| Summary: | 碩士 === 國立成功大學 === 材料科學(工程)學系 === 86 === The surface overlaying treatment is aimed to give
different special properties to surfaces and substrates of
materials. Microhardness, wear-resistance, corrosion-resistance
etc. can be enhanced after treatment. Due to superior mechanical
properties, spheroidal graphite (SG) cast irons are widely used
in industries such as machine production, automobile components
etc. These components generally need to have surfaces with
higher microhardness to increase wear-resistance while their
cores need to main The results reveal that the overlayer
specimen after overlaid can be divided into overlayer, interface
region and substrate. The interface region includes interfacial
layer and partially melted region which is mainly composed of
fine pearlite and ledeburite. The substrate includes heat effect
region. The Stellite 6 overlayer melted on SG iron cast with
3.5wt% carbon under low overlaying current (I=140A) is a
dentritic structure with M7C3 and M23C6 carbides. On the other
hand, the Stellite 1 overlaye The microhardness of
Stellite alloy overlayers increases with overlaying currents and
so does the amount of carbides. The main reason is that the
overlayers are diluted by substrates. Hence, it shows that the
microhardness of overlayers is related to overlaying current and
the amount of carbides. The results of cutting wear test reaveal
that the flank wear width of Stellite alloy overlayers tend to
increase as the sliding distance and cutting speed . The flank
wear width of Stellite 6 overlayer redu In the cutting
wear test, the wear mechanisms of overlayers are mainly plastic
groove, surface polish and adhesive wear as adhered to
overlayers. Others minor mechanisms include brittle crack and
fracture. Among these, the case to plastic groove include
microcutting and plough.
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