Search

Abstract Additive manufacturing of a high-entropy alloy, AlCoCrFeNi, was studied with selective laser melting from gas atomized powder. A wide process parameter window in the SLM process was investigated but it was impossible to produce crack-free samples, attributed to stresses that originate during the building processes. The microstructure and elemental segregation in the SLM samples were compared with induction-melted AlCoCrFeNi. The induction-melted sample crystallizes in randomly oriented large grains (several hundred microns). Dendritic and inter-dendritic areas with slightly different chemical composition can be observed. Within these areas a spinodal decomposition occurs with a separation into FeCr- and NiAl-rich domains. Further spinodal decomposition within the FeCr-rich regions into Cr- and Fe-rich domains was observed by atom probe tomography. In contrast, the SLM-samples crystallizes in much smaller grains (less than 20 μm) with a dendrite-like substructure. These dendrite-like features exhibit distinct chemical fluctuations on the nm-scale. During annealing more pronounced chemical fluctuations and the formation of Cr-rich and Cr-poor regions can be observed. The difference in microstructure and spinodal decomposition between the induction-melted and SLM samples is attributed to the significantly higher cooling rate for SLM. This study shows that, by using different synthesis pathways, it is possible to modify the microstructure and segregation of element within alloys. This can be used to tune the materials properties, if the cracking behavior is handled e.g. by change of alloy composition to minimize phase transformations or use of a heating stage. Highlights • Selective laser melting has been demonstrated for the AlCoCrFeNi alloy. • Cracking was observed during the manufacturing process. • Induction melt samples show a hierarchical microstructure with bcc and B2 phases. • Selective laser melting offers a unique microstructure due to extreme cooling rates. • Spinodal decomposition into Cr-rich domains was observed for both materials. [ABSTRACT FROM AUTHOR]

Abstract Non-equiatomic Co 17.5 Cr 12.5 Fe 55 Ni 10 Mo 5 (Mo5) and Co 18 Cr 12.5 Fe 55 Ni 7 Mo 7.5 (Mo7.5) medium-entropy alloys were synthesized by vacuum induction melting, cold rolling, and subsequent annealing treatment at various temperatures (900–1200 °C) and they were investigated to exploit the precipitation strengthening in addition to solid solution strengthening of alloys. The effect of annealing temperature and Mo content on the microstructure and mechanical properties are systematically analyzed. From the microstructural analysis, a Mo-rich μ phase is observed in the face-centered cubic (fcc) matrix. Increasing the Mo content and low annealing temperature enhance the formation of μ phase, which is consistent with the thermodynamic calculation results. The formation of μ phase effectively enhances the strength of the Mo7.5 alloy by precipitation strengthening, and suppression of grain growth and recrystallization by Zener pinning effect. These lead to superior combination of tensile strength as high as 1100 MPa and large ductility. Our results provide insights not only into μ-phase strengthening of fcc-structured alloys, but also into the future development of high-performance MEAs. Graphical abstract Image 1 Highlights • The effect of μ-precipitates in the non-equiatomic CoCrFeNiMo alloys is discussed. • Further addition of Mo and decrease in annealing temperature enhances the formation of μ phase. • Formation of μ phase retards the recrystallization and grain growth by Zener pinning effect. • The present non-equiatomic CoCrFeNiMo alloys exhibits superior tensile properties by multiple strengthening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract A series of (TiCr 1.8) 1- x V x alloys with x = 0.2, 0.4, 0.6 and 0.8 was synthetized by induction melting of a mixture of TiCr 1.8 alloy and pure V. It has been found that after hydrogenation all the compounds turn into bct structure. The present bct metal hydrides could be considered forming a pre-martensite state during the transformation (Ti-V-Cr)H x min (bcc) ↔ (Ti-V-Cr)H x max (fcc). Proton NMR studies reveal that distribution of hydrogen over all samples is not homogeneous. The modified Bloembergen-Purcell-Pound model, which supposes existence of two hydrogen fractions in different metal environment, provides the lowest averaged activation energy of hydrogen motion corresponding to (TiCr 1.8) 0.6 V 0.4 , the composition that exhibits the highest reversible hydrogen capacity. Following a regularity in changes of both structural parameters of the studied compounds before and after hydrogenation and those parameters that answer for hydrogen mobility we anticipate the existence of a percolation threshold in properties of the alloys (close to the compositions x = 0.4÷0.5). Highlights • Hydrogen storage properties of Ti-V-Cr alloys are impacted by metal atom distribution. • 1H NMR reveals inhomogeneous distribution of hydrogen for all studied samples. • A percolation threshold in hydrogenation properties of (TiCr 1.8) 1-x V x hydrides is pointed out for x ≈ 0.5. [ABSTRACT FROM AUTHOR]

