Preparation of nanostructured composites of titanium nitride ? nickel

Abstract

The nanostructured materials, named polycrystals, with a small crystalline size at length scale below 100 nm, possess a special structure in the interfaces between the crystallites. This gives rise to novel material properties and may promise future technological applications. The first studies on nanostructured materials, produced by evaporating and compacting small crystallites, were initiated by Professor Gleiter and his co-workers [1]. Further investigations have been performed by many researchers in recent years [2, 3]. However, nanostructured metal-non-metal composites have not been studied in detail. This letter reports the preparation of nanostructured composites of titanium nitride-nickel (TiN-Ni) by synthesis and condensation of TiN-Ni nanosize powders in d.c. arc plasma and in situ powder compacting at high pressure in high vacuum. The grain growth of nanostructured TiN-Ni composites and their density at different temperatures were also studie& High purity alloy of titanium and nickel was evaporated and nitrided by d.c. plasma in nitrogen atmosphere of 60 kPa. The reactants of TiN-Ni were carried rapidly to a cold finger of liquid nitrogen by plasma gas and were scraped, in situ, into a high pressure compacting device. There, the powders were compacted at a pressure of 3 GPa in high vacuum (1.333 x 10-4pa). Meanwhile the compacted TiN-Ni specimens were sintered for 1 h sequentially at 500 °C, at intervals of 200 °C, up to 1500 °C in nitrogen atmosphere. The particle size of the TiN-Ni composites was analysed by transmission electron microscopy (TEM). The purity of the powders was examined by chemical methods and an HZG4-PC X-ray diffractometer using CoK« radiation. Scanning electron microscopy (SEM) was performed to study the microstructure of nanostructured TiN-Ni specimens at different temperatures. The purity and particle size of TiN-Ni powders can be controlled by adjusting the temperature distribution of plasma in the reactor, the partial pressure of nitrogen and the cooling temperature of the cold finger. Fig. 1 shows the XRD pattern of nanosized TiN--Ni powders. A T E M micrograph of nanosized powders is shown in Fig. 2. The results indicate that the average particle size was about 20 nm and the purity was more than 98% (wt%), with Ni content of about 20% (wt %).