Zr Powders Research Articles

Low-temperature synthesis of nanocrystalline ZrC coatings on flake graphite by molten salts

A novel molten salt synthetic route has been developed to prepare nanocrystalline zirconium carbide (ZrC) coatings on flake graphite at 900°C, using Zr powder and flake graphite as the source materials in a static argon atmosphere, along with molten salts as the media. The effects of different molten salt media, the sintered temperature, and the heat preservation time on the phase and microstructure of the synthetic materials were investigated. The ZrC coatings formed on the flake graphite were uniform and composed of nanosized particles (30–50nm). With an increase in the reaction temperature, the ZrC nanosized particles were more denser, and the heat preservation time and thickness of the ZrC coating also increased accordingly. Electron microscopy was used to observe the ZrC coatings on the flake graphite, indicating that a “template mechanism” played an important role during the molten salt synthesis.

Consolidation of aerospace grade aluminum 7055 powder through SPS-forge processing

ABSTRACTThe objective of this research was to assess the SPS-forge response of fully pre-alloyed aerospace grade 7055 (Al–8Zn–2.1Mg–2.3Cu–0.2Zr) powder. The core variables investigated were the sintering temperature, time, and atmosphere employed, as well as the average particle size and the manner of uni-axial loading. Samples sintered in vacuum at 500°C for 40 min with delayed loading offered the most desirable combination of density, hardness, and bend properties but remained relatively brittle. Hot forging of the sintered preforms was found to impart sizable gains in mechanical properties. The SPS-forge product exhibited tensile yield strength of 603 MPa coupled with a ductility of 9.1% and a hardness of 93 HRB. All such properties were largely equivalent to those measured for the wrought counterpart.

The preparation of Zr-deuteride and phase stability studies of the Zr-D system

Deuteride phases in the zirconium-deuterium system in the temperature range 25–286 °C have been studied in-situ by high resolution neutron diffraction. The study primarily focused on observations of δ→γ transformation at 180 °C, and the peritectoid reaction α + δ ↔ γ at 255 °C in commercial grade Zr powder that was deuterated to a deuterium/Zr ratio of one to one. A detailed description of the zirconium deuteride preparation route by high temperature gas loading is also described. The lattice parameters of α-Zr, δ-ZrDx and ε-ZrDx were determined by whole pattern crystal structure analysis, using Rietveld and Pawley refinements, and are in good agreement with values reported in the literature. The controversial γ-hydride phase was observed both in-situ and ex-situ in deuterated Zr powder after a heat treatment at 286 °C and slow cooling.

Kinetics and high-temperature oxidation mechanism of ceramic materials in ZrB2–SiC–MoSi2 system

The paper focuses on the production of compact ceramics ZrB2–SiC–(MoSi2) using the hybrid SHS + HP technology, as well as on its phase composition, structure and high-temperature oxidation kinetics. Reaction mixtures were obtained according to the following scheme: mechanical activation of Si + C powders; wet admixing of Zr, B and MA powders of Si + C mixture; drying of mixtures in a drying cabinet. The composite SHS powder ZrB2–SiC was obtained in the SHS-reactor in combustion mode by element synthesis. Compact samples were produced using the hot pressing method by SHS powder consolidation. Resulting samples characterized by a homogeneous structure and low residual porosity not exceeding 1,3 %. In total, two compositions were chosen for tests: the first one rated for ZrB2 + 25 % SiC formation, the second one similar to the first one, but with the addition of 5 % commercial MoSi2 powder. The microstructure of samples is represented by dispersed dark gray rounded SiC grains distributed among the light faceted ZrB2 grains. The sample with the MoSi2 additive has a more finely dispersed structure. High-temperature oxidation of samples at 1200 °С forms complex oxide films SiO2–ZrO2–(B2O3) about 20–30 μm in thickness on their surface, which serve as an effective diffusion barrier and reduce oxidation rate. The complex ZrSiO4 oxide is also present in the oxide film structure after long holding times (more than 10 hours). In addition, after 10 hours of testing, a slight decrease in the mass of the samples is observed, which is due to the volatilization of B2O2, CO/CO2, MoO3 gaseous oxidation products. The sample with MoSi2 added demonstrates better resistance to oxidation.

