Elisa B. Taddei

Characterization of Ti-35Nb-7Zr-5Ta Alloy Produced by Powder Metallurgy

Abstract: Titanium and titanium alloys present the highest biocompatibility among metallic biomaterials. The ideal titanium alloy for orthopedic applications should have low modulus of elasticity (near the bone), excellent mechanical strength, high corrosion resistance, formability and no potential toxic elements. Among titanium alloys, the Ti-35Nb-7Zr-5Ta alloy, due its high biocompatibility and lower Young’s modulus is a promising candidate for implants material. The titanium alloys production by powder metallurgy, starting from the elementary powders, is a viable route due at the smaller costs and larger operational facilities. The Ti-35Nb-7Zr-5Ta samples were manufactured by blended elemental method from a sequence of uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 at 1700 °C, in vacuum, under a heating rate of 20 °C×min-1 for 1h. The objective of this work is the analysis of alloy microstructural evolution from the powders dissolution under the increase of the sintering temperature. For the alloy microstructural characterization, scanning electron microscopy and Vickers microhardness measurements, were used. Density was measured by Archimedes method. The samples presented high densification, an homogeneous microstructural development, with complete dissolution of alloying elements in the titanium matrix with the temperature increase.

Ti-13Nb-13Zr Foams for Surgical Implants

The use of titanium and its alloy as biomaterial is increasing due to their low modulus, superior biocompatibility and enhanced corrosion resistance when compared to more conventional stainless steel and cobalt-based alloys. Ti-13Nb-13Zr is a titanium alloy specifically developed for surgical implants. In this work, highly porous titanium foams, with porosities above from 50%, are reached using an efficient powder metallurgical process, which includes the introduction of a selected spacer into the starting powders. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering. The samples presented a Widmanstättenlike microstructure in an open cellular morphology with pore size between 200-500 μm.

Age-hardening of Ti-35Nb-7Zr-5Ta alloy for orthopaedic implants

Bone injuries and failures often require the inception of implant biomaterial. Research in this field has received increasing attention recently. In particular, porous metals are attractive due to its unique physical, mechanical, and new bone tissue ingrowth properties. The aim of this work is to investigate age hardening behavior of Ti-35Nb-7Zr-5Ta alloy produced by powder metallurgy. Samples of Ti-35Nb-7Zr-5Ta were produced from a mixture of hydrided powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering at 1500 °C, in vacuum. After that, the samples were heat treated in three steps; solution treatment (1100/°C), air cooling and aging (600 °C for 4 and 6 hours). Sintered samples were characterized for microstructure and microhardness by scanning electron microscopy and Vickers indentation, respectively. In the homogenized condition alloy exhibited a microstructure consisting primarily of a b Ti matrix with grain boundary a precipitates and a low volume fraction of primary a precipitates. In the ageing condition the alloy exhibited the precipitation of refined scale secondary a precipitates distributed homogeneously in the b matrix.

Densification and Microstructural Behaviour on the Sintering of Blended Elemental Ti-35Nb-7Zr-5Ta Alloy

Beta titanium alloys, e.g., are now the main target for medical materials. Ti-35Nb-7Zr- 5Ta alloy were manufactured by blended elemental (BE) powder method, which appears to be one of the most promising technique for titanium parts production at reduced cost. The process employs hydrided powders as raw materials with low production costs and oxygen content. Among the titanium alloys recently developed, Ti-35Nb-7Zr-5Ta is distinguished for presenting low modulus of elasticity, high mechanical resistance and superior biocompatibility. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering among 800 at 1500 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. In this work, an alternative blending technique (with planetary mill) was used. The samples presented a good densification and a totally β-type microstructure, with complete dissolution of alloying elements in the titanium matrix with the temperature increase with low pore content.

Properties of Porous Ti-35Nb-7Zr-5Ta Processed by the Spacer Method for Use in Biomedical Applications

Ti-35Nb-7Zr-5Ta alloy is a promising new material for a bone graft substitute with good strength properties and an elastic modulus closer to that of bone than any other metallic material. TNZT samples until 50 vol % porosity were manufactured using ‘‘space holder’’ technique and sintering methods. Irregular ammonium carbonate powders were used as a space holder material. Complete removal carbonate from the green compact was achieved by heating at 200 °C for 5 hours and subsequent sintering at 1600 °C, with heating rate of 10 °C/min. For the alloy microstructural characterization, scanning electron microscopy was used. Density was measured by Archimedes method. The results show that the blended elemental P/M process and the space holder technique are efficient for the obtainment of highly porous samples. Foams with porosities in the range between 10% and 50% could be reached.

Isochronal Sintering of Ti-35Nb-7Zr-5Ta

Ti-35Nb-7Zr-5Ta alloy is considered an attractive material for implants manufacture due to an excellent combination of properties, including high mechanical and corrosion resistance, beyond the lowest elastic modulus among the titanium alloys. The alloy processing by powder metallurgy (P/M) eases the obtainment of parts with near-net shape forming and low production costs. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 800-1600 °C, in vacuum. The isochronal sintering demonstrated to be efficient for the study of the microstructural evolution. The samples presented high densification and adequate microstructure. The results show that a beta-homogeneous microstructure is obtained in the whole sample extension when sintered at high temperatures beyond that P/M technology allows an effective porosity control.

Ceramic Bonding to Biocompatible Titanium Alloys Obtained by Powder Metallurgy

The shear bond strength between a ceramic material (Titankeramik®, Vita Zahnfabrik, Germany) and two biocompatible titanium alloys was investigated. Ti-13%Nb-13%Zr (TNZ) and Ti-35%Nb-7%Zr-5%Ta (TNZT) alloys were obtained based on the blended elemental technique followed by a sequence of cold uniaxial and isostatic pressing and sintering. Characterization involved microstructural analysis (SEM) and crystalline phase identification (XRD). Subsequently, samples were machined to 4 x 4 mm with a base of 5 x 1 mm. The base metals were blasted with Al2O3 particles followed by the application of a coupling agent and opaque ceramic. After ceramic firing, the specimens were loaded in a universal testing machine (0,5mm/min). XRD revealed the presence of α and β-phases for TNZ, and peaks related to β phases and Nb and Ta for the TNZT alloy. SEM evaluation (TNZ) depicted remaining pores and biphasic microstructure formation. SEM micrographs of the TNZT alloy revealed good densification and a homogeneous β structure. Shear bond strength data (MPa) were statistically analyzed (one-way ANOVA and Tukey test, α=.05) revealing that TNZT (37.6 ± 2.91) presented significant higher values (p=0.0002) compared to TNZ (26.03 ± 2.92). In conclusion, it seems that Ti alloy composition plays a significant role on ceramic bonding.

Biomimetic Coatings on Ti-Based Alloys Obtained by Powder Metallurgy for Biomedical Applications

Comparing to hydroxyapatite (HA), which forms a strong chemical bond with the bony tissues, metallic materials are not able to bond with bone. For this reason, a great variety of complex coating methods, such as pulse-laser deposition, ion-beam assisted deposition and plasma-spray has been used to form a HA layer onto metallic surfaces. This study evaluated the performance of the biomimetic technique on apatite-based coating formation on two Tialloys. Ti-13Nb-13Zr and Ti-35Nb-7Zr-5Ta were obtained via powder metallurgy. The Tibased alloys were biomimetically coated using a technique which was modified from the conventional ones using a sodium silicate solution as the nucleant agent. Both alloys presented similar behavior in the evaluated conditions which means the formation of a homogeneous and well defined HA coating. These results show that these new non-toxic Tialloys seem to be very promising for biomedical applications.