Perilaku Korosi pada Paduan Titanium Ti-Mo-Nb setelah Perlakuan Termomekanis
Keywords:
Titanium, Ti-Mo-Nb, Korosi, Perlakuan Termomekanis, PengecoranAbstract
Paduan titanium yang dipadukan dengan unsur penstabil fasa beta (Mo dan Nb) termasuk dalam kelompok β-titanium alloys, yang menawarkan keuletan tinggi, biokompatibilitas yang baik, serta resistansi terhadap korosi yang unggul. Kombinasi unsur Mo dan Nb dapat menstabilkan fasa β, menghambat pertumbuhan butir, dan meningkatkan pasivasi permukaan. Namun demikian, paduan hasil pengecoran (as-cast) sering kali mengalami segregasi unsur dan ketidakhomogenan mikrostruktur yang dapat menurunkan ketahanan korosinya. Oleh karena itu, perlakuan termomekanis seperti hot rolling perlu dilakukan untuk memperbaiki mikrostruktur dan mengoptimalkan sifat korosinya. Bahan baku dengan kemurnian 99,9% dipadukan sesuai dengan target komposisi paduan Ti-5Mo-9Nb. Ketiga bahan tersebut kemudian dicor menggunakan tungku busur listrik vakum dengan cetakan tembaga berpendingin air di dalam atmosfer argon. Ingot hasil coran kemudian dihomogenisasi (homogenizing) menggunakan vacuum tube furnace dalam kondisi lingkungan gas inert argon pada suhu 1.150 °C, dengan waktu penahanan (holding time) selama 3, 6, dan 9 jam, lalu didinginkan secara cepat. Selanjutnya, dilakukan proses pengerolan panas (reduksi 50%) dengan pemanasan awal pada suhu 1.000 °C. Paduan kemudian dikarakterisasi menggunakan mikroskop optik untuk mengamati struktur mikronya dan diuji korosi dalam larutan Hank's untuk mengukur perilaku korosi pada cairan tubuh buatan. Proses termomekanis paduan Ti-5Mo-9Nb telah berhasil dilakukan. Secara keseluruhan, hasil penelitian menunjukkan bahwa peningkatan waktu homogenisasi memberikan pengaruh yang signifikan terhadap peningkatan ketahanan korosi paduan Ti-5Mo-9Nb dibandingkan dengan perlakuan termomekanis tanpa homogenisasi optimum. Perlakuan homogenisasi selama 9 jam menghasilkan kombinasi ketahanan korosi terbaik, yaitu densitas arus korosi paling rendah (211,420 nA) dan laju korosi paling kecil (0,0012406 mm/tahun), sehingga memberikan perlindungan korosi yang lebih baik dibandingkan homogenisasi selama 3 maupun 6 jam.
Abstract: Titanium alloys containing β,-phase stabilizing elements (Mo and Nb) belong to the β-titanium alloy group, which offers high ductility, good biocompatibility, and superior corrosion resistance. The combination of Mo and Nb stabilizes the β-phase, inhibits grain growth, and enhances surface passivation. However, as-cast alloys often exhibit elemental segregation and microstructural inhomogeneity, which can compromise corrosion resistance. Therefore, thermomechanical treatments such as hot rolling are necessary to refine the microstructure and optimize corrosion properties. High-purity (99.9%) raw materials were combined to achieve the target Ti-5Mo-9Nb alloy composition. The materials were cast using a vacuum arc furnace equipped with a water-cooled copper mold under an argon atmosphere. The resulting ingots underwent homogenization in a vacuum tube furnace under an inert argon atmosphere at 1150 °C for holding times of 3, 6, and 9 hours, followed by rapid cooling. Subsequently, hot rolling (50% reduction) was performed after preheating at 1000 °C. The alloys were characterized using optical microscopy to observe their microstructure and subjected to corrosion testing in Hank's solution to evaluate corrosion behavior in a simulated body fluid. The thermomechanical processing of the Ti-5Mo-9Nb alloy was successfully completed. Overall, the results indicate that increasing the homogenization time significantly improved the corrosion resistance of the Ti-5Mo-9Nb alloy. Homogenization for 9 hours yielded the best combination of corrosion resistance, specifically the lowest corrosion current density (211.420 nA) and the lowest corrosion rate (0.0012406 mm/year), thereby providing superior corrosion protection compared to homogenization for 3 or 6 hours.
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