Abstract
The paper presents the results of fatigue-testing ultrafine-grained and coarse-grained Ti-45 wt.% Nb alloy samples under very high cycle fatigue (gigacycle regime), with the stress ratio R = −1. The ultrafine-grained (UFG) structure in the investigated alloy was formed by the two-stage SPD method, which included multidirectional forging (abc–forging) and multipass rolling in grooved rollers, with further recrystallization annealing. The UFG structure of the Ti-45 wt.% Nb alloy samples increased the fatigue limit under the high-cycle fatigue conditions up to 1.5 times compared with that of the coarse-grained (CG) samples. The infrared thermography method was applied to investigate the evolution of temperature fields in the samples under cyclic loading. Based on numerical morphology analysis, the scale invariance (the Hurst exponent) and qualitative differences for UFG and CG structures were determined. The latter resulted from the initiation and propagation of fatigue cracks in both ultra-fine grained and coarse-grained alloy samples under very high-cycle fatigue loading.
Highlights
The prediction of fatigue strength and the development of further upgrading methods to improve the structure of materials in engineering and medical applications are the current most popular research directions, embracing applications in different areas of materials science
Bioinert metal alloys could be used for manufacturing carrier implants for artificial hip joints, bone plates and instruments for spinal and dental screws, which are subjected to cyclic loading [1,2,3,4,5,6,7]
The dependence of the UFG Ti-45Nb alloy on fatigue limit was determined in different cyclic loading regimes
Summary
The prediction of fatigue strength and the development of further upgrading methods to improve the structure of materials in engineering and medical applications are the current most popular research directions, embracing applications in different areas of materials science. Due to its high specific strength, improved fatigue life, corrosion resistance and biocompatibility, titanium and its alloys are among the most widely used materials in different industrial applications, including the production of medical implants. The production of medical implants requires materials without any toxic alloying elements, such as Al, V, Mo and others, which could negatively affect the organism [1,2,3,4]. In this respect, the most promising materials for medical applications are valve bioinert metals, such as Ti, Nb, Zr, Hf, Ta and others [5,6]. Bioinert metal alloys could be used for manufacturing carrier implants for artificial hip joints, bone plates and instruments for spinal and dental screws, which are subjected to cyclic loading [1,2,3,4,5,6,7]
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