[en] The microstructures, phase transformations and shape memory properties of Ti-30Zr-xNb (x = 5, 7, 9, 13 at.%) alloys were investigated. The X-ray diffraction and transmission electron microscopy observations showed that the Ti-30Zr-5Nb, Ti-30Zr-7/9Nb and Ti-30Zr-13Nb alloys were composed of the hcp α′-martensite, orthorhombic α″-martensite and β phases, respectively. The results indicated the enhanced β-stabilizing effect of Nb in Ti-30Zr-xNb alloys than that in Ti-Nb alloys due to the high content of Zr. The differential scanning calorimetry test indicated that the Ti-30Zr-5Nb alloy displayed a reversible transformation with a high martensitic transformation start temperature of 776 K and a reverse martensitic transformation start temperature (A_s) of 790 K. For the Ti-30Zr-7Nb and Ti-30Zr-9Nb alloys, the martensitic transformation temperatures decreased with the increasing Nb content. Moreover, an ω phase transformation occurred in the both alloys upon heating at a temperature lower than the corresponding A_s, which is prompted by more addition of Nb. Although the critical stress in tension of the three martensitic alloys decreased with increasing Nb content, the Ti-30Zr-9Nb alloy showed a critical stress of as high as 300 MPa. Among all the alloys, the Ti-30Zr-9Nb alloy exhibited the maximum shape memory effect of 1.61%, due to the lowest critical stress for the martensite reorientation. - Highlights: •Ti-30Zr-5Nb alloy is composed of hcp α′-martensite with the M_s of 776 K. •Ti-30Zr-7Nb and Ti-30Zr-9Nb alloys are predominated by orthorhombic α″-martensite. •Ti-30Zr-13Nb alloy consists of a single β phase due to the β-stabilizing effect of Nb. •The martensitic transformation temperatures decrease with increasing Nb content. •Ti-30Zr-9Nb alloy shows the maximum shape memory effect of 1.61%.

[en] The phase transformation, the microstructure and the shape memory effect of the Ti–20Zr–10Nb–4Ta alloy are investigated. The X-ray diffraction measurements indicated that the alloy is composed of single orthorhombic α″-martensite. The alloy showed a two-stage yielding behavior upon tension at 0.5% and 6% strain with a yield stress of 215 MPa and 565 MPa, respectively. The strain induced martensite stabilization was identified because the reverse martensite transformation start temperature of the alloy increases from 348 to 405 K, with the pre-strain increasing from 0% to 8%. This can be ascribed to the martensite reorientation that occurred at a low strain level and the dislocations formed at a large strain level. The maximum shape memory strain is 3.3% in the Ti–20Zr–10Nb–4Ta alloy.

[en] The phase transformation and microstructures of the deformed Ti-30Zr-5Nb shape memory alloy were investigated. The X-ray diffraction measurements indicated that the Ti-30Zr-5Nb alloy was composed of a single orthorhombic α″-martensite phase. The alloy exhibited one yielding behavior in the tensile test, with a critical stress of ~ 600 MPa and a tensile strain of approximately 15%. A shape memory recovery accompanied by a permanent strain was exhibited in the deformed alloys when heated at 873 K. The permanent strain increased with increasing pre-strain. The microstructure evolution of the deformed alloy was investigated by transmission electron microscopy. The results showed that the martensite reorientation occurred and the dislocations were generated during deformation. The alloy displayed a reversible martensite transformation start temperature as high as 763 K. However, no strain-induced martensite stabilization was found in the deformed alloy with different pre-strain levels, potentially because the large chemical energy of the Ti-30Zr-5Nb alloy depressed the effects of the elastic energy and the dissipative energy. - Highlights: • Ti-30Zr-5Nb alloy is composed of single orthorhombic α″-martensite phase with M_s of 721 K. • No martensite stabilization has been found in Ti-30Zr-5Nb alloy with different pre-strain. • Ti-30Zr-5Nb shows the maximum shape memory effect of 2.75% with a pre-strain of 8%.

[en] Highlights: • Co/Si co-doped β-NiAl coating on nickel based superalloy was obtained. • Co/Si co-doped β-NiAl coating exhibits a good cyclic oxidation resistance. • Role of Si for the improvement of cyclic oxidation resistance has been revealed. - Abstract: Co/Si co-doped β-NiAl coating on nickel based superalloys was prepared using pack cementation method. Microstructure and cyclic oxidation behaviour of the coating were investigated. The weight loss of the coating is less than 3 mg/cm² after 3200 cycles at 1050 °C. The coating exhibits a good cyclic oxidation resistance. The addition of Si decreases the growth stress in the oxide scale by inhibiting the formation of harmful NiO. The formation of SiO₂ particles at the scale/coating interface decreases the growth rate of the Al₂O₃ scale. Moreover, Si addition promotes the formation of the high Al-content phase β-NiAl.

[en] The microstructures, phase transformations, mechanical properties and shape memory effect of Ti-20Zr-10Nb-xAl (x=1, 2, 3, 4 at%) alloys were investigated. The X-ray diffraction results show that the alloys are composed of a single martensitic α″-phase and that the corresponding unit cell volume decreases with increasing Al content. The reverse martensitic transformation start temperature (A_s) of the Ti-20Zr-10Nb-Al alloy is 534 K and decreases with increasing Al content. The addition of Al results in solid solution strengthening and grain refinement strengthening, thus improving the mechanical properties and the shape memory effect of the Ti-20Zr-10 Nb-xAl alloys. The Ti-20Zr-10Nb-3Al alloy shows the greatest shape memory strain (3.2%) and the largest tensile strain (17.6%) as well as a very high tensile strength (886 MPa).

[en] Highlights: • The thickness of α″-martensite increases with increasing annealing temperature. • A_S temperature slightly increases after annealing above 873 K. • The tensile elongation is remarkably improved after annealing at 873 K. • The maximum shape memory strain is 2.7% as obtained in the alloy annealed at 873 K. -- Abstract: The effects of annealing temperature on the microstructures, mechanical properties and shape memory effect of Ti-19Zr-11Nb-2Ta alloy sheets have been investigated. The X-ray diffraction results show that the as-received Ti-19Zr-11Nb-2Ta alloy and those annealed between 873 K and 1073 K are composed of single α″-martensite. The recrystallization temperature of the alloy is between 823 K and 873 K indicated by the optical morphologies, and the thickness of martensite variants increases with the elevating of annealing temperature as detected by transmission electron microscopy (TEM) observations. The reverse martensitic transformation start temperature (A_S) slightly increases after annealing above 873 K. The as-received alloy exhibits elongation of only 4.3%, and the plasticity is remarkably improved after annealing above 873 K. The alloy annealed at 873 K exhibits the largest elongation of 21.2% and a maximum shape memory strain of 2.7% among all the samples corresponding to an ultimate tensile strength of 607 MPa.