Electrospark deposited coating
Electrospark deposited coating
(OP)
Electrospark deposition (ESD) was developed in the Soviet Union and came to the USA when one of the national laboratories, used it for depositing zirconium on stainless steel. This is a good technique to put a metallic or a cermet such as WC, TiB on a component for wear resistance. The mechanical engineers have not caught on to this in preference to the more exotic PVD, CVD, and laser deposition. The technique can complement laser alloying by first depositing a metal, alloy or an electrically conducting cermet on the surface and then zapping with a laser to form a metallurgical bond. I would like to know if there are other applications of ESD, which can reduced wear of components or in such application as depositing a high conductivity metal for improved electrical contact





RE: Electrospark deposited coating
RE: Electrospark deposited coating
RE: Electrospark deposited coating
Mike Halloran
Pembroke Pines, FL, USA
RE: Electrospark deposited coating
RE: Electrospark deposited coating
Therefore, if you insist that it is a mechanical bond, then have it your way. A rose by any other name smells just as sweet (if you do not have an allergy to rose). The Materials Science Engineers call any bulk bond by a process such as melting, diffusion or even surface migration, etc., a metallurgical bond if the atoms in the bond are held by the interatomic force and do not fall apart by mere attrition. In the galvanizing of steel a metallurgical bond is created by the reaction of zinc atoms with iron atoms. In ESD the carbides and borides of W,Ti,Cr, etc dissociate at the localized high temperature created in the electric micro-arc, and get incorporated with the substrate elements. We call this a metallurgical bond. But if you want to emulate calling a legitimate football as soccer, and wish to "think" that a diffusion bond is a mechanical bond, have it your way, We live in a free country with the freedom of expression. But the wear resistance of ESD coatings with cermets is an established scientific fact based on hard experimental evidence.
"Goodwill towards all and Malice to none"
RE: Electrospark deposited coating
The ESD uses an "electrode", which is more a "rod" than a wire. The wire would perhaps melt and spatter too much and may give a very rough coating. I have not used a wire but cermet and metal rods with 1/8 inch diameter to 1/2 inch diameter. The other characteristics are similar to the 'exploding wire technique'. I do not have the exact parameters but it is also a rapid charging and discharge of a capacitor creating localized very high temperatures. I also have observed a plasma around the electrode; but it is from the ionization of air or the gas surrounding the electrode. The deposited materials is in the form of imperfect spheres which form a bond with the substrate and with each other. There are many good publications on ESD especially from the Russian scientists and some from the US Energy Research laboratories. They are better "Pundits" than "yours truly" who is basically a practicing scientist and a "technician".
"Goodwill to all and malice towards none"
RE: Electrospark deposited coating
Diffusion bonding is a solid state joining process where atoms of the contacting surfaces intermingle over time if subjected to the right combination of pressure, temperature, and atmosphere. However, the depth of the diffusion zone can be quite limited when dissimilar materials are being joined. While I believe the material within the diffusion zone can technically be described as an alloy, I also think there might be a better term that could be used.
I've done some work with friction welding, which is a solid state process. And one thing I recall looking at micro-sections taken from the welds is that it is very hard to see any grain boundary around the weld zone.
Below is a cross section of a carbon steel surface that was ESD coated with a dissimilar material. You can clearly see a well defined boundary between the coating and substrate. This is not what I would describe as "alloying", but that is the term the author uses. To me the interface looks more mechanical than metallurgical in nature, but I'm no expert.
Interesting discussion and I've learned a bit about ESD processes.