Abstract The Half-Heusler (Hf 0.5 Zr 0.5) 1-x Ti x NiSn 0.998 Sb 0.002 (x = 0, 0.1, 0.3, 0.5 and 0.7) compounds were prepared by vacuum induction melting method combined with annealing, mechanical grinding and spark plasma sintering (SPS) process. For the sintered bodies, the phase and the temperature dependent thermoelectric properties were characterized. The pure phases of Half-Heusler (HH) structure were successfully obtained by subsequent SPS at 1273 K for 1 h under vacuum. With Ti substitution the lattice parameter decreased systematically and carrier concentration increased showing n -type semiconducting behavior, and the thermal conductivity decreased due to reduction of lattice thermal conduction. As a result, it was obtained the figure of merit ZT∼0.92 at 837 K at x = 0.3. Highlights • Synthesis of (Hf 0.5 Zr 0.5) 1-x Ti x NiSn 0.998 Sb 0.002 compounds via induction melting. • Substantial reduction in lattice thermal conductivity by Ti substitution. • Reduction of hafnium content in the Half-Heuslers (HH) compounds reduces the cost of HH compounds. [ABSTRACT FROM AUTHOR]

A true change of NiAl-Cr(Mo) eutectic lamellar structure during high temperature treatment is investigated at 1150 °C (≈0.8 T m ). The result indicates that the lamellar structure is instable, and the lamellar structure at the eutectic cell center possesses poorer stability compared to that at the eutectic cell boundary. The deep etching demonstrates that the pinching off and spheroidization of Cr(Mo) lamellae observed by mild etching are not true. A true case is that only local dissolution of Cr(Mo) lamellae (corresponding to pinching off) occurs. In particular, the observation way inclining 45° to growth direction could clearly verify that the spheroidization of Cr(Mo) lamellae does not occur, and actually the cylinderization of Cr(Mo) lamellae occurs. The relative instability mechanism is also discussed. [ABSTRACT FROM AUTHOR]

Al-Cu-Li alloy (AA2195) was produced using vacuum induction melting (VIM) furnace under dynamic argon atmosphere. The as-cast billets were homogenized using a two-step homogenization cycle. The hot deformation behavior of homogenized and forged AA2195 alloy was studied by hot isothermal compression in a thermo-mechanical simulator. The contour maps of efficiency of power dissipation and instability maps have been generated within the temperature range of 250–450 °C and strain rate range of 10 −3 –10 2 s −1 . Various deformation mechanisms, which operate in different temperature–strain rate regimes, were identified with the aid of these maps and complementary microstructural analysis of the deformed specimens was carried out. Results indicate four distinct deformation domains within the range of experimental conditions examined. Out of these four domains, the optimum temperature and strain rate range for obtaining a completely reconstituted microstructure is T: 400 °C-450 °C and ε ˙ : 10 −2 -10 −1.5 s −1 and ε ˙ : 10 −0.5 -10 1 s −1 . Instability mechanisms in the material are attributed to localized plastic flow and cracking. A constitutive equation that describes the flow stress of AA2195 alloy as a function of strain rate and deformation temperature was also established. [ABSTRACT FROM AUTHOR]

