研究了不同工艺电子束焊接TC4钛合金板材的疲劳性能及断口金相组织.结果表明:工艺为V=150kV、I_f=366mA、v=600mm/min、I_b=69mA的试样焊缝的疲劳性能最好;气孔和冷隔作为应力集中源起作用而易成为裂纹源;焊缝及母材断口均由小断块组成,断块上有典型的疲劳辉纹;工艺为V=90kV、I_f=1654mA、v=600mm/min、I_b-51.1mA和V=150kV、I_f=342mA、v=200mm/min、I_b=29mA的试样焊缝疲劳辉纹间距较母材大,即扩展速率较母材快,疲劳性能不如母材;焊缝柱状晶内的网篮状马氏体组织越粗大,裂纹扩展性能越差;裂纹的扩展方式主要是穿晶断裂,相邻柱状晶内的网篮状组织取向差别太大,穿晶扩展受阻,裂纹便改沿晶扩展.
The fatigue properties and the metallurgical structure of electron beam welded joints of TC4 titanium alloy sheets were investigated.The results indicated that the welded joints welded at V=150kV,I_f=366mA,v=600mm/min,I_b=69mA had the best fatigue properties.Pores and cold cracks were stress concentration sources which could develop into crack-roots.All the fracture surfaces of the base metal and welded seam samples were comprised of a large number of small facets,on which there were much more typical fatigue striations observed under microscope.The striation spacings in welded seams of the samples welded at V=90kV,I_f=1654mA,v=600mm/min,I_b=51.1mA and V=150kV,I_f=342mA,v=200mm/min,I_b=29mA were wider than those in base metal,this shows that the fatigue crack propagation resistance in the three samples was smaller than that of base metal.The coarser the acicular martensite of welded seam was,the worse the fatigue crack expansion property was.Most of the fatigue crack expansion zones were tough transgranular fracture.If the directions of the acicular martensites in two adjacent columnar grains were too different,transgranular fracture was restrained,the fatigue cracks changed to fracture along grain boundaries.
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