Zr Carbides Research Articles

Development of irradiation tolerant tungsten alloys for high temperature nuclear applications

Development of refractory metals for application as plasma-facing armour material remains among priorities of fusion research programmes in Europe, China and Japan. Improving the resistance to high temperature recrystallization, enhancing material strength to sustain thermal fatigue cracking and tolerance to neutron irradiation are the key indicators used for the down selection of materials and manufacturing processes to be applied to deliver engineering materials. In this work we investigate the effect of neutron irradiation on mechanical properties and microstructure of several tungsten grades recently developed. Neutron irradiation campaign is arranged for screening purposes and therefore is limited to the fluence relevant for the ITER plasma facing components. At the same time, the neutron exposure covers a large span of irradiation temperatures from 600 up to 1000 °C. Four different grades are included in the study, namely: fine-grain tungsten strengthened by W-carbide (W–4wt.% W2C), fine-grain tungsten strengthened by Zr carbides (W–0.5% ZrC), W alloyed with 10 at.% chromium and 0.5 at.% yttrium (W–10Cr–0.5Y) and technologically pure W plate manufactured according to the ITER specification by Plansee (Austria). The strengthening by W2C and ZrC particles leads to an enhanced strength, moreover, the W–0.5ZrC material exhibits reduced DBTT (compared to ITER specification grade) and is available in the form of thick plate (i.e. high up-scaling potential). The W–10Cr–0.5Y grade is included as the material offering the self-passivation protection against the high temperature oxidation.

Corrosion characteristics of Mo and TZM alloy for plasma facing components in molten lithium at 623 K

In this study, the corrosion behaviours of molybdenum (Mo) and a Mo-based alloy (TZM) were investigated using a static immersion corrosion technique. Weight loss, surface microstructure, and corrosion depth of Mo and the TZM alloy were correlated with elements. The compatibility of Mo and the TZM alloy in static liquid Li was suitable. Mo demonstrated uniform corrosion with a homogenous dissolution of free C and Mo, and TZM alloy exhibited a nonuniform corrosion behaviour with a preferential grain boundary attack caused by the selective dissolution of free C, Ti, and Zr. When the surface oxidation layer of the samples was consumed, free C from Mo and TZM diffused into molten Li to form Li2C2 and then was captured by Zr, Ti, and Mo to form thermodynamically stable carbides, which resulted in the enrichment of the C layer near the sample surfaces. In addition, Ti and Zr acted as N-trappers in liquid Li; the formation of Zr and Ti nitrides resulted in the enrichment of N, Ti, and Zr elements on the surface and led to TZM corrosion increase. Thus, Zr and Ti depletion, pitting, and grain boundary corrosion were problematic for TZM under long-term exposure to liquid Li. Reducing the content of free C and nonmetallic N and increasing the amount of Ti and Zr carbides on the surface of and inside the raw TZM alloy helped improve the corrosion resistance of TZM in liquid Li.

Surface Treatment of S355JR Carbon Steel Surfaces with ZrB2 Nanocrystals by CO2 Laser

To improve mechanical properties of S2355JR carbon steel, pre-synthesized ZrB2 nanocrystals were used to coat the metal surface by laser cladding using 2000 W CO2 laser. ZrB2 nanocrystals were synthesized by mechanochemical process. The effect of laser power on the coating layers was examined for optimizing the most effective coating conditions. Microstructural studies were carried out using optical microscope, scanning electron microscope and X-ray diffraction to analyze phase structures of the coated layers. Mechanical characteristics of the laser coated layers were evaluated by studying microhardness, wear and scratch resistance properties. Maximum hardness of the coated layers was observed while cladding with 75 and 125 W laser powers, when other processing parameters and conditions were kept at optimum levels. EDS analysis of these laser cladded layers indicated the formation of complex boro-nitrides, nitrides and carbides of Zr and Fe that contributed to vast increase in hardness of the laser-clad coating on S2355JR steel. Depending upon the laser powers used, the thickness of the coated layers was found to be in the range of 15–37 µm. The wear and micro-scratch tests results revealed significant improvement in wear properties.