Preparation of MB2/SiC and MB2/SiC-MC (M = Zr or Hf) powder composites which are promising materials for design of ultra-high-temperature ceramics

This survey shows the prospects of studies targeted at preparing MB2/SiC and MB2/SiC-MC (M = Zr or Hf) nanosized composite powders for use in the manufacture of ultra-high-temperature ceramics (UHTCs) and antioxidant protective coatings on Cf/C and Cf/SiC composites. The survey considers the specifics of various preparation methods, including sol-gel technology or precipitation followed by borothermic/ carbothermic reduction, self-propagating high-temperature synthesis (SHS), specifically variants combined with mechanochemical activation or spark plasma sintering (SPS), chemical modification of ZrB2(HfB2) powders with polycarbosilane followed by pyrolysis, and dispersion of appropriate ceramics with the stabilization of the slurry. The elemental and phase compositions, particle sizes, microstructures, and some other characteristics of the products reported in the related literature are summarized.

In situ observation of γ-ZrH formation by X-ray diffraction

We report on the measurement of the formation of γ-ZrH during in situ gaseous charging. The measurements were undertaken using high-energy synchrotron X-ray diffraction. Experimental observation shows that γ-ZrH can form at 180 °C from a mixture of α+δ while dehydrogenating at slow cooling rates. The observation is further supported by ex situ laboratory X-ray diffraction on deuterated Zr powder that has undergone a similar heat-treatment cycle. The crystal structure of γ-ZrH refinement agrees with the reported P42/n structure found in the literature.

Oxidation resistance of a SiC–ZrB2 coating prepared by a novel pack cementation on SiC-coated graphite

In this study, a functionally graded SiC layer was prepared on a graphite substrate by a pack cementation method with Si, C, and Al2O3 powders. Then a SiC–ZrB2 coating was developed by an in situ reaction method through a novel pack cementation technique at 1873 K with Zr, Si, and B4C powders to improve the oxidation protection ability of SiC-coated graphite. The phase compositions, microstructure, and element distribution of the coating were identified by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. The isothermal oxidation test of the coated samples was accomplished at 1773 K in air for 10 h. According to the results, a 550-μm thick graded C–SiC layer was detected at the graphite–coating interface and a SiC–ZrB2 coating was formed on the first coating. The SiC–ZrB2 coating could efficiently enhance oxidation resistance of graphite with a mass gain of +1.1 %, as compared with a −1.2 % mass loss of the first step coating. The excellent protection ability of SiC–ZrB2 coating could be ascribed to the high thermally stable ZrSiO4.

Structure and magnetic properties of Zr–Mn substituted strontium hexaferrite Sr(Zr,Mn) x Fe12−2x O19 nanoparticles synthesized by sol–gel auto-combustion method

In this research, nano-sized powders of Zr–Mn substituted strontium hexaferrite (Sr(Zr,Mn) x Fe12−2x O19 (x = 0, 2, 2.5, 3)) were synthesized by sol–gel auto-combustion route using subsequent heat treatment. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibration sample magnetometer (VSM) techniques. XRD and Mössbauer spectroscopy results revealed formation of Sr(Zr,Mn) x Fe12−2x O19 accompanied with Mn δ Fe2−δ O4 lateral phase in the samples. Also, FTIR and XRD results demonstrated presence of SrO impurity phase. FESEM micrographs show particle size reduction and presence of two distinct powder morphologies with different brightness levels with Zr4+ and Mn2+ substitutions which approves existence of lateral phases in the substituted samples. TEM micrographs show nanometric particles with sizes smaller than 100 nm with high crystallinity. Mössbauer results showed that at low level of substitution, Zr4+ ions prefer to occupy both 4f1 and 2b however, at higher level of substitution, they prefer exclusively 4f1 site. While, Mn2+ ions distributed approximately equally between 12k and 2a sites. The presence of nonmagnetic Zr4+ cation leads to decrease in exchange interaction, especially at 12k and 2a sites. VSM results showed decrement of coercivity force ( i H c ) from 5593.60 to 3282.46 Oe and maximum magnetization from 62.60 to 46.15 emu g−1, respectively, by increment of Zr–Mn substitution values. Variations in maximum magnetization magnitude have been explained on the basis of occupation of the substituted cations at different iron sites.

