Microstructural engineering for Improved Corrosion Resistance of a Ti-5％Ta-1.8％Nb Alloy
Titanium possesses good corrosion resistance in many oxidizing environments. The addition of Tantalum and Niobium to Titanium improves its corrosion resistance due to their similar atomic size,higher valency,stabilization of the oxide film and low solubility in oxidizing media. Addition of 5％Tantalum and 1. 8％Niobium increases the corrosion resistance of Titanium by nearly 7 times. Corrosion behavior of an alloy is controlled by microstructure, which in turn is strongly influenced by alloying elements and process parameters. Microstructural engineering using appropriate design of thermo-mechanical and thermal treatments is the methodology adopted for enhancing the corrosion resistance of this Ti-5Ta-l. 8Nb alloy. Ti-5Ta-l. 8Nb is an α+β alloy, where the high temperature β phase undergoes several types of transformations depending on its solute content and cooling rate. On cooling from high temperatures,β phase with low solute contents, transforms to hexagonal close packed martensite at fast cooling rates, while slow cooling a results in a lamellar α+β microstructure. Transformation product of β phase at lower temperatures with concomitant increase in solute enrichment changes to orthorhombic martensite to omega to finally retention of β phase. Modification of a lamellar α+β microstructure to an equiaxed microstructure achieved through a series of thermo-mechanical processing resulted in a significant decrease in corrosion rate of the alloy in boiling 11. 5M nitric acid from 1. 25mpy to 0. 25±0. 07mpy. Through a systematic design of thermal treatments, the optimum microstructure with lowest corrosion rate was identified to be fine retained beta particles (＜50nm) distributed uniformly in an equiaxed alpha matrix. Microstructure influences the nature of passive oxide film also, which dictates corrosion behavior of the alloy. Detailed characterization of the oxide film after corrosion testing showed the formation of a nanocrystalline anatase along with oxides of Ta and Nb.
Titanium (Ti) Tir5 Ta-l.8 Nb microstructure phase trans formations corrosion resistance anatase
R. Mythili S. Saroja M. Vijayalakshmi
Indira Gandhi Centre for Atomic Research,Kalpakkam-603 102,India
国际会议
The 12th World Conference Titanium(第十二届世界钛会 Ti-2011)
北京
英文
531-535
2011-06-19（万方平台首次上网日期，不代表论文的发表时间）