增材制造Ti-6Al-4V合金超高周疲劳裂纹萌生和演化机理

介绍增材制造Ti-6Al-4V合金在航空航天、生物医学等领域具有广泛的应用前景,其中的某些零部件在服役过程中会承受超高周次疲劳载荷作用,因此,阐明增材制造Ti-6Al-4V合金的超高周疲劳裂纹萌生和演化机理至关重要。通过采用旋转弯曲疲劳测试(f=50 Hz,R=-1)与超声频率(20 kHz)疲劳测试方法研究了选区激光熔化技术制造的Ti-6Al-4V合金超高周疲劳行为,研究结果表明,经热等静压处理的增材制造Ti-6Al-4V合金与锻造的Ti-6Al-4V合金疲劳性能相当

High cycle fatigue behavior of additively manufactured Ti-6Al-4V alloy with HIP treatment at elevated temperatures

The fatigue tests at 200 degrees C and 400 degrees C were conducted to investigate the elevated-temperature fatigue behavior of additively manufactured (AM) Ti-6Al-4V alloy with hot isostatic pressing (HIP) treatment. Since the manufacturing defects (i.e., pores) were significantly reduced by HIP treatment, no specimen failed from the pores. Consequently, the present AM Ti-6Al-4V alloy behaved superior to that without HIP treatment. Moreover, the specimens exhibited different failure mechanisms at 200 degrees C and 400 degrees C. Fatigue crack initiation at 200 degrees C mainly was due to surface deformation and strain localization, while the cause became fracture of surface oxygen-rich layer at 400 degrees C

Nanograin formation mechanism under fatigue loadings in additively manufactured Ti-6Al-4V alloy

Quasi in-situ observation indicates that the basal slips, prismatic slips and pyramidal a slips are main slip types in & alpha; grains, and twinning tends to occur in & alpha; grains with c-axis nearly parallel to the applied stress for additively manufactured Ti-6Al-4V alloy in low cycle fatigue regime. The slip induces dense dislocation of cells or walls, and the deformation twinning leads to subgrains with higher misorientation. Nanograins with low-angle grain boundaries (2 degrees -10 degrees) and {1012} twins are also found in very high cycle regime. The slip and deformation twinning are both contributors to the nanograin formation during fatigue loadings

A method of quasi in-situ EBSD observation for microstructure and damage evolution in fatigue and dwell fatigue of Ti alloys

A method of quasi in-situ electron backscattered diffraction observation is developed for investigating microstructure and damage evolution of Ti-6Al-4V ELI alloy under cyclic loadings. It indicates that the slip tends to occur in & alpha; grains with bigger Schmid factors (SFs) for basal slip or prismatic slip and twinning occurs in & alpha; grains with SFs not bigger than 0.2 for prismatic slip for both fatigue and dwell fatigue. The plastic strain caused by dwell stress could restrain the sliding or cleavage induced microcrack growth. Subgrain formation in & alpha; grains due to twinning and dislocation sliding are also captured during cyclic loadings