抄録
In order to clarify the effect of hydrogen on the decomposition of β phase in a Zr-20 mass%Nb alloy, the Zr-20 mass%Nb alloys containing up to 200 ppm of hydrogen were prepared, and the change in microstructure and mechanical property with aging has been investigated.
As for the aging behavior, both the time required for start of age hardening and the time required for attainment of the maximum hardness bcome longer, as the hydrogen content increases. When the alloy is aged at temperatures below 773 K, the decomposition process is not affected by the addition of hydrogen. However, when the alloy is aged at 823 K, though only continuous precipitation occurs in the alloy without hydrogen, discontinuous precipitation occurs together with the continuous one in the alloy containing 200 ppm of hydrogen.
Microstructures of the alloy at the solution treated condition was not affected by the addition or hydrogen. However, during aging ω and α particles precipitated are coarsened by the existence of hydrogen. When the alloy containing 200 ppm of hydrogen is aged at 823 K, the microstructure changes from a globular type to a nodular type because of the change in precipitation mechanism in the alloy.
As the content of hydrogen increases, the hardness and tensile strength decrease. No deterioration in toughness was observed throughout this experiments.
