Refine
Document Type
- Doctoral thesis (2)
Has Fulltext
- yes (2)
Is part of the Bibliography
- no (2)
Language
- English (2)
Keywords
- Nioblegierung (2) (remove)
Institute
Titanium and its alloys have been widely used as implant biomaterials due to their suitable combination of mechanical properties and biological compatibilities. At present, about 70-80% of implants are made of metallic biomaterials. Compared with magnesium alloys, stainless steel and cobalt alloys, titanium alloys have a higher specific strength, high corrosion resistance, and excellent biocompatibility. With research, Ti-Nb biomedical titanium alloys have been constantly developed. In the Ti-Nb alloy, the amount of Nb is usually from 16% to 42% (wt.%) which is about 10% to 30% (at.%). As reported, Mn as a trace element to the human body has the potential to be used in bio-materials. Therefore, this study aims at the partial replacement of Nb by Mn to reduce the costs, without deteriorating the mechanical properties. Moreover, it must be ensured good biocompatibility and corrosion resistance. This is the first investigated on Ti-Mn-Nb ternary alloys.
In this work, According to β single-phase field, Ti-xMn-yNb (x=4, 10, 16; y=2, 8, 14, at.%) alloys (arc-melted) have been fabricated. The Ti-Mn-Nb alloys are investigated by optical microscopy (OM), X-ray diffraction (XRD), hardness test, transmission electron microscopy (TEM) and mechanical testing. By screening study on alloy, Ti-10Mn-14Nb (at.%) (Ti-10Mn-23.7Nb (wt.%)) is the optimal alloy with tensile strength (760 MPa) and elongation (10.5%). After that, the Metal Injection Moulding (MIM) is used to prepare Ti-Mn-Nb alloys. The MIM method can greatly reduce the processing cost. MIM Ti-xMn-yNb (x=3, 4, 6; y=1, 2, 4, at.%), Ti-4Mn-14Nb and Ti-10Mn-14Nb alloys are fabricated. Among them, a very good combination of mechanical properties is achieved for MIM processed Ti-4Mn-2Nb (at.%) (Ti-4.5Mn-3.8Nb (wt.%)), namely a YS of 642 MPa, UTS of 725 MPa and high ductility of 16% elongation to fracture. With further investigations, when the yttrium content is 0.1% (at.%), the tensile strength of Ti-4Mn-2Nb-0.1Y (at.%) (Ti-4.5Mn-3.8Nb-0.18Y (wt.%)) is increased to 785 MPa while elongation of 12.9%. These mechanical properties already exceed Ti-6Al-4V (ASTM F2885 Grade 5 undensified).
In the in vitro evaluation, in comparison with MIM pure titanium, human osteoblasts MG63 adhered as well and proliferated on the surface of MIM Ti-Mn-Nb specimens. In the supernatant after cell culture, the Ti-Mn-Nb alloy shows similar osmolality and pH value results as MIM pure titanium. By LDH assay and DNA isolation, the MIM Ti-Mn-Nb alloys are not found to be toxic to MG63 cells.
In the study of corrosion resistance in Hanks’ balanced salt solution (HBSS) at 37 °C, the corrosion current densities as well as the impedance of MIM Ti-Mn-Nb alloys are all better than those of MIM pure titanium and even better than those of MIM Ti-6Al-4V alloy.
The main subject of this work was the investigation of sintering behavior, microstructure, mechanical properties and biocompatibility of metal injection moulded (MIM) Ti-Nb alloys for biomedical applications. Commercially pure titanium (CP-Ti) samples were also fabricated by MIM as a reference. The sintering behavior of MIM Ti-Nb alloys was studied at first, in order to roughly determine the sintering parameters in the following investigations. Dilatometry was applied to investigate the linear shrinkage of MIM Ti-Nb samples from room temperature to 1500 °C at a heating rate of 3 °C/min under argon atmosphere. Various sintering parameters and Nb contents were used to investigate their influences on microstructure and mechanical properties of MIM Ti-Nb alloys by means of density measurements, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical testing. Transmission electron microscopy (TEM) and high energy X-ray diffraction (HEXRD) measurement were applied to investigate the nature and precipitation of the unexpected titanium carbide precipitates in MIM Ti-Nb alloys. Initial cell adhesion and cell proliferation assays of human umbilical cord perivascular cells (HUCPV) on MIM Ti-Nb alloys were performed for biocompatibility characterization. The results of this work show that MIM Ti-Nb and MIM CP-Ti samples have been successfully fabricated and the as-sintered samples show good shape retention without distortion compared to the green sample. The sintering process of MIM Ti-Nb alloys consists of three main steps – Ti-diffusion step, Ti-Nb-diffusion step and Matrix-diffusion step. With increasing sintering temperatures and time, MIM Ti-Nb alloys exhibit lower porosity and higher Young’s modulus. A higher Nb content in MIM Ti-Nb alloys leads to an increase of carbide area fraction and porosity. The three factors – Nb content, carbide area fraction and porosity – determine the mechanical properties of MIM Ti-Nb alloys. An increase of Nb content and amount of carbides as well as a lowered porosity lead to a higher tensile strength. A decrease of Young’s modulus can be expected with higher Nb content and porosity. A high amount of titanium carbides can result in very poor ductility, but annealing and quenching process can significantly improve the elongation by dissolving the carbides. MIM Ti-Nb alloys exhibit good biocompatibility, indicating their potential for implant applications.