利用SEM和物理化学相分析方法研究了5种Hf含量的FGH97粉末高温合金中γ’相和MC型碳化物形貌、化学组成及含量. 结果表明: Hf促进γ’相和MC相析出, 改变γ’相和MC相的化学组成, 对MC相的尺寸和形貌影响不大, 显著影响γ’相的尺寸和形貌, 促使γ’相的形态失稳, 导致立方状γ’相发生分裂, 使γ’相更快地进入稳定的立方状择优形态. 在FGH97合金中添加Hf, 可通过改变错配度d, 从而改变γ’相发生分裂的临界尺寸D_c. 建立了D_c与Hf含量w(Hf)的关系式: D_c=315.4+640.2w(Hf)-358.2[w(Hf)]². 随着Hf含量的增加, |d|逐渐变小, D_c增大. γ’相长大到临界尺寸时, γ’相由立方状分裂为八重小立方体状.

Microelement Hf added in Ni-based powder metallurgy (PM) superalloy can modify microstructure and improve mechanical properties, such as stress-rupture life, creep resistance and crack growth resistance, and also benefit to eliminate notch sensitivity. So systematically studying the effect of microelement Hf on PM superalloy microctructure will help to comprehend its corresponding mechanism. The effects of microelement Hf on the morphologies, chemical compositions and content of γ’ phase and MC carbide in FGH97 PM Superalloy were investigated by means of SEM and physiochemical phase analysis. The results showed that Hf facilitated the precipitations of γ’ phase and MC carbide, and changed chemical compositions of γ’ phase and MC carbide, the effect of Hf on the size and morphology of MC carbide was not obvious, while Hf greatly affected the size and morphology of γ’ phase and accelerated the splitting of γ’ phase from one instable cubic γ’ particle to stable octet of cubes. As Hf affected the lattice misfit of γ’/γ phase (d), modifying Hf content changed the critical splitting size of γ’ phase (D_c). The relationship between D_c and Hf content (w(Hf)) was found to be D_c=315.4+640.2w(Hf)-358.2[w(Hf)]². With Hf content increased, the absolute value of d decreased and D_c increased. Cubic γ’ particle split into an octet of cubes when γ’ phase grew up to the critical splitting size.