without aluminium oxide products could pour down and deposited
on the lower layer powder compacts (type-I powder) and ignite the
SHS reaction of Ti–C–Cu system.
It has been well studied to prepare TiC by SHS reaction
from (Ti + C) powder mixture [12–14]. In the Ti–C system, the
ignition temperature was generally close to the melting point
of Ti, and can be lowered by adding another metallic powder
such as Cu. Differential thermal analysis showed that the reaction
initiated at around 960 ◦C which was the eutectic point
for the melting of CuTi2 and CuTi in Ti–C–Cu system [15].
The formation mechanism of TiC in the ternary system can
be described as dissolution-precipitation, namely, Ti and C dissolve
in the Cu melt which then precipitates out TiC upon
cooling.
Therefore, a proposed mechanism and speculation of the formation
of TiC reinforced Cu/Ni matrix coating follows. In present work,
Cu started to melt initially upon the molten Cu/Ni metal depositing
on the lower layer compacts. With increasing temperature, the
Cu–Ti liquids formed via the diffusion reactions between the Cu
and Ti. The unreacted Ti and C particles dissolved into the Cu–Ti
liquids and led to the formation of the Cu–Ti–C ternary liquids;
subsequently, TiC formed in the liquids. Then Ti and C particles
continuously dissolved into the Cu–Ti–C liquid and TiC particulates
gradually precipitated out of the saturated liquids.
4. Conclusions
A novel method to prepare MMC coatings via SHS was developed.
The main aim was to obtain ceramic particulate reinforced
metal matrix composites coatings employing a simple and energysaving
process.
An in situ synthesized TiC reinforced Cu/Ni based MMC coating
was successfully produced on a steel substrate via this process.
Fine (less than 10 m) columnar morphology TiC particles were
uniformly distributed in the metal matrix and no pores or microcracks
were found in the coating. A strong metallurgical bonding
was achieved at the interface between the MMC coating and the
steel substrate. We believe that this method can be also applied
to a large number of other SHS systems to obtain different MMC
layers.