Effect of minor Zr element on microstructure and properties of Fe-16Cr-2.5Mo damping alloys

The Fe-16Cr-2.5Mo damping alloy was microalloyed with different amount of Zr element ranging from 0% to 0.5%. In this study, the effects of the different amount of Zr on the microstructure, mechanical properties and damping property of Fe-16Cr-2.5Mo alloys were investigated. The results suggested that the mean grain sizes of the Fe-16Cr-2.5Mo alloys with 0%, 0.1%, 0.3% and 0.5% Zr addition were 440 μm, 285 μm, 155 μm and 98 μm, respectively. The grain refinement strengthening was caused by Zener pinning and it leaded to improving the strength and elongation of the alloys. In addition, the Fe-16Cr-2.5Mo alloy with 0.1% Zr amount exhibited an impact toughness of 296J, which was much higher than those (<12J) of the alloys with more Zr element or without. On the other hand, Zr (Fe, Cr)2 or Zr carbide precipitations (>0.5 μm) formed in the alloys notablely, based on the results of TEM and EDX. The large precipitations were apt to establish the cleavage initiation sites, thus damaging the impact toughness of the alloy. The maximum internal friction (Q−1) of the alloys fluctuated within 0.016–0.014 with the increase of Zr content at a low strain amplitude (9 × 10−6∼3 × 10−4). However, their damping properties are still marvelous.

Kinetics of solid-state reactions between zirconium thin film and silicon carbide at elevated temperatures

Solid state reactions between a thin film (133nm) of Zr and bulk single crystalline 6H-SiC substrates have been studied at temperatures between 600°C and 850°C for durations of 30, 60 and 120min under high vacuum conditions. The deposited film and reaction zones were investigated by Rutherford backscattering spectrometry (RBS) and X-ray diffraction. The RBS spectra were simulated in order to obtain the deposited layer thickness, reaction zone compositions and reaction zone thickness. The as-deposited spectra fit well with those annealed at 600°C, thus showing there were no reactions taking place. At temperatures of 700°C and above, Zr reacted with the SiC substrate and formed a mixed layer of Zr carbide (ZrCx) and Zr silicides (ZrSi, Zr2Si and Zr5Si3). Annealing at 850°C for 240min revealed that all the deposited Zr had completely reacted. The interface reaction follows the parabolic growth law thereby indicating diffusion controlled reaction kinetics. The activation energy for the diffusion process obtained was 1.6eV in the relatively narrow temperature range 700–850°C.

Microstructure, High Temperature Strength and CO-Gas Emission of Liquid-Phase Sintered and Forged Low Oxygen TiC-ZrC-Mo Alloy

A new process for producing 0.5%Ti-0.07%Zr-Mo alloy with low-oxygen content and high strength at elevated temperature was successfully developed, where the mixed TiC, ZrC and Mo powders were liquid-sintered without addition of C or Mo2C as aids for degassing of oxygen. The developed new TiZrC alloy indicated high strength at elevated temperature even under low forging rate compared to the conventional TiZrO alloy and commercial TZM alloy. Ti and Zr carbides with high melting points were precipitated along Mo grain boundaries in TiZrC alloy, while Ti and Zr combined oxide particles with low melting points were precipitated in Mo grain boundaries in TiZrO alloy. The high strength at elevated temperature in TiZrC alloy will result from the grain boundary precipitation of the carbides, which suppressed grain growth and were stable at elevated temperature. The amount of CO gas emission from the TiZrC alloy were almost equivalent to that from the conventional TiZrO alloy during heating in X ray tube.

Experimental verification of PTC diagrams for TiC and ZrC PVD coatings and determination of free carbon state by AES, XPS and HREELS methods

AbstractSeveral PVD coatings based on Ti and Zr carbides and on HSS steel were investigated. The partial pressure of the active gas (N2, C2H2) and substrate temperature were varied over a wide range. The PTC diagrams for prediction of coating compositions, dependent on substrate temperature and gas pressure, were calculated using the thermodynamic technique for phase equilibria based on the principle of maximum entropy in an isolated thermodynamic system. The chemical composition, and electronic and atomic structure of coatings were investigated using the AES, XPS and HREELS methods. Comparison of the calculated chemical composition of coatings with one measured by AES shows good agreement. XPS analysis of the C 1s line in carbides of Ti and Zr shows the presence of carbon in non‐stoichiometric carbides and in the free state. The fraction of bound and free carbon was measured by relation of the shifted and normal C 1s peaks. HREELS spectra near the line of elastically scattered electrons show a peak at 165 meV (1332 cm−1 in Raman spectroscopy) corresponding to sp3 hybridization of carbon. Copyright © 2004 John Wiley &amp; Sons, Ltd.

