| The phase transformations in (Ni,Cu)(,3)Sn alloys containing Cu contents ranging between 10 and 22 at% were investigated in detail by means of optical and scanning and transmission electron microscopy, electron and X-ray diffraction techniques, and differential thermal analysis. A high-temperature DO(,3) phase was transformed to an ordered 2H (beta-Cu(,3)Ti-type) orthorhombic phase at a temperature of around 700(DEGREES)C in alloys containing Cu contents between 14 and 20 at%. Residual areas of the DO(,3) phase then were transformed to both the 2H phase and a new phase at around 460(DEGREES)C. Electron and X-ray diffraction analyses revealed that the new phase exhibited a triclinic structure, slightly distorted from the 2H structure. Below that temperature, the three phases of DO(,3), 2H, and d2H are present. These results were consistent with those obtained from specimens containing 20 at% Cu, aged at various temperatures.;TEM observations of specimens quenched from 1000(DEGREES)C to ice water revealed that the high-temperature DO(,3) phase was retained for alloys containing Cu ranging from 16 and 22 at%. For an alloy with a Cu content of 14 at%, a 2H martensite was formed containing (121) twins.;A new phase diagram is proposed for the (Ni,Cu)(,3)Sn alloys in the range of Cu between 10 and 22 at%. This phase diagram is different from the one found in literature, showing a single phase of 2H at temperatures below about 900(DEGREES)C in the range of Cu contents between 8 and 18 at%. It is also proposed that the d2H phase can be formed from an L2(,1) phase via the DO(,3) phase.;Transmission electron microscope observations of specimens with Cu contents of 14, 17.5, and 20 at%, furnace-cooled from 1000(DEGREES)C, demonstrated that the d2H phase exhibited acicular structures containing a large number of uniformly distributed internal faults. These d2H structures are surrounded by the 2H phase, which contains rod-shape structures having (101) faults and a low density of dislocations. |
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