M. Cernansky et al., QUANTITATIVE PHASE-ANALYSIS OF METASTABLE STRUCTURE IN A LASER MELTEDFE-C ALLOY .2. STRUCTURAL-ANALYSIS OF OVERLAPPING TRACKS BY X-RAY-DIFFRACTION, Journal of Materials Science, 31(4), 1996, pp. 995-1004
Quantitative X-ray diffraction phase analysis was utilized to investig
ate the structure of a Fe-3.5 wt% C alloy after laser melting. The mea
surements were taken on surfaces modified by a series of equidistant l
aser tracks with overlappings k = 0.25, 0.50 and 0.75, and the results
were extrapolated to the non-interfering tracks. On the same samples,
the microstructure was observed by scanning electron microscopy. The
structure of the rapidly solidified surface layers consists of alpha-F
e (ferrite and martensite), gamma-Fe (retained austenite) and cementit
e. The results of X-ray diffraction point to a very high amount of car
bide indicating a non-stoichiometric composition of cementite. Besides
, the volume fraction of alpha-Fe increases with increasing coefficien
t of overlapping k. At the same time, the volume fraction of cementite
decreases while the content of gamma-Fe remains nearly constant. The
changes are attributed to decomposition of the metastable carbide due
to tempering of the former tracks by the following laser passes. This
thermal effect was quantified on the base of the heat-transfer model o
f moving Gaussian beam.