EFFECT OF LASER INFLUENCE ON MARTENSITE TRANSFORMATION INTO THE NEARSURFACE LAYERS OF Fe-Al-C ALLOYS
V.A.Andrushchenko,E.N.Dzevin
Institute of Metal Physics
Ukrainian National Academy of Sciences,
Vernadsky blvd. 36, 252142 Kiev,
Ukraine
The solid solution of Fe-Al-C alloys in the wide concentration and temperature intervals consists of austenite phase with f.c.c. lattice (g-phase), carbide FeAlC, tetragonal -martensite and aluminium ferrite with b.c.c. Coherency and mutual orientation of f.c.c. lattices of g- and K-phases interchangeably with injected into g-lattice carbon atoms determine not only parameters but OR being formed from austenite of a-martensite with b.c.t. lattice:
1) a-martensite formed from austenite with f.c.c. lattice which isn't coherent with K-phase f.c.c. lattice has tetragonality degree proportional to the quantity of dissolved in austenite carbon and 24 OR K-S;
2) a-martensite formed from austenite with f.c.c. lattice being coherent with K-phase f.c.c. lattice has anomalous high meaning of b.c.t. lattice elementary cell c/a and 48 twinned G-T OR. The reason of arising the anomalous high tetragonality and additional a-martensite twinning, apart from other factors, consists in a value of coherent stresses between f.c.c. and b.c.t. crystal lattices of K- and a-phases, respectively.
It was chosen the monocrystallic Fe-4%wt.Al-2%wt.C sample (after quenching the alloy from 1150oC into the water) the axis of which was coincided with the axis [100] of austenite f.c.c. lattice. This specimen was exposed to fivehold (8msec) laser impulse action (10J) in the end of it, i.e. along the axis [001]g. Then the sample was cooled into the liquid nitrogen (-196oC). The series of X-ray surveys was performed in the X-ray chambers of rotation RKV-86.
The obtained data allow to determine the character of martensite transition in different nearsurface layers of syngle crystal sample after laser exposure:
Thus, with the help of X-ray structural
investigations it has been established that in austenite single
crystal samples Fe-4%Al-2%C subjected to fivehold impulse laser
exposure (8 msec,10J) in the direction of crystal lattice [001]g ,
structure change of austenite reaches the depth of 4,5 mm from
the surface. Analysis of martensite crystal lattice parameter and
its orientation relations allowed to make a supposition that
after laser exposure near-surface 4,5 mm layer consisted of six
different in structure austenite interlayers. Martensite has
different orientation in reference to residual austenite in these
interlayers.