High Temperature Interaction Behavior at Liquid Metal-Ceramic Interfaces

Liquid metal/ceramic interaction experiments were undertaken at elevated temperatures with the purpose of developing reusable crucibles for melting reactive metals. The metals used in this work included zirconium (Zr), Zr-8 wt.% stainless steel, and stainless steel containing 15 wt.% Zr. The ceramic substrates include yttria, Zr carbide, and hafnium (Hf) carbide. The metal-ceramic samples were placed on top of a tungsten (W) dish. These experiments were conducted with the temperature increasing at a controlled rate until reaching set points above 2000 °C; the systems were held at the peak temperature for about five min and then cooled. The atmosphere in the furnace was argon (Ar). An outside video recording system was used to monitor the changes on heating up and cooling down. All samples underwent a post-test metallurgical examination. Pure Zr was found to react with yttria, resulting in oxygen (O) evolution at the liquid metal-ceramic interface. In addition, dissolved O was observed in the as-cooled Zr metal. Yttrium (Y) was also present in the Zr metal, but it had segregated to the grain boundaries on cooling. Despite the normal expectations for reactive wetting, no transition interface was developed, but the Zr metal was tightly bound to yttria ceramic. Similar reactions occurred between the yttria and the Zr-stainless steel alloys. Two other ceramic samples were Zr carbide and Hf carbide; both carbide substrates were wetted readily by the molten Zr, which flowed easily to the sides of the substrates. The molten Zr caused a very limited dissolution of the Zr carbide, and it reacted more strongly with the Hf carbide. These reactive wetting results are relevant to the design of interfaces and the development of reactive filler metals for the fabrication of high temperature components through metal-ceramic joining. Parameters that have a marked impact on this interface reaction include the thermodynamic stability of the substrate, the properties of the modified interface, the temperature-dependent solubility limits of the liquids and solid phases, and the high-temperature stoichiometry of the ceramic.

Ｚｒを添加したＨＫ４０およびＨＰ耐熱遠心鋳造管のクリープ・疲労特性

Creep-fatigue and oxidation properties of Zr-free and Zr-containing HK40 and HP centrifugal heat-resisting alloys were studied. The mechanism of improving these properties by Zr addition was discussed through microstructural examination of materials. The following results were obtained;(1) A small amount of Zr addition markedly impoves the low-cycle-fatigue life under creep conditions, creep rupture strength and ductility, and oxidation resistance of HK40 and HP.(2) The improvement of creep-fatigue properties is thought to be brought about by the following two effects;(i) Zirconium gives an excellent resistance to the localized oxidation of eutectic carbides and/or grain-boundaries, which can be fatigue crack initiation sites.(ii) A number of small Zr-carbides (ZrC) are precipitated homogeneously in grains at elevated temperatures. These carbides suppress the formation of sub-boundaries and the precipitation of coarse carbides (M23C6) on sub-boundaries, which can be fatigue crack propagation paths.

QUANTITATIVE ELECTRON PROBE MICROANALYSIS OF CARBON IN CARBIDES USING A GAUSSIAN ϕ( ρz) EQUATION

CKα X-ray intensities from a number of carbides have been measured over a range of energies and at 3 different take-off angles. Quantitative calculations were performed using a Gaussian ϕ(ρz) equation. Analysis of the data shows that peak area intensities should be used for quantitative analysis. Problems still exist in the analysis of Nb and Zr carbides either because of the small size of the particles or due to inaccurate mass absorption coefficients.

Erratum to: Transition metal alloys of extraordinary stability; An example of generalized Lewis-acid-base interactions in metallic systems

The Engel theory of metals predicts unusually high thermodynamic stability for certain classes of alloys of transition metals for which generalized Lewis-acid-base interactions are possible. To test these predictions, phase equilibria were studied for ternary systems of Zr, C, and the transition metals Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, and Au. Similar literature data for Nb, Ta, Hf, Th, Y, Ce, Er, and Pu with Re, Ru, Rh, Ir, Pt, and Au were evaluated. Thermodynamic data for the carbides of Zr, Hf, Th, Nb, Ta, U, and Y were critically evaluated, tabulated for 1200 to 2300 K, and used to fix the Gibbs energies of formation in kcal/g-atom of alloy, or their limits, for the binary phases of the above metals. In addition, for Zr, activity coefficients and excess Gibbs energies are tabulated. The predicted high stabilities for alloys of Rh, Ir, Pd, and Pt are confirmed with excess Gibbs energies ranging to —100 kcal/g-atom and activity coefficients as low as 10-12 for zirconium or hafnium in dilute solutions of platinum at 1800 K. Some of the properties of these unusually stable compounds have been measured.