Hot Hydrostatic Extrusion of Mechanically Alloyed Al-4.9Fe-4.9Ni Powders

Al-4.9 Fe-4.9 Ni alloy powders have been synthesized by mechanical alloying. The rnechanically alloyed powders are consolidated by hot hydrostatic extrusion. The results show that extrusion tempereture. extrusion ratio and lubricant have great effects on the quality of extruded rods and their mechanical properties, The mixture of graphite and glass powders as lubricant can prevent the oxidization of cold compacted billet by cladding the billet with this lubricant before heating. This technique greatly simplifies the conventional densification process of powders

Preparation of ultra-fine fibrous Fe-Ni alloy powder by coordinated co-precipitation-direct reduction process

The precursor prepared by coordinated co-precipitation was direct reduced by hydrogen to ultra-fine fibrous Fe-Ni alloy powder. The effects of concentrations of reactants, pH value, reaction temperature and additive on the preparation of precursor were systematically investigated. The structures, thermal decomposition processes and morphologies of the precursors were characterized by X-ray diffraction (XRD), thermal gravity-differential thermal analysis (TG-DTA) and scanning electron microscoy (SEM). The results show that using 2% polyvinylpyrrolidone (PVP) (in mass fraction) as additive, a well-dispersed precursor with a uniform morphology can be obtained in a solution with Fe2+ and Ni2+ total concentration (1:1) of 0.8 mol/L, pH value of 6.2 at 60 °C, and a pure and well dispersed fibrous iron-nickel powder can be prepared by direct reduction of this precursor in a mixed atmosphere of nitrogen and hydrogen at the temperature of 420 °C.

In-situ hydrothermal synthesis of Ni−MoO_(2)heterostructure on porous bulk NiMo alloy for efficient hydrogen evolution reaction

The Ni−MoO_(2) heterostructure was synthesized in suit on porous bulk NiMo alloy by a facile powder metallurgy and hydrothermal method.The results of field emission scanning electron microscopy(SEM),field emission transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS)reveal that the as-prepared electrode possesses the heterostructure and a layer of Ni(OH)_(2) nanosheets is formed on the surface of Ni−MoO_(2) electrode simultaneously after hydrothermal treatment,which provides abundant interface and much active sites,as well as much active specific surface area.The results of hydrogen evolution reaction indicate that the Ni−MoO_(2) heterostructure electrode exhibits excellent catalytic performance,requiring only 41 mV overpotential to reach the current density of 10 mA/cm^(2).It also possesses a small Tafel slope of 52.7 mV/dec and long-term stability of electrolysis in alkaline medium.

Laser powder bed fusion of a Ni3Al-based intermetallic alloy with tailored microstructure and superior mechanical performance

Ni3Al-based alloys are excellent candidates for the structural materials used for turbine engines due to their excellent high-temperature properties.This study aims at laser powder bed fusion and post-hot isostatic pressing(HIP)treatment of Ni3Al-based IC^(-2)21 M alloy with a highγ0 volume fraction.The as-built samples exhibits unavoidable solidification cracking and ductility dip cracking,and the laser parameter optimization can reduce the crack density to 1.34 mm/mm^(2).Transmission electron microscope(TEM)analysis reveals ultra-fine nanoscaleγ0 phases in the as-built samples due to the high cooling rate during rapid solidification.After HIP treatment,a fully dense structure without cracking defects is achieved,which exhibits an equiaxed structure with grain size~120-180μm and irregularly shapedγ0 precipitates~1-3μm with a prominently high fraction of 86%.The room-temperature tensile test of as-built samples shows a high ultimate tensile strength(σUTS)of 1039.7 MPa and low fracture elongation of 6.4%.After HIP treatment,a significant improvement in ductility(15.7%)and a slight loss of strength(σUTS of 831.7 MPa)are obtained by eliminating the crack defects.Both the as-built and HIP samples exhibit retained highσUTS values of 589.8 MPa and 786.2 MPa,respectively,at 900C.The HIP samples exhibita slight decrease in ductility to~12.9%,indicating excellent high-temperature mechanical performance.Moreover,the abnormal increase in strength and decrease in ductility suggest the critical role of a highγ0 fraction in cracking formation.The intrinsic heat treatment during repeating thermal cycles can induce brittleness and trigger cracking initiation in the heat-affected zone with notable deteriorating ductility.The results indicate that the combination of LPBF and HIP can effectively reduce the crack density and enhance the mechanical properties of Ni_(3)Al-based alloy,making it a promising material for high-temperature applications.

Microstructure and hydrogen storage properties of Mg-based Mg85Zn5Ni10 alloy powders

Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning electron micro- scopy (SEM).By utilizing a Sieverts apparatus,the hydrogenation and dehydrogenation properties of Mg85Zn5Ni10 powders were measured systematically.XRD and SEM results indicated that the Mg85Zn5Ni10 alloy powders contained the major phase Mg,the eutectic Mg-Mg2Ni and Mg-MgZn2 mixtures.The possible reaction pathway can be inferred as follows:Mg +Mg2Ni +MgZn2 +H2←→MgH2+Mg2NiH4 +MgZn2,indicating that MgZn2 did not react with H2. After activation,the Mg85Zn5Ni10 alloy powders could absorb 5.4 wt.% hydrogen reversibly and held an excellent hydrogenation kinetics at a relatively low temperature.At 360 ℃,the alloy powders desorbed 5.351 wt.% hydrogen in 264 s.However,it only had fast dehydrogenation kinetics above 300 ℃.The existence of MgZn2 contributed to improving the kinetic properties.During the hydriding and dehydriding,the formed cracks and defects promoted the kinetics and thermodynamic properties.The activation energy for dehydrogenation was 75.514 kJ/mol.The enthalpy change values of hydrogenation and dehydrogenation were calculated to be -73.064 kJ/mol and 76.674 kJ/mol,respectively,indicating that melting with Ni and Zn could improve the thermodynamic property of Mg slightly.

Microstructure and mechanical properties at elevated temperature of Mg-Al-Ni alloys prepared through powder metallurgy

Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al;Ni;particles and fine Al Ni nano-particles exist in the Mg-Al-Ni alloys. The strength at 150?C is improved with the increase in Ni content. Mg-18.3Al-8Ni alloy possesses a compressive strength of234.7 MPa and a yield strength of 146.5 MPa. Plasticity is also improved with a low concentration of Ni. Mg-11.3Al-2Ni alloy possesses a compression ratio of 17.3%. The phases of Al;Ni;and Al Ni in the alloys block the movements of grain boundaries and dislocations during the deformation at elevated temperature. The existence of Al Ni phase provides a non-basal slip system, leading to the improvement in plasticity. Finally, the formation mechanism of Al-Ni phases in the process is discussed with thermodynamics and kinetics.

Development of a computational tool for materials design

An integrated modeling tool coupling thermo- dynamic calculation and kinetic simulation of multicom- ponent alloys is developed under the framework of integrated computational materials engineering. On the basis of PandatTM software for multicomponent phase diagram calculation, the new tool is designed in an inte- grated workspace and is targeted to understand the com- position-processing-structure-property relationships of multicomponent systems. In particular, the phase diagram calculation module is used to understand the phase stability under the given conditions. The calculated phase equilib- rium information, such as phase composition and chemical driving force, provides input for the kinetic simulation. In this paper, the design of the modeling tool will be pre- sented and the calculation examples from the different modules will also be demonstrated.