Impact of the electrochemical modification of WC-Co materials on the wetting of their surface by copper-based filler metals

摘要

Mining activities, and particularly work involving surface, underground excavation and drilling of earth, rock and deposits, requires the use of excavation tools, in which WC-Co sintered materials play a leading role. WC-Co materials are commonly used only in those fragments of cutting tools, which, owing to their mechanical parameters, are responsible for the quantity, quality, accuracy, drilling speed and acquisition of excavated material Mouldings based on WC-Co material that forms the tool blades, are combined with the tool body by brazing. To guarantee a strong connection, it is very important to ensure that the following materials are chosen correctly: WC-Co mouldings, the tool body, brazing type, flux. It is necessary to determine the right parameters of the brazing process, including time, temperature, and to keep a high level of purity of the brazing operation. WC-Co carbides do not wet easily, and in order to make a proper connection, it is necessary to sandblast their surface. It is also necessary to use flux during brazing, or sometimes to carry out the process in a furnace with a reducing atmosphere. Leaving residual oxides, Le. the products of primary corrosion, during the brazing process, including flux residues or slag inside the brazing gap and on the brazing surface, leads to secondary corrosion, which significantly reduces the tool's lifespan. Reducing the amount of the fluxes needed is possible after the application of short electrochemical surface modification of WC-Co mouldings, which is carried out in a sodium hydroxide solution. During the treatment process, the WC-Co grains that are located on the moulding's surface are etched, which leads to a significant increase of the exposed areas of easily wettable cobalt. The processes of surface wetting of the materials forming the brazed joints were examined using the following equipment: equipment for measuring the kinetics of brazed substrate wetting - submitted by GONAR-BIS Ltd Company, as Patent No: UPP4682558. The process of filler metal spreading over the surface of the tested materials was recorded using a camera at a rate of 529fps. Analysis of the produced film frames made it possible to compare the spread time of the front wave of molten filler metal on all the tested brazed substrates.