Abstract
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.
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