Nana Zhao

Gradually varying mechanical properties of in situ synthesized NbC–Fe-graded composite coating

NbC–Fe-graded composite coating was fabricated by in situ synthesis using a pure niobium plate and grey cast iron as the raw materials. SEM analysis demonstrates that the thickness of coating is about 400 μm. From the surface to the matrix, the volume fraction of NbC particulates continuously decreases from 95 to 0%, while the average particulate diameter gradually increases from 200 nm to 1 μm. Along the depth towards the matrix, the nano-hardness and elastic modulus of the graded coating decrease from 23.5 to 3 GPa and from 435 to 150 GPa, respectively. In addition, the fracture toughness (KC) of 8.62 MPa m1/2 is obtained on the surface of the coating by the Vickers indentation technique. And the fracture mechanism is intergranular cracking.

Abrasive Wear Characteristics of Surface Gradient Composites of TaC Reinforced Iron Matrix Prepared by In-Situ Technology

Tantalum carbide gradient composite was fabricated via in-situ reaction of pure tantalum plate with gray cast at high temperature. The morphology, phase constituent, microhardness, and relative abrasion resistance of the composite were characterized by scanning electron microscopy, X-ray diffraction, microhardness tester and abrasive wear testing machine. The results show that the thickness of the gradient composite is about 475 μm. The cast 170 μm thick surface layer is a dense ceramic layer consisted of ~95% submicron TaC particles, and the highest micro-hardness value of which is 2328HV0.1; In the sub-layer, there exists a gradient distribution of TaC particles from 90% to 0% in volume fraction, correspondingly the microhardness value decreased from 915HV0.1to 410HV0.1, and the size of the TaC particles increased to 0.5-1.5 μm; the interface between the composite and matrix exhibits a perfect metallurgical bonding. The TaC reinforced iron matrix surface gradient composite shows far superior wear resistance than the gray cast iron. The wear mechanism is mainly related with the local plastic deformation,micro cracking caused by misrouted broken carbide particles.

Nanophase modification of the superficial layer of cast iron during the interaction of the melt with a carbide-forming metal

In the present publication, we report on the results of a study of the structural-phase state of the superficial layer of cast iron formed as a result of an interaction of cast-iron melt with a plate of carbide-forming Ta metal. It is found that, as a result of the interaction, in the superficial layer of cast iron there forms a cermet-type heterophase structure with nanocrystalline carbide phase. The influence of the formed heterophase structure on the physical properties of the superficial layer of cast iron is demonstrated.