In-situ synthesis of SiC-ZrB2 coating by a novel pack cementation technique to protect graphite against oxidation

A multiphase coating was prepared on a graphite substrate by a two-step technique to enhance the oxidation protection ability of graphite. The first step was to obtain a functionally graded SiC layer and the second one was to develop a SiC-ZrB2 coating by an in-situ reaction method through a novel pack cementation technique with Zr, Si and B4C powders. The phase compositions, microstructure and element distribution of the coating were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The isothermal oxidation and thermal shock tests of the coated samples were performed at 1773 K in air for 10 h. A 650 μm thick graded CSiC layer was observed at the graphite-coating interface and a SiC-ZrB2 coating was formed on the first coating. The v coating could efficiently improve oxidation resistance of graphite with a mass gain of +1.7%, as compared with a −63.2% mass loss of the first step coating. The excellent protection ability SiC-ZrB2 coating could be attributed to the formation of the thermally stable phase ZrSiO4.

Effect of Al and Si Additions on the Synthesis of Spark Plasma Sintered Zr<sub>2</sub>Al<sub>4</sub>C<sub>5</sub> Creamic

The Zr2Al4C5 ceramic was successfully fabricated by the spark plasma sintering at 1800 °C for 10 min under uniaxial 20 MPa pressure in vacuum using a mixed raw materials of Zr, Al, Si and graphite powders. The X-ray diffraction analysis results showed that the unexpected Zr2Al3C5 phase rather than target compound Zr2Al4C5 formed in the sintered samples. An initial Zr:Al:C molar ratio of 2:4.2:4.8 for raw powders, and even 55 mol.% excess Al, did not lead to a phase transformation from Zr2Al3C5 to Zr2Al4C5. When 4 wt.% Si was induced in the starting powders, the major phase became Zr2Al4C5 and no obvious Zr2Al3C5 was detected in the sintered samples with an initial Zr:Al:C molar ratio of 2:6.2:4.8 (55 mol.% excess Al). The introduction of Si could suppress and even remove additional ZrC, and Si atoms would exclusively occupy the site of Al to make Zr2Al4C5 become a stable solid solution. The scanning electron microscopy observation showed that the as-synthesized Zr2Al4C5 grains had elongated, rod-like and/or plate-like shapes. The mechanical properties of the sintered Zr2Al4C5 ceramic were also investigated, and it showed a hardness of 11.06±0.34 GPa and a fracture toughness of 4.6 ± 0.4 MPa×m1/2.

Microstructure, mechanical properties, and electronic simulations of steel/aluminum alloy joint during deep penetration laser welding

This paper presents microstructure and mechanical properties of deep penetration laser welding joints with/without Mn, Zr, or Sn powder in an overlap steel-on-aluminum configuration. Heats of formation, elastic modulus, and thermodynamic properties of intermetallic phases (IMCs) formed in joining steel to aluminum are determined by the use of first-principle calculation. A good agreement between the experimental results and theoretical predictions can be seen. In the case of adding Sn powder, no obvious porosity, cracks, and other defects are seen, and the layer thickness of IMCs is smallest among all the powders. In addition, the FeSn phase is formed at the steel/aluminum interface, the structure of FeSn is more stable than that of FeAl, and the ductility of FeSn is also better than that of FeAl; hence, mechanical properties of the welding joint are significantly improved.