Recently, we successfully prepared L1 0 -ordered Mn 1.15 Ga alloy with space group P4/mmm by induction melting high purity Mn and Ga followed by annealing the as-melt ingot at 465 °C for 2 days. The highest experimental room-temperature saturation magnetization, Ms, of 92 emu/g, is reported, and the Curie temperature and anisotropy field are estimated to be 595 K and 6.3 T, respectively. Based on the compound, low-energy ball milling technique, along with size-selection and annealing treatment are utilized to study the magnetic hardening and magnetic anisotropy inducement. It was found that milling can effectively improve the coercivity. With increasing the milling time to 210 min, the coercivity gradually increases from 0.8 kOe to a maximum value of 4.71 kOe for powders milled for 120 min, and then decreases. After classifying the powders milled for 120 min into different sizes, the coercivity is caused varying degrees of improvement and up to 5.03 kOe for the particles less than 10 μm. However, the remanence and magnetization are getting worse with long ball-milling time. After annealing at 465 °C for 1 min, remanence and magnetization are recovered without losing too much coercivity, leading to a great promotion of energy product, and the (BH) max of 2.96 MGOe is achieved for the L1 0 -Mn 1.15 Ga powders with particle size in the range of 20–37 μm. In addition, the annealed powder shows possible magnetic anisotropy. The degree of alignment reaches 0.47 for the L1 0 -Mn 1.15 Ga powder, which is 18% higher than the as-milled powders with same size distribution. [ABSTRACT FROM AUTHOR]

The (Fe x Co 1−x ) 3 B (x = 0.0, 0.1, 0.2, 0.3) compounds have been prepared by induction melting with subsequent annealing. All of the compounds form in the orthorhombic Fe 3 C-type structure and exhibit ferromagnetic behaviour: the Curie temperature increases from 750 K for x = 0.0 to 923 K for x = 0.3. Magnetic domain images obtained by Kerr microscopy reveal the presence of uniaxial magnetocrystalline anisotropy. The magnetocrystalline anisotropy energy and anisotropy field of magnetically oriented fine particles have been determined. An anisotropy energy of 651 kJm −3 was obtained for Co 3 B (x = 0.0), the anisotropy energy was found to decrease with increasing Fe content reaching a value of 507 kJm −3 for x = 0.3. These compounds with uniaxial magnetocrystalline anisotropy are potential candidates to be used as semi-hard magnetic phase for the preparation of rare-earth free nanocomposite permanent magnets. [ABSTRACT FROM AUTHOR]

A La 0.59 Nd 0.14 Mg 0.27 Ni 3.3 alloy with 72 wt% Gd 2 Co 7 -type (3R-A 2 B 7 ) and 28 wt% Ce 2 Ni 7 -type (2H-A 2 B 7 ) phases is prepared by induction melting followed by the annealing at 1148 K. Upon further increasing the annealing temperature to 1248 K, the 3R-A 2 B 7 phase transforms into the 2H-A 2 B 7 phase, forming an alloy with a 97 wt% 2H-A 2 B 7 phase and a 3 wt% 3R-A 2 B 7 phase. Electrochemical measurement shows that the discharge capacity retention of the alloy electrode at the 100 th cycle increases from 88.5% to 92.4% as the 2H-A 2 B 7 phase increases from 28 wt% to 97 wt%. Compared to the 3R-A 2 B 7 phase, the 2H-A 2 B 7 phase shows a stronger ability to resist amorphousiation during dehydrogenation and has better structural stability. Therefore, the transformation from the 3R-A 2 B 7 phase to the 2H-A 2 B 7 phase stabilizes the structure of the alloy against amorphization and oxidation, thus improving the cyclic stability of the alloy. Electrochemical pressure–composition ( P–C ) isotherms contain two discharge plateaus; the higher plateau corresponds to the 3R-A 2 B 7 phase and the lower one is associated with the 2H-A 2 B 7 phase. As the 2H-A 2 B 7 phase increases, the high-rate dischargeability of the alloy electrodes increases from 56.8% to 66.3%. [ABSTRACT FROM AUTHOR]

