Compositional Stability Of The P-Phase In Ti11(Ni,Pd)13 Alloys

In 2010, a new precipitate phase was discovered in the NiTiPt system and termed the P-phase. It is a monoclinic structure that precipitates with three inter-grown variants, which previously plagued clear interpretation from electron diffraction. A subtle version of this phase, denoted as P1-phase, has also been reported. The same P-phase precipitate has been identified in the NiTiPd system.  The composition of the P-phase precipitate, whether with Pt or Pd, has been shown to have a stoichiometry ratio of Ti₁₁(Ni,Pd/Pt)_13. In the present study, the compositional stability of this phase with respect to the Ni:Pd content has been explored. A series of ternary compounds (Ti₁₁Ni₃Pd₁₀, Ti₁₁Ni₅Pd₈, Ti₁₁Ni₇Pd₆, Ti₁₁Ni₉Pd₄, and Ti₁₁Ni₁₁Pd₂) were arc melted and aged at 400 °C for 100 hours. X-ray and electron diffraction were used to determine the phase(s) within each alloy. The Ti₁₁Ni₁₁Pd₂ formed the P1 and B2 phases; the Ti₁₁Ni₉Pd₄ stabilized the B2, P1 and P-phases; Ti₁₁Ni₇Pd₆ yielded the P- and B2 phases; Ti₁₁Ni₅Pd₈ was composed of the P-, B2, and B19 phases; and finally the Ti₁₁Ni₃Pd₁₀ alloy consisted of the B19 and the Pd-rich phase, Ti₂(Pd,Ni)_3. At the highest Ni-contents, the P1 phase appears to be more stable than the P-phase. For the lowest Ni-content, the alloy ratio is unable to stabilize either P- or P1 phases. These experimental results are currently being compared to density functional theory calculations to identify the most energetically favorable phases for each of the studied compositions.