Xiu-Bo Liu

Tribology and high-temperature oxidation behaviors of NiCrBSiFe composite coatings on Ti6Al4V alloy by laser cladding

In order to improve the high-temperature wear and oxidation resistance of Ti6Al4V alloys simultaneously, NiCrBSiFe composite coatings were deposited on a Ti6Al4V alloy by laser cladding. The microstructure, tribological properties and high-temperature oxidation resistance of the composite coatings were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and an energy dispersive spectrometer (EDS). The results indicate that the combination between cladding zone and substrate is metallurgical bonding, and the coatings have few pores, and are crack free and homogeneous structures. In situ synthetic TiC, TiB2 and CrB particulates-reinforced γ-(Ni, Cr, Fe) matrix composite coatings are formed. The average micro-hardness of the composite coating is 950 HV0.5, and it is almost three times that of the substrate. The laser clad coatings possess better tribology properties than Ti6Al4V alloys at all test temperatures (RT, 600 °C) and the formation of dense oxide layers played an important role in improving the high temperature oxidation resistance of Ti6Al4V alloys.

The effect of Zr addition on the formation and structural properties of 3:29 compounds in the Fe-Nd-Ti-Zr system

A new series of 3:29 compounds in the Fe–Nd–Ti–Zr quaternary system were synthesized successfully. The formation and structural properties were studied by means of powder x-ray and powder neutron diffraction. The results reveal that only a small amount of Zr content can exist in the 3:29-type compounds in the Fe–Nd–Ti–Zr quaternary system. Higher Zr content induces the formation of rhombohedral Th2Zn17-type phase. In the structures of 3:29-type compounds, the Zr content partially substitutes for Nd and enters the 2a and 4i crystallographic sites exclusively. Upon Zr substitution, the lattice parameters a, b, c and the unit cell volumes V of (Nd,Zr)3(Fe,Ti)29 compounds decrease monotonically and their intrinsic magnetic properties, including the Curie temperature and saturation magnetization, lessen as well.