金属材料疲劳损伤的界面效应

INTERFACIAL EFFECTS OF FATIGUE CRACKING IN METALLIC MATERIALS

总结了不同金属材料在低周疲劳过程中典型的晶界、孪晶界、相界和微电子互连界面的损伤开裂行为.纯Cu中疲劳裂纹萌生的难易顺序为:小角度晶界、驻留滑移带和大角度晶界.对于纯Cu与铜合金中退火孪晶界,是否萌生疲劳裂纹与合金成分有关,随合金元素的加入降低了层错能,退火孪晶界相对容易萌生疲劳裂纹.对于Cu-Ag二元合金,由于存在不同的晶界和相界面,是否萌生疲劳裂纹取决于界面两侧晶体的取向差,通常两侧取向差大的界面容易萌生疲劳裂纹.在微电子互连界面中,疲劳裂纹萌生位置与焊料成分和时效时间有关,对于Sn-Ag/Cu互连界面,疲劳裂纹通常沿焊料与界面化合物结合处萌生;对于Sn-Bi/Cu互连界面,随时效时间增加会出现明显的由于Bi元素偏聚造成的界面脆性.

Interfacial fatigue cracking behaviors along large-angle grain boundaries （GBs）, twin boundaries （TBs）, phase boundaries （PBs） and joint interfaces in metallic materials were summarized. It is found that the resistance to fatigue crack initiation decreases in the order of low-angle GBs, persistent slip bands and the large angle GBs in pure Cu. For annealing TBs, fatigue cracking initiation strongly depends on the stacking fault energy （SFE） in Cu alloys. With decreasing SFE, fatigue cracking along TBs becomes easy. In Cu-Ag binary alloys, the misorientation across GBs or PBs plays an important role in the fatigue cracking, and large misorientation often makes the final fatigue cracking. For the Cu/solder joint interface, the interfacial fatigue cracking modes are affected by the solders and aging time. In Sn-Ag/Cu solder joints, fatigue crack normally nucleates along the interface between the Sn-Ag solder and the intermetallics compounds （IMCs）; however, for Sn-Bi/Cu solder joints, brittle interracial fatigue cracking always occurs along the interface between Cu and the IMCs due to the Bi segregation after aging for a long time.