Callister - An introduction - 8th edition

214 • Chapter 7 / Dislocations and Strengthening Mechanisms
180
25
400
60
160
Tensile strength (MPa)
300
50
40
Tensile strength (ksi)
Yield strength (MPa)
140
120
100
20
15
Yield strength (ksi)
200
30
0 10 20 30 40 50
Nickel content (wt%)
(a)
80
10
60
0 10 20 30 40 50
Nickel content (wt%)
(b)
60
Elongation (% in 2 in.)
50
40
30
20
0 10 20 30 40 50
Nickel content (wt%)
(c)
Figure 7.16 Variation with nickel content of (a) tensile
strength, (b) yield strength, and (c) ductility (%EL) for
copper–nickel alloys, showing strengthening.
VMSE
Alloys are stronger than pure metals because impurity atoms that go into solid
solution ordinarily impose lattice strains on the surrounding host atoms. Lattice
strain field interactions between dislocations and these impurity atoms result, and,
consequently, dislocation movement is restricted. For example, an impurity atom
that is smaller than a host atom for which it substitutes exerts tensile strains on the
surrounding crystal lattice, as illustrated in Figure 7.17a. Conversely, a larger
Figure 7.17 (a) Representation
of tensile lattice strains
imposed on host atoms by a
smaller substitutional impurity
atom. (b) Possible locations of
smaller impurity atoms relative
to an edge dislocation such that
there is partial cancellation of
impurity–dislocation lattice
strains.
(a)
(b)