Abstract
The influence of duplex aging (DA) heat treatment and consequent microstructural changes in the stress corrosion cracking (SCC) resistance of Ti-6Al-4V α+β titanium alloy was examined through constant load SCC test and metallographic examination. The time for fracture (TFF) of duplex aged samples in the SCC test was compared with single aged samples TFF. The results of the constant load SCC test showed an improvement in corrosion resistance with the second stage of aging in the duplex aging heat treatment. Microstructural examination revealed a preferential path for SCC crack propagation through prior β grains (lamellar structure alternating α and β phases) which indicated that the bigger SCC resistance observed in DA samples is a consequence of greater β phase decomposition due to the second stage of aging. It wasn’t observed a bigger grain growth in the DA heat treatment, in comparison with single aged (SA) samples. The observed fracture aspect was mixed (ductile-fragile) in peripheral regions and ductile in the interior of the body proofs, what indicate the major influence of SCC in the fracture mechanism.
Highlights
Because of its high strength/weight ratio, its good mechanical properties in high temperatures and its high corrosion resistance, about 50% of the titanium produced in the world becomes Ti-6Al-4V1
The main objective of this work is to analyze the effects of an additional stage of aging in stress corrosion cracking (SCC) resistance in methanol, in order to put it in perspective a new route of heat treatment for titanium α + β alloys submitted to critical circumstances of tension and corrosion
The preferential propagation of cracks in prior β grains explains the lower susceptibility to stress corrosion cracking of TI-6Al-4V after duplex aging (DA) aging, in comparison with single aged (SA) samples, once the second aging stage caused stronger β phase decomposition, reducing the volumetric fraction of prior β grains. It can be drawn the following conclusions: The two stages aging process causes a stronger decomposition of lamellar structure in prior β grains, without any substantial grain growth
Summary
Because of its high strength/weight ratio, its good mechanical properties in high temperatures and its high corrosion resistance, about 50% of the titanium produced in the world becomes Ti-6Al-4V1. It has several applications, such as biomedical implants and aerospace components. This alloy is putted into service after some solution and aging heat treatment[2], once these treatments gives substantial raise in strength to Ti-6Al-4V alloy[3]. Solution and aging heat treatments can affect the susceptibility of α + β titanium alloys to SCC5
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