单晶合金中孔洞对蠕变行为的影响

通过对有/无缺陷单晶镍基合金蠕变性能测试、组织形貌观察及采用有限元对近孔洞区域的应力场分析,研究了组织缺陷对单晶合金蠕变行为及组织演化的影响。结果表明:组织缺陷可明显降低单晶镍基合金的塑性和蠕变寿命。在高温蠕变期间,近孔洞区域的应力等值线具有碟形分布特征,并沿与施加应力轴成45°角方向有较大值,该应力分布特征可使合金中γ′相转变成与施加应力轴成45°角的筏状结构,并使圆形孔洞沿应力轴方向伸长成椭圆状。蠕变期间,在合金圆形孔洞缺陷的上、下区域具有较小的应力值,而在圆形孔洞的两侧极点处具有最大应力值,随蠕变时间延长,应力值增大,促使裂纹在该处萌生,并沿垂直于应力轴方向扩展是降低合金蠕变寿命的主要原因。

Influence of Void on Creep Behavior of Single Crystal Nickel-Based Superalloy

By means of creep property test, microstructure observation and FEM analysis of the stress field near the voids, the influence of the microstructure defects on creep behavior and microstructure evolution of single crystal nickel-based superalloys was investigated. Results show that the plasticity and creep lifetime of the single crystal nickel-based superalloys are obviously decreased by microstructure defects. During high temperature creep, the stress isoline near the voids displays the feature of acetabuliform distribution, and possesses bigger values in the direction of 45° angle to the applied stress axis. That results in the γ' phase transformed into the rafted structure in the direction of 45° angle to the applied stress axis, and the circular voids defects are elongated into the ellipse in the applied stress axis direction. During creep, smaller values of the stress distribution are in the up and down regions of the circular voids, and the maximum value of the stress distribution appears in the apices region at the sides of the void. Furthermore, the fact that the value of the stres sdistribution increases as creep goes on results in the germination there and expanding vertically to the stress axis of the cracks, which is a main reason of creep lifetime decrease of the alloys.