Hence, below the temperature of 850°C, structure of Cu-Fe binary alloys is represented
by ε-Cu + α-Fe, i.e. products of eutectic transformation.
Al-Fe. Completely different character of inter-particle interaction occurs in Al-Fe
system [12-15]. In alloys of Fe-Al system five stable phases form: Fe
3
Al (β
1
), FeAl
(β
2
), FeAl
2
(ξ), Fe
2
Al
5
(η), FeAl
3
(ΰ), each of which has a certain homogeneity area.
Phase FeAl with an ordered BCC lattice type B
2
(CsCl) forms directly at alloy
crystallization per peritectic reaction.
Alloys containing 32-40 wt. % Al, in temperature range 1022 … 700°C,
secondary arrangement undergo. This, apparently, associated with type of distant order
change. At 552°C and 26,8% Al degenerate peritectoid transformation realizes.
Point with coordinates above is sometimes called Curie double point, since here
ferromagnetic α-Fe phase and paramagnetic Fe
3
Al phase coexist.
Crystal lattice of this Fe
3
Al ordered phase – cubic type BiFe
3
.
Cu-Al-Fe. In general [16, 20], iron increases the strength properties of aluminum
bronzes at a certain decreasing in their plasticity, greatly lowering grain size during
crystallization and recrystallization. In the case of slow cooling, in alloys containing 8-
11 wt. % Al (see Table 2.1), β-phase eutectoid transformation leads to α + γ
2
structure
formation with big γ
2
-phase crystals, which are arranged in continuous chains form and
lead to brittleness of details. This effect is most dangerous for large-sized products.
Iron slows β-phase eutectoid decay and, thus, prevents brittleness development. Even
if it occurs, its harmful effects are less marked, since iron strongly shreds γ
2
-crystals
and α-phase grains.
Such character of bronze BrA9Zh3L formation provides alloy mechanical
properties achievement, which are standardized by GOST 493 [4] and are presented in
Table 2.2.
Typical microstructure of BrA9Zh3L foundry bronze, which was formed during
realization of considered phase transformations regularities, is presented in Figure
2.1,a. Figure 2.1,a analysis shows that alloying of aluminum bronze with iron affects
the lines and points of phase equilibriums positions (according to Cu-Al-Fe ternary
phase diagram [15]) with appropriate structure formation characterized by the presence
of α-Cu crystals of solid solution and eutectoid component, which basis is eutectoid
γ
2
+α of Cu-Al system.
Table 2.2 Tin-free bronze mechanical properties and implementation
Grade
Method of
casting
UTS (σ
в
),
MPa
Elongation (δ
5
),
%
Brinell Hardness
(НВ), MPa
Implementation
No less, than
Fittings, antifriction
parts
BrA9Zh3L
Chill
490
12
980
Sand
392
10
980
Source: borrowed by the authors according to source [4]
- 1811 -