Structural and wear properties of sputter-deposited laves intermetallic alloy

Abstract

An adhesive wear-resistant alloy, with a type MgZn 2 close-packed hexagonal Laves intermetallic phase to promote abrasive wear resistance, was d.c. sputter deposited onto steel substrates at temperatures in the range 20–800°C using a hollow cathode sputtering device. Coating thicknesses were in the range 20–60 μm. Coating structures were examined by preparing metallographic cross sections and by X-ray diffraction. The wear properties of coated and uncoated steel rings (hardness, Rc 60), sliding against blocks of cast iron, a soft steel, a tool steel, a cobalt alloy, WC-Co and a cast form of a different Laves phase intermetallic alloy, were compared in both room air and a non-lubricating liquid. Coatings deposited at a substrate temperature of about 800 °C exhibited the Laves phase diffraction profiles. Coatings deposited at lower temperatures exhibited fine-grained (amorphous type) X-ray diffraction patterns. Metallographic cross sections revealed a dense columnar structure. Microhardnesses were about 900 kg mm -2 (KHN) independent of substrate temperature. In room temperature air with no lubricant, the wear properties of the rings with the sputter-deposited coatings were superior to the uncoated ones when sliding against the tool steel, cobalt alloy and cast Laves phase blocks. No significant improvement was seen for sliding against the cast iron, soft steel and WC-Co blocks. With a poor lubricant and higher normal forces, the coated and uncoated rings performed well against the Laves phase and tool steel blocks; however, the coated rings were generally inferior for the other couples tested.