ZrB2 Addition Research Articles

Improved oxidation resistance of Mo-12Si-8.5B composite at 1400 °C due to development of Zr-rich borosilicate scale

A fine-grained Mo-12Si-8.5B composite with ZrB2 addition showed excellent oxidation resistance up to 1400 °C owing to the formation of a protective Zr-rich borosilicate scale. The addition of ZrB2, as a supplier of B and Zr, controlled the fluidity of the borosilicate glass, which caused the borosilicate glass to rapidly cover the entire surface of the composite at the initial oxidation stage, followed by quick passivation at the next oxidation stage. The increased amount of B combined with the refined microstructure ensured that the glass scale retained sufficient liquidity for the rapid coverage. Simultaneously, Zr as a crucial glass former improved the passivation of the glass scale and reduced its O diffusivity by enhancing the viscosity. Therefore, the degeneration of the substrate was reduced by 98% during 27 h of the oxidation.

High temperature compression properties of hot-pressed NbMo-matrix composites reinforced with ZrB2 particles

The effects of 15, 30, 45, 60 vol% ZrB2 additions on high temperature compression properties of hot-pressed NbMo-matrix were investigated by the compression experiments in the temperature range of 800 °C–1300 °C. ZrB2 particle additions to NbMo matrix could significantly improve the high temperature compressive strength of the composites. The best comprehensive property including strength and ductility belongs to the composites containing 30 vol% ZrB2 with refined grains at the temperature below 1100 °C. The resistant ability to high temperature was directly proportional to ZrB2 content. The compressive strength of composite containing 60 vol% ZrB2 (from 1236.56 MPa to 700.46 MPa) was inversely proportional to temperature. The failure planes of composite containing 15 vol% and 30 vol% ZrB2 were always at angle of 45° to the axis of the compression direction, whereas the failure pattern of composite containing 45 vol% and 60 vol% ZrB2 changed from splitting along the compression direction to cracking at certain angle to the axis of the compression direction with temperature rising.

INFLUENCE OF ZrB2 ADDITION ON MICROSTRUCTURAL DEVELOPMENT AND MICROHARDNESS OF Ti-SiC CLAD COATINGS ON Ti6Al4V SUBSTRATE

The microstructural features and microhardness of ZrB2-reinforced Ti-SiC coatings on Ti-6Al-4V substrate were studied. The deposition of these coatings was achieved via laser cladding technique. A 4.0[Formula: see text]kW fiber-delivered Nd: YAG laser was used to deposit the coatings on the titanium substrate at a laser power of 700[Formula: see text]W and a laser scan speed of 0.8[Formula: see text]m/min. An initial Ti-SiC coating was deposited with no ZrB2 addition followed by deposition of two other coatings with the incorporation of ZrB2 powder at 5 and 10[Formula: see text]wt.%. The coatings were examined using scanning electron microscope (SEM) coupled with energy dispersive spectroscopy. SEM images of Ti-SiC-ZrB2 coatings revealed good metallurgical bond between the coatings and the substrate and also a significant increment in dendritic formation and inter-dendritic eutectics during solidification within the [Formula: see text]-Ti matrix, exhibiting the presence of newly formed phases as the weight percentage of ZrB2 increased. Back-scattered electron images also showed the dissolution effect of SiC particles, as the particle–matrix bond strength is influenced by ZrB2 addition. Furthermore, the microhardness of the Ti-SiC coating was enhanced with increasing ZrB2 weight percentage. X-ray diffraction analysis revealed dominant compounds formed during laser material processing. This study deepens the knowledge of possible microstructural features associated with Ti-SiC-ZrB2 cermet coatings.

Effect of ZrB2 content on phase assemblage and mechanical properties of Si3N4–ZrB2 ceramics prepared at low temperature

AbstractBased on the previous work on Si3N4–ZrB2 [Wu et al. J Eur Ceram Soc;2017,37:4217], the influence of ZrB2 addition on the phase and microstructure evolution of Si3N4–ZrB2 composites was emphatically investigated, and the mechanical properties were compared with pure Si3N4 ceramics. It was revealed that the ratio of β‐ to (α+β)‐Si3N4 significantly increased from 14.3% in pure Si3N4 ceramics to 39.8% in Si3N4 with 15 vol% ZrB2 addition, indicating that the introduction of ZrB2 promoted α‐ to β‐Si3N4 phase transformation. As a consequence, the microstructure of the composite showed the bimodal distribution, containing both elongated and equiaxed Si3N4 grains. For the pure Si3N4, Vickers hardness, fracture toughness and flexural strength was 22.8 GPa, 7.6 MPa m1/2, and 334.5 MPa, respectively. In contrast, the composite of Si3N4–30 vol% ZrB2 simultaneously possessed an excellent combination of mechanical properties: 19.5 GPa in hardness, 9.8 MPa m1/2 in toughness and 702.0 MPa in strength. Present study suggested that Si3N4‐based ceramics with high hardness, high toughness, and high strength could be obtained by the combination of appropriate ZrB2 content and low hot‐pressing temperature.

