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The Cu-12Al-4Ni-1Mn-xB（x=0%，0.1%，0.2%，0.3%，mass fraction，the same below） shape memory alloys were prepared by vacuum arc melting furnace after introducing trace boron element into the alloy. The influence of boron addition on the microstructure， phase transformation， and mechanical properties of the alloy was investigated. The results show that the addition of boron significantly refines the grain size， with the grain size decreasing from hundreds of microns to （11±3.45） μm. The phase transformation temperature shifts to the high-temperature side after boron is added， indicating that the phase transformation process requires higher thermal activation energy. When the boron content is 0.2%， the microhardness of the alloy is enhanced， from （301.7±2.6）HV without adding boron element to （334.3±3.4）HV， which is attributed to grain refinement and the precipitation of hard and brittle borides. The tensile fracture strength and elongation are greatly improved， with the fracture strength increasing from （320±2.6） MPa to （788±17） MPa， and the elongation increasing from （1.44±0.05）% to （3.74±0.12）%. After solid solution annealing， the fracture strength and the elongation are both further increased to （856±10.7）MPa and （5.78±0.16）%， respectively. Analysis indicates that grain refinement strengthening， precipitation strengthening of borides， and solid solution strengthening are the main mechanisms for the improvement of mechanical properties. The fracture mode of the alloy shifts from brittle fracture to ductile fracture.

CuAlMn shape memory alloys have specific target demands in various fields due to excellent thermal stability and high damping properties.However， the mechanical property of the alloy is severely weakened due to the intergranular fracture arising from the coarse grain size. To improve the mechanical properties， the Cu-11.36Al-5Mn-xY （x=0-3， mass fraction/%，the same below） alloys were prepared by using a vacuum arc melting furnace by introducing rare earth Y element. The microstructure of the as-cast CuAlMn alloy was subsequently tailored and homogenized through solid solution and aging treatment. The phase transformation， phase composition， and microstructure of the alloy were respectively characterized by DSC， XRD， metallography and SEM observations. The hardness and mechanical properties of the alloy were tested by using a microhardness tester and a universal materials testing machine. Results show that the addition of Y element effectively refines the CuAlMn alloy grain， and the grain size even reduces from several hundred μm to around 10 μm. The grain refinement is mainly associated with the increased grain nucleation areas and the inhibition of grain growth during the cooling process. Moreover， quite numbers of Y-containing precipitates with the network structure are formed and distributed along the grain boundaries. The hardness of the alloy increases with the enhancement of Y element addition， which is associated with the precipitation of a large amount of hard and brittle containing Y phases.The hardness of the solution-aged sample is higher than that of the cast sample， due to the precipitate distribution throughout the entire matrix and higher volume fraction of precipitates for the former sample.In addition， the compressive and tensile fracture strength of the alloy are significantly improved when the Y content is in the range of 0.1%-0.4%. The strengthening mechanism can be understood by grain refinement strengthening， precipitation strengthening and solution strengthening. The compressive fracture strain of the alloy reaches its maximum when the Y content is 0.4%， while the elongation after fracture exhibits the maximum value with Y content of 0.1%. The changing trend is closely related to the coupling effect between grain refinement and precipitation phases.

The Ti50-0.5xNi50-0.5xZrx series alloys were prepared by vacuum arc melting and subsequent suction casting. Metallographic observation and tensile mechanical tests show that adding trace amount of Zr can reduce grain size and increase higher tensile strength and elongation， however， excessive Zr content can easily lead to the formation of brittle intermetallic compound Zr2Ni and reduce its mechanical properties. The multi-pass cold-rolling deformation and annealing treatment on Ti49.9Ni49.9Zr0.2 alloy were carried out. The results show that the tensile strength σb and the elongation δ of the Ti50－0.5xNi50－0.5xZrx alloys increase with the increase of cold-rolling deformation. Compared with the unrolled alloys， after four-passes cold-rolling deformation， the tensile strength and the elongation after fracture of the alloys increase from 561 MPa，1.14% to 768 MPa ，35.1%，respectively.Microscopic observation of SEM and TEM show that the hard Ti2Ni particles distributed along the grain boundaries during the cold rolling process are sheared and broken， resulting in a discontinuous distribution of refinement. After 700 ℃ annealing process， the deformed microstructure has recovery recrystallization， resulting in the appearance of nanocrystalline and amorphous regions. Moreover， a large number of plate-like nano-twin structures and high-density dislocations appear in the TiNi matrix with the increase of cold-rolling deformation.

