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The method of selective laser melting (SLM) is a new manufacturing technology which has been regarded as a potential candidate to prepare bulk metallic glasses (BMGs) without limit of critical dimensions. However, obstacles still remain since the crystallization is rather hard to be sustained in the heat affected zone (HAZ) during the preparation of BMGs, due to the existence of cyclic heating process. In order to find the possibility of inhibiting the crystallization behavior in the HAZ, the micro-structural evolution of Ni 75 Al 25 metallic glass during the cyclic heating process at different temperature variation rates was studied with Molecular Dynamics (MD) simulation. The results reveal that at low temperature variation rates relatively, the crystallization begins during the heating or cooling process depends on the relaxation time between the glass transition temperature T G and the maximum heating temperature T MAX . The relaxation time also affects the transformation mode of crystal structure after the completion of crystallization behavior. When the temperature variation rate rises to 5 × 10 13 K/s, the decline of nucleation occurred: during the heating process, the heating rate is so high that the nuclei at the low temperature could come into the embryo at the high temperature which lead to the fusion of crystal embryos. And the decline of nucleation provides a new possibility for the research on the inhibition of crystallization behavior in the HAZ during the preparation of BMGs with SLM. [ABSTRACT FROM AUTHOR]

• Mo-containing RCCAs have in general a higher σ y 1000 than those RCCAs not containing Mo. • The effect of Mo on σ y 1000 is attributed to its large χ rather than to its high T m. • The large electronegativity of Mo also favors the σ y 25 of single-bcc-phase RCCAs. Refractory complex concentrated alloys, RCCAs, show great potential for ultrahigh-temperature applications. High-temperature strength is one of the key requirements for RCCAs to qualify for that purpose. Some RCCAs already show superior high-temperature strength than that of commercial Ni-based superalloys, but many other RCCAs do not. It is thus important to identify the key factors that control the high-temperature strength of RCCAs. In this work, based on a statistic analysis of the yield strength at 1000 °C (σ y 1000) for 55 reported RCCAs, interestingly, it is revealed that Mo-containing RCCAs have in general a higher σ y 1000 than those RCCAs not containing Mo. The effect of Mo is attributed to its larger electronegativity and hence the larger electronegativity difference to other alloying elements, rather than to its higher melting point. The previously established proposal that a large electronegativity difference favoring the charge transfer and creating an atomic-level pressure that contributes to the strengthening of RCCAs at room temperature, seems effective even at a high temperature of 1000 °C. In addition, the large electronegativity difference also favors the room-temperature strength of single-bcc-phase RCCAs. The findings from this work, further verified experimentally in six new RCCAs, shed light on new research directions to develop RCCAs with decent strength at both high temperatures and room temperature, using a simple descriptor on the electronegativity difference. [ABSTRACT FROM AUTHOR]

Abstract: Exchange bias (EB) and EB training effect have been studied in Ni/NiO nanocomposites, in which a negative EB field of about 2.2kOe at 5K is achieved in as-milled Ni/NiO powders upon cooling in a field of 10kOe. The coercivity of the Ni nanoparticles is significantly enhanced by coupling with NiO. The EB training effect is activated by consecutive application of magnetic hysteresis loops. Besides the FM/AFM interfacial interaction and bulk AFM domain-state model, the model presented by Hoffmann may play an important role to induce such a beneficial initial spin configuration for a typical EB training effect system. Furthermore, a phenomenological relaxation model proposed by Binek is used to describe the next spin configurational relaxation process of AFM interface magnetization towards equilibrium. [Copyright &y& Elsevier]

Using electrophoretic deposition (EPD) method, we coated DyF 3 powder onto the sintered Nd–Fe–B magnets, investigated the changes in magnetic and microstructural properties of DyF 3 EPD-coated magnets and clarified the optimum diffusion temperature and time. Through controlling the process parameters (such as temperature and time), the coercivity was increased from 16.1 to 22.8 kOe with a slight reduction in remanence after the diffusion. A significant increment in coercivity of more than 6.5 kOe was achieved with less than 1.2 wt.% Dy in the Dy-free original magnets. Microstructure analysis suggested that the increase of the coercivity was closely related to the concentration and the distribution of Dy. At 100 μm from the surface of the magnet, Dy concentration gradually increased with the diffusion temperature and time, which corresponds well with the change of coercivity. During the diffusion, Dy favors to substitute for Nd to form the (Nd, Dy) 2 Fe 14 B core–shell phases in the outer region of Nd 2 Fe 14 B grains. The higher magnetocrystalline anisotropy of the core–shell phase and the improved decoupling by the continuous grain boundary phase contribute to the coercivity enhancement. [ABSTRACT FROM AUTHOR]

