We have investigated the influences of potential and pH on environment-assisted cracking (EAC) of Ti-6Al-4V in aqueous solutions. The EAC test was conducted by slow strain rate technique. Solution pH was controlled from 1 to 7, and applied potential was fixed between À1:8 and þ0:2 V SHE . In the solutions of pHs 3 and 7, mechanical properties of the material was almost independent of applied potential. This means that the material shows almost no EAC susceptibility in the potential-pH region for the EAC test period. At pH 1, however, both maximum stress and fracture strain changed with applied potential, and showed minimum values at an applied potential of about À1:0 V SHE . According to surface analyses by scanning electron microscopy and X-ray diffraction technique, some cracks and Ti hydride were detected from only the specimens fractured at about À1:0 V SHE in the solution of pH 1. Therefore, it can be concluded that Ti-6Al-4V is most susceptible to the EAC at about À1:0 V SHE and a pH less than 1. The EAC region was in good agreement with Ti ion stable region in a potential-pH diagram of Ti/water system, and was quite similar to that on the EAC of TiAl.

The impurity-induced infrared absorption bands are measured a t low temperatures for AgBr : Li, AgBr : Na, and AgCl: Li. The absorption bands consist of those due to the localized mode, including the fundamental band, the higher frequency sidebands and the third harmonic bands, and those due to the band modes. The force constant change at the impurity site is discussed using a diatomic three dimensional model. The sideband spectra of the lithium and sodium localized mode in silver bromide are described by the theory based on two-phonon absorption processes. There are apparent differences in the phonon coupling mechanisms to the host lattice between the lithium localized mode and the sodium one in silver bromide. It is found that for AgBr:Li, the phonon coupling mechanism due to the cubic anharmonicity is dominant and the impurity is vupled to its surrounding ions more softly. On the contrary, for AgBr:Na, the contribution due to the second-order electricdipole moment mechanism is nearly equal to that due to the anharmonicity in high frequency limit of the sideband. Some absorption bands due to the impurity-induced band mode are observed a t 30,48, and 61 cm-1 in AgBr :'Li and AgBr : Na a t 2 K.Die defekt-induzierten infraroten Absorptionsbanden von AgBr : Li, AgBr : Na und AgCl : Li wurden bei tiefen Temperaturen gemessen. Die Absorptionsbanden bestehen aus denen der lokalisierten Moden, einschliel3lich der fundamentalen Bande, der hochfrequenten Seitenbanden und der dritten harmonischen Bande, und aus denen der Band-Moden. Die Federkonstantenanderung an der Defekt-Stelle wurde mittels eines zweiatomigen dreidimensionalen Modells diskutiert. Die Spektren der Seitenbanden der durch die Li-und Na-Defekte hervorgerufenen lokalisierten Moden in AgBr wurden mit der auf Zweiphononabsorptions-Prozessen begrundeten Theorie beschrieben. Es gibt einen deutlichen Unterschied im Phonon-Kopplungsmechanismus zum Wirtsgitter zwischen den lokalisierten Moden von Li und denen von Na. Es wird gefunden, dal3 fur AgBr : Li der Phonon-Kopplungsmechanismus infolge der kubischen Anharnionizitat uberwiegt und die Storstelk an die umgebenden Ionen schwacher gekoppelt ist. Im Gegensatz dazu ist fur AgBr:Na der Beitrag vom Dipolmoment zweiter Ordnung fast gleich dem der Anharmonizitat im hochfrequenten Grenzbereich der Seitenbanden. Einige Absorptionsbanden der defekt-induzierten Band-Moden wurden bei 30,48 und 61 cm-1 fur AgBr :'Li und AgBr : Na bei 2 K beobachtet.

No abstract