Research On Fabrication And Properties Of Network Ti₂AlN Particles Refoiced TiAl Composite

In this paper, Ti₂AlN ceramic, in the form of network, reinforced TiAl alloy was synthesized by combining powder metallurgy and in situ synthesis methods.The N element was introduced into the material system by gas nitriding of Ti powder, which was studied detailedly. The Ti powders with N element in the powder surface and Al powders were selected as raw materials. And vacuum hot pressing was employed to synthesized the composite material with special structure, Ti₂AlN ceramic with continuous network structure reinforced TiAl alloy. The nitriding process, the Ti, Al powder ratio and the hot pressing process were studied to analyzed their affects on the produced composite material's structure and properties.The results show that Ti powder with a particle size of 25μm can be smoothly nitrided in pure nitrogen environment at 600℃, generating nitrogen-rich phase Ti₂N at the surface of the powders. And with the nitriding time prolonging, the surface N concentration increased and finally formed the stable phase TiN. The Ti powders with such treatment and Al powders were mixed homogeneously and the hot pressed to produced the Ti₂AlN/TiAl composite with special reinforcement structure. The results show that the optimal nitriding process is that nitriding Ti powders in pure flowing nitrogen atmosphere at 600℃for 48 hours and followed by air cooling.Considering the microstructure of TiAl alloy is sensitive to the composition, the influence the moral ratio of the Ti powder with nitriding treatment to Al powder and the following heat treatment on the microstructure of the matrix were studied. The results show that TiAl alloy matrix with Al-rich TiAl2 phase, singleγ-TiAl phase, duplex, near lamellar and full lamellar microstructure respectively.Compressing property of the produced composite were studied. The compressing strength of the composite reinforced by the continuous network Ti₂AlN ceramic decreases with the temperature increasing. When compressed at ambient temperature, the material crushed at the maximum stress, showing completely brittleness. While deformed at high temperature, the material show some softening phenomenon after the compressing stress reaches maximum. Compressive properties can be enhanced Ti₂AlN/TiAl network compressive strength composites increase as the temperature decreased gradually phase at room temperature compressive strength of materials to achieve break-time, while at high temperature materials have a compressive strength after reaching the softeningphenomenon. The ratio of Ti and Al in 1:0.6, the network enhanced Ti₂AlN/TiAl matrix composites for the nearly lamellar organization, its compressive strength is higher than in the more than 800℃when the proportion of 1:0.75 get near TiAl matrix composites,at 900℃800℃higher than the rate enhancement significantly improves the time, at higher temperatures, the rate is only slightly enhanced.