Oxidation Behavior of W-Ta Alloys

Abstract

Although the refractorymetals typified by W, Ta and Mo show good mechanical properties at high temperature, their application is greatly limited because of their poor oxidation resistance. In this paper, oxidation properties of the W-Ta system were investigated. Samples were prepared by means of electron beam melting. The results are summarized as follows:
(1) All of the W-Ta alloys showed lower oxidation rates than pure W and Ta.
(2) Addition of 5%Ta to the W brought about a remarkable reduction oxidation rate, and the decrement remained almost unchanged until the addition of 30%Ta. The scale of these alloys consisted of WO_2.90.
(3) The lowest oxidation rate was attained at the composition of W-40∼50%Ta, and its oxidation product was 3WO₃·Ta₂O₅.
(4) Although the scale of these alloys was generally porous and had poor adherency with the metal matrix, only W-70%Ta alloy formed a compact and strong adheasive scale. But this W-70%Ta alloy was broken at the grain boundary when it was held for 30∼40 min at 1000°C in oxidation atmosphere.
(5) W and Ta alloys make a continuous solid solution and the lattice parameters of the alloys used in this investigation also supported this fact, but the hardness curves of our specimens showed abnormality.