SOME CHARACTERISTICS OF NICKEL-THORIA ALLOYS PREPARED BY HOT PRESSING IN CARBON DIES *

Fully dense nickel-thoria alloys, varying in ThO₂ content from 1·0 to 3·0 vol.-%, have been prepared by a powder-metallurgical method. The structures of the as-pressed alloys were examined and some of their mechanical properties measured. The effect on the yielding behaviour of the alloys of substituting MgO for ThO₂, and of varying the grain size of the matrix, has also been studied. An initial discontinuous yield is observed for as-pressed alloys and a strain-ageing effect for both as-pressed alloys and worked material. Decarburization has no influence on the initial discontinuous yield, but removes the strain-ageing effect. The strain-ageing behaviour of the alloys has been investigated and the interaction of carbon with dislocations demonstrated.