Chapter 11
Martensitic Strengthening
Systems that Show Martensitic Transformations
Free Energy vs. Temperature for Austenite and Martensite
Free energy versus temperature for austenite (parent phase) and martensite.
Morphologies of Martensite
(a) Lenticular martensite in an Fe–30% Ni alloy. (Courtesy of J. R. C. Guimarães.)
(b) Lenticular (thermoelastic) martensite in Cu–Al–Ni alloy. (Courtesy of R. J. Salzbrenner.)
Lath Martensite
Lath martensite. (Reprinted with permission from C. A. Apple, R. N. Caron, and G.
Krauss, Met. Trans., 5 (1974) 593.)
Twinned and Dislocated Martensites
Fracture toughness vs. yield strength for twinned and dislocated martensites in a medium-carbon
(0.3% C) steel. (Courtesy of G. Thomas.)
Acicular Martensite
Acicular martensite in stainless steel forming at intersection of slip
bands.(Courtesy of G. A. Stone.)
Twins Inside Martensite
(a) Transmission electron micrograph showing
a group of twins inside martensite transformed
at –140 ◦C and 2 GPa.
(b) Dark-field image of twins on (112)b plane;
(c) Stereographic analysis for habit (in FCC)
and twin (in BCC) planes.
(From S. N. Chang and M. A. Meyers, Acta
Met., 36 (1988) 1085.)
Twins within Martensite Lenses
Martensite lenses (M) being traversed by twins, which produce self accommodation.
(Courtesy of A. R. Romig.)
Strength of Martensite
0.6% proof stress (one-half of tensile stress) vs. (carbon concentration)0.5 for
Fe–Ni–C lath martensite at various temperatures. The slopes are shown as
fractions of the shear modulus, G. (Adapted with permission from M. J.
Roberts and W. J. Owen, J. Iron Steel Inst., 206 (1968) 37.)
Strength of Martensite
Effect of prior austenite grain size on the yield stress of
three commercial martensitic steels. (Adapted with
permission from R. A. Grange, Trans. ASM, 59 (1966) 26.)
Distortion Produced by Martensite Lens
Distortion produced by martensite lens on a fiducial mark on surface of specimen.
Martensite Start Temperature as Function of
Loading Condition
Change in Ms temperature as a function of loading condition.
(Adapted with permission from J. R. Patel and M. Cohen, Acta Met.,
1 (1953) 531.)
Mechanical Effects
Temperature dependence of the yield strength of
Fe–31% Ni–0.1% C. , predeformed by shock
loading.
(Adapted with permission from J. R. C. Guimarães,
J. C. Gomes, and M. A. Meyers, Supp. Trans.
Japan Inst. of Metals, 17 (1976) 41.)
Tensile curves for Fe–Ni–C alloy above
Ms, showing martensite forming in
elastic range (stress assisted). (Courtesy
of J. R. C. Guimarães.)
Strain-induced Martensite
Volume fraction transformed (right-hand side), f, and stress (left-hand side) as a function
of plastic strain for an austenitic (metastable) steel deformed at –50 ◦C; experimental
and idealized stress–strain curves for austenite, martensite, and mixture are shown.
(After R. G. Stringfellow, D. M. Parks, and G. B. Olson, Acta Met., 40 (1992) 1703.)
Microcracks in Martensite
Microcracks generated by martensite.
(a) Fe–8% Cr–1% C (225 martensite sectioned parallel to habit plane).
(Courtesy of J. S. Bowles, University of South Wales.)
(b) Carburized steel. (Reprinted with permission from C. A. Apple and G.
Krauss, Met. Trans., 4(1973) 1195.)
Shape Memory Effect
(a) Pseudoelastic stress–strain curve for a singlecrystal Cu–Al–Ni, alloy at 24 ◦C (72 ◦C above Ms).
(b) Dependence on temperature of stress–strain
characteristics along the characteristic transformation
temperatures. Strain rate: 2.5 × 10−3 min−1.
(Reprinted with permission from C. Rodriguez and L.
C. Brown, in Shape Memory Effects, (New York:
Plenum Press, 1975), p. 29.)
Pseudoelastic Effect
Schematic representation of pseudoelastic (or
superelastic) effect. (a) Initial specimen with
length L0. (b, c, d) Formation of martensite
and growth by glissile motion of interfaces
under increasing compressive loading. (e)
Unloadingof specimen with decreasing
martensite. (f) Final unloaded configuration
with length L0. (g) Corresponding stress–
strain curve with different stages indicated.
Strain Memory Effect
Sequence showing how growth of one martensite variant and shrinkage of
others results in strain εL. (Courtesy of R. Vandermeer.)
Strain-Memory Effect in Compression
Schematic representation of strain-memory
effect in compression, tension, and bending.
Variant A favors a decrease in dimension in
the direction of its length, whereas variant B
favors an increase in dimension.
Strain-Memory Effect
Schematic representation of strain-memory effect.
(a) Initial specimen with length L0 . (b, c, d)
Formation of martensite and growth by glissile
motion of interfaces under increasing compressive
stresses. (e) Unloading of specimen. (f) Heating of
specimen with reverse transformation. (g)
Corresponding stress–strain curve with different
stages indicated.
Martensitic Transformation in Ceramics
(a) Lenticular tetragonal zirconia precipitates in cubic
zirconia (PSZ). (b) Equiaxial ZrO2 particles (bright)
dispersed in alumina (ZTA). (Courtesy of A. H. Heuer.)
Martensite in Cubic Zirconia
Atomic-resolution transmission electron micrograph showing extremity of
tetragonal lens in cubic zirconia; notice the coherency of boundary. (Courtesy
of A. H. Heuer).
Zirconia Phase Diagram
ZrO2-rich portion of ZrO2–MgO phase diagram. Notice the
three crystal structures of ZrO2: cubic, monoclinic, and
tetragonal.
Martensite in Zirconia
TEM of martensitic monoclinic lenses in ZrO2
stabilized with 4 wt% Y2O3 and rapidly solidified;
the zigzag pattern of lenses is due to autocatalysis.
(Courtesy of B. A. Bender and R. P. Ingel.)
Zirconia-Toughened Alumina
(a) Zirconia-toughened alumina (ZTA) traversed
by a crack. Black regions represent monoclinic
(transformed) zirconia, gray regions tetragonal
(untransformed) zirconia.
(b) Partially stabilized zirconia (PSZ). Lenticular
precipitates transformed from tetragonal to
monoclinic in the vicinity of a crack. Notice the
brighter transformed precipitates.
(Courtesy of A. H. Heuer.)