Steel scraps were used as the main raw materials (including 70% steel scraps and 30% pig iron) to prepare the gray cast iron HT250 in a medium-frequency induction melting furnace. A new inoculant X, which mainly contains SiC, and a conventional one (FeSi75) were added into the molten iron, respectively. The effects of the inoculants were investigated through metallurgical analysis of the matrix microstructure and the mechanical properties of the cast test bar, and scanning electron microscope (SEM) observation of the tensile fractured surfaces. The properties of the graphite morphology, matrix structure, mechanical properties and fracture characteristics of the cast iron were examined. The results show that both the new inoculant X and the conventional inoculant FeSi75 resulted in improved properties of the molten iron over the original uninoculated molten iron. The inoculants produced smaller graphite particles, reduced tendency to form shrinkage cavities and porosities during the solidification of the molten iron, decreased supercooling degree, reduced formation of non-metal inclusions, and enhanced mechanical properties (of the cast irons). Most important, the new inoculants X displayed more significant effects than the conventional one because SiC had a high melting point and did not dissolve immediately after being added into the molten iron, which helped to form a large number of micro-zones with high carbon and silicon concentrations and induced heterogeneous nucleation of graphite. [ABSTRACT FROM AUTHOR]

Biphasic Gd + GdZn composites (Gd (50+x) Zn (50−x) ; x = 0, 5, 15 and 25 at.%) were successfully obtained in a single fabrication step by induction melting. X-ray microdiffraction results reveal the homogeneity of all the prepared samples and indicate a combination of GdZn and Gd phases with different proportions. With this method, the main drawbacks of preparing composites have been avoided, providing the additional advantage of enhanced thermal conductivity between phases. The biphasic Gd + GdZn composite shows an enhanced refrigerant capacity in comparison to Gd (11%) as well as to single phase GdZn (45%). Heat capacity measurements provide an adiabatic temperature change of around 3.5 K for 20 kOe for the optimal composite. [ABSTRACT FROM AUTHOR]

The effect of Ni content on microstructural evolution and hydrogen storage properties of Mg– x Ni–3La ( x = 5, 10, 15, 20 at.%) ternary alloys prepared by vacuum induction melting has been investigated. The as-cast Mg– x Ni–3La ( x = 5, 10, 15, 20 at.%) alloys consist of Mg, Mg 2 Ni, LaMg 12 and La 2 Mg 17 phases. An increase of Ni content results in an amount increase of the Mg 2 Ni phase and coarsening of the Mg 2 Ni microstructure in the alloys. The P–C-isotherms of the Mg-based alloys show that the hydrogen storage capacity decreases in the order “Mg–5Ni–3La (5.50 wt%) > Mg–10Ni–3La (5.16 wt%) > Mg–15Ni–3La (4.60 wt%) > Mg–20Ni–3La (4.51 wt%)”. But the change of Ni content does not alter the thermodynamic properties of Mg–H 2 system and Mg 2 Ni–H 2 system in Mg– x Ni–3La ( x = 5, 10, 15, 20 at.%) alloys. All of the four alloys show excellent desorption kinetics. The desorption kinetics of the alloys first increases, and then decreases with the increase of Ni content. The Mg–15Ni–3La alloy shows the highest dehydriding rate and the lowest apparent activation energy value of 80.36 kJ/mol, which is the optimum kinetics of hydrogen desorption among the alloys. This is attributed to the most appropriate amount of the Mg 2 Ni phase and eutectic microstructures in the alloy. [ABSTRACT FROM AUTHOR]

