| Summary: | The use of aluminum in the automobile engines and other critical parts require a
superior surface property of the same. This has led to the development of plasma
sprayable surface coatings for the components. To impart the maximum bonding
strength, along with hardness to the coatings an aluminum based composite (Al-SiC) was
found to be the most suitable. The presence of a hard ceramic second phase within a soft
metallic matrix greatly improves the wear resistance of the composite material. The
powders for spraying were prepared by mechanical agglomeration of 6061 Al alloy
(particle size between 40 and 60 um) with fine SiC particles ( « 8 um) by using high
energy vibratory mills. The concentration of SiC was varied from 20-75 vol%, the
balance being the matrix A l alloy. The size of the reinforcement was varied from 8 to 37
um in the Al-50vol%SiC composite coatings. A Process Control Agent (PCA) was used
to modify the morphology of the powders during the process of mechanical alloying.
Mechanical alloying produced composite powders in a size range between 40 and 120 u.m
with the SiC phase uniformly dispersed within the matrix. The powders used for
spraying were fractionated between the size range of 44 and 149 um by sieving.
The powders were sprayed using two types of axial feed plasma torches.
Coatings were sprayed on mild steel coupons, rods and thin foils of A l , Ni, plain carbon
steel and stainless steel, which were used for conducting tests to assess the physical
properties of the coatings. The cross sections of the coatings sprayed on the coupons
were observed under an SEM and optical microscope. The hardness, porosity and SiC
distribution of the coatings were assessed on these cross sections. The coatings were
tested for different physical and mechanical properties like adhesion and wear strength.
Adhesion was tested on the mild steel rods using the standard ASTM C633 pull
tests but the results were mostly inconclusive. Adhesion strength on the foils was also
measured by peel tests which is a modification of the ASTM D-3167 tests. The coatings
showed high adhesion strength compared to the other commercially available coatings
reported in a recent work [40]. Adhesion strength was found to decrease with the
increase in the SiC content and decrease in SiC particle sizes.
Erosive wear of the coatings was assessed using a dry erosion test which is a
modification of the ASTM G76-83 test. The increase in the SiC content and decrease in
the reinforcing particle size improved the wear resistance of the coatings. The abrasive
wear resistance was found to improve with the increase in SiC particle size and also with
the SiC content in the composite powders (or coatings). === Applied Science, Faculty of === Materials Engineering, Department of === Graduate
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