Metal-matrix composites with high damping capacity and excellent energy absorption properties have extensive application requirements. Porous TiNi shape memory alloys with a three-dimensional connected structure were firstly prepared by powder metallurgy technology consisting of "uniform-mixing, compaction, dissolution and sintering" four stages. Then, the novel Acrylic/TiNi composites were manufactured in light of vacuum negative pressure infiltration technology. The damping properties were characterized by internal friction. It was found that Acrylic/TiNi composites exhibit a much higher damping capacity than that of corresponding TiNi porous materials, especially in around room temperature zone. It was rationalized that the great improvement of the damping capacity is originated from the intrinsic high-damping of Acrylic phase as well as induced massive interface damping between TiNi porous matrix and Acrylic phases. The quasi-static compressive mechanical measurement shows that Acrylic/TiNi composites can achieve energy absorption efficiency similar to that of TiNi porous alloy, the reason of which is confirmed to be associated with the longer and smoother compression plateau area of TiNi composites. In addition, the full penetration of the Acrylic reinforced phase greatly enhances the energy absorption capacity and yield strength of the composites. Deformation mechanism analysis of the TiNi composites indicates that the mutual compensation and coupling between porous matrix and Acrylic fillings during the compressive process can be considered to account for the improved energy absorption characteristics.

BaBiNb5O15- based oxide ion conductors have shown promise for solid fuel cell applications at medium temperatures. In this study, BaBi0.98Sr0.02Nb5-xTixO15-δ (x = 0.02, 0.04, 0.05, 0.06, 0.08) samples were prepared by the conventional solid-state synthesis with two-step sintering method. The electrical properties and oxygen relaxation behaviors of the BaBi0.98Sr0.02Nb5-xTixO15-δ samples were investigated. With increasing the Ti content, the bulk conductivity of the BaBi0.98Sr0.02Nb5-xTixO15-δ samples showed a trend of increasing first and then decreasing. When the doped Ti content reached 5 mol%, the highest bulk conductivity of BaBi0.98Sr0.02Nb5-xTixO15-δ samples can be got, 5.27 × 10−5 S/cm at 773 K. According to the dielectric relaxation spectroscopy measurement, the BaBi0.98Sr0.02Nb4.95Ti0.05O15-δ sample exhibits the higher moveable oxygen vacancy concentration and mobility of oxygen vacancies. This could be the possible reason that there is the highest bulk conductivity in the BaBi0.98Sr0.02Nb4.95Ti0.05O15-δ sample. Additionally, the influence of sintering temperature on the electrical properties of the BaBi0.98Sr0.02Nb4.95Ti0.05O15-δ compound was investigated. When the BaBi0.98Sr0.02Nb4.95Ti0.05O15-δ sample is sintered at a temperature of 1423 K, it exhibits the best bulk conductivity and total conductivity. [ABSTRACT FROM AUTHOR]

Porous Cu–Al–Ni shape memory alloys (SMAs) are fabricated via powder metallurgy method using Cu, Al, Ni powders and Cu–Al–Ni alloy powder as raw materials, respectively. It is found that the two kinds of specimens have similar macroscopic morphologies: connected pores are uniformly distributed in the Cu–Al–Ni matrix, forming a 3D network structure. By comparison, the specimen fabricated using alloy powder has much finer microstructures than the specimens fabricated using Cu, Al, Ni powders. After adding Ce element to the latter, the microstructure of the Cu–Al–Ni matrix is significantly refined because of the formation of Ce‐rich particles. Damping tests show that the latter has superior damping capacity than the former. With the increase of Ce content, the damping of the latter increases first and then decreases. When the Ce content reaches 0.05 wt%, the highest damping can be achieved. Correlated mechanisms are discussed based on the microstructural observations. [ABSTRACT FROM AUTHOR]

Ti-modified BaBiNb0.95Ti0.05O15-δ (BBN-Ti5-TS) oxygen ion conductors with tungsten bronze structure were prepared by solid-phase reaction and two-step sintering-assisted sintering method. The electrical conductivity and oxygen ion diffusion of the Ti-modified BaBiNb5O15 (BBN) specimen were investigated. Both the grain conductivity and total conductivity of the BBN-Ti5-TS specimen are enhanced relative to the BBN compound. At 623 K, the BBN-Ti5-TS specimen grain conductivity can get up to 1.28 × 10–4 S/cm, half an order of magnitude higher of the pristine BBN specimen. A relaxation peak associated with thermal activation was observed in the BBN-Ti5-TS specimen with a relaxation activation energy parameter of E = 0.44 eV. The value is slightly lower than the activation energy of oxygen ion migration in the parent compound. Combining the relaxation parameter and structural analysis, the titanium doping and two-step sintering-assisted sintering can reduce the energy barrier for oxygen ion diffusion to a certain extent. Compared with the BBN specimen, the lower oxygen diffusion activation energy and smaller grain size are the main reasons for the significant increase in the conductivity of the BBN-Ti5-TS compound. [ABSTRACT FROM AUTHOR]

