拉伸与低周疲劳载荷作用下夹杂物特征参数对航空用超高强度钢中裂纹萌生与扩展的影响

Influence of characteristic inclusion parameters on crack initiation and propagation in ultra-high strength steels for aerospace application under tensile and low cyclic fatigue loading

为了研究非金属夹杂物对航空用超高强度钢性能的影响,采用扫描电镜原位观测的方法,跟踪观察了拉伸和低周疲劳载荷作用下两种航空用超高强度钢中不同种类、形态和尺寸的夹杂物导致裂纹萌生与扩展的微观行为.结果表明,对于单个TiN和AlN夹杂,在拉伸载荷作用下,裂纹均首先在夹杂内部萌生.夹杂面积越大,夹杂内萌生的裂纹条数越多,第1条裂纹萌生所需的应力越小.在疲劳载荷作用下,对于单个TiN夹杂,裂纹也首先萌生于夹杂内部.但对于以点链状形式存在的AlN夹杂,无论是在拉伸还是疲劳载荷作用下,裂纹均首先在点链状夹杂内部两夹杂之间的母材中萌生,然后沿点链状夹杂向两侧扩展.以点链状形式存在的夹杂对材料疲劳性能的危害比单个夹杂严重得多,夹杂物对材料疲劳性能的危害远大于对拉伸性能的危害.

In order to study the effect of non-metallic inclusions on the mechanical properties of ultra-high strength steels for aerospace application, the micro-behavior of inclusion inducing crack initiation and propagation in two ultra-high strength steels under tensile and low cyclic fatigue loading was investigated by means of SEM in situ observations. The influence of inclusions＇ shape and size on crack initiation and propagation was analyzed. The results show that cracks initiate in a TiN or AIN inclusion alone under tensile loading. The larger the size of an inclusion, the more the number of cracks initiated in the inclusion is, and the lower the initiation stress of the first crack is. Cracks also initiate in a TiN inclusion alone under fatigue loading. But for a chain of AIN inclusions, cracks initiate in the matrix between two inclusions under tensile and fatigue loading. A chain of inclusions is more harmful to the fatigue properties of ultra-high strength steels than an inclusion alone, and an inclusion is more harmful to the fatigue properties than to the tensile properties.