ELECTRODE EROSION AND COATING PROPERTIES IN PULSED AIR ARC DEPOSITIONOF WC-BASED HARD ALLOYS

WC-based hard alloys were deposited from a slab source anode on to low carbon steel and pure Ti substrates using a pulsed air are. The depos itions were conducted with a series of pulses with current amplitudes of 75 A, 300 A, and 500 A, a pulse duration of 150 mu s, and a pulse r epetition rate of 100 Wt. The influence of the electrode material, dis charge energy and deposition time on the electrode erosion rater mass transfer direction, and the wear resistance and friction coefficient o f the coatings was investigated. Anodic and cathodic mass change chara cteristics depended on both the anode and cathode materials. Using a s teel cathode and a WC anode, depositions of the anode material always formed on the cathode. For the same WC anode but a Ti cathode, coating s only formed locally in the craters of the eroded cathode. The anodic mass loss when using the steel cathodes was about a factor of 3 large r than when using the Ti cathodes. The microhardness of the coated sub strates was larger by factors of 5-12 than the uncoated Ti and low car bon steel substrates. The coatings increased the wear resistance of th e steel and Ti substrates by factors of 4.3 and 1.4. respectively. The poorer performance of the coated Ti substrates is attributed to the i ntensive erosion of the Ti cathodes (compared to the steel cathodes) a nd the discontinuous nature of the coatings (i.e. only in the erosion caters). (C) 1998 Elsevier Science S.A.