Mechanism of Fatigue Crack Growth in Biomedical Alloy Ti-27Nb

Abstract

Implants are widely used in the human body for the replacement of affected bones. Fatigue failure is one of the serious concerns for implants. Therefore, understanding of the underlying mechanism leading to fatigue failure is important for the longevity of biomaterial implants. In this paper, the fracture toughness and fatigue crack growth of titanium alloy biomaterial Ti-27Nb has been experimentally investigated. The Ti-27Nb material is tested for fatigue crack growth in different environmental conditions representing the ambient and in vitro environments for 504 hours and 816 hours, respectively. Fractography of the tested specimen is conducted using Scanning Electron Microscope (SEM). The results of the fatigue crack growth propagation of the ambient and in vitro samples are similar in the Paris crack growth region. However, in the threshold region, the crack growth rate is higher for the Simulated Body Fluid (SBF) treated specimen. The fracture surface morphology of in vitro samples shows brittle fracture as compared to ambient specimens with significant plasticity and striations marks. It is proposed that a similar investigation may be conducted with specimens treated in SBF for prolonged periods to further ascertain the findings of this study.

Fracture Toughness and Fatigue Crack Growth Analyses on a Biomedical Ti-27Nb Alloy under Constant Amplitude Loading Using Extended Finite Element Modelling

“…The boundary conditions are explained according to the experimental data in Ref. [ 29 ]; the two loaded pins were loaded with a peak load PQ of 3030 N, and the initial value per crack was 1.3 mm. No DOF was allowed across the z -axis or x -axis, and one degree of freedom was allowed across the y -axis (see Figure 2 b).…”

“…The mechanical properties were determined using a simple tensile test described in Ref. [ 29 ], and the hardening properties were determined using the logarithmic scale of the yield curve ( Figure 1 b). These types of alloys have attractive applications in human implants, where they exhibit good biocompatibility and high durability.…”

“…These types of alloys have attractive applications in human implants, where they exhibit good biocompatibility and high durability. The main component of the Ti-2Nb alloy is titanium (Ti) and niobium (Nb), with 26.01 ± 1.05 wt% each [ 29 ]. The durability of the implant is more dependent on the fatigue life; therefore, it is important to study the behaviour of such a bioactive alloy under fatigue.…”

“…It has lower ductility but higher fatigue strength, which makes it more suitable for cyclic loading applications such as implants [ 26 , 27 , 28 ]. In addition, the fracture toughness of the Ti-27Nb alloy was 50 , which was less than the other known biomedical titanium alloy Ti-6Al-4V, which was 65 [ 29 ]. The fatigue fracture behaviour of the Ti-27Nb alloy showed brittle fracture with transgranular and intergranular fracture patterns as reported in [ 29 , 30 ].…”

“…In addition, the fracture toughness of the Ti-27Nb alloy was 50 , which was less than the other known biomedical titanium alloy Ti-6Al-4V, which was 65 [ 29 ]. The fatigue fracture behaviour of the Ti-27Nb alloy showed brittle fracture with transgranular and intergranular fracture patterns as reported in [ 29 , 30 ]. An older study by Amjad et al [ 31 ] looked at the Ti-27Nb alloy and simulated the effects of daily life on the performance of a human implant made from this alloy.…”