GB949785A - - Google Patents

Abstract

949,785. Alloys. E. I. DU PONT DE NEMOURS & CO. June 13, 1960, No. 20668/60. Drawings to Specification. Heading C7A. Compositions consisting of chromium together with one or more metals the oxides of which have a free energy of formation at 27 ‹C. of up to 75 milocals. per gram-atom of oxygen are hardened by the dispersion therein of one or more refractory oxides in the form of substantially discrete particles having an average dimension of 5-500 mÁ and a surface area of 12/D to 1200/D sq.m./gm. where D is the density in gm./ml. The refractory oxide phase is insoluble in the metal phase, has a melting point of at least 1000 ‹C. and a free energy of formation at 1000 ‹C. in excess of 90 milocals. per gram-atom of oxygen. The melting point of the metallic phase is not less than 700 ‹C. and the hardened composition has a 0À2% yield strength at a temperature 75% of the melting point of the metallic phase in degrees absolute # which is at least 1.5 times that of the metallic phase. Metals listed as suitable are Fe, Co, Ni, Cu, Cd, Th, Ge, In, Sn, Pb, Sb, Bi, Mo, W, Re, Ag, Au, Ru, Rh, Pd, Os, Pt, and they may be hardened with oxides of Y, Ca, La, Be, Th, Mg, U, Hf, Ce, Al, Zr, Ba, Ti, or with compounds such as MgAl 2 O 4 , aluminates, silicates and zirconates where each constituent oxide fulfils the above requirements. The ratio of metal : oxide may be as high as 1:1 by volume but such compositions may be pyrophoric in fine powder form and up to 30% oxide by volume is a more usual range. In a preferred method of preparing the compositions the constituents of the metallic phase are co-precipitated in the form of hydrous oxygen-containing compounds from suitable solutions with the refractory oxide particles which may be added in the form of a colloidal aquasol. The mixed oxides are then reduced in a stream of hydrogen or other reducing gas and the resulting powder compacted, sintered and worked. A preferred range of metallic composition is Fe+Co+Ni 50-90 Mo+W 0-20 Cr 10-25.