|
New type copper-based
alloys for valve seats of automotive engines have
been developed, which are directly deposited onto
an aluminium-alloyed cylinder head by a laser cladding
technique.
These alloys have unique
microstructures resulted from rapid solidification
of immiscible two liquid phases, in which coarse
grains containing fine hard particles of borides
and/or silicides ( from liquid B ) are homogeneously
dispersed in the heat-resistant copper-based solid
solution ( from liquid A ) .
The controlled irradiation
of a high-frequency oscillated CO2 laser beam results
in melting of only the material powder for cladding
on the aluminium-alloyed substrate and stirring
of the molten pool to form a homogeneous dispersion
of liquid B in liquid A, followed by rapid solidification
to freeze the dispersion by heat conductivity of
the aluminium-alloyed substrate.
The deposited alloys
provide considerable abrasive- and adhesive-wear
resistances in a wide temperature range owing to
the unique microstructures consisting of hard particles,
heat-resistant matrices and/or lubricating phases.
|
