Research Of Porous Materials Fabricated By Self-Propagating High-Temperature Synthesis

The history of the formation and development of SHS (Self-propagatingHigh-temperature Synthesis) had been introduced briefly. Dissertations publicized bynational researchers and institutes , which they are studying SHS had beensummarized in this paper, along with the directions of their study and some of thematerials fabricated by them.Comparison of the privilege and disadvantage of all kinds of ways which they can produce porous materials had been done. We can find that the SHS is the most applicable and valuable means, which be used to fabricated Ni-Al porous material. Energy-saving, simple equipment, high purity and easy operation are its characters, together with high porosity and higher strength than made by conventional means under the same porosity.Through the change of the pre-heating temperature, effect of the pre-heating on the ignition had been attained. We can see, along the pre-heating temperature rising, the delay time of the igniting become shorter and shorter. By the calculation of the gas adsorded by the powder themselves and sealed in the cavity of the powder stacking, we can see: along with the combustion reaction proceeding, the heat released raising, the temperature of the specimen went up. Under the desired volume of the gas ,the more heat released ,the higher the temperature. Therefore ,the gas in the powder can get so high pressure that it can escape from inside specimen. The passes made by the gas's breakaway are the holes. At the same time, a part of the powders began to melt from the raising the temperature. So, stacking of the powders came to deform and even be destroyed. This deformation provides the space which the turn-up of the hole need. So we can say that the escapement of the high pressure and the deformation of the powders' stacking lead to the formation of the hole. In the NiAl binary phase diagram , there is a long distance between liquid line and solidus curve. Area of the over-cooling is bigger. It is prone to get by the pine-tree crystal. The sketches of he pine-tree crystal overlapped so that the liquid was sealed inside. Therefor, the feeding of the liquid is difficult. This is one of the reasons which lead tothe formation of the hole.