Mechanochemical synthesis and fast consolidation of a nanostructured CoTi-ZrO2 composite by high-frequency induction heating

CoTi and ZrO2 nanopowders were mechanochemically synthesized from CoTiO3 and Zr powders according to the reaction (2CoTiO3+3Zr→2CoTi+3ZrO2). The milled powders were then consolidated using high frequency induction heated sintering (HFIHS) within one minute under the applied pressure of 80MPa. The average hardness and fracture toughness of the nanostructured 2CoTi-3ZrO2 composite sintered from high energy ball milled powder were 1205kg/mm2 and 6.9MPam1/2, respectively. The mechanical properties of composite were compared with those of monolithic CoTi and ZrO2, respectively.

ChemInform Abstract: Observations of Temperature Stability of γ‐Zirconium Hydride by High‐Resolution Neutron Powder Diffraction.

AbstractIn the view of the problem of delayed hydride cracking via hydrogen embrittlement of fuel claddings of the nuclear industry, a Zr‐50D alloy is prepared by heating Zr powder with gaseous D2 (pressure furnace, 573 K, 1.9 bar, 10 h).

Additive Manufacturing of Reactive In Situ Zr Based Ultra-High Temperature Ceramic Composites

Reactive in situ multi-material additive manufacturing of ZrB2-based ultra-high-temperature ceramics in a Zr metal matrix was demonstrated using LENS™. Sound metallurgical bonding was achieved between the Zr metal and Zr-BN composites with Ti6Al4V substrate. Though the feedstock Zr power had α phase, LENS™ processing of the Zr powder and Zr-BN premix powder mixture led to the formation of some β phase of Zr. Microstructure of the Zr-BN composite showed primary grains of zirconium diboride phase in zirconium metal matrix. The presence of ZrB2 ceramic phase was confirmed by X-ray diffraction (XRD) analysis. Hardness of pure Zr was measured as 280 ± 12 HV and, by increasing the BN content in the feedstock, the hardness was found to increase. In Zr-5%BN composite, the hardness was 421 ± 10 HV and the same for Zr-10%BN composite was 562 ± 10 HV. It is envisioned that such multi-materials additive manufacturing will enable products in the future that cannot be manufactured using traditional approaches particularly in the areas of high-temperature metal–ceramic composites with compositional and functional gradation.

Thermoanalytical Investigation of Some Binary Pyrotechnic Mixtures of Ammonium Azide as Chemical Gas Generating Systems

AbstractThe conventional NaN3/oxidants gas generator pyrotechnic mixtures suffer from leaving undesirable solid residues. The presented investigation aimed to overcome this problem through mixing of NH4N3 particles with some metallic components, and to introduce some new gas generator pyrotechnic mixtures. In this work, volatile ammonium azide particles were initially stabilized via microencapsulation technique, and blended with Zr, Ti, ZrH2, and TiH2 powders to produce different gas generation mixtures. Thermal properties and kinetic parameters of these pyrotechnic mixtures were investigated by using thermal analysis (TG/DTA and DSC) techniques. The apparent activation energy (E), ΔG#, ΔH#, ΔS#, and critical ignition temperature (Tb) of the ignition processes of the mixtures were obtained from the DSC experiments. Among the investigated mixtures, NH4N3/ZrH2 composition was found to show desirable efficiency, and also it can be considered as a safe pyrotechnic composition for gas generation property, due to its moderate ignition temperature.

Effect of substituting Pr for Nd on magnetic properties of Nd–Fe–B HDDR powder

The effect of partially substituting Nd by Pr on magnetic properties of HDDR (hydrogenation-decomposition-desorption-recombination)-processed Nd–Fe–Co–B–Ga–Zr powder was studied. It was found that coercivity HcJ of the (Nd1−x,Prx)12.9Febal.Co5.8B6.3Ga0.5Zr0.1 (x = 0–0.40) powder at room temperature is increased with increasing Pr content x, while residual induction was kept almost constant. The increase in HcJ is larger than that expected from the increase in magnetocrystalline anisotropy field Ha of the magnetic phase (Nd,Pr)2Fe14B. This can be attributed to change in grain-boundary microstructures. Temperature-dependence of HcJ in the injection-molded-bonded magnets made from the powders was also examined. It was confirmed that the decrease in HcJ of the magnet with x = 0.24 is kept almost the same as the magnet with no Pr addition in the temperatures ranging from room temperature to 150 °C.

