The effects of annealing temperature on microstructures, phase transformation, mechanical properties, and shape memory effect of Ti-20Zr-10Nb-5Al alloy were investigated. X-ray diffraction（XRD） patterns show that the alloy is composed of single hexagonal ɑ＇-martensite phase for both as-rolled sample and sample annealed at773 K for 30 min, while single orthorhombic ɑ＇＇ phase exists in the samples annealed at 873 and 973 K for30 min. The optical observations indicate that the alloy is recrystallized when annealed at 873 K, and the grain size of the sample annealed at 973 K is about five times larger than that annealed at 873 K. Both of the samples annealed at 873 and 973 K show almost the same reverse martensite transformation start temperature of 483 K as demonstrated by thermal dilatation tests. The critical stress values for martensite reorientation（σ_M） are 392 and 438 MPa for the alloys annealed at 873 and 973 K, respectively. The maximum shape memory strain is 2.8 %, which is obtained in the alloy annealed at 873 K due to the lower σ_M. Moreover,the sample annealed at 873 K exhibits larger tensile stress and tensile strain due to the smaller grain size.
The effect of ternary alloying element Al and quaternary alloying element Co on the martensitic transformation of ZrCu-based shape memory alloy was investigated. The results show that the addition of Al and Co in ZrCu alloy decreases both the martensitic transformation temperature and the martensitic transformation temperature hysteresis. Transmission electron microscope (TEM) observations reveal that theCm martensite structure is the preferential formation phase. The intervariant structures in ZrCuAlCo alloy are (021) type I twins, while the dominant substructures inside the martensite variant are the (001) compound twins. With the increase of Co content, tensile fracture strength and strain are improved obviously.
To develop new type of high damping metal matrix composites, large grain size barium titanate （BaTiO3） ceramic was sintered and added into Al powder to fabricate BaTiO3/Al composites through the powder metallurgy method and hot extrusion. The damping properties of BaTiO3 ceramic, Al matrix and BaTiO3/Al composites were examined by dynamic mechanical analysis in the temperature range from 273 K to 573 K. The results show that although BaTiO3 exhibits high damping （tan δ=0.12） below 400 K, the damping capacity of 10%BaTiO3/Al （mass fraction） composites below 400 K is not increased as compared to the Al matrix. On the other hand, the damping capacity above 450 K is greatly enhanced due to the motion of dislocations at the interfaces between ceramic particles and Al matrix. The failure of exerting the intrinsic damping of BaTiO3 particles in the composites is attributed to the poor interface bonding between the particles and the matrix. The tensile strength of the composite is 42% higher than that of the Al matrix, which indicates the possibility of obtaining high strength and high damping composites via interface improvement and the addition of high volume fraction of large grain BaTiO3 particles.
0.67BiFeO_(3)-0.33BaTiO_(3)multiferroic ceramics doped with x mol%MnO_(2)(x=2-10)were synthesized by solid-state reaction.The formation of a perovskite phase with rhombohedral symmetry was confirmed by X-ray diffraction(XRD).The average grain sizes were reduced from 0.80mm to 0.50mm as increasing the Mn-doped levels.Single crystalline nature of the grains was revealed by high-resolution transmission electron microscopy(HRTEM)images and electron diffraction patterns.Polar nano-sized ferroelectric domains with an average size of 9 nm randomly distributed in the ceramic samples were revealed by TEM images.Ferroelectric domain lamellae(71°ferroelectric domains)with an average width of 5 nm were also observed.Vibrational modes were examined by Raman spectra,where only four Raman peaks at 272 cm^(-1)(E-4 mode),496 cm^(-1)(A_(1)-4 mode),639 cm^(-1),and 1338 cm^(-1)were observed.The blue shifts in the E-4 and A_(1)-4 Raman mode frequencies were interpreted by a spring oscillator model.The dieletric constants of the present ceramics as a function of the Mn-doped levels exhibited a V-typed curve.They were in the range of 350-700 measured at 10^(3)Hz,and the corresponding dielectric losses were in range of 0.43-0.96,approaching to 0.09 at 10^(6)Hz.