Microstructural evolution and mechanical properties of friction stir processed ZrB2/6061Al nanocomposites

In the present work, homogeneously dispersed ZrB2 nanoparticles and fine-grained structures were successfully achieved by friction stir processing (FSP) of in situ 0–2 vol% ZrB2/6061Al nanocomposites. The effects of ZrB2 additions on the microstructures and tensile properties were investigated. A combination of EBSD and TEM analyses revealed that ZrB2 nanoparticles strongly suppressed (sub)grain boundary migration and/or orientation, and thus led to a continuous decrease in grain size, HAGBs fraction as well as B/B¯ shear texture intensity at higher ZrB2 content. Moreover, compared with the processed 6061Al alloy, microhardness, strengths and elongation of the FSPed composites were significantly improved mainly due to the refined grains and ZrB2 nanodispersoids. Quantitative calculation indicated that as ZrB2 content increased, Orowan strengthening instead of grain refinement strengthening contributed the most to the yield strength.

Enhanced oxidation resistance of Mo-12Si-8.5B alloys with ZrB2 addition at 1300 °C

Mo-12Si-8.5B and Mo-12Si-8.5B-1.0wt%ZrB2 alloys were fabricated using mechanical alloying, followed by hot-pressing. Both alloys exhibited uniform microstructure, with the Mo3Si and Mo5SiB2 phases distributing dispersedly in the α-Mo matrix. Mo-12Si-8.5B-1.0wt%ZrB2 showed a finer-grained microstructure than Mo-12Si-8.5B alloy owing to the addition of ZrB2. The results of isothermal oxidation tests at 1300°C in air revealed that Mo-12Si-8.5B and Mo-12Si-8.5B-1.0wt%ZrB2 alloys initially suffered a transient stage with high mass loss due to the volatilization of MoO3, and then achieved a steady stage owing to the formation of a protective borosilicate scale on the alloy surface. Especially, the transient stage of Mo-12Si-8.5B-1.0wt%ZrB2 alloy was shortened to be less than 300s, and the mass loss of this stage was reduced by at least 88% compared with that of Mo-12Si-8.5B alloy, indicating a significant improvement in the oxidation resistance. The addition of ZrB2 not only resulted in a continuous borosilicate scale quickly covering the entire base alloy during the transient stage, but also improved the protectiveness of the borosilicate scale of the steady stage by bringing out a large number of ZrO2/ZrSiO4 particles embedded discontinuously in the borosilicate scale, which effectively restricted the inward diffusion of oxygen by acting as diffusion barriers and decreased the thickness of inner oxide layers in particular.

Effect of TiB2 and ZrB2 additions on structure and properties of Fe-7Al based light weight steel

Microstructural modifications and their effect on tensile properties in an Fe-7 wt.% Al alloy by additions of 0.5% TiB2, 0.5% ZrB2 or both has been studied. Alloys are examined in the as-cast as well as in the hot-rolled and annealed conditions. Solidification structure of the Vacuum Arc Remelted pancake ingots was columnar dendritic. Further, boride modified alloys are found to have finer grains in as-cast as well as in hot-rolled and annealed conditions. In the annealed condition, boride containing alloys were found to have superior tensile yield strength, ductility and strain hardening behaviour. These property improvements are attributed to boride aided grain refinement during casting as well as during thermo-mechanical processing of the steels.

Influence of sol-gel derived ZrB2 additions on microstructure and mechanical properties of SiBCN composites

A simple method for introducing ZrB2 using sol-gel processing into a SiBCN matrix is presented in this paper. Zirconium n-propoxide (ZNP), boric acid and furfuryl alcohol (C5H6O2) (FA) were added as the precursors of zirconia, boron oxide and carbon forming ZrB2 dispersed in a SiBCN matrix. SiBCN/ZrB2 composites with different contents of ZrB2 (5, 10, 15, and 20wt%) were formed at 2000°C for 5min by spark plasma sintering (SPS). The microstructures were carefully studied. TEM analysis showed that the as formed ZrB2 grains were typically 100–500nm in size and had uniform distribution. HRTEM revealed clean grain boundaries between ZrB2 and SiC, however, a separation of C near the SiC boundary was observed. The flexural strength, fracture toughness, Young's modulus and Vicker's hardness of composites all improved with the ZrB2 contents and SiBCN matrix containing 20wt% of ZrB2 could reach 351±18MPa, 4.5±0.2MPam1/2, 172±8GPa and 7.2±0.2GPa, respectively. The improvement in fracture toughness can be attributed to the tortuous crack paths due to the presence of reinforcing particles.

