Research on performance and improvement of electroplated diamond tools II

Therefore, NiCo binary alloy coating has become a widely used matrix material. However, sometimes the hardness of NiCo binary alloy coating is still insufficient. When processing hard and highly abrasive materials, the matrix is ​​consumed quickly. Moreover, NiCo plating can only ensure high hardness and wear resistance when the cobalt content reaches about 30%. A large amount of expensive metallic cobalt increases the cost.

1.1.2NiMn binary alloy coating

Metal manganese can improve the hardness, strength and wear resistance of the nickel matrix better than cobalt. The hardness of the nickel-manganese matrix is ​​about 10 degrees Rockwell (HRC) higher than that of the nickel-cobalt matrix. Although the manganese content in the alloy is very small, it has a great impact on the performance of the matrix. When drilling in hard and highly abrasive formations, the average life and aging efficiency of nickel-manganese matrix diamond drill bits are 55% and 30% higher than those of nickel-cobalt matrix drill bits respectively. At the same time, nickel-manganese matrix diamond drill bits do not require high speeds and high pressures, which is beneficial to reducing material consumption and drilling costs. However, the NiMn binary alloy coating is highly brittle and easy to crack, making the working layer prone to fragmentation.

1.1.3NiCoMn ternary alloy coating

NiCoMn ternary alloy coating has higher comprehensive mechanical properties. The hardness is higher than NiCo and the brittleness is lower than NiMn, which meets the requirements of electroplated diamond products for the matrix. Stone tools made of NiCoMn ternary alloy coating are sharper and more durable than NiCo binary alloy coating products, especially for hard stones, they can show their advantages. Due to saving a large amount of expensive material cobalt, the cost of NiCoMn ternary alloy coating is low. The mechanical properties of NiCoMn ternary alloy coating can be adjusted within a wide range to meet the needs of a wider range of occasions. However, when obtaining NiCoMn ternary alloy coating, the composition of the plating solution is complex and the stability is difficult to control.

1.2 Composite metal coating

Composite coating is a special coating formed by uniformly mixing one or several insoluble solid particles and fibers into the metal coating through co-deposition. Since a large number of solid particles are evenly dispersed in the composite coating, these hard particles will greatly hinder the slip between grains and effectively strengthen the metal.

1.2.1NiCo fine-grained diamond composite coating

By adding an appropriate amount of nano-diamond powder to the plating solution, the hardness of the NiCo diamond composite coating obtained is significantly improved, and the hardness can reach 601.53HV[8 ], the friction and wear performance is significantly improved: the friction coefficient of the nickel-cobalt alloy coating is about 0.35, and the service life is 0.022km on average when the friction radius is 14mm; the friction coefficient of the NiCodiamond composite coating containing nanodiamond powder is about 0.3, and the coating life is 0.15km when the friction radius is 14mm [9]. NiCodiamond composite coating is used as the diamond drill bit matrix. The prepared diamond drill bit can drill in hard and highly abrasive formations. It has good wear resistance, fast drill bit penetration, long life, and can prevent hole deflection [10]. Since ultrafine diamond powder is easily agglomerated and its performance cannot be fully exerted, measures must be taken to disperse the diamond powder. This will inevitably restrict the use value and application prospects of ultrafine powder.

1.2.2NiCo rare earth element composite coating

The addition of a small amount of rare earth compounds can improve the properties of the plating solution and coating to varying degrees. During the electrodeposition process, mainly anodized Ions are adsorbed on the surface of metal deposits, and rare earth metal ions show strong adsorption on electrodes. Rare earth metal ions are easily adsorbed on the active points of crystal growth, that is, adsorbed on the growth points of crystal faces, effectively inhibiting the growth of crystals. Therefore, after adding rare earth elements to the plating solution, a coating with fine grains can be obtained. Through the grinding experiments of bright nickel coating and bright nickel coating diamond tools adding rare earth elements to grind ceramics using the universal cylindrical grinder M1420E, it was found that the addition of rare earth elements improved the grinding ratio of diamond tools.