A Review of Subsurface Crack Initiation Models in High-Cycle Fatigue for Titanium Alloys

2017 ◽  
Vol 741 ◽  
pp. 76-81 ◽  
Author(s):  
Wei Bo Li ◽  
Osamu Umezawa
Keyword(s):  
Crack Initiation ◽  
Titanium Alloys ◽  
Normal Stress ◽  
Basal Plane ◽  
High Cycle Fatigue ◽  
Cycle Fatigue ◽  
Subtle Difference ◽  
High Normal Stress ◽  
Loading Axis

The characterization of subsurface fatigue crack initiate sites of near α and α-β types titanium alloys and their cracking models proposed were reviewed. The crack initiation sites consisted of facets mostly on near basal plane of α grain, although the crystallographic orientation and surface topography of the facets presented a subtle difference. The crack initiation mechanisms were a quasi-cleavage accompanying high normal stress on the plane, a combination of basal slip and normal stress across the basal plane, and a pure slip on facet plane inclined near 45 degree to loading axis.

Fatigue Behaviour of the Novel Titanium Alloys TIMETAL® 407 and TIMETAL® 412

2021 ◽  
Author(s):  
◽  
William Davey
Keyword(s):  
Crack Initiation ◽  
Titanium Alloys ◽  
Low Cycle Fatigue ◽  
Fatigue Crack Initiation ◽  
Charpy Impact ◽  
Fatigue Behaviour ◽  
High Energy ◽  
Process Window ◽  
Cycle Fatigue ◽  
The Impact

TIMETAL®407 (Ti-407) is a medium strength (~650MPa 0.2%YS) titanium alloy, recently developed by TIMET, in conjunction with Rolls-Royce plc for use in applications requiring high energy absorption at impact. Preliminary Charpy Impact (V notch) testing showed Ti-407 to absorb nearly twice the impact energy of Ti-6-4 and exhibit more than 2.5 times the lateral expansion. Further initial testing suggested the high cycle fatigue (HCF) run out stress of Ti-407 matches that of Ti-6-4 and other high strength alpha-beta titanium alloys. Ti-407 displayed more than double the tool life than that of Ti-6-4. The reduction in tool wear supports lower forces required for faster, more efficient machining. Compared to Ti-6-4, the relatively low elevated temperature flow stress, greater malleability and wide process window should allow Ti-407 to be processed with fewer reheats, while exhibiting reduced surface cracking and giving a consistently good surface finish. Optimised Ti-407 manufacturing processes should allow parts to be formed closer to net shape giving higher yields and requiring less machining to the components finished size. This project has evaluated HCF, as well as low cycle fatigue (LCF) and dwell fatigue crack initiation mechanisms in Ti-407, to clarify the effects of alloy chemistry, microstructural morphology and scale, and crystallographic texture. A derivative of Ti-407, Ti-412 (~750MPa 0.2%YS) was also tested towards the end of the project and helped to further elucidate understanding of the fatigue characteristics of the two alloys. Of interest was the strong HCF response displayed relative to the monotonic tensile strength. As well as the investigation into the crack initiation mechanisms, an assessment of crack propagation across a range of microstructural conditions was carried out on Ti-407 material.

High Cycle Fatigue Properties of Multi-Directionally Forged Commercial Purity Grade 2 Ti Plate

2018 ◽  
Vol 916 ◽  
pp. 166-169
Author(s):  
Ilhamdi ◽  
Toshifumi Kakiuchi ◽  
Hiromi Miura ◽  
Yoshihiko Uematsu
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Pure Titanium ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Commercially Pure Titanium ◽  
Cycle Fatigue ◽  
Subsurface Crack ◽  
Initiation Mechanism ◽  
Fish Eye

Tension-tension fatigue tests were conducted using ultrafine-grained commercially pure Titanium (Ti) plates fabricated by multi-directional forging (MDFing). The MDFed pure Ti plates with the thickness of 1 mm were developed aiming at dental implant application. The fatigue properties of MDFed pure Ti plates were superior to those of the conventional rolled pure Ti plates. The higher fatigue strengths in MDFed plates could be attributed to the much finer grains evolved by MDFing. Fatigue crack initiated from specimen surface, when number of cycles to failure was shorter than 106 cycles. In the high cycle fatigue (HCF) region, however, subsurface crack initiation with typical fish-eye feature was recognized in the MDFed pure Ti plate in spite of the thin thickness. Fractographic analyses revealed that no inclusion existed at the center of fish-eye. The subsurface crack initiation mechanism could be related to the inhomogeneity of microstructure with some coarse grains in the inner part of the plate.

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