Properties of NbC-TiAl and TiB 2 -TiAI composites produced by plasma transferred arc process

Abstract

Intermetallic compound based composites (IMCs) consisting of particles of NbC and TiB₂ in Ti-36 wt-%Al (NbC-TiAl and TiB₂-TiAl respectively), with varying volume fraction of reinforcing particles, were produced by a plasma transferred arc process. In NbC-TiAl IMCs, the hardness and 0·2% compressive proof stress increased steadily with increasing volume fraction of NbC whereas the tensile strength was lower than that of the unreinforced TiAl regardless of the volume fraction of NbC. In TiB₂-TiAl IMCs, the hardness and 0·2% compressive proof stress exhibited maximum values at a volume fraction of 5 vol.-%TiB₂. The maximum tensile strength of ∼500 MN m⁻², which is almost twice that of the unreinforced TiAl, was obtained at a volume fraction of 5 vol.-%TiB₂. The initial improvement of mechanical properties due to the addition of TiB₂ was considered to be caused by the reinforcing effect of the TiB₂ particles, grain refinement, and the disappearance of γ grains in 3–5 vol.-%TiB₂-TiAl IMCs. The deterioration of the mechanical properties observed for a volume fraction of >5 vol.-%TiB₂ may be attributed to the increase in the amount of y grains with increasing volume fraction of TiB₂ particles from 7 to 15 vol.-% and the increase in coarse TiB₂ particles that can act as crack initiation sites in tensile tests.

MST/3434