Abstract
Technically optimizing the processing cleanliness of Metal-Injection-Molded titanium alloys (Ti-MIM) is not economically feasible. This problem is common in the materials processing field. In the search for an alternative approach, the work tries to achieve superior high-cycle fatigue (HCF) performance while tolerating very high impurity levels. The concept arose from the large tolerance of β-class Ti-alloys for oxygen-solutes and the feasibility to mitigate detrimental effects of carbide-inclusions, under monotonous loading. In this paper, MIM β Ti-Nb-Zr biomaterials for fatigue-critical applications were deliberately produced with very high O-level and normal/very high C-levels. The impurity-resistant Ti-biomaterials exhibit superior HCF endurance limits beyond 600 MPa irrespective of processing cleanliness, being significantly higher than those of the α-β Ti-reference alloys produced with tight restrictions on impurity levels. This superior fatigue performance while tolerating amounts of impurities stems from the “weak”-microstructural features insensitive to impurities and increased resistance of the Ti-matrix against fatigue small-cracks. Furthermore, a conditional fatigue duality triggered by two competing mechanisms of crack initiation in certain cases, initiating at microscale pore α-platelets and at large pore TiC-inclusions can occur. The success of the present alloy-process development might greatly relax the processing demands for active metals.
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