Novel constructional materials with an oriented porous structure – gazars

Abstract

Modern construction metallic materials often work under conditions, where it is necessary to show properties uninherent to continuous materials. High–porous materials have a cellular structure and are characterized with low dencity, high specific stiffness that provides specific advantages above dense materials. The paper reviews such materials with the oriented porous structure – gasars. The theoretical and technological bases of their manufacturing were first developed in Ukraine. Their difference from foamed metals by powder or liquid methods, which are formed under the action of gas–forming reagents, is noted. The formation of gas pores in gasars occurs as a result of a gas–eutectic reaction with the formation of bubbles at the crystallization front in gas–metal systems due to changes in the solubility of gases. The morphology of the pore channels depends on many factors, including the intensity and direction of heat removal. Techniques and equipment are considered, which provides control the macrostructure of the material with the formation of various morphologies – from large cavities, spherical pores to evenly distributed elongated channels of the same or variable cross–section and gradient monolithic porous structures. It is determined that most technologies use hydrogen as a pore formed gas, although there are examples of successful use of hydrocarbons (CH4), water vapor, nitrogen, ammonia and the like. Over the years of research, scientists from different countries have developed methods for obtaining gasars not only on the basis of iron–carbon alloys but also aluminum, copper, nickel, titanium alloys. An analysis of the existing and future opportunities for gasars application noted that it depends on more complete study of gas–eutectic transformations and related processes in the crystallization of melts for their control and development of cost–effective technologies for such materials. Keywords: gasars, oriented porous structure, gas–eutectic reaction, mechanical properties.