Mm 0.75 Mg 0.25 Ni 3.5 Co 0.2 Al x ( x = 0.0–0.4) alloys were prepared by the magnetic induction melting method. The influence of Al content on the hydrogen storage and electrochemical properties of the alloy was investigated. The results show that the hydrogen storage capacity is gradually reduced as the Al content increases. The (La,Pr,Nd)Ni 5 cell volume and the change of enthalpy also decrease as Al is added. Although the discharge capacity decreases with increasing Al content, the addition of Al can reduce the stability of Mm 0.75 Mg 0.25 Ni 3.5 Co 0.2 Al x ( x = 0.0–0.4) hydride and improve the performance of hydrogen desorption thermodynamics. For the alloy electrode without Al, the maximum discharge capacity ( C max ) and retention discharge capacity after 100 charge–discharge cycles ( C 100 ) is 385 mA h g − 1 and 202 mA h g −1 , respectively. For the alloy electrode with x = 0.4, while C max is only 323 mA h g −1 , C100 is 273 mA h g −1 , which is much higher than that of the alloy without Al. The addition of Al can improve the charge–discharge cycle lifetime effectively and can increase the limiting current I L . The kinetic performance of the Mm 0.75 Mg 0.25 Ni 3.5 Co 0.2 Al x ( x = 0.0–0.4) alloy electrode can also be improved by increasing the Al content. [ABSTRACT FROM AUTHOR]

LaMgNi 3.6 M 0.4 (M = Ni, Co, Mn, Cu, Al) alloys were prepared through induction melting process. The phase compositions and crystal structures were characterised via X-ray diffraction (XRD). The hydrogen storage properties, including activation performance, hydrogen absorption capacity, cycle stability, alloy particle pulverisation and plateau pressure, were systemically investigated. Results show that Ni, Co, Mn and Cu substitution alloys exhibit multiphase structures comprising the main phase LaMgNi 4 and the secondary phase LaNi 5 . However, the secondary phase of the Al substitution alloy changes into LaAlNi 4 . The lattice parameters and cell volumes of the LaMgNi 4 phase follow the order Ni < Co < Al < Cu < Mn. Activation is simplified through partial substitution of Ni with Al, Cu and Co. The hydrogen absorption capacities of all of the alloys are approximately 1.7 wt.% at the first activation process; however, they rapidly decrease with increasing cycle number. In addition, the stabilities of hydriding and dehydriding cycles decrease in the order Al > Co > Ni > Cu > Mn. Hydriding processes result in numerous cracks and amorphisation of the LaMgNi 4 phase in the alloys. The p – c isotherms were determined by a Sieverts-type apparatus. Two plateaus were observed for the Ni, Co and Al substitution alloys, whereas only one plateau was found for Mn and Cu. This result was caused by the amorphisation of the LaMgNi 4 phase during the hydriding cycles. Reversible absorption and desorption of hydrogen are difficult to achieve. Substitutions of Ni with Co, Mn, Cu and Al significantly influence the reduction of hysteresis between hydriding and dehydriding. [ABSTRACT FROM AUTHOR]

Abstract: Encapsulated induction melting was attempted to prepare the Sn-doped CoSb3 skutterudites (CoSb3−y Sn y ) and their thermoelectric properties were investigated. Single phase δ-CoSb3 was successfully obtained by the encapsulated induction melting and subsequent annealing at 773K for 24h. However, if the Sn content (y) was larger than 0.4, δ-CoSb3 was decomposed to γ-CoSb2 and Sn. Sn atoms successfully acted as electron acceptors by substituting Sb atoms. Seebeck coefficients of the Sn-doped samples showed positive values, and electrical resistivity was remarkably reduced by Sn doping. Thermal conductivity was considerably reduced by doping due to the phonon scattering. Thermoelectric properties were improved by the appropriate post-annealing and Sn doping, and they were closely related to phase transitions and dopant activation. [Copyright &y& Elsevier]