Abstract: It is known that cooling rate can affect the atomic structure and thus may possibly affect the mechanical properties of metallic glasses (MGs). In spite of the considerable efforts on the cooling rate, its effect on the mechanical properties is controversial at the present time. In this study, we present a micromechanical study of the cooling-rate effect on Young''s moduli and hardness of the cast bulks and melt-spun ribbons for a Zr55Pd10Cu20Ni5Al10 metallic glass. Using the classic nanoindentation method, the Young''s moduli of the ribbon samples obtained at higher cooling rates were measured which appeared to be much lower than those of the bulk samples. However, through further experiments on slice samples cut from the as-cast bulks and finite-element (FE) analyses, we have clearly demonstrated that the measured difference in elastic moduli was mainly caused by the sample thickness effect in nanoindentation tests. To overcome such a confounding effect, microcompression experiments were performed on the as-cast and as-spun MG samples, respectively. Being consistent with the findings from nanoindentation, the microcompression results showed that the cooling rate, as ranging from ∼102 to ∼106 K/s, essentially has no influence on the Young''s modulus and hardness of the metallic glasses. [Copyright &y& Elsevier]

Abstract: The temperature dependence of competition between interlayer and interfacial couplings is observed at different temperatures in Co (3nm)/Cr2O3 (t)/Fe (10nm) trilayers with t =3nm, 6nm, 15nm and 25nm, respectively. The interlayer coupling enhances and the interfacial coupling weakens with increasing temperature. The balanceable temperature between interfacial and interlayer couplings shifts to low temperatures with increasing spacer thickness. Furthermore, the competition between interfacial and interlayer couplings greatly affects the magnetotransport properties of the trilayers. The negative magnetoresistance and the minimum resistance corresponding to balanceable temperature are found in trilayers. [ABSTRACT FROM AUTHOR]

Abstract: A sign change of the magnetocaloric effect is induced by a magnetic field, which is related to a field-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature of CoCl2 nanoparticles. The reversible magnetic-entropy change −ΔS m (4.1 and 11.5Jkg−1 K−1 at 27K for a field change of 3 and 7T, respectively) almost without hysteresis and the large cooling power (83.4 and 148Jkg−1, correspondingly) indicates that CoCl2 is a potential candidate for application in magnetic refrigeration in the low-temperature range. [Copyright &y& Elsevier]

Microstructure and hardness of a powder-bed-type selective laser melted Ti–6Al–4V alloy after post heat treatments at from 300 °C to 1020 °C were systematically investigated by using optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and Vickers hardness (HV) tester. Long columnar original β grains together with the inside dominated parallel acicular martensite in the side view, and chessboard pattern in the top view, were found in the as-received specimen. The subtransus heat treatment does not enable modification of the morphology of the original columnar β grain, only leading to the acicular α′ martensite decomposition into the α platelet and whether surrounded β phase or transformed α′ phase depending on the heating temperature; while the supertransus heat treatment would thoroughly break up the original long columnar β grain, leaving only big original equiaxial β grain filled with the new forming weave-type acicular α′ martensite like the supertransus heat treated wrought specimen. Vickers hardness evolution strictly follows the trend of the microstructural change as the heating temperature increasing, and the double peak phenomenon of the Hardness–Temperature plot should be attributed to substructural refinement effect at around 500 °C, martensitic refinement effect at around 1000 °C, and softening effect resulting from the completely decomposition of the martensite at around 875 °C. [ABSTRACT FROM AUTHOR]

Abstract: The magnetocaloric effects in MnAs1−x Si x (x =0.03, 0.06 and 0.09) compounds have been investigated. The Curie temperature can be tunable in a wide range by changing the Si content. With increasing Si doping, the thermal hysteresis is decreased to nearly zero (x >0.06) and the metamagnetic transition becomes ambiguous, being a second-order-like one. The maximum of the magnetic entropy change is maintained above 10Jkg−1 K−1 and 5Jkg−1 K−1 in MnAs1−x Si x for the field change of 5T and 2T, respectively. These results indicate that the Si-doped MnAs compounds with reduced thermal hysteresis are potential candidates of the room-temperature magnetic refrigeration. [Copyright &y& Elsevier]