Effect of oxide layers formed by thermal oxidation on mechanical properties and NaCl-induced hot corrosion behavior of TC21 Ti-alloy

Abstract

In the current study on TC21 Ti-alloy (6.5Al-3Mo-1.9Nb-2.2Sn-2.2Zr-1.5Cr), the thermal oxidation formed oxide layers that considerably influenced mechanical properties (hardness and wear). The corrosion of raw and oxidized specimen by NaCl-induced hot salt was also examined. TC21 alloy specimens were oxidized at 600, 700, 800, and 900°C for 5, 20, and 50 h. Salt spray test was utilized on raw and oxidized (600°C /50 h & 800°C/50 h) specimens of salt corrosion evaluated at 600°C for cycling 5, 10, 20, 30, 40, and 50 h. Average thickness of the layer grew with increasing oxidation time and temperature. Thin oxide layer (average 0.16 µm) was generated by oxidation temperature at 600°C duration 5 h. at 800°C oxide layer thickness was 10.8 µm large layer. Most significant surface hardness was 1108 HV0.5 which is produced for an oxidized layer at 900°C. However, lowest hardness of 360 HV0.5 was recorded for raw materials. The best wear resistance had at 800°C specimens, while raw ones had the lowest. During NaCl hot corrosion test, weight loss of the raw specimen was 6.4 mg/cm2 because the corrosion product was flaking off. However, for oxidized at 600°C for 50 h, weight loss after corrosion testing was 0.54 mg/cm2, which was less than that of specimen before corrosion. Oxidized specimens at 800 exhibited the best mechanical characteristics and corrosion resistance.

Analisis Pengaruh Variasi Holding Time Annealing Terhadap Laju Korosi Titanium Pada Larutan Cairan Tubuh Sintetis

“…Gambar 7 menunjukkan adanya porositas pada lapisan oksida terliht pada sampel annealing dengan waktu tahan selama 90 menit. Dengan temperatur pemanasan yang semakin tinggi maka semakin tebal lapisan oksida diikuti dengan sifat adhesi yang semakin menurun dikarenakan adanya perbedaan ekspansi termal antara lapisan oksida yang terbentuk dengan base metal [6] . Dengan penambahan waktu tahan annealing seperti yang terlihat pada Gambar 7 pore yang terbentuk semakin banyak, ditunjukan oleh bagian dengan warna yang tampak lebih gelap dari bagian yang lain.…”