Improved fracture toughness of boride coating developed with a diffusion annealing process

In this study, the fracture toughness of boride coatings formed at the surface of AISI 1045 steel was improved by means of a diffusion annealing process. First, the boriding of AISI 1045 steel was performed by the powder-pack method at a temperature of 1223 K and a range of exposure times (8–12 h). The diffusion annealing process was conducted on the borided steels at a temperature of 1273 K with 8 h of exposure using a diluent atmosphere of SiC powder and bentonite. To establish the mechanical behavior of the boride coatings developed by both treatments, properties such as the real hardness and the Youngʹs modulus were estimated at 50 μm from the surface using Vickers and Knoop testing, respectively. The fracture toughness of the boride coatings was estimated using a universal crack equation applicable independently of the cracking mode. The boride coating obtained by the boriding process exhibited an intermediate cracking mode, while the coatings obtained by the diffusion annealing process showed a radial-median mode. fect of the diffusion annealing process on the fracture toughness of the boride coatings revealed an increase of approximately 50% in comparison with the coatings developed by the powder-pack boriding process.