BaBiNb5O15 (BBN) based oxide-ion conductors have great potential for application in intermediate-temperature solid oxide fuel cells. In this work, electrical property enhancement is achieved by Sr2+ ion doping and sintering process improvement. The BaBi1−xSrxNb5O15−δ samples are prepared by the traditional solid-state reaction to investigate their electrical properties and oxygen relaxation behavior. Upon increasing the Sr2+ doping amount, the bulk conductivity of BaBi1−xSrxNb5O15−δ compounds increases first and then gradually decreases, and the bulk conductivity of the sample is the best when the doping concentration is 2 mol%. With the increase of Sr2+ doping, the activation energy shows a first decreasing and then increasing trend. Compared with the traditional sintering method, the total conductivity of the BaBi0.98Sr0.02Nb5O15−δ sample prepared by the two-step sintering method is greatly improved. These results have great implications for improving the electrical performances of BBN-based oxide conductors and studying their sintering process. [ABSTRACT FROM AUTHOR]

Strain amplitude (SA) dependence of internal friction (IF) in a Cu–Al–Mn shape memory alloy (SMA) is investigated. Microstructure observation is conducted with the aim to clarify related mechanisms. It is found that the IF measured during the continuous heating process shows a nonmonotonous dependence on SA, that is, the IF increases first and then decreases. The increase of IF can be attributed to the mergence of martensite laths promoted by the reorientation of martensite variants, whereas the decrease of IF is related to the decrease in the density of moveable interfaces. The isothermal IF measured at low temperatures increases monotonously with the increase in SA, because the density of movable interfaces and the sliding distance of these interfaces in the tangential direction increase. Thermal cycles can significantly improve the isothermal IF because of the annihilation of quenched‐in vacancies and the reorientation of martensite variants. At around 240 °C, the isothermal IF in all specimens shows a nonmonotonous dependence on SA, which can be ascribed to the dragging effect of quenched‐in vacancies on dislocations and the breakaway of dislocations from these vacancies when the SA is high enough. [ABSTRACT FROM AUTHOR]

The damping properties of the Cu-Al-Mn shape memory alloy are closely related to the microstructure evolution. Deeply understanding the relationship between the two will greatly contribute to the control of microstructure as well as damping properties to meet different target requirements. In this paper, the internal friction behaviors of as-cast Cu-11 Al-5 Mn (wt %) shape memory alloy was systematically studied by means of internal friction technique, with the expectation of obtaining the alloy microstructure evolution law and the dependence on heat treatment history. Four typical internal friction peaks (respectively named P1, P2, P3 and P4 peak) were observed during heating process ranging from room temperature to 500 °C. P1, P2 and P4 peaks exhibit obvious characteristics of phase transformation internal friction peaks, that is, with the increase of heating rate, the peak temperature shift towards the high temperature direction, and with the increase of measurement frequency, the peak height gradually decreases. It was rationalized that the appearance of P1, P2 and P4 peaks are related to the reverse martensitic transformation, twin refinement and bainite precipitation, respectively. While, the P3 peak is a thermally activated relaxation internal friction peak with an activation energy of 2. 32 eV. It is concluded that the peak is originated from viscous sliding of grain boundaries and can be understood as a solid solution grain boundary peak. [ABSTRACT FROM AUTHOR]

It is recognized that both parent phase aging and element addition can dramatically enhance the comprehensive properties of Cu‐based shape memory alloys (SMAs). However, further in‐depth studies are still needed to clarify the detailed laws and mechanisms. Herein, the effects of parent phase aging and Nb element on the microstructure, martensitic transformation (MT), and damping behaviors of a Cu–Al–Mn SMA are systematically studied. It is found that both the damping at low temperatures and the height of internal friction peak arising from the reverse MT of the Cu–Al–Mn SMA can be improved by the parent phase aging due to the increase in interfacial mobility. When the aging temperature reaches 600 °C, the best damping can be obtained. Nb forms AlNb3 phase in the Cu–Al–Mn matrix. Due to the pinning effect of the AlNb3 phase on grain boundaries, the grains of the Cu–Al–Mn SMA can be remarkably refined. With the increase in Nb content, the damping of the 600 °C aged Cu–Al–Mn SMA increases first and then decreases. The associated mechanisms are discussed. This work aims to provide theoretical basis and technical support for the improvement of damping property of Cu‐based SMAs. [ABSTRACT FROM AUTHOR]

