A STUDY OF THE LOW STRESS SLIDING ABRASION WEAR BEHAVIOR OF MULLITE COATINGS

Mullite (3Al2O3–2SiO2), a ceramic with good thermal barrier and wear properties, was plasma sprayed on cast Aluminum A 356.0 alloy pins, to study the wear resistance of Aluminum parts coated with ceramics for use in aerospace, automobile, and industrial applications. The bond strength at the interface was improved by spraying Nickel-Chrome as a bond coat. This paper pertains to the study of low stress 3 body sliding abrasion wear loss of Mullite coatings. A specially designed pin on disc tribometer with features to apply lower pressures of 20 to 100 KPa was fabricated and tests conducted to measure the wear mass loss of all the specimens. Mullite was sprayed on cast Aluminum 356.0 T6 treated, with and without a bond coat and the wear performance was compared with that of bare wrought Aluminum 6063 and bare cast Aluminum A 356.0 in the soft and T6 treated conditions. The effect of heat treatment on cast alloy and the coating (with and without bond coat) on the wear performance has been studied. The wear scars were observed through a metallurgical microscope. The coating was found to be amorphous in nature and showed good wear resistance. The counter face was pasted with SiC emery of particle size 75 μm and with higher hardness and compressive strength than the coating. The results revealed that severe wear occurred, the wear factor falling in the range 10-2 to 10-5 mg/Nm, the regime of severe wear, in spite of the low stress applied. The wear behavior was correlated to the test conditions and the properties of the materials used. Mullite coatings on cast Aluminum with bond coat and the substrate T 6 treated performed better than other materials.