Spray processing of reactive alloys (titanium-aluminum, zirconium)

As a novel, cost-effective processing technology, which is capable of fabricating tonnage bulk materials with improved properties, spray forming has been successfully employed for many alloys systems. However, its application to chemically reactive, such as titanium and zirconium based, alloys is very limited. The theme of the present study is to enhance our fundamental understanding of spray-formed Ti and Zr based reactive alloys using a modified technique: induction skull melting and spray forming.; Five titanium aluminide alloy compositions (three monolithic and two composite) and one zirconium alloy composition (Zircaloy-4) were successfully spray formed using the induction skull melting/spray forming technique. Compared with the conventional processing techniques, spray forming led to significant microstructural refinement for these alloys. The creep behavior for one of the spray formed titanium aluminide alloys, Ti-47Al, was studied in a temperature-stress regime of 780 to 850{dollar}spcirc{dollar}C and 180 to 320 MPa. Compared with the FL {dollar}gamma{dollar}-TiAl which was obtained through conventional casting + heat treatment processes, the spray formed {dollar}gamma{dollar}-TiAl exhibited higher creep resistance levels. For the TiAl/TiB{dollar}sb2{dollar} composite that was fabricated using spray forming and co-injection technique, TiB{dollar}sb2{dollar} particulates were effectively incorporated into the TiAl matrix, while their distribution in the matrix exhibited a layered morphology. Detailed analysis has suggested that the most likely approach to improve the distribution of the reinforcements in the deposit is to decrease the co-injector/atomizer distance.; To investigate the transient physical phenomena associated with spray forming, a two dimensional model was formulated. This model predicts the following: the two dimensional droplet size distribution in the spray cone changes from being heterogeneous to being almost homogeneous as axial flight distance increases; the two dimensional distribution of the solid-fraction in the spray cone is heterogeneous, increasing from the central region to the peripheral region. The size distribution of powders is another important topic in many powder related processing fields, including spray forming. The procedure conventionally employed to interpret experimentally determined sieving data was demonstrated to be inherently flawed in several aspects, and consequently a novel procedure was formulated.