Home – Home – Jornals – Chemistry for Sustainable Development 2005 number 2

Titanium alloys are typically brazed in the USA and Russia with two powder filler metals of Ticuni® family having compositions of 70Ti-15Cu-15Ni and 60Ti-15Cu-25Ni, several pre-alloyed filler metals of Ti-Zr-Cu-Ni system such as VPr16 and VPr28 powders, and amorphous foils of Stemet® family. All these brazing materials are characterized by high price that may be attributed to both the cost of the components and atomization process of Ti- and Zr-based alloys or with the production of amorphous tapes. The technology of producing mechanically-alloyed filler metals from elemental metal powders or hydrides was developed to cut manufacturing expenses by 40-50%. Some of these alloys such as TiBraze®375 (Ti-37.5Zr-15Cu-10Ni), TiBrazeâ260 (Ti-26Zr-14Cu-14Ni-0.5Mo), and TiBrazeâ15-15 (Ti-15Cu-15Ni) were successfully tested and accepted by the USA industry. These mechanically-alloyed filler metals are characterized by low erosion of base materials, tensile strength of Ti-6Al-4V brazed joints in the range of 670-740 MPa depending on the brazing gap and temperature, shear strength of joints 520-580 MPa, and by relatively low brazing temperature in the range of 850-890^oC that allows to perform the brazing process below b-transus temperature of most titanium base alloys. Solid-state synthesis of Ti-Zr-Cu-Ni alloys was investigated by varying the time of high-energy ball milling. The products were studied by DTA, EDS analysis, and scanning electron microscopy. Clear evidences of solid-state reactions obtained in this study confirm that the resulting alloys are partially pre-alloyed and comprise Cu and Ni dispersed throughout the Ti and Zr phases. DTA results displayed a decrease in the liquidus temperature. The notable effect of milling is the induced exothermic effect prior to melting of mechanically-alloyed brazing alloys.