Abstract
Abstract Three batches of Ti–Ni–Cu powders (Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 ) were prepared by gas atomization and porous specimens were fabricated by spark plasma sintering (SPS). The microstructure of as-solidified powders exhibited a cellular structure. XRD analysis showed that one-step martensitic transformation of B2–B19 occurred in all alloy powders and SPS specimens. DSC measurements of as-atomized powder, sintered bulk specimens and as-cast ingots were performed in order to study the effect of rapid solidification on martensitic transformation behaviors. The dependence of powder size on martensitic transformation temperature is very small in the rapidly solidified powders. However, the transformation temperatures were strongly dependent on the Cu-content. The martensitic transformation starting temperatures ( M s ) of Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 powders ranging between 25 and 150 μm are −4.9, −17.6 and 32.1 °C and the austenite transformation finishing temperatures ( A f ) of Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 powders were 15.6, −4.4 and 38.3 °C, respectively. The M s and A f of the as-atomized powders are much smaller than those of SPS specimens and as-cast ingots for all Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 alloy systems. The temperature hysteresis ( A f − M s ) of Ti 50 Ni 45 Cu 5 powders was 20 °C and continued to decrease with increasing Cu-content. The temperature hysteresis of Ti 50 Ni 30 Cu 20 powders was only 7 °C.
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