Search

In the present study, the influence of training on the microstructural evolution, martensitic transformation behavior and mechanical/functional properties of Ti–V–Al–Zr shape memory alloy was investigated systematically. With the increasing of training cycling number, the degree of martensite reorientation became larger and larger. Moreover, higher density of dislocations appeared in the interior of martensite variants, upon the excessive training cycling number was applied. The international stress can be brought into the matrix, which not only promoted to the ω→αˊˊ transition, but also made the martensite phase stabilizer and even suppressed the αˊˊ→β martensitic transformation during training process. The superior mechanical properties including maximum fracture stress of 906 MPa and the higher fracture strain of 33.6% can be obtained in Ti–V–Al–Zr shape memory alloy subjected with the training cycles number of 5th, which can be attributed to the matrix strengthening stemmed from work hardening and suppression of ω precipitation. Meanwhile, the lower critical stress for the martensite variant reorientation and enhanced matrix strength synergistically contributed to the superior strain recovery characteristics with total completely recoverable strain of 6% in Ti–V–Al–Zr shape memory alloy by controlling training cycles number of 5th. Meanwhile, the higher micro-hardness can be obtained by training.

In the present study, in-situ TiN ceramic particles were introduced into Ti–V–Al based shape memory alloys to optimize mechanical properties and friction resistance. The results revealed that increasing the TiN content resulted in the transition from α'' to β phase, and led to a reduction in the martensitic transformation temperature. Additionally, the TiN ceramic particles were found to significantly reduced the grain size of the Ti–V–Al based shape memory alloys. Compared to other Ti–V–Al-X shape memory alloys, the introduction of TiN ceramic particles enhanced the mechanical and wear properties of the Ti–V–Al shape memory alloy. These improvements can be attributed to a combination of solid solution strengthening, grain refinement and precipitation strengthening. Notably, the (Ti–V–Al)100-xNx shape memory alloy exhibited a maximum yield strength of 568 MPa and a fracture strength of 788 MPa. Furthermore, the micro-hardness of the Ti–V–Al based shape memory alloy increased monotonously from 355HV to 393HV, while the wear coefficient steadily decreased from 0.53 to 0.48. In conclusion, by adjusting content of TiN ceramic particles, it is possible to obtain a lightweight Ti–V–Al shape memory alloy with tailored martensitic transformation temperatures, enhanced strength and hardness, as well as excellent friction properties.

In the present work, minor Sc addition was employed to control the microstructural features, further optimizing the mechanical/functional performances of Ti–V–Al based shape memory alloy. The results revealed that phase constituents of Ti–V–Al based shape memory alloys were dominated by single αˊˊ martensite phase, regardless of Sc content. Nevertheless, Sc addition caused the significant lattice distortion of Ti–V–Al based shape memory alloy. Meanwhile, the grain size of Ti–V–Al based shape memory alloys were reduced due to Sc addition. Besides, the martensite morphologies evolved from self-accommodation configuration to optimal orientation configuration, but the types of twins kept unchanged. All Ti–V–Al based shape memory alloys showed the reversible αˊˊ→β martensitic transformation in heating curves, irrespective of Sc content. With Sc content increasing, the martensitic transformation temperatures increased linearly due to the chemical composition effect and mechanical effect. Moderate Sc addition was favor to the improvement of thermal cycling stability of Ti–V–Al based shape memory alloys, which can enhance its functional stability. In proportion, the mechanical and functional properties of Ti–V–Al based shape memory alloys firstly increased and then decreased. Ti–V–Al based shape memory alloy with moderate Sc content of 0.025 at.% possess the higher fracture strength of 748.4 MPa, superior ductility of 18.7% and the larger shape memory effect strain of 4.31% under the 8% pre-strain condition. The higher performances in Ti–V–Al shape memory alloy with 0.025 at.% Sc can be attributed to the compressive effect of solution strengthening and grain refinement.

Hemp is an environmentally friendly porous fiber, and has good sound absorption properties, which can be used to reduce noise. In recent years, hemp-based composites have been widely studied, but most of them study the preparation methods of materials, Therefore, this paper studies the topic. Firstly, the material and specimens with different thickness and diameter were prepared, then, the standing wave tube method experiment was carried out, and the values of sound absorption coefficient of the specimens were measured and analyzed, while a novel model using genetic algorithm and artificial neural network is proposed. Secondly, the artificial neural network structure was designed, and the training data, verification data, test data are divided and the data is preprocessed. Thirdly, improved genetic algorithm is proposed to design to determine an optimal solution. Fourthly, the optimal solution was as the initial weight and threshold, and were input into the artificial neural network together with training data and verification data. Levenberg Marquardt algorithm were used to train the network. Finally, input the test data into the trained network to test the model. The results showed that there is only a minor deviation between the model output values and the measured values, the values of sound absorption coefficient of specimens with 10 mm thickness are between 0.9 and 1. It was also found that compared with artificial neural network model without genetic algorithm, the proposed model has the lower root mean squared error (RMSE) value, the larger coefficient of determination (R2) value.

The effect of V addition on the microstructural evolution, martensitic transformation behaviors and mechanical performances of Ti–Ni–Nb shape memory alloys was systematically investigated. The results reveal that the phase remains almost equal in Ti–Ni–Nb–V shape memory alloys, irrespective of the V content. With increasing V content, the amount of β-Nb phase is increased, which further leads to a reduction in the interspace and width of the β-Nb phase. When the V content changes, Ti–Ni–Nb–V shape memory alloys possess a single stage B2⇌B19´ martensitic transformation. In addition, the martensitic transformation temperatures first increase and then decrease owing to the variation in the chemical composition of the TiNi matrix and microstructural features as the V content increases. The higher yield strength of Ti–Ni–Nb shape memory alloys can be obtained by adding a moderate V content. In conclusion, the lower martensitic transformation temperature and the higher yield strength can be tailored by optimizing the V content in Ti–Ni–Nb shape memory alloys, which would further widen their application fields.

In the present study, the effects of annealing temperature on the microstructure, martensitic transformation and mechanical properties of Ti–V–Al-Gd shape memory alloys were investigated. The results revealed that the phase constituents were dependent on annealing temperatures. The coexistence of the α'´ martensite phase, β phase, hard α second phase and ω phase was found in Ti–V–Al-Gd shape memory alloy annealed at 650 °C. With increasing annealing temperature, the amount of β phase and α second phase gradually decreased. Meanwhile, the grain size of the Ti–V–Al-Gd shape memory alloy increased continuously with increasing annealing temperature. Merely α'´→β reverse martensitic transformation was found in all annealed Ti–V–Al-Gd shape memory alloys, regardless of the annealing temperature. The evolution of the martensitic transformation temperatures can be attributed to the compressive effect of the chemical composition, grain size and type and number of second phases. In addition, the yield strength gradually decreased owing to the coarsening of the grain size and reduction in the amount of the α phase, whereas the elongation became superior in Ti–V–Al-Gd shape memory alloy annealed at higher annealing temperatures due to the elimination of dislocations and defects. In proportion, the strain recovery characteristics gradually decreased as the annealing temperature increased from 700 °C to 800 °C.