Titanium alloys are the primary choice for orthopedic devices, such as knee and hip implants, because of their excellent mechanical properties and resistance to infection. A team from Nanyang Technological has now found a way to use titanium-tantalum powder with attractive properties to produce custom-made, patient-specific implants that improve stress absorption.
Selective Laser Melting (SLM) is a form of additive manufacturing, more commonly known as 3D printing, which uses lasers to fuse powder materials directly from computer-aided design (CAD) files to form functional parts. As we all know, the existing SLM materials include stainless steel, tool steel, Ti6Al4V and AlSi10MG. Titanium alloys are excellent biomedical materials due to their excellent biocompatibility, corrosion resistance and mechanical properties. At present, extensive research has been done on SLM of titanium alloy, especially Ti6Al4V and Ti6Al7Nb, which have a wide application prospect. Both titanium alloys are more commonly used in biomedical applications. However, questions have been raised about the safety of these materials because they contain aluminium and/or cytotoxic vanadium, which can cause neurological problems in humans after long-term use.
Therefore, the development of new titanium alloys that do not contain these toxic elements has become a demand. In addition, materials with reduced modulus need to be developed to avoid a modulus mismatch between the implant and the adjacent bone. Clinical studies have shown that this mismatch results in insufficient load transfer from the implant to the adjacent bone. This leads to bone resorption and potential loosening of the implant. This effect is called "stress shielding".
Tantalum has high biocompatibility, corrosion resistance and good mechanical properties, which makes it an excellent choice for titanium alloying in biomedical applications. In addition, titanium-tantalum (TiTa) alloy is a promising material due to its high strength to density ratio and low cost. The alloying elements in titanium can be divided into three groups :(1) α phase stabilizers, (2) β phase stabilizers, and (3) no obvious effect on the phase. Depending on the specific application of the material, the different phases of titanium can provide a wide range of properties. β-stable element of tantalum, especially in titanium alloys. Compared with alloys commonly used in the biomedical field (for example, stainless steel and cobalt-chromium alloys and Ti6Al4V as α+β titanium alloy), β-titanium alloys show excellent properties with low modulus.
The lower modulus is ideal for biomedical applications because it minimizes the adverse effects of stress shielding. Despite these advantages, TiTa alloys have not been widely used in applications. The main reason is because the melting points and densities of the two metals are so different that they are difficult to combine. In particular, tantalum has a density of 16.6 /cm3, about four times that of commercial pure titanium. This may lead to inhomogeneity in the formation of the alloy, as density differences lead to segregation of the elements in the alloy.
