摘要
研究了近层片组织γ-TiAl合金Ti-44Al-4Nb-4Zr-0.2Si-1B(原子分数,%)在不同表面加工状态下的疲劳性能。研究发现:在该高强度TiAl合金的疲劳过程中,交变疲劳最大应力往往低于其条件屈服应力,最大受力面上不易出现局部区域塑性变形。在这样的情况下,最大受力面的表面质量变得极为关键。直接线切割的样品其条件疲劳强度呈现较大的不确定性。试样经表面磨削后喷丸处理引入约250μm的表面压应力层,疲劳强度提高1/3左右。磨削后经电解抛光处理的试样,表面光滑平整无缺陷,其条件疲劳强度相对于直接线切割试样提高了约70%。带有V型缺口(kt=3.0)的试样,相比于其他平面样品,其疲劳寿命显著降低,且无"缺口强化"现象出现,表现出较强的缺口敏感性。同时发现,在低于条件屈服应力下疲劳裂纹萌生均属于材料屈服前的早期裂纹萌生,合金中弱的组织和相成为其萌生的优先选择:这包括等轴γ晶粒聚集区域,偏聚在晶界位置的B2(ω)晶块以及处于软位向的α2/γ片层界面。
A high strength γ-TiA1 based near lamellar alloy Ti-44Al-4Nb-4Zr-0.2Si-lB （at%） has been studied to assess the effects of different surface conditions on S-N fatigue behavior. It has been found that the maximum stress of fatigued specimens is always lower than the yield stress of the alloy. Local plastic deformation is difficult to occur on the maximum-stressed surface. The surface quality with or without prior cracks therefore becomes critical in determining the fatigue strength. Fatigue life of electrodischarge machined specimens shows great uncertainty. Shot peening of the machined surface is able to introduce a compressively stressed surface layer of 250um in depth and its fatigue strength is increased by 1/3 accordingly. Electropolishing after grinding the machined surface can increase the fatigue strength by 70% since a very smooth surface without defects is produced. On the other hand, V-notched specimens （kt = 3.0） show a significant reduction in fatigue life, in which no notch strengthening is observed. The study has also found that under the condition of amax〈a0.1 in the alloy, microcrack initiation always occurs before yielding. The relatively weak microstructures and phases therefore become the preferential initiation sites and propagation routes. They are observed to be equiaxed 7 grains, B2＋ω grains and a2-7 lamellar interface in soft orientations.
出处
《稀有金属材料与工程》
SCIE
EI
CAS
CSCD
北大核心
2014年第3期589-594,共6页
Rare Metal Materials and Engineering
基金
国家自然科学基金(51141011)