Abstract: The decarburization and deoxidation technique for permanent Nd–Fe–B magnet scrap is investigated. The carbon and oxygen contamination damage the magnetic properties. The carbon content decreased less than 0.001% by heating in air. The two stage deoxidation is applied, iron oxides are reduced by heating in hydrogen thereafter rare earth oxides are removed by Ca-reduction and leaching. The appropriate conditions for deoxidation in the Ca-reduction and suppressing the re-oxidation in the leaching are investigated. The heating pattern in Ca-reduction and the leaching condition for the mixture composed of Ca compounds and Nd–Fe–B alloy powder greatly affects the oxygen content of recycled material. The decarburized and deoxidized Nd–Fe–B magnet scrap can be recycled as alloying elements by melting. [Copyright &y& Elsevier]

Three Zn–Mg–Y alloys with nominal compositions of Zn 50 Mg 42 Y 8 and Zn 60 Mg 30 Y 10 were prepared by induction melting or gas atomisation. XRD and SEM analysis shows samples ZMY-1 and ZMY-2 consisted of multiple phases including icosahedral quasicrystal (QC) i-phase, hexagonal H-phase and Mg 7 Zn 3 , whilst ZMY-3 contained QC only. The hydrogen storage properties of the Zn–Mg–Y quasicrystal and ternary alloys were investigated for the first time. The quasicrystal sample ZMY-3 hydrogenated at 300 °C had 0.3 wt.% capacity and the DSC decomposition peak temperature was 503 °C. Amongst the three samples, the highest hydrogen storage capacity (0.9 wt.%) and the lowest decomposition peak temperature (445 °C) was achieved by sample ZMY-1. The pressure–composition–isotherm (PCI) curve of ZMY-1 sample showed a flat plateau gave a plateau pressure of 3.5 bar at 300 °C, which indicates a lower dehydrogenation enthalpy than MgH 2 . [ABSTRACT FROM AUTHOR]

In order to improve the hydrogen storage performances of Mg-based materials, LaMg 11 Ni alloy was prepared by vacuum induction melting. Then the nanocrystalline/amorphous LaMg 11 Ni + x wt% Ni ( x = 100, 200) hydrogen storage alloys were synthesized by ball milling technology. The structure characterizations of the alloys were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical hydrogen storage characteristics were tested by using programmed control battery testing system. The electrochemical impedance spectra (EIS), potentiodynamic polarization curves and potential-step curves were also plotted by an electrochemical workstation (PARSTAT 2273). The results indicate that the as-milled alloys exhibit a nanocrystalline and amorphous structure, and the amorphization degree of the alloys visibly increases with extending milling time. Prolonging the milling duration markedly enhances the electrochemical discharge capacity and cyclic stability of the alloys. The electrochemical kinetics, including high rate discharge ability (HRD), charge transfer rate, limiting current density ( I L ), hydrogen diffusion coefficient ( D ), monotonously decrease with milling time prolonging. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline Mg2Ni intermetallic compound was produced from elemental components by induction melting and subsequent mechanical alloying in a planetary ball mill. Then the powder was compacted into bulk samples keeping the nanocrystalline structure. Hydrogen storage capacity of the Mg2Ni bulk samples was found to be of about 1.9wt.%. The absorption isotherm had a long plateau, corresponding to pressure of 0.1MPa at the temperature of 553K. The bulk samples demonstrated high durability after 21 absorption–desorption cycles. [Copyright &y& Elsevier]

Abstract: Advanced Ag8Al8Cu36Zr48 master alloys were produced by arc- and induction melting and examined. The arc-melted ingot has an amorphous structure with a certain amount of metastable phase, compared to the induction-melted ingot, which contained AlCu2Zr, CuZr2 and Ag3Al phases. Amorphous wedge-shape samples were produced by centrifugal casting from the arc-melted master alloy. Amorphous/crystalline powders were synthesized by ball-milling with different milling times from the induction-melted master alloy. The resulting powder contained Ag2Al phase after 5h milling, the amount of which was reduced after 9h milling. The thermal stability of the samples was investigated by DSC. The effective activation energies of the first crystallization were evaluated according to Kissinger’s method and there were found to be the same, 271–268J/g. The low activation energy suggests a good ductility. [Copyright &y& Elsevier]