COBEM99

S18 Processos Mecânico-Metalúrgicos

Title:

INFLUENCE OF AGING TEMPERATURE ON THE ELECTROCHEMICAL BEHAVIOR OF THE TI-15V-3CR-3SN-3AL ALLOY IN THE KROLL REAGENT

Summary :

ABSTRACT. THE MICROSTRUCTURE OF THE BETA TI-15V-3CR-3SN-3AL ALLOY CAN BE CHANGED BY AGING, LEADING TO BETA TO ALPHA PHASE TRANSFORMATION AND PRECIPITATION OF INTERMETALLIC COMPOUNDS. THE ELECTROCHEMICAL BEHAVIOR OF THIS ALLOY IN THE KROLL REAGENT ( HNO3, HF AND H2O MIXTURES) AT ROOM TEMPERATURE, AFTER AGING DURING 2 HOURS IN THE 350-600°C TEMPERATURE RANGE WAS STUDIED. A TYPICAL THREE-ELECTRODE CELL (WE: TI ALLOY; CE: PT; RE: SCE) WAS USED. THE COMPOSITIONS OF THE KROLL REAGENT WERE 200 ML H2O + 4 OR 12 ML HNO3 (65%) + 2 OR 6 ML HF (48%). THE CORROSION POTENTIALS OSCILLATED BETWEEN -0.85 AND -0.45 V/SCE FOR ALL SOLUTIONS AND ALL SAMPLES BUT REMAINED AT THE LOWER LEVEL DURING MORE TIME WHEN HIGHER HF CONCENTRATIONS WERE USED. THESE POTENTIAL VARIATIONS SHOWED THE INSTABILITY OF THE METAL SURFACE, WHICH WAS SUCCESSIVELY IN THE ACTIVE AND PASSIVE STATES DUE TO THE REDUCING CHARACTER OF HF AND OXIDIZING CHARACTER OF HNO3. THE POLARIZATION CURVES SHOWED THAT THE CORROSION CURRENT, CRITICAL CURRENT AND PASSIVE CURRENT DENSITIES INCREASED WITH AN INCREASE OF THE HF CONCENTRATION. WE OBSERVED THAT THE HIGHER WAS THE AGING TEMPERATURE, THE HIGHER WERE THESE CURRENT DENSITIES FOR ALL THE COMPOSITIONS, WHICH INDICATED THAT SAMPLES AGED AT HIGHER TEMPERATURES WERE MORE SUSCEPTIBLE TO CORROSION. THIS BEHAVIOR WAS ATTRIBUTED TO THE FORMATION OF INTRA- AND INTERGRANULAR -PHASE PRECIPITATES , AS REVEALED BY MICROSCOPICAL ANALYSIS AND X-RAY DIFFRACTOMETRY. KEY WORDS: TITANIUM ALLOY, AGING, KROLL REAGENT, ELECTROCHEMICAL BEHAVIOR

Author :

Hein, Luis Rogério de O.
Ribeiro, Rosinei Batista
Robin, Alain L. M.

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