Publication: Evaluation of mechanical and bioactivity properties of surface modified titanium-molybdenum-iron alloys.
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Date
2025-08
Authors
Tsauri, Bashir Tukur
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Abstract
High modulus and poor cellular response limit the use of Ti alloys in orthopaedic application, Ti-Mo-Fe alloy was designed using d-orbital design and
Molybdenum Equivalent (MoE) methods such that low modulus phase (β-Ti) of Ti is achieved. The research leveraged on polymorphic transformation in Ti and the influence of alloying elements on such transformations in designing low modulus alloys. On the other hand, surface topography-bioactivity property dependence was used as a basis for improving cellular response. Using ingot metallurgy and powder metallurgy as fabrication processes, Ti-(y-x) Mo-xFe (where y=15 and x = 0, 2, 4, 6, 8, and 10) were produced. The choice of these alloying elements (Mo and Fe) was based on established safety and the ability to stabilize β-Ti at room temperature. Properties of the alloys were assessed at various stages with the view to achieving the best combination of properties. Density was assessed to establish atomic interactions. Phases present were also characterized using X-Ray Diffraction (XRD) and Electron Backscattered Diffraction (EBSD) techniques. The phase is predominantly β in IM samples; whereas a transition from high modulus phase (α) to a low modulus phase (β)
as a function of Mo and Fe co-additions was seen in PM samples. For instance, the 100% α pure titanium transformed to 46.9% β and 53.1% α by adding 15 % Mo ( Ti15Mo,). Addition of 2% Fe further increased the amount of β phase to 47.7% β in Ti13Mo-2Fe and continued upto 53.4 % β (Ti-5Mo-10Fe). Also, EBSD revealed increasing microstructural uniformity when Fe was added to the alloy(s). Furthermore, compression test, nanoindendation and Vicker’s hardness tests were performed to evaluate the mechanical properties. The modulus decreased from 48.38 GPa (Ti-15Mo) to 41.78GPa (Ti-13Mo-2Fe) but increased to 56.06 GPa at Ti-9Mo-6F and 69.73 GPa at Ti-5Mo-10Fe. Consequently, Ti-13Mo-2Fe alloys were considered for biological studies as they exhibited not only lowest modulus (41.78GPa) but also a combination hardness (269.12 HV) and good strength among all the alloys. To improve bioactivity, the alloys were anodized in ethylene-glycol based electrolyte. This led to an increased surface roughness and wettability as determined through atomic force microscopy and water contact angle measurement respectively. Cell culture study revealed that the alloys (Ti-13Mo-2Fe) are biocompatible and pose no risk to the L929 cell line. The cells were viable and proliferated the more compared to Ti6Al4V alloy. However, cell attachment depend strongly on surface morphology as the cells were only attached to anodized substrates. Going by the reduction of modulus through alloying and enhanced biological response due to anodization induced surface roughness, the challenges of modulus mismatch and poor bonding ability limiting the use of Ti alloys in orthopaedic application may be addressed by considering the Ti-Mo-Fe alloys whose surface has been modified via anodization.