Results (
Thai) 2:
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3.1. Microstructure
The typical microstructure of the studied hardfacing alloys
is shown in Fig. 4. The first and second layers of Cr-rich
deposits have a eutectic matrix with proeutectic M7C3-type
chromium carbides (1800 HV micro-hardness), which were
identified by EDS-SEM due to their large size. In the second
layer, both the volume fraction and the mean size of
chromium carbides are higher than in the first one. The volume
fraction of chromium carbides in the second layer, calculated
by using an empirical relation from literature [7], is
circa 52%.
The microstructure of the W-rich deposit is composed
by proeutectic MC-type carbides (2500 HV micro-hardness)
surrounded by the eutectic structure containing M6C-type
(fishbone-type) carbides (1600 HV micro-hardness) and
some martensite.
The first layer of the complex carbides deposit is mainly
eutectic with finely dispersed (Nb, Mo)-rich hard particles,
while the second and third deposit layers have
a similar microstructure which includes chromium-rich
M7C3, Nb-rich MC, Mo-rich M2C and W-rich WC carbides.
Figs. 5–7 show EDS compositional maps of the deposits,
in which it is possible to identify the carbide types present
in the microstructure. In Fig. 8, localized spectra are taken to
identify M2C (Mo-rich), M7C3 (Cr-rich) and MC (Nb-rich)
carbides.
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