Novel approach to Zr powder production by smooth ZrCl4 bubbling through molten salt

A reduction process using ZrCl4 bubbles as a reactant was investigated to produce zirconium metals. ZrCl4 vapor was bubbled through the lance in the bath, in which Mg melt and MgCl2 salt were separated. Zr powder was formed by a reduction of ZrCl4 bubbles in magnesium layer. However, the lance was clogged by the aggregate of zirconium occurred during ZrCl4 vapor injecting leading to interruption of ZrCl4 supply into the bath. This phenomenon could be caused by the presence of magnesium at the lance tip, which passes through MgCl2 salt during bubbling, and then zirconium was formed in the forms of intermetallic compounds with aluminum. In this study, the effect of molten salt on the troubled phenomena was investigated and it was verified that CaCl2 with relatively low Weber number meaning relatively high surface tension as molten salt is effective in inhibiting the lance clogging phenomena. Then, a few micrometer-sized Zr powder with the high purity of 91.6 wt% was obtained smoothly without the formation of intermetallic compound.

Enhanced mechanical properties and fast consolidation of a nanostructured Ti–ZrO2 composite by pulsed current activated heating

Nanopowders of TiO2 and Zr were fabricated using high energy ball milling. Dense nanostuctured Ti–ZrO2 composite was simultaneously synthesized and sintered by pulsed current activated heating within 2min in one step from mechanically activated powders of TiO2 and Zr. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostructured materials. Highly dense Ti–ZrO2 with relative density of up to 99.9% was produced under simultaneous application of a 80MPa pressure and the pulsed current. The average hardness and fracture toughness values of the composite were 1713kg/mm2 and 14.3MPam1/2, respectively. Not only the hardness but also the fracture toughness of a Ti–ZrO2 composite in this study are higher than those of the pure ZrO2.

High-Temperature Stability and Grain Boundary Complexion Formation in a Nanocrystalline Cu-Zr Alloy

Nanocrystalline Cu-3 at.% Zr powders with ~20 nm average grain size were created with mechanical alloying and their thermal stability was studied from 550–950°C. Annealing drove Zr segregation to the grain boundaries, which led to the formation of amorphous intergranular complexions at higher temperatures. Grain growth was retarded significantly, with 1 week of annealing at 950°C, or 98% of the solidus temperature, only leading to coarsening of the average grain size to 54 nm. The enhanced thermal stability can be connected to both a reduction in grain boundary energy with doping as well as the precipitation of ZrC particles. High mechanical strength is retained even after these aggressive heat treatments, showing that complexion engineering may be a viable path toward the fabrication of bulk nanostructured materials with excellent properties.

Effect of Zr, Nb and Ti Additions on Injection Molded 316L Stainless Steel: Microstructural, Mechanical Properties and Corrosion Resistance

The objective of this research is to investigate the effect of Zr, Nb and Ti additions on microstructural, mechanical and electrochemical properties of injection molded 316L stainless steel. The amount of additive powder plays a role in determining the sintered microstructure and all properties. In this study, 316L stainless steel powders used with the elemental Zr, Nb and Ti powders. The binders were completely removed from molded components by solvent and thermal debinding. The debinded samples were sintered at different temperature for 60 min. at different temperatures. Mechanical property, microstructural characterization and electrochemical property of the sintered samples were performed using tensile testing, hardness, optical, scanning electron microscopy and electrochemical experiments. Results of study showed that sintered 316L and 316L with additive powder samples exhibited high mechanical and corrosion properties in a physiological environment.