
Cu
o Al
Fe
Cu
co
U'Ul) C
t'-
=2h m
-
20
Figure 1:
40
60 80 100 2 0 [degrees]
120
40
X-ray diffraction patterns for
Fe7 2(A15P 11C 6 B4 )1+2/26 after
St
50
60 70 80 90 100 110 2 0 [degrees]
Figure 2: X-ray diffraction patterns for Fe 79P11C 6 B 4 , Fe74AA5P1 IC6B 4 and Fe 72 A15P[ IC6 B4 Ga 2 after 130 h of milling.
different milling
times.
508
Fe.
(AIP
CB.)
tm= 130h
t = 130h
74-x" 5 11 6 4 1+x/26 x =2 mx=2Tj
Fe
-
P GB
T
79 11 6 4
Cd
T
xx=4
o
M
Fe Al5P C6B4Ga
-
64
72 511
[Z
x
2
X=5x 0
FeFAIsP1C B 4
E x 6
50
60
70
80
90
T
4
x
X
-
40
74 5 11 6 4
ILl
100
640
110
2 0 [degrees]
680
720
760
800
Temperature [ K]
Figure 3: X-ray diffraction patterns for Fe 74 _x(A15P1 lC 6B4 )1 +,/ 26 after 130 h of milling.
Figure 4: DSC scans (heating rate 40 K/min) for Fe 79 P11 C6 B 4 , Fe 72A15 PIIC 6B4 Ga 2 and Fe 74A15PIIC 6B 4 after 130 h of milling.
The thermal stability of the milled powders was investigated by DSC. All samples exhibit an endothermic event reflecting the heat capacity anomaly characteristic of the glass transition and a sharp exothermic reaction at higher tem
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