Zr-2．5Nb合金中β-Nb相的氧化过程

OXIDATION BEHAVIOR OF THEβ-Nb PHASE PRECIPITATED IN Zr-2.5Nb ALLOY

Zr-2.5Nb合金经β相水淬、冷轧变形及580℃,50 h退火处理,在静态高压釜中进行500℃/10.3 MPa的过热蒸汽腐蚀实验.HRTEM观测表明,580℃,50 h退火处理的锆合金析出了颗粒细小(<100 nm)的β-Nb第二相,其数量较多,分布较均匀.β-Nb相的氧化速率比锆合金基体缓慢,在氧化过程中首先生成NbO_2,呈现晶态和非晶态的混合组织,然后转变成非晶态占主导的氧化物,最后流失到腐蚀介质中.

The corrosion behavior for Zr 2.5Nb specimens heat treated at 580 ℃ for 50 h after β- quenching and cold rolling has been investigated in 500 ℃/10.3 MPa superheated steam by autoclave tests. HRTEM equipped with EDS was employed to investigate the matrix microstructure and the oxidation behavior of the β-Nb second phase particles （SPPs）. It was found that many β-Nb SPPs with small sizes （〈100 nm） randomly precipitated after heat treating at 580 ℃ for 50 h. It was noted that the （3 Nb SPPs were more slowly oxidized than the zirconium matrix. The β-Nb SPPs of bcc structure were oxidized to form the mixed structure of amorphous oxide and crystalline NbO2 at the initial oxidation stage, and then the amorphous phase was changed to the main structure at the middle oxidation stage, finally the niobium oxides were dissolved into the corrosion medium.