对开裂的发动机排气阀的宏观形貌、显微组织、晶粒度、化学成分、硬度、断口形貌以及腐蚀产物相组成进行研究,并对其开裂原因进行了分析。结果表明：排气阀的开裂为疲劳断裂;疲劳裂纹源位于堆焊层中,由于堆焊工艺操作不当造成显微孔洞;排气阀的堆焊层中及阀基体的固溶体晶界处存在大量碳化物,导致其性能严重下降,在工作载荷的作用下裂纹很容易自显微孔洞处扩展最终形成开裂;腐蚀产物主要为氧化锌、磷酸盐和硫酸盐类等。
The macrophotoes,microstructure,grain size,chemical composition,hardness,fracture morphology and phase composition of corrosion products for cracked evacuation valves of an engine were studied and the cracking causes were analyzed.The results show that the cracking of evacuations valve was fatigue cracking and the fatigue crack sources were in the cladding layer,and the microholes caused by improper cladding process.A lot of carbides,which were found in cladding layer of evacuation valves and the grains boundaries of solid solution in the valve matrix,made the properties decrease seriously.Cracks easily extended from microvoids and fracture at last.Corrosion products mainly were ZnO,phosphate,sulfate and so on.
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