Preparation of V8C7-Fe/iron dual-scale composite via two-step in situ reaction

To overcome the disadvantages of low toughness and low fracture energy of conventional particle reinforced steel/iron-based composites, a novel V8C7-Fe/iron dual-scale composite was designed and fabricated via a two-step in situ reaction at 1150 °C for 5 min and 1100 °C for 12 h (denoted as 1150 °C-5 min + 1100 °C-12 h). The composite consists of a bundle-shaped V8C7-Fe dual-scale structure and cast iron matrix. Predominant features of the bundle-shaped V8C7-Fe dual-scale structure, which has a diameter of approximately 3 mm, include a toughness of the α-Fe phase and a high volume fraction of V8C7 particles that have different sizes and morphologies. The interface of the V8C7-Fe dual-scale structure/matrix has distinct gradient distribution characteristics. From the center of the V8C7-Fe dual-scale structure to the matrix, the morphology of the V8C7 particles evolves from nearly spherical to cubic. This is mainly because of changes in the growth environment that lead to the competitive growth between different crystal faces and orientation attachment growth during nucleation and growth. In addition, from the center of the V8C7-Fe dual-scale structure to the matrix, the hardness gradually decreases from 1306 HV0.2 to 410 HV0.2. For the V8C7-Fe/iron dual-scale composite, the yield strength, maximum compressive strength, and maximum compressive strain are approximately 1150 MPa, 1390 MPa, and 15.2%, respectively. Compared to cast iron (420 MPa, 830 MPa and 21.8%, respectively), the V8C7-Fe/iron dual-scale composite achieves both high strength and reasonable toughness.