High temperature flexural strength and oxidation behavior of hot-pressed B4C–ZrB2 ceramics with various ZrB2 contents at 1000–1600 °C in air

High temperature flexural and oxidation behavior of hot-pressed B4C–ZrB2 ceramics with various ZrB2 addition amounts was measured and analyzed in the temperature range of 1000 to 1600°C in ambient air atmosphere. The high temperature flexural strength is a strong function of temperature. With the temperature increasing, the high temperature flexural strength decreases. The oxidation behavior was investigated in detail, and the oxidation mechanism was summarized. The purpose of this study is to give fundamental understanding of the high temperature behavior of B4C based ceramics.

Effect of micron and nano-sized ZrB2 addition on the microstructure and properties of spark plasma sintered graphite–aluminum hybrid composite

The need to improve the thermal properties of materials used in electronics and automobile industries has led to the search for light materials such as graphite aluminum (Gr–Al) composites. This work was aimed at studying the effect of micron and nano-sized zirconium diboride (ZrB2) on the microstructure and properties of Gr–Al composite. In this study, ZrB2 powder with average particle size of 5.91 μm was milled for 24 h using planetary mill. The particle sizes and shapes of the micron and nano-sized particles were studied using scanning electron microscopy. Sintering of Gr–Al composite reinforced with 2, 4, 6 and 8 % of micron and nano-sized ZrB2 particles was done at a temperature of 550 °C and pressure of 50 MPa. The heating rates were 50 and 100 °C/min with a soaking time of 10 min. The average nano particle size obtained after the milling process was 60 nm with regular and irregular shapes. The results show that the electrical conductivity only improved slightly in the temperature range 219–282 °C for 6 % micron size addition and 230–251 °C for 4 % nano size addition. In addition, nano ZrB2 improved the densification, hardness and the peak intensity ratio of Gr–Al composite with the highest values being 99.3 %, 38 HV0.1 and 92.23 % respectively. A significant reduction in the coefficient of thermal expansion from 0.238 × 10−6/°C for the matrix to 0.0.980 × 10−7/°C for the hybrid composite was also noticed. These improvements were more obvious at 4 and 6 % composition and a heating rate of 50 °C/min.

Ductilizing Mo–La 2 O 3 alloys with ZrB 2 addition

Mo–0.6 wt%La2O3–xZrB2 (x=0, 0.5, 1.0, 1.5, 2.0 wt%) alloys were prepared by using the solid–solid mixing/doping method. Microstructure, tensile strength, and ductility were experimentally examined to investigate the effect of ZrB2 addition. Microstructural observations showed that the addition of 0.5–1.5 wt% ZrB2 effectively reduces the grain size of the alloys and remarkably varies the second phase particles distributed at grain boundaries (GBs). The size of intergranular La2O3 particles was decreased with the increasing ZrB2 addition up to 1.5 wt%. ZrO2 particles were produced through reaction between ZrB2 and oxygen, which were predominantly distributed at GBs, increasing the volume fraction of intergranular second phase particles while decreasing the oxygen concentration at GBs. Tensile testing results displayed that the yield strength of alloys was relatively insensitive to the ZrB2 addition, which was quantitatively understood with respect to the strengthening mechanisms. The ductility, however, was strongly dependent on the additions. In particular, the 1.5 wt% ZrB2-doped alloy exhibited a striking ductility increased by over 40% when compared with the ZrB2-free Mo–La2O3 alloy, although the two alloys have the same level in yield strength. The ductilization is mainly related to the GB purifying effect derived from the reaction addition, which overwhelms the weakening effect of intergranular particles on ductility. The findings in the current work provide a possible approach to modify the GBs and hence to improve the ductility of BCC alloys such as in present Mo alloys.

Evidence for Zr site-substitution for Mg in PLD-deposited MgB2 thin films

In an investigation of possible atomic substitution for the Mg site in MgB2, superconducting thin films were deposited by pulsed laser deposition using MgB2 and ZrB2 targets. The resulting c-axis-oriented thin films contained various concentrations of Zr. The structural, chemical, and superconductive properties of these films were investigated. ZrB2 additions were found to increase the a lattice parameter; STEM-based chemical analysis showed Zr to be present within the grains. The superconducting critical temperature was suppressed for the heavily-doped samples. These observations are strong evidence for the substitution of Zr for Mg in the Mg sublattice of MgB2.

Effect of ZrB2 and SiC addition on TiB2-based ceramic composites prepared by spark plasma sintering

TiB2-based ceramic composites with different amounts of ZrB2 and SiC were prepared by spark plasma sintering at 1700°C with an initial pressure of 40MPa and a holding time of 10min. The (TixZry)B2 solid solution was found in the sintered TiB2/ZrB2/SiC composites by XRD. The microstructural and mechanical properties of the prepared samples were investigated. The composite with the addition of 30vol.% ZrB2 shows better comprehensive performances, and the bending strength and the fracture toughness of the composite are 780.5MPa and 7.34MPam1/2, respectively. The generation of the (TixZry)B2 solid solution makes the microstructures of the composites finer and more homogeneous, which has played a very important role in grain refinement and interface fusion.

