| Summary: | In the present work, the phase equilibria of the Ni-Ga-Cr ternary system at 850, 1000 and 1150 °C were experimentally investigated to provide the essential data for developing the high-entropy shape memory alloys (HESMAs) containing Ni, Ga and Cr. At 850 °C, in the Ni-rich portion, the B2 phase shows equilibrium with the L12 phase when the Cr content is less than 10.49 at. %, while displaying the equilibrium with L12 and BCC phases when the Cr content increases. The B2 + L12 + BCC changes into B2 + FCC + BCC three-phase equilibria from 850 to 1150 °C, as the L12 phase region becomes narrow with rising temperature. The two-phase equilibrium, B2 + BCC, was found at all the isothermal sections investigated. Other three-phase equilibria were also discovered: B2 + α-Cr3Ga + BCC and Ni2Ga3 + α-Cr3Ga + L at 850 °C, and B2 + α-Cr3Ga + L at 1000 °C. Significantly, an athermal ω intermetallic compound with the space group of P<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mover accent="true"><mn>3</mn><mo>¯</mo></mover></semantics></math></inline-formula>m1 was observed distributing at the B2 phase in the quenched Ni45.98-Ga25.50-Cr28.52, Ni42.23-Ga15.70-Cr42.07 and Ni16.54-Ga13.63-Cr69.83 (at. %) alloys after being annealed at 1150 °C for 10 days. The high-resolution transmission electron microscopy (HRTEM) results reveal that the ω shows a crystallographic orientation of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mrow><mo stretchy="false">[</mo><mrow><mn>1</mn><mover accent="true"><mn>1</mn><mo>¯</mo></mover><mn>0</mn><msub><mo stretchy="false">]</mo><mrow><mi>B</mi><mn>2</mn></mrow></msub><mo>/</mo><mo>/</mo></mrow><mo stretchy="false">[</mo></mrow><mn>11</mn><mover accent="true"><mn>2</mn><mo>¯</mo></mover><mn>0</mn><msub><mo stretchy="false">]</mo><mi mathvariant="sans-serif">ω</mi></msub></mrow></semantics></math></inline-formula>; <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mo stretchy="false">(</mo><mn>111</mn><mo stretchy="false">)</mo></mrow><mrow><mi>B</mi><mn>2</mn></mrow></msub><mo>/</mo><mo>/</mo><msub><mrow><mo stretchy="false">(</mo><mn>0001</mn><mo stretchy="false">)</mo></mrow><mi mathvariant="sans-serif">ω</mi></msub></mrow></semantics></math></inline-formula> with the B2 parent phase.
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