Prakt. Met. Sonderband 46 (2014) 269
bably, due to The origin microstructure of NiTi alloy, before carburizing is homogeneous and has acicular
like morphology (fig. 2a). Meanwhile, after carburizing, in the surface layer of the alloy, the
concentration profile of Ti, Ni and C was build up (fig. 3a,b). The intensity of Ti Ka line, firstly
slightly decreases from the center part of the matrix to the TiNi/TiC interface and finally
strongly increases in the TiC layer. The intensity of Ni Ka line shows firstly constant
concentration profile of Ni in the surface layer of the matrix and drastic decrease of
concentration in the TiC layer. Finally, the intensity of C Ka. line is weak in the TiNi matrix,
corresponding probably to the surface contamination of the sample, but when reaching the
TiC layer the intensity of C Ka line increases, which proves that the TiC layer was formed
on the surface of the sample during vacuum carburizing. The TiC layer is uniform and about
5 um thick (fig. 2b).
(a) ta=6 min,
=10 mbar
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Fig. 3: The EDX line scan analysis (dashed line) of vacuum carburized NiTi wire at
1000°C, ta=6 min, pc,H,=10 mbar
Consequently, the microstructure of the surface layer of the alloy becomes after vacuum
carburizing heterogeneous, consisting of matrix and numerous precipitates with different
morphological forms (fig 2b, 2c). With SEM/EDX analysis, we found out, that the matrix has
acicular morphology formed probably by eutectoid reaction and consisting of Ti2Ni and TiNis
phases [12]. The round precipitate corresponds to the TisNis phase and the oblong one to
the TiNis phase, respectively [13]. The precipitates of TiNis phase could also be found on
the grain boundaries (fig. 2c) [14].
4. CONCLUSIONS
In this research work was shown, that vacuum carburizing technology which is in general
ing (b, c) at used for case hardening of steels, can also be successfully applied in the field of NiTi shape
memory alloys for improvement of wear resistance. At optimal process parameters. a
; Ti Ka
Ni Ka
C Ka
