Microstructure/processing relationships in reaction-synthesized titanium aluminide intermetallic matrix composites

Abstract

Near-␥ TiAl-and Al 3 Ti-based intermetallic matrix composites have been produced using in-situ reaction-synthesis techniques. The intermetallic matrices have been reinforced with relatively high loadings (e.g., 20 to 50 vol pct) of dispersed TiB 2 particulates. It is shown that the as-synthesized TiB 2 size is strongly dependent on the specific alloy formulation; specifically, the TiB 2 size tends to increase as the nominal volume percent of TiB 2 in the composite increases. The observed size effect is determined to be associated with the temperature that is attained during the synthesis event, which is established primarily by the net exothermicity of the participating synthesis reaction(s). The exothermicity of the reactions can be assessed through the calculation of a formulation's adiabatic temperature, which is found to increase with the percentage of TiB 2 over the range of approximately 10 to 60 vol pct. The coupling of a composite's characteristic adiabatic temperature with the resulting reinforcement size provides direct links among composition, processing, and mechanical performance, since the size of a reinforcing particle is influential in establishing the interparticle spacing, which, in turn, establishes the strengthening potency of the dispersed phase within the composite.

Co-deformation processing and modeling of In-Situ multiphase composites

“…If conditions are conducive to co-deformation, both components will commensurately deform, creating a multilithic metal matrix composite (MMMC) with approximately aligned DR-IMC "reinforcement" of an increased aspect ratio as a consequence of the deformation imposed. [10,11,12] …”

“…The DR-IMC component was comprised of variations of Al 3 Ti or the Ti-47Al matrix composites, discontinuously reinforced with a dispersion of TiB 2 particulate. Details of the process, synthesis, densification, and monolithic deformation behavior of these DR composites have been presented previously; [8,10,13] however, the process will be briefly summarized here. The DR-IMC composites were produced using an in-situ, reaction-synthesis technique.…”

“…The DR-IMC exhibits a relatively high population of approximately 1-m-diameter TiB 2 single-crystal particulate and has been metallographically characterized previously. [8,10,13] Previous work has shown that both DR-IMC compositions exhibit working thermodynamic stability (i.e., no discernable reaction zones) with ␤-containing titanium alloy compositions. [16] In the second instance (Figure 4(b)), extrusion appears to have imparted relatively little deformation of the Ti-47Al ϩ 40 vol pct TiB 2 dispersed IMC microconstituent, as indicated by the retention of the original, nominally equiaxed shape.…”

Research on TiAl Alloy Porous Metal Flow Restrictors

“…When the sintering temperature is lower than the melting point of Al, Ti and Al diffuse to form TiAl 3 phase on the particle boundary. 8) At the Al melting point temperature, the diffusion velocity of Al in Ti is 0.075 mm/s and vise verse is 0.066 mm/s. In addition, Al element is main diffusion unit in the Ti-Al diffusion system because the solid solubility of Al in Ti is much more than that of Ti in Al.…”

The hot extrusion reaction synthesis of nickel aluminide alloys

“…Previous studies have demonstrated the reaction synthesis of metal aluminides from elemental powders, including those based on titanium [1,2], nickel [3][4][5][6][7][8][9], iron [10][11][12][13][14], zirconium, niobium [15] and tantalum [3]. Concurrent and post synthesis hot pressing has often been used in combination with reaction synthesis to improve the density of the aluminides produced [3,6,7,13].…”