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Phase transformation and electron structure effects in BiTl
vi
3.
ABSTRACTS
OF ARTICLES
TO APPEAR
PHASE TRANSFORMATION AND ELECTRON STRUCTURE EFFECTS IN Bi-TI T. Claeson and O. ~stklint Dept. of Physics, Chalmers University of Technology, Fack, S-402 20 Gothenburg Sweden Received June 25, 1973; Revised November 26, 1973
Bi-TI alloys, of an intermediate fcc phase in the range 6-40 at.% Bi and 20-200°C, have been investigated by several experimental methods. Between about 20 and 30 at.% Bi and below 100°C there appears a new hexagonal phase that can be indexed as anohcp one with a = 3.52 and c = 5.61 A at 75°C and 25 at.% Bi. T h e e x t e n s i o n of the phase is mapped via X-ray and resistance vs. temperature measurements. Its superconducting transition temperature, Tc, is more than 10% lower than the value found in the same samples quenched from the high temperature fcc phase. T c increases from 2.0K at 6 at.% Bi to 5.4K at 35 at.%Bi in the fcc phase. The increase is particularly rapid and the transitions are wide in a compositional range where also the thermoelectric power displays a minimum. The behaviour is correlated with the expected electronic structure in this type of alloy. 4.
THE DYNAMICS OF NUCLEATION AND GROWTH OF A THERMOELASTIC MARTENSITE IN A SPLAT QUENCHED Au-47.5 at.% Cd ALLOY P. L. Ferraglio and K. Mukherjee Dept. Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, 333 Jay Street Brooklyn, New York 11201 Received
September
4, 1973
The dynamics of nucleation and growth of a thermoelastic martensite in a splat quenched Au-47.5 at.% Cd alloy has been studied utilizing electron microscopy. The high temperature Cs C1 type E-phase is retained at room temperature by splat quenching. A reversible martensite transformation has been induced in the electron transparent regions of the liquid quenched foils by varying the intensity of the illuminating electron beam while the foil was under observation in
IN ACTA MET
Vol.
8, No. 2
the electron microscope. This control over the transformation has permitted a study of the nature and types of martensite nucleation sites, as well as, the crystallography, morphology and growth mechanisms of the martensite embryos in this alloy. The nucleation of the 3R martensite laths is heterogenous. The lath initially appears as a planar feature on a {110}8 plane and rapidly increases in thickness until a wedge shape is achieved. Growth of the lath occurs by the propagation of this wedge into the E-phase The screw dislocation-like nature of this wedge interface is discussed. S.
A HVEM STUDY OF THE ROLES OF DISLOCATION MOVEMENTS AND VACANCY FLOW DURING DISSOLUTION OF CEMENTITE IN STEEL M. Nemoto Division of Physical Metallurgy The Royal Institute of Technology S-100 44 Stockholm 70, Sweden -** **On leave from Dept. of Materials Science, Tohoku University, Sendai, Japan Received September 6, 1973 Revised December i0, 1973
Dislocation mechanisms during dissolution of cementite particles in a plain carbon steel have been investigated in-situ by high voltage electron microscopy. During dissolution of remaining particles of cementite in austenite above the eutectoid temperature, dislocation helices, loops and complex dislocation configurations in the austenite are formed from the interfaces to the particles. Dissolution of cementite in ferrite during austenitization and decarburization at about 700°C also causes the formation and movement of dislocations in the ferrite matrix. The dislocation movements are somewhat different from those in austenite. The configurations of dislocations depend on the dissolution rate and the shape of the particle. When the dissolution rate is sufficiently slow, the particle dissolves without appreciable formation of helices or loops. The critical misfit at which dislocations nucleate and start to move at the interface between matrix and particle during decarburization is estimated to be in the order of 10 -3 . The contribution of dislocation movements as a stress relieving mechanism during dissolution of cementite in ferrite and austenite is also estimated.
3.
ABSTRACTS
OF ARTICLES
TO APPEAR
PHASE TRANSFORMATION AND ELECTRON STRUCTURE EFFECTS IN Bi-TI T. Claeson and O. ~stklint Dept. of Physics, Chalmers University of Technology, Fack, S-402 20 Gothenburg Sweden Received June 25, 1973; Revised November 26, 1973
Bi-TI alloys, of an intermediate fcc phase in the range 6-40 at.% Bi and 20-200°C, have been investigated by several experimental methods. Between about 20 and 30 at.% Bi and below 100°C there appears a new hexagonal phase that can be indexed as anohcp one with a = 3.52 and c = 5.61 A at 75°C and 25 at.% Bi. T h e e x t e n s i o n of the phase is mapped via X-ray and resistance vs. temperature measurements. Its superconducting transition temperature, Tc, is more than 10% lower than the value found in the same samples quenched from the high temperature fcc phase. T c increases from 2.0K at 6 at.% Bi to 5.4K at 35 at.%Bi in the fcc phase. The increase is particularly rapid and the transitions are wide in a compositional range where also the thermoelectric power displays a minimum. The behaviour is correlated with the expected electronic structure in this type of alloy. 4.
THE DYNAMICS OF NUCLEATION AND GROWTH OF A THERMOELASTIC MARTENSITE IN A SPLAT QUENCHED Au-47.5 at.% Cd ALLOY P. L. Ferraglio and K. Mukherjee Dept. Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, 333 Jay Street Brooklyn, New York 11201 Received
September
4, 1973
The dynamics of nucleation and growth of a thermoelastic martensite in a splat quenched Au-47.5 at.% Cd alloy has been studied utilizing electron microscopy. The high temperature Cs C1 type E-phase is retained at room temperature by splat quenching. A reversible martensite transformation has been induced in the electron transparent regions of the liquid quenched foils by varying the intensity of the illuminating electron beam while the foil was under observation in
IN ACTA MET
Vol.
8, No. 2
the electron microscope. This control over the transformation has permitted a study of the nature and types of martensite nucleation sites, as well as, the crystallography, morphology and growth mechanisms of the martensite embryos in this alloy. The nucleation of the 3R martensite laths is heterogenous. The lath initially appears as a planar feature on a {110}8 plane and rapidly increases in thickness until a wedge shape is achieved. Growth of the lath occurs by the propagation of this wedge into the E-phase The screw dislocation-like nature of this wedge interface is discussed. S.
A HVEM STUDY OF THE ROLES OF DISLOCATION MOVEMENTS AND VACANCY FLOW DURING DISSOLUTION OF CEMENTITE IN STEEL M. Nemoto Division of Physical Metallurgy The Royal Institute of Technology S-100 44 Stockholm 70, Sweden -** **On leave from Dept. of Materials Science, Tohoku University, Sendai, Japan Received September 6, 1973 Revised December i0, 1973
Dislocation mechanisms during dissolution of cementite particles in a plain carbon steel have been investigated in-situ by high voltage electron microscopy. During dissolution of remaining particles of cementite in austenite above the eutectoid temperature, dislocation helices, loops and complex dislocation configurations in the austenite are formed from the interfaces to the particles. Dissolution of cementite in ferrite during austenitization and decarburization at about 700°C also causes the formation and movement of dislocations in the ferrite matrix. The dislocation movements are somewhat different from those in austenite. The configurations of dislocations depend on the dissolution rate and the shape of the particle. When the dissolution rate is sufficiently slow, the particle dissolves without appreciable formation of helices or loops. The critical misfit at which dislocations nucleate and start to move at the interface between matrix and particle during decarburization is estimated to be in the order of 10 -3 . The contribution of dislocation movements as a stress relieving mechanism during dissolution of cementite in ferrite and austenite is also estimated.