Laser melting of plasma-sprayed copper-ceramic coatings for improved erosion resistance

Copper-based coatings containing a hard ceramic phase can provide an engine ering solution to components exposed to particle erosion environments provi ded the microstructure of these coatings is appropriate. Single-phase ducti le copper is damaged by micromachining and ploughing while single-phase bri ttle materials are thought to be damaged by the generation and propagation of subsurface lateral cracks. Therefore, a multicomponent system composed o f a ductile metal such as copper containing hard and brittle ceramic partic les is expected to be tough enough to resist particle impacts at 90 degrees and sufficiently hard to deflect eroding particles at low impact angles. C opper-ceramic coatings were manufactured by plasma spraying composite powde rs. These spray powders were obtained by agglomerating fine copper and bori de powders by means of an organic binder in a rotating tumbler. The thickne ss of as-sprayed coatings reaches about 350 mu m. After surface polishing, these coatings were laser melted with parameters ensuring in-depth melting. Polished as-sprayed, surface milled laser-melted coatings and bulk copper specimens were erosion tested at 25 degrees and 300 degrees C at impact ang les of 25 degrees and 90 degrees in a laboratory erosion device. This devic e was designed to impact materials with coarse (32-300 mu m) iron ore parti cles at a speed of 100 m/s. The evaluation of wear damages was done with a laser profilometer and scanning electron microscopy was used to evaluate mi crostructural changes upon laser treatment as well as surface modifications after erosion tests. Particle erosion resistance of laser-melted plasma-sp rayed copper coatings containing 45 vol.% boride phase is improved in compa rison with bulk copper. The low angle impact erosion is reduced at both 25 degrees C and 300 degrees C (1.7 times at 25 degrees C and 4.8 times at 300 degrees C) and the normal angle impact erosion resistance is the same as p ure copper at both temperatures. As-plasma-sprayed coatings presented the w orst erosion resistance. The improvement in erosion resistance of laser-mel ted coatings is attributed to the formation of large clusters of boride par ticles upon laser melting plasma-sprayed copper-boride coatings. These roun ded boride islands are large enough to deflect the incoming eroding particl es and the elastic copper phase dissipates the energy of particles with a h igh impingement angle. (C) 1999 Published by Elsevier Science S.A. All righ ts reserved.