Fatigue crack initiation in hot isostatically pressed Ti-6Al-4V castings
Fatigue crack initiation in hot isostatically pressed Ti-6Al-4V castings
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热等静压 Ti-6Al-4V 铸件中疲劳裂纹的萌生
DOI：
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发表时间：
1979
期刊：
影响因子：
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通讯作者：
D. Eylon
中科院分区：
文献类型：
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作者：
D. Eylon
为了提高高周疲劳强度，对含气孔缺陷的Ti-6Al-4V合金精密铸件进行了热等静压。尽管所有缺陷都愈合了，但与组织相似的β加工锻造材料相比，疲劳强度仍然较低。包括精密切片在内的疲劳裂纹萌生分析表明，疲劳裂纹萌生的早期位置与较大的α-α集落和大量的晶界α相有关。穿过大殖民地或沿GBα界面的剪切提供了大的初始裂纹，从而导致疲劳寿命退化。在铸造孔的髋部愈合区形成了大的菌落和大量的GBα。尽管完全关闭了髋关节的气孔，但与锻造材料相比，疲劳强度的提高很小，这是因为在髋关节周期的某些位置发展了粗大的微观结构。还观察到了横跨几个殖民地的大的平面剪切起始面。多群体小平面剪切是群体取向之间Burgers型关系的结果，增加了早期疲劳裂纹萌生的几率。
Precision castings of the Ti-6Al-4V alloy containing pore defects were hot isostatically pressed (HIP) in an attempt to improve the high cycle fatigue strength. Although all defects were healed, the fatigue strength was still low when compared to β-processed wrought material with a similar microstructure. Fatigue-crack initiation analysis, which included precision sectioning, indicated that early fatigue-crack initiation sites were related to relatively large α-platelet colonies and massive grain-boundary α(GBα) phase. Shear across the large colonies or along the GBα interfaces provided large initial cracks which resulted in the fatigue-life degradation. Large colonies and massive GBα developed in the HIP healed zones of the casting pores. In spite of the total HIP pore closure, the fatigue-strength improvement was small when compared to wrought material due to the coarse microstructure that developed in some locations during the HIP cycle. Large planar-shear initiation facets across several colonies were also observed. The multicolony faceted shear is the result of the Burgers relation between the colony orientations and increases the chance of early fatigue-crack inititation.