compounds of beryllium with other metals. They were discovered during research on beryllium alloys (1916). The crystalline structures of the beryllides of copper, nickel, and iron were determined in 1935. The beryllides have been considered as a class of high-temperature materials since the 1950’s.
Methods of powder metallurgy are generally used in obtaining beryllides. The higher beryllides of the transition metals (Nb, Zr, Ta, and others), which retain their strength at high temperatures, are the most useful as construction materials; their strength increases somewhat in the temperature interval 1100°-1300° C owing to the appearance of plasticity (see Figure 1). The mechanical properties of a number of beryllides are given in Table 1.
The strength properties of the beryllides depend on grain size (see Figure 2), impurity content, porosity, and surface quality after machining. An increase in grain size from 12 to 45 microns in TaBe12 reduces the high-temperature (1500° C) strength by a factor of almost 4, and the presence of 0.5 percent Al in ZrBe13 reduces the strength by a factor of 2. Sections, rods, tubes, cones, cylinders, blocks, bars, and disks are obtained from beryllides by means of hot compacting of powders, cold pressing and sintering, isostatic molding, slip casting, extrusion with a plasticizer and subsequent sintering, and plasma plating. The beryllides are used in those fields of technology in which high specific strength, low density, high resistance to thermal stresses, resistance to oxidation, and retention of strength at high temperatures are required. For example, beryllides are used in aviation and rocket construction to make the edges of fairings, wing and fuselage panels, and the mounting and supporting structures of rocket systems with operating temperatures of up to
|Table 1. Mechanical Properties of Beryllides|
|Density (percent of theoretical)||Average grain size (microns)||Testing temperature (°C)||Vlckers hardness (load 24.5 N)||Bending strength (MN/m2)||Elastic modulus (GN/m2)||Specific elongation (percent)|
|Hafnium beryllide (Hf2Be21) Density 4,260 kg/m3; Tm = 1927°C|
|Zirconium beryllide (ZrBe13) Density 2,720 kg/m3; Tm = 871 °C|
|Niobium beryllide (NbBe12) Density 2,910 kg/m3; Tm = 1688°C|
|Tantalum beryllide (TaBe12) Density 4,180 kg/m3; Tm = 1848°C|
1700° C. The resistance of beryllides to thermal shocks at high temperatures is high in comparison with the majority of metallic oxides. Plutonium and americium beryllides can be used as neutron sources, and uranium, zirconium, and hafnium beryllides can serve as fissionable material and moderators. Upon the beryllization of commercial iron, stainless steel, and molybdenum at 800°-1250°C, layers are formed that contain the beryllides of iron, nickel, and molybdenum respectively, providing increased hardness and thermal stability in the temperature range 800°-1200° C. The known technological properties of beryllides are not the ultimate properties inherent to this class of compounds. Impurities, large grain size, and imperfect machining hinder the attainment of maximal positive properties.
REFERENCESMekhanicheskie svoistva metallicheskikh soedinenii: Sb. st. Edited by I.I. Kornilov. Moscow, 1962. (Translated from English.)
Samsonov, G. V. Berillidy. Kiev, 1966.
Ogneupory dlia kosmosa: Spravochnik. Moscow, 1967. (Translated from English.)
V. F. GOGULIA