Tensile fracture behavior of Ni- and Cr-C/Ni-coated high-carbon tool steel (AISI 1090)

The tensile fracture behavior of Ni- and Cr-C/Ni-coated high-carbon tool steel specimens was studied. The Cr-C coating was prepared in a Cr³⁺-based plating bath, and the Ni coating was prepared in a Ni-sulfate bath. The experimental results indicate that the yield and ultimate tensile strengths were not changed after Ni- or Cr-C/Ni-coating. However, the elongation percentage of the steel specimen was clearly reduced after Cr-C/Ni-coating. According to the fractography study, the fracture feature with necking and a cup-and-cone appearance was observed in the steel and Ni-coated steel specimens after the tensile test. However, the fracture feature of the Cr-C/Ni-coated steel specimens with relatively low elongation percentages exhibited an obvious cracking plateau. Under the application of tensile stress, cracks in the Cr-C coating propagated through the Ni coating and then into the steel substrate, forming a cracking plateau and, decreasing its elongation percentage. Moreover, branch cracking was observed during crack propagation to develop a fracture appearance with some cracks and crack facets.