Boron Particle Composite Plating with Ni–B Alloy Matrix

Abstract

Ni-B alloy films containing amorphous boron particles ͑referred to as "Ni-B alloy composite films"͒ were fabricated by electrodeposition and were subsequently subjected to heat-treatment. Their compositions and microstructures were characterized, and their hardness was evaluated. The content of boron particles in the alloy composite films increased with boron particle concentration in the plating baths. In addition, the total boron content in the films increased with decreasing current density, reaching a maximum value of 34.3 atom %. The boron particles were homogeneously distributed in these alloy composite films and exhibited no cohesion. Heat-treatment of the alloy composite films consisting of a Ni-B alloy matrix and the boron particles led to a phase conversion from an inhomogeneous amorphous phase to stable homogeneous crystalline phases, which were similar to those in the Ni-B binary alloy phase diagram. The hardness of the Ni-B alloy 34.3 atom % B composite film was higher than that of a Ni-B alloy film both before and after heat-treatment. Ni-B alloy films are attractive for industrial applications because they possess several desirable properties, including high hardness and wear resistance. To date, such films have mainly been deposited by electroless plating methods, 1-11 and their applications have also been studied. [12][13][14][15][16][17][18] However, very few studies have been undertaken on Ni-B alloy films produced by electroplating methods.19-21 Most reports discuss alloy films with a boron content of under 25 atom %, which have the stable phases of Ni and Ni 3 B according to the Ni-B binary phase diagram. However, the phase diagram also indicates that Ni 2 B and other crystalline phases are stable when the boron content of Ni-B alloys exceeds 25 atom %. A comparison of the microstructure and characteristics of Ni-B alloy films having boron contents above and below 25 atom % is interesting from both an academic and a practical viewpoint. We initially attempted to fabricate Ni-B alloy films using a conventional electroplating method. However, the maximum boron content that could be achieved by this method was less than 25 atom %. We have already reported that Ni-P alloy films containing over 25 atom % phosphorus could be obtained using a unique technique, which involves the formation of a composite film of a Ni-P alloy and phosphorus particles and a subsequent heat-treatment. 22In the present study, to fabricate Ni-B alloy films with boron contents greater than 25 atom %, we used a similar technique, producing composite films of a Ni-B alloy and boron particles and then subjecting them to heat-treatments. Furthermore, we analyzed the microstructure and hardness of the alloy composite films both before and after heat-treatment. Experimental

Properties of Borided Cemented Carbides with Various Binders

“…The presence of the complex boride CoWB improves the wear resistance of the surface [13]. It is because this boride has higher hardness than other borides, such as CoB, Co2B or Ni2B, Ni3B [13,14]. Hence, the CoWB diffusion layer can be applied as the surface finish for cutting tools.…”