Preparation And Properties Of Ti-Al Alloy Porous Materials

In this thesis, the Ti-Al intermetallic porous filtering materials were firstly fabricated by the elemental powder reactive synthesis through the pressureless sintering of elemental Ti and Al powders. The processes of phase transition, as well as pore formation mechanism, were investigated by X-ray diffraction(XRD),scanning electron microscopy (SEM), differential scanning calorimetry(DSC). The relationships between cold pressing pressure, powder size, sintering temperature and pore structure, filtering performance were systematically researched, and their influence mechanics were analysized also. The oxidation resistance of the Ti-Al filtering material was investigated by cyclical oxidation mathod.The main research results can be summarized as follows:The Ti-Al intermetallic filtering material, mainly consisting of TiAl phase and with 38.4%～41.7% pylome, pore size distributing in the range of 1～9μm, can be obtained by reactive sintering under 620℃～640℃(constant temperature 3～4h)and 1300℃(constant temperature 1h) process conditions.The prime reason for the pore formation is considered to be Kirkendall effect. The final pore structure results from the following processes: (i) Frenkel pores form during low temperature solid state interdiffusion, (ii) with increasing the temperature, the above Frenkel pores and the pores in the green compact redistribute, congregate and grow up to the mazy connected structure pores.When pressing pressure increased, the maximum aperture, pylome porosity and permeability coefficient are reduced because of mesopore decreased and bias diffusing pore increased, but when pressing pressure was 250MPa, the maximum pylome porosity can be obtained. When powder size increased, the maximum aperture, pylome porosity and permeability coefficient are increased because of mesopore increased, but the effect of aluminium powder size is smaller than Ti powder size because of Al deformability. When sintering temperature heightened, because of growth of crystal grains and pores, the maximum aperture and permeability coefficient are increased, but pylome porosity is reduced.The oxidation resistance of the Ti-Al filtering material was systematically investigated by cyclical oxidation mathod. The oxidation resistance of the TiAl filtering material is better than the traditional 316L stainless filtering material.