Producing Foils From Direct Cast Titanium Alloy Strip

This research was undertaken to demonstrate the feasibility of producing high-quality, thin-gage, titanium foil from direct cast titanium strip. Melt Overflow Rapid Solidification Technology (MORST) was used to cast several different titanium alloys into 500 microns thick strip, 10 cm wide and up to 3 m long. The strip was then either ground, hot pack rolled or cold rolled, as appropriate, into foil. Gamma titanium aluminide (TiAl) was cast and ground to approximately 100 microns thick foil and alpha-2 titanium aluminide (Ti3AI) was cast and hot pack rolled to approximately 70 microns thick foil. CP Ti, Ti6Al2Sn4Zr2Mo, and Ti22AI23Nb (Orthorhombic), were successfully cast and cold-rolled into good quality foil (less than 125 microns thick). The foils were generally fully dense with smooth surfaces, had fine, uniform microstructures, and demonstrated mechanical properties equivalent to conventionally produced titanium. By eliminating many manufacturing steps, this technology has the potential to produce thin gage, titanium foil with good engineering properties at significantly reduced cost relative to conventional ingot metallurgy processing

Mechanical properties of rapidly solidified copper alloys: dependence on composition and microstructure

Rapidly solidified microcrystalline alloys are typically characterized by a fine grain size together with a well-dispersed distribution of particles. The particles serve the important purpose of helping to maintain the refined structure at high temperatures. Strengthening is achieved by a combination of several factors, including grain size, particle distribution and segregation effects. The roles of these respective factors are examined within ternary copper alloys with a selection of different particle stabilities

Microstructural stability of rapidly-solidified Cu-B alloys

The ability to retain refined microstructures at high temperatures is a necessity for those materials which will have a high service temperature or will experience a high-temperature stage during processing, for example during extrusion or forming. It is therefore essential to understand the factors controlling stability and coarsening of the refined and metastable structures typical of rapid solidification. The present study examines the stability of CuB alloys prepared by melt spinning. As-cast ribbons exhibit the typical two-zone structure, namely a fine, microcrystalline wheel side with a certain boron solubility, and a columnar-grained free side with boron-rich particles outlining the cell walls. This microstructure demonstrates a remarkable resistance to change on initial heat treatment. However, after a critical time and temperature state is reached, the microstructure becomes locally unstable and then changes rapidly. The grain boundaries remain immobile as long as particle coarsening is negligible. The boron particles are initially amorphous and highly resistant to coarsening: an interface-controlled process appears to be the cause. Following the crystallization of the boron particles, these coarsen very rapidly because of enhanced solute diffusion along the high-density region of the grain boundaries

Thermomechanical processing and mechanical characteristics of particle-strengthened iron aluminide-based alloys

By the introduction of a fine dispersion of stable particles, a new family of chromium-containing iron aluminide-based alloys, has been developed. These alloys exhibited modified recrystallisation kinetics, creep and tensile strengths and welding characteristics. The existence of a second phase dispersion reduced the tendency for localised deformation. Uniform deformation was promoted and ductility improved. Dispersoid additions improved microstructural stability and the recrystallisation rate was retarded by more than a factor of two. The room temperature tensile ductility as well as the tensile strength of the particle-modified alloy were increased. Furthermore, the onset of micro void coalescence occurred at lower temperatures. At 700°C both alloys exhibited similar strain rate sensitivities. Charpy impact toughness tests showed that the ductile to brittle transition temperature for the thermomechanically treated alloys was approximately 250°C and about 50°C higher for the particle-containing alloy. This apparent decrease in impact toughness was attributed to large inclusions observed in the cast microstructure

Effect of small alloying additions on behaviour of rapidly solidified Cu-Cr alloys

The mechanical properties of as well as microstructural changes in rapidly solidified ternary Cu–Cr based alloys were studied for various ternary additions. The flow stresses of the binary and various ternary alloys are explained in terms of Orowan strengthening mechanisms. Zirconium, magnesium, and, to a lesser extent, silicon affected the age hardenability of the alloys, refining the chromium dispersion by modifying the precipitation sequence described by Tang. The coarsening kinetics was insensitive to the presence of a third alloying element, showing that these additions did not affect chromium transport within the copper matrix. Nevertheless, these additions influenced the morphology of the chromium particles during coarsening; zirconium tended to keep the particles spherical, while titanium additions increased their aspect ratio. Titanium reduced dramatically the age hardenability of the alloy by provoking heterogeneous nucleation of bcc chromium on small Ti02 particles present in the as cast structure, resulting in a coarser particle size distribution at peak strength

Structural Instability in rapidly-solidified copper-boron based alloys on heat treating

The structure and stability of a rapidly-solidified copper-boron state there exist amorphous boron particles which are highly resistant to coarsening. Structural instability is determined by the phase change of the amorphous boron to a crystalline phase which grows rapidly after nucleation. Growth rates are determined by boron diffusion along grain boundaries, with the same parameters controlling for the two alloys. Nucleation rates of the crystalline phase are orders of magnitude lower in the yttrium-modified alloy, and this accounts for the much better stability of this alloy. Nucleation appears to occur by the precipitation of excess solute retained in solution by the rapid solidification