In order to solve the problem of intergranular brittle fracture of Cu-based shape memory alloys (SMAs) and further improve their mechanical properties, an in situ LaB6/Al inoculant was designed and used for the first time to significantly refine the grains of a CuAlMn SMA. Through phase analysis, microscopic observation, and theoretical calculation, it was confirmed that the LaB6 particles in the inoculant could act as efficient heterogeneous nuclei of the CuAlMn SMA. The evolution of microstructures with grain refinement and its influence on the mechanical and damping properties were also investigated. It was found that with the decrease of the average grain size, the martensite structure of the CuAlMn SMA was also dramatically refined. Consequently, because of the increase of phase interface density, the damping capacity of the CuAlMn SMA was improved and the elongation, tensile strength, and yield strength were also significantly improved due to the principle of fine grain strengthening. After hot rolling, the average grain size of the refined CuAlMn SMA increased slightly, while the damping, tensile strength, and elongation were further improved, which has been ascribed to the elimination of casting defects and the increase of density. [ABSTRACT FROM AUTHOR]

The grain-boundary relaxation as well as corresponding internal friction (IF) mechanism in Cu-based shape-memory alloy was investigated taking Cu-20.4Al-8.7Mn (at%) as an example. A relaxational IF peak was found at around 214 °C during the heating process, whereas the peak completely disappears during the subsequence cooling process. The IF peak with the activation energy and pre-exponential factor of 1.60 eV and 3.8 × 10−18, respectively, shifting towards higher temperature as the measuring frequency increased indicates that the peak correlates to a thermal-activation process. The results obtained revealed that the viscous sliding of the grain boundaries should be the operative mechanism for the appearance of the peak. However, the appearance of the γ2 precipitate particles formed during the heating process provides a reverse contribution to the peak, leading to the disappearance of the peak due to their pinning effect on the grain boundaries. [ABSTRACT FROM AUTHOR]

To address the issues of existing powder metallurgy particle reinforced composites, such as poor wettability between ceramic reinforcement and Al matrix, the toxicity of quasicrystal, the compositional limitations of high entropy alloy, and poor thermal stability of amorphous alloy reinforcement, etc. Al matrix composites reinforced with Co-based hard particles (M7) were synthesized by a powder metallurgy process. The effects of sintering temperature, M7 hard particle content, and particle size on the microstructure and mechanical behavior of the composites were investigated. The results show that as the sintering temperature rises, the interdiffusion reaction between M7 particles and Al matrix is enhanced, the diffusion layer becomes thicker, the in-situ generated intermetallic compounds such as Al 3 Ni 2 , Al 13 Cr 2 , Co 2 Al 9 and Al 72.5 Co 16.5 Ni 11 become more abundant, and parts of M7 particles gradually dissolve in the Al matrix and the interdiffusion layer disappeared. When the sintering temperature was raised from 580°C to 640°C, the microhardness and yield strength were improved from 23.9 to 34.7 HV 0.1 and 40.9–175.2 MPa, respectively. The composites' microhardness and strength increase as the M7 particle content increases. Meanwhile, the smaller the particle size, the greater the microhardness and yield strength. The strengthening mechanism of M7/Al composites is mainly attributed to the synergistic effects of the in-situ generated multiphase intermetallic compounds strengthening, solid solution strengthening, and M7 hard particles dispersion strengthening. Furthermore, the M7/Al composites' microhardness and strength were respectively 27.6% and 146.1% higher than those of the SiC/Al composites containing the same size and content of SiC particles, which is mainly due to the good interfacial wettability between M7 and Al matrix. It indicates that metal-based hard particles could be better alternative reinforcements to produce high performance composites. • Al matrix composites reinforced with Co-based hard particles were synthesized by PM. • There was a significant improvement in the mechanical properties of the M7 /Al composites. • The synergistic reinforcement mechanism for M7 /Al composites is proposed. [ABSTRACT FROM AUTHOR]

BaBiNb 5 O 15 (BBN) based oxide-ion conductors have great potential for application in intermediate-temperature solid oxide fuel cells. In this work, electrical property enhancement is achieved by Sr 2+ ion doping and sintering process improvement. The BaBi 1- x Sr x Nb 5 O 15- δ samples are prepared by the traditional solid-state reaction to investigate their electrical properties and oxygen relaxation behavior. Upon increasing the Sr 2+ doping amount, the bulk conductivity of BaBi 1- x Sr x Nb 5 O 15- δ compounds increases first and then gradually decreases, and the bulk conductivity of the sample is the best when the doping concentration is 2 mol%. With the increase of Sr 2+ doping, the activation energy shows a first decreasing and then increasing trend. Compared with the traditional sintering method, the total conductivity of the BaBi 0.98 Sr 0.02 Nb 5 O 15- δ sample prepared by the two-step sintering method is greatly improved. These results have great implications for improving the electrical performances of BBN-based oxide conductors and studying their sintering process.