α＋β型（Near β型）Ti-17合金線形摩擦接合継手の組織と機械的性質

抄録

This study investigated low-temperature linear friction welding (LFW) of Ti-17 alloy, performed below the β transus temperature (applied pressure: 550 MPa), and compared its microstructures and mechanical properties with conventional LFW joints fabricated above the β transus temperature (applied pressure: 50 MPa). Both joints were sound without joining defects. At an applied pressure of 50 MPa, the joint interface consisted of equiaxed β grains　with a grain size of 5 μm, and Vickers hardness measurements indicated significant softening at the interface region. In contrast, at 550 MPa, the joint interface contained ultrafine equiaxed β grains having a grain size of 0.7 μm with a small fraction of α phase, exhibiting hardness comparable to the base material. Tensile tests showed that at 50 MPa, fracture occurred at the softened joint interface region, whereas at 550 MPa, fracture occurred in the base material, indicating the improved joint efficiency of about 100%. In cyclic fatigue tests of specimen at 550 MPa, the joint fractured at the interface but exhibited a fatigue life nearly equivalent to that of the base material. In cold dwell fatigue tests, the joint at 550 MPa exhibited the base material fracture, and the fatigue life was extended by a factor of 3.2 compared to the base material. These results demonstrate that the low-temperature LFW joint (550 MPa) possesses superior mechanical properties compared to conventional LFW joints (50 MPa). This improvement highlights its potential applicability to high-performance aerospace components such as blisks, where enhanced strength and fatigue resistance are critical.