Diamond and common metals and their alloys have a high interface energy, so that diamond cannot be infiltrated by common low melting point alloys, and the weldability is extremely poor. At present, the weldability between diamond and metal is mainly improved by adding strong carbide forming elements in copper-silver alloy solder or by metalizing the diamond surface.
① Active solder method Solder generally uses Ti-containing copper-silver alloy, and soldering in inert gas or vacuum without flux. Commonly used solder composition Ag=68.8wt%, Cu=26.7wt%, Ti=4.5wt%, the commonly used preparation methods are arc melting and powder metallurgy. As an active element, Ti reacts with C to generate TiC during the welding process, which can improve the wettability and bonding strength of diamond and solder. The heating temperature is generally 850°C, keep for 10 minutes, and slowly cool down to reduce internal stress.
② Welding after surface metallization The metallization of the diamond surface is to plate metal on the diamond surface through surface treatment technology to make the surface have metal or metalloid properties. Generally, Ti is plated on the surface of diamond. Ti reacts with C to generate TiC. TiC and Ag-Cu alloy brazing filler metal have good wettability and bonding strength. Currently commonly used titanium plating methods are: vacuum physical vapor deposition (PVD, mainly including vacuum evaporation plating, vacuum sputtering, vacuum ion plating, etc.), chemical vapor plating and powder coating sintering. The PVD method has a low single coating amount, the temperature of the diamond during the coating is lower than 500 ℃, and the coating is physically attached to the diamond without chemical metallurgy. CVD method Ti and diamond chemically react to form a strong metallurgical bond, the reaction temperature is high, and the diamond is damaged.
