Influence of Al Addition on Microstructures and Mechanical Properties of Ti-Fe Alloys

Abstract

The influence of Al content on the evolution of microstructures and mechanical properties of Ti xFe yAl alloys quenched from a b field was investigated via hardness measurements, tensile tests, scanning electron microscopy (SEM) equipped with electron back scattering pattern (EBSP) analyzer, and conventional transmission electron microscopy (TEM). The hardness of Ti (3 6)Fe yAl decreased remarkably on addition of 1 Al. In comparison to binary alloys, the maximum hardness decrease was achieved in Ti 4Fe 1Al. The hardness of Ti 4Fe yAl decreased with increasing Al content up to around 5, reaching a minimum, then gradually increased. Though all of the Ti 3Fe yAl alloys showed the martensite structure, Ti 4Fe yAl showed a structural change of b＋v → b＋v＋martensite → b＋v with increasing Al content. Consequently, Ti 4Fe 7Al had the lowest density in the b type alloys equivalent to that of Ti 6Al 4V. The ratio of reciprocal distance d 0002v /d 222b on selected area diffraction (SAD) pattern, which is often used as an indicator of {332} 〈113〉twin formation, was nearly constant up to 5 Al of Ti 4Fe yAl, but decreased over 6 Al. The tensile tests of both Ti 4Fe 5Al and Ti 4Fe 7Al showed ductility. The deformation behavior of Ti 4Fe 5Al producing strain induced martensite resembled that of Ti 8Mo. On the other hand, Ti 4Fe 7Al was deformed by a coarse slip of {112} 〈111〉in the same manner as Ti 20Mo, and the SAD pattern analysis revealed that the diffuse reflection of the v phase in the non deformed area turned into the spots at the deformation band. It was suggested that Al behaves as a b stabilizer element when added to the lowest b alloy and is available for weight saving, while maintaining the b structure. (Received January 26, 2012; Accepted February 13, 2012; Published May 1, 2012) Keywords: b stabilizer, a stabilizer, ubiquitous element, lightweight alloy, omega phase, martensite

Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

“…The peculiar phenomena associated with tempering that we have reported for Ti(4Fe,10Mo,35Nb)7Al are all due to ¡AA iso formation. 1315) The third phase is ¡AA martensite (¡AA M ), which is formed by several non-diffusion processes, such as STQ, 16) sub-zero processing, 17) and work processing; 15) herein, we refer to these three products as ¡AA Mq , ¡AA Mz , and ¡AA Md , respectively. The size of the ¡AA M grains formed depends on the initial ¢grain size.…”