The Study On Al₂O₃-TiB₂ Complex Phase Coating On The Surface Of Spot Welding Electrode By Electro-Spark Deposition

Because of excellent mechanical properties and the electrical conductivity of Al₂O₃-TiB₂, in this study, complex phase Al₂O₃-TiB₂ coating on spot welding electrode by electro-spark deposition was proposed for further improving the service life of the spot welding electrode. This research mainly focuses on the preparation of Al₂O₃-TiB₂ composite ceramic powders by mechanically alloying, then the preparation of Al₂O₃-TiB₂ composite deposition rods by pressureless sintering of ball milled powders, and the last complex phase Al₂O₃-TiB₂ coating on spot welding electrode using the Al₂O₃-TiB₂ composite rods by electro-spark deposition. Based on the consideration of the wettability between Al₂O₃-TiB₂ and Cu substrate, different content of Ni powder was added to the Al-TiO₂-B₂O₃ ternary ball milled system to synthesize Ni/Al₂O₃-TiB₂ metal ceramic powder. Surprisingly, it was found that the existence of ductile metal Ni accelerate the whole process of mechanical alloying during the Al-TiO₂-B₂O₃-Ni quaternary system ball mill experiment. Ball mill reaction rate is promoted along with increase of the Ni content（lower than 20 wt.%）. When the Ni content is high than 20 wt.%, the promoting effect is gradually weakened. To further confirm the promoting effect of Ni addition and explore the mechanism of the phase transformation during Al-TiO₂-B₂O₃-Ni high-energy ball milling, the group I（Ni-10） and group II（Ni-0） were selected for verification experiment（the ball-to-powder weight ratio 10:1, the rotational speed of the vial 500 rpm）. Different metal additives Mn, Co（0¹0wt.%） was added to Ni/Al₂O₃-TiB₂ ball milled powders for 10 MPa single-action pressure molding（?8mm × 27mm）with liquid paraffin as forming agent after appropriate hand blender. The Ni/Al₂O₃-TiB₂ compacts with different additives were sintered under the same sintering process（10°C/min heat up to 800°C preservation for 2 hours, 10°C/min heat up to 1400°C preservation for half an hour, furnace cooling） for preparation of deposition rods. Successfully, complex phase Al₂O₃-TiB₂ coating was obtained on spot welding electrode by electro-spark deposition using the sintered deposition rods（8wt.%Mn deposition rod and 5wt.%Mn+5wt.%Co deposition rod）. Due to the difference of the conductivity of deposition rods, the best discharge voltage of 8wt.%Mn deposition rod is 150 V, while that of 5wt.%Mn+5wt.%Co deposition rod is 175 V.