Welding Technology of PDC

PDC cutters feature high hardness, high wear resistance of diamond, and good impact toughness of cemented carbide. It has been widely used in geological drilling, oil and gas drilling, and cutting tools. The failure temperature of the polycrystalline diamond layer is 700°C, so the temperature of the diamond layer must be controlled below 700°C during the welding process. The heating method plays a decisive role in the PDC brazing process. According to the heating method, the brazing method can be divided into flame brazing, vacuum brazing, vacuum diffusion bonding, high-frequency induction brazing, laser beam welding, etc.

PDC flame brazing

Flame brazing is a welding method that uses a flame generated by gas combustion for heating. Firstly, use the flame to heat the steel body, then move the flame to the PDC when the flux begins to melt. The main process of flame brazing includes pre-weld treatment, heating, heat preservation, cooling, post-weld treatment, etc.

PDC vacuum brazing

Vacuum brazing is a welding method that heats the workpiece in a vacuum state in an atmosphere without oxidizing gas. Vacuum brazing is to use the resistance heat of the workpiece as a heat source meanwhile locally cools the polycrystalline diamond layer to implement high-temperature brazing. Using continuous water cooling during the brazing process to ensure that the temperature of the diamond layer is controlled below 700°C; the vacuum degree in the cold state of brazing is required to be lower than 6. 65×10-3 Pa, and the vacuum degree in the hot state is lower than 1. 33×10-2 Pa. After welding, put the workpiece into an incubator for heat preservation to eliminate the thermal stress generated during the brazing process. The shear strength of vacuum brazing joints is relatively stable, the joint strength is high, and the average shear strength can reach 451.9 MPa.

PDC vacuum diffusion bonding

Vacuum diffusion bonding is to make the surfaces of clean workpieces in a vacuum close to each other at high temperature and high pressure, atoms diffuse to each other within a relatively small distance, thereby joining two parts together.

The most fundamental feature of diffusion bonding :

1. the liquid alloy formed in the brazing seam during the brazing heating process

2. the liquid alloy is kept for a long time at a temperature higher than the solidus temperature of the brazing filler metal so that it is isothermally solidified to form a brazing seam.

This method is very effective for PDC's cemented carbide substrate and diamond, which are with very different expansion coefficients. The vacuum diffusion bonding process can overcome the problem that PDC is easy to fall off due to the sharp drop in the strength of the brazing filler metal. (during drilling, the temperature is increased, and the strength of the brazing metal will sharply drop.)

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