Preparation of a gradient nanostructured surface TaC layer-reinforced Fe substrate by in situ reaction

摘要

A gradient nanostructured surface tantalum carbide (TaC) layer was prepared by a general heat treatment process on the surface of grey cast iron at 1135 degrees C for 15 min. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results reveal that the topmost surface of the layer consists of dense TaC ceramic grains; the average grain size is less than 10 nm and increases with depth. The chemical composition also presents a gradient distribution. The investigation indicates that the formation of the TaC layer can be attributed to a reaction between tantalum atoms provided by the tantalum plate and carbon atoms supplied by the graphite phase in the substrate. Furthermore, microhardness, elastic modulus and fracture toughness tests have been performed on the TaC layer under nano indentation mode. The microhardness, in the range of 21.3-28.1 GPa, is 3-4 times that of the substrate. The fracture toughness is calculated to be 3.9 +/- 0.2 MPa m(1/2). The results emphasize that the gradient nanostructured TaC layer improved the comprehensive mechanical properties of the substrate surface by its ultrafine microstructure. (C) 2017 Elsevier B.V. All rights reserved.