Selective Surface Hardening

Choose material couples that are resistant to interaction in sliding (metal-to-metal wear resistance). Hardfacing alloys such as cobalt-base and nickel-chromium-boron alloys have been used for many years for applications involving metal-to-metal wear. Other surfaceengineering options include through-hardened tool steels, diffusion (case)-hardened surfaces, selective surface-hardened alloy steels, and some platings. 

A second mechanism in the. aging of CTPB propellants also exists and proceeds concurrently with the reactions proposed above. It consists of an attack at the reactive points of unsaturation in the backbone polymer, which causes additional crosslinking and hence an increase in propellant modulus, particularly at the surface. The exposed surface of CTPB propellants changes, as indicated by an increase in hardness. Heavy metal ions are particularly harmful, and it was found that an increase from 10 to 80 p.p.m. of iron caused a significant increase in surface hardening by catalytic attack on the double bonds. Antioxidants in general provide sufficient protection for polymer storage. In CTPB propellants the antioxidant selected to protect the double bond is very important. Amine-type antioxidants have provided better surface stability than phenolic compounds. 

Cu 60-150 Softer than Ni ductile resistant to fretting good electrical and thermal conductivity As a resist for selective case hardening of steel electroforming surface lubrication in metal working... 

Surface hardening involves selective hardening of just the surface of a part or changing the composition of the surface by diffusing a small atom into the surface (usually C or N), followed by heat treatment of the surface. An example is case hardening of steel by increasing the carbon content of the surface by heating the part for about one hour in contact with some source of carbon (such as methane gas) followed by heat treatment. 

The laser spray process uses a high power carbon dioxide laser focused onto the surface of the part to be metallized. A carrier gas such as belium blows metal particles into the path of the laser and onto the part. The laser melted particles may fuse to the surface, or may be incorporated into an aHoy in a molten surface up to 1-mm thick. The laser can be used for selective aHoying of the surface, for production of amorphous coatings, or for laser hardening. 

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