Tohoku University · Materials Science
Professor Xiao Xu's research lab specializes in functional materials, with a primary focus on shape memory alloys, Heusler phases, and caloric materials for advanced applications. The lab investigates martensitic transformations, magnetic and mechanical properties, and phase transitions under thermal, magnetic, and mechanical stimuli, aiming to develop materials with unique functionalities such as cooling-induced shape memory effect and superelasticity. Key research directions include designing biomaterials with low Young's modulus and high wear resistance, as well as exploring shock-compression behaviors and solid-state refrigeration using elastocaloric effects in shape memory alloys. The lab integrates experimental techniques such as in situ XRD, TEM, and high-field magnetometry to uncover fundamental mechanisms and enable next-generation smart materials.
Figures are computed from collected data and may differ slightly.
Normally, shape memory effect (SME) is obtained by the reverse martensitic transformation, therefore only induced by heating a sample from the deformed martensite phase. In this study, we report a phenomenon of cooling-induced SME, observed in a Co2Cr(Ga,Si) Heusler alloy, where the normal heating-induced SME can be obtained at the same time. The cooling-induced SME is attributed to an abnormal martensitic transformation in Co2Cr(Ga,Si) Heusler alloy. Moreover, an inverse temperature dependence
Magnetic properties and martensitic transformation behaviors of NiCoMnAl metamagnetic shape memory alloys were investigated. The kinetic arrest phenomenon was observed at about 40 K during thermomagnetization measurements. At temperatures ranging from 4.2 to 200 K, magnetic field-induced reverse transformation was confirmed by a pulse magnetometer with a magnetic field up to 45 T. By plotting the equilibrium magnetic fields against the measured temperature, the transformation entropy change was
The demand for biomaterials has been increasing along with the increase in the population of elderly people worldwide. The mechanical properties and high wear resistance of metallic biomaterials make them well-suited for use as substitutes or as support for damaged hard tissues. However, unless these biomaterials also have a low Young's modulus similar to that of human bones, bone atrophy inevitably occurs. Because a low Young's modulus is typically associated with poor wear resistance, it is di
The shock-compression response of as-blended and ball-milled elemental Ni and Ti powder mixtures is investigated in this study. An 80-mm diameter single-stage gas-gun was employed to perform time-resolved measurements using piezoelectric stress gauges to monitor the stress wave profiles at the front (input) and back (propagated) surfaces of the ∼50% dense Ni+Ti powder mixture compacts. Shock-compression experiments performed on as-blended Ni+Ti powder mixtures in the range of 522m∕sto1046m∕s imp
We report the martensitic transformation behavior in Co-V-Ga Heusler alloys. Thermoanalysis and thermomagnetization measurements were conducted to observe the martensitic transformation. By using a transmission electron microscope and an in situ X-ray diffractometer, martensitic transformation was found to occur from the L21 Heusler parent phase to the D022 martensite phase. Phase diagrams were determined for two pseudo-binary sections where martensitic transformation was detected. Magnetic prop
Stress-induced martensitic transformation below room temperature for a Ni45Co5Mn36.1In13.9 single-crystal, in which no martensitic transformation occurs during cooling down to 4.2 K under zero stress, was investigated by using compression test. The equilibrium stress estimated from the critical stresses in stress-induced forward and reverse transformations decreased with decreasing temperature, while it became almost constant at temperatures below about 140 K. This anomaly can be explained by th
Vapor compression technologies widely used for refrigeration, heating, and air-conditioning have consumed a large fraction of global energy. Efforts have been made to improve the efficiency to save the energy, and to search for new refrigerants to take the place of the ones with high global warming potentials. The solid-state refrigeration using caloric materials are regarded as high-efficiency and environmentally friendly technologies. Among them, the elastocaloric refrigeration using shape mem
In this report, we present findings of systematic research on NiCoMnAl alloys, with the purpose of acquiring a higher thermal transformation arrest temperature (TA). By systematic research, TA in the NiCoMnAl alloy systems was raised up to 190 K, compared to the highest TA of 130 K in NiCoMnIn. For a selected alloy of Ni40Co10Mn33Al17, magnetization measurements were performed under a pulsed high magnetic field, and the critical magnetic field-temperature phase diagram was determined. The magnet
Martensitic and magnetic properties of Ni33.0Co13.4Mn39.7Ga13.9 metamagnetic shape memory alloy were investigated. The kinetic arrest phenomenon was observed at about 120 K by thermomagnetization measurements, and magnetic field-induced transformation (MFIT) was also detected at various temperatures ranging from 4.2 to 300 K. By evaluation of the equilibrium magnetic fields and temperatures based on the transformation fields and temperatures, it was confirmed that the transformation entropy chan
Electronic, magnetic, and thermodynamic properties of ${\text{Co}}_{2}\text{Cr(Ga,Si)}$-based shape-memory alloys, which exhibit reentrant martensitic transformation (RMT) behavior, were studied experimentally. For electric resistivity (ER), an inverse (semiconductor-like) temperature dependence in the parent phase was found, along with anomalous behavior below its Curie temperature. A pseudobinary phase diagram was determined, which gives a ``martensite loop'' clearly showing the reentrant beha
Magnetic field-induced transition of Ni45Co5Mn36.7In13.3 was investigated under magnetic fields with different sweeping rates. A static magnetic field produced by a superconducting magnet, a semi-static magnetic field created by a flywheel DC generator-powered magnet, and a pulsed magnetic field resulting from a condenser bank-powered magnet were used in this study, which covers sweeping rates of more than 6 orders. The magnetic field hysteresis is enlarged with increasing sweeping rate. The exp
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