| Summary: | 碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 106 === By virtue of a unique combination of high specific strength, outstanding corrosion resistance, and excellent biocompatibility, titanium alloys are the favored structural materials for a wide range of applications spanning the military, as well as the aerospace, chemical, automotive and biomedical industries. Among the alloys, Ti-Ta alloys possess lower elastic modulus and higher strength-to-modulus ratios than those of the currently used implant materials. In the past, titanium alloys were usually prepared by casting and subsequent thermomechanical treatment. However, this fabrication technique is expensive due to the unavoidable machining and associated materials loss; this aspect severely limits their applicability in everyday applications like in the automotive industry. Therefore, the cost-effective techniques of powder metallurgy (P/M) of titanium alloys have been investigated in recent years. This fabrication process is easily used to produce complex-shaped titanium alloy components to avoid the loss of materials.
In this study, two different powders: Titanium and Tantalum, were uniformly mixed and used to produce four different proportions of Ti-Ta alloys: Ti-4Ta, Ti-6Ta, Ti-8Ta and Ti-10Ta alloys, respectively. Meanwhile, the Ti-Ta alloys underwent a vacuum sintering process at various sintering temperatures of 1200°C, 1250°C, 1300°C and 1350°C for 1 h, respectively. To evaluate the microstructure and mechanical properties of the Ti-Ta alloys via the vacuum sintering processes, tests on the relative density, apparent porosity, hardness and transverse rupture strength (TRS), and microstructure inspections were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), with the purpose of improving the microstructure and properties of sintered Ti-Ta alloys. Finally, the optimal sintered parameters, with the addition of Carbonyl Iron Powder as a strengthening phase, were employed to produce the Ti-Ta-Fe alloys and improve the mechanical properties of Ti-Ta alloys.
The experimental results show that good apparent porosity (0.14 %), as well as optimal relative density (93.1 %), hardness (62.18 HRA), transverse rupture strength (1196.1 MPa), and polarization resistance achieved (427.26 Ω·cm2) of Ti-8Ta alloys were obtained after sintering at 1250°C for 1 h. Consequently, this study utilized the Ti-8Ta alloys with the addition of Carbonyl Iron Powder (4, 6, 8 and 10 wt%, respectively) for a vacuum sintering process at various sintering temperatures of 1225°C, 1250°C, 1275°C and 1300°C for 1 h for further improvement and analysis. The test results also indicated that when 8 wt% Fe was added to the Ti-8Ta alloys, the resultant specimen (Ti-8Ta-8Fe) possessed the optimal properties after sintering at 1275°C for 1 h. Simultaneously, the good apparent porosity 0.08 %, as well as optimal relative density 95.2 %, hardness was enhanced to 67.92 HRA, TRS was increased to 1073.3 MPa and polarization resistance achieved 391.26 Ω·cm2, respectively.
|
|---|
