Abstract <p>X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to investigate the disorder–order phase transformation of Ni₅₀Pt₅₀ and Ni₂₀Pt₄₅Al₃₅ (at %) alloys. DSC analyses showed that the disorder–order transformation from the face centered cubic (fcc) structure to the face centered tetragonal (fct) <i>L</i>1₀ α-NiPt(Al) structure occurred in Ni₅₀Pt₅₀ at 660°C and in Ni₂₀Pt₄₅Al₃₅ at 1250°C, respectively. Transmission electron microscopy and XRD analysis revealed <i>L</i>1₀ NiPt and <i>L</i>1₀ α-NiPt(Al) phases with superlattice reflections (110) and (100) appeared in diffraction patterns of the Ni₅₀Pt₅₀ and Ni₂₀Pt₄₅Al₃₅ alloys annealed at 1100°C for 72 h and 500°C for 120 h. At room temperature, the annealed Ni₅₀Pt₅₀ alloy contained both disordered fcc NiPt and ordered <i>L</i>1₀ NiPt phases with (001)[010<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11508_2025_4427_Article_IEq1.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">\({{]}_{{L{{1}_{0}}{\text{NiPt}}}}}\)</EquationSource> <!--PhysMet2560026Zhou-m1--> </InlineEquation>] || (001)[010]_{fcc NiPt} relationship, only ordered <i>L</i>1₀ α-NiPt(Al) phase was present in Ni₂₀Pt₄₅Al₃₅ alloy indicating that Al is an α-NiPt(Al) stabilizer.</p>