In this study, microstructural and mechanical properties of the extruded and heat-treated TiNi alloys by sintering the mixture of TiNi pre-mixed powder with titanium dioxide (TiO 2) particles were investigated. Pure Ti and pure Ni powder with TiO 2 particles were mixed and consolidated by spark plasma sintering (SPS). SPSed TiNi alloy compacts were extruded and heat-treated subsequently. SPSed TiNi alloy compacts had TiNi matrix and Ti 4 Ni 2 O phase. Ti 4 Ni 2 O phase was formed during SPS by reaction between TiNi matrix and oxygen atoms originated from additive TiO 2 particles. Consequently, the heat-treated Ti-50.5 at.%Ni alloy using pre-mixed powder with 1.0 vol.% TiO 2 particles showed a high plateau stress of 630 MPa and a good shape recovery of 79.7% in 8% strain applied. The heat-treated TiNi alloy with 1.0 vol.% TiO 2 particles revealed the high strength and good shape memory properties. The high strengthening mechanism of the TiNi alloy using pre-mixed powder with TiO 2 particles was mainly due to a decrease martensitic transformation temperature by an increase soluted Ni content in TiNi matrix after reaction between TiNi and TiO 2 .
In this study, microstructural and mechanical properties of the extruded and heat-treated TiNi alloys by sintering the mixture of TiNi pre-mixed powder with titanium dioxide (TiO 2) particles were investigated. Pure Ti and pure Ni powder with TiO 2 particles were mixed and consolidated by spark plasma sintering (SPS). SPSed TiNi alloy compacts were extruded and heat-treated subsequently. SPSed TiNi alloy compacts had TiNi matrix and Ti 4 Ni 2 O phase. Ti 4 Ni 2 O phase was formed during SPS by reaction between TiNi matrix and oxygen atoms originated from additive TiO 2 particles. Consequently, the heat-treated Ti-50.5 at%Ni alloy using pre-mixed powder with 1.0 vol% TiO 2 particles showed a high plateau stress of 630 MPa and a good shape recovery of 79.7% in 8% strain applied. The heat-treated TiNi alloy with 1.0 vol% TiO 2 particles revealed the high strength and good shape memory properties. The high strengthening mechanism of the TiNi alloy using pre-mixed powder with TiO 2 particles was mainly due to a decrease martensitic transformation temperature by an increase solute Ni content in TiNi matrix after reaction between TiNi and TiO 2 .
The shape memory heat treatment effects on the microstructures and the mechanical properties of TiNi shape memory alloys fabricated by powder metallurgy (PM) process were investigated in this study. Through the optimization of the shape memory heat treatment conditions, PM TiNi alloy showed a high plateau stress of 454 MPa and a good shape recovery of 96.4% in 8% strain applied via the heat treatment at 773 K for 10 min. A longtime heat treatment applied to PM TiNi alloys caused an increase of the amount of Ti 3 Ni 4 precipitates in the TiNi matrix, and led to the relative decrease of Ni solid solution in the matrix which resulted in the decrease of the plateau stress.
The shape memory heat treatment effects on the microstructures and mechanical properties of TiNi shape memory alloys fabricated by powder metallurgy (PM) process were investigated in this study. Through the optimization of the shape memory heat treatment conditions, PM TiNi alloy showed a high plateau stress of 454 MPa and good shape recovery of 96.4% in 8% tensile strain applied via the heat treatment at 773 K for 10 min. A longtime heat treatment applied to PM TiNi alloys caused an increase of the amount of Ti 3 Ni 4 precipitates in the TiNi matrix, and resulted in the relative decrease of Ni solid solution in the matrix which caused the decrease of the plateau stress.
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