On the reciprocal lattice of the “premartensitic” R-phase in tini shape memory alloys

The reciprocal lattice of a single R-phase variant formed in a Ti₄₀NI₅₁ shape memory alloy was investigated and it was found that $\text{1}\text{3}$$\text{1}\text{3}$$\text{1}\text{3}$ reflections arc situated on the elongated 〈111〉_B2^∗ direction corresponding to the rhombohedral expansion axis and that 0 $\text{1}\text{3}$$\text{1}\text{3}$ reflections lie on three 〈011〉_B2^∗ directions which are all perpendicular to the elongated 〈111〉_B2^∗ direction. There are four distinct R-phase reciprocal lattices corresponding to four distinct R-phasc variants. The four R-phase reciprocal lattices are related by twinning. Based on the R-phase reciprocal lattice, atomic shuffles in the R-phase transition are proposed. The high density of Ti₁₁ Ni₁₄ precipitates in the aged Ti₄₉Ni₅₁ alloy restrict the growth of R-phase variants, and therefore, superimposed reciprocal lattices of the distinct R-phase variants are often observed.