Effects of ZrB2 and SiC dual addition on the oxidation resistance of graphite at 1600–2000°C

Abstract The effects of ZrB2 and ZrB2 + SiC additions on the oxidation kinetics of graphite at 1600–2000 °C in air were investigated. The ZrB2 + SiC dual addition improves the oxidation resistance of graphite more effectively than the ZrB2 single addition, because the oxide scale formed on C–ZrB2–SiC is denser and thinner due to the existence of glassy SiO2. As the oxidation temperature increases, the oxidation rate of C–ZrB2–SiC gradually increases and oxide scales with layered microstructures form on its surface due to the greatly enhanced active oxidation of SiC at higher temperatures.

A Comparison between B<sub>4</sub>C-ZrB<sub>2</sub>-Al Composite and B<sub>4</sub>C-Al Composite on Microstructure and Mechanical Properties

B4C-Al and B4C-ZrB2-Al composites were fabricated by infiltrating aluminum into porous B4C and B4C-ZrB2 preforms in vacuum. The effect of ZrB2 addition on the microstucture and mechanical properties of the B4C-Al composites were investigated. The flexural strength and the fracture toughness of composite improved greatly as the result of ZrB2 addition. The ZrB2 addition inhibited the reaction between B4C and Al. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. Inter/transgranular fracture mode with many tear ridges and dimples was showing in the fracture surface of the B4C-ZrB2-Al composite. The relationships between the microstructures and the mechanical properties of the B4C-ZrB2-Al composites were discussed.

Microstructure and Mechanical Properties of Hot Pressed ZrC-SiC-ZrB<sub>2</sub> Composites

Ternary ZrC-SiC-ZrB2 ceramic composites were prepared by hot pressing at 1900 °C for 60 min under a pressure of 30 MPa in argon. The influence of ZrB2 content on the microstructure and mechanical properties of ZrC-SiC-ZrB2 composites was investigated. Examination of SEM showed that the microstructure of the composites consisted of the equiaxed ZrB2, ZrC and SiC grains, and there was a slight tendency of reduction for grain size in ZrC with increasing ZrB2 content. The hardness increased considerably from 23.3 GPa for the ZS material to 26.4 GPa for the ZS20B material. Flexural strength was a strong function of ZrB2 content, increasing from 407 MPa without ZrB2 addition to 627 MPa when the ZrB2 content was 20vol.%. However, the addition of ZrB2 has little influence on the fracture toughness, ranging between 5.5 and 5.7 MPam1/2.

Ablation Resistance and Mechanical/ Conductive Properties of ZrB2 Reinforced Carbon Based Composites

Zirconium diboride reinforced carbon (ZrB2/C) particulate composites are prepared from petroleum coke, coal tar pitch, and ZrB2 powder by hot-pressing. The ablation, mechanical, thermal, and electrical properties of the composites are studied. Results show that the composites have excellent flexural strength and thermal conductivity, with highest values reaching 131 MPa and 161 W/mK for a 10% ZrB2 addition in raw materials. The electrical resistivity reduces rapidly with increasing amount of ZrB2. The values of mass and linear ablation rates are lower in the composites than those measured for pure carbon, decreasing with increasing ZrB2 content, confirming that these materials are promising for ultrahigh temperature materials. Correlations between properties and microstructure of the composites are also discussed.

Doping effects of ZrC and ZrB2 in the powder-in-tube processed MgB2 tapes

We have investigated the effects of ZrC and ZrB2 doping on the superconducting properties of the powder-in-tube processed MgB2/Fe tapes. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), transport and magnetic measurements. We confirmed the following quite different roles of ZrC and ZrB2 in MgB2. ZrC doping was found to decrease the transport critical current density (Jc) at 4.2 K, while the critical temperature (Tc) kept constant. In contrast, the Jc values in magnetic fields were enhanced greatly by the ZrB2 addition, which resulted in a decrease in Tc by only 0.5 K. The reason for different effects of two dopants is also discussed.

Improved critical current densities in MgB2 tapes with ZrB2 doping

Mg B 2 ∕ Fe tapes with 2.5–15at.% ZrB2 additions were prepared through the in situ powder-in-tube method. The phases, microstructures, critical current density, and flux pinning were characterized by means of x-ray diffraction, scanning electron microscope, and magnetic and transport property measurements. Compared to the pure tape, a significant improvement in the in-field JC was observed for all the ZrB2 doped samples, while the critical temperature decreased slightly. The highest JC value was achieved for the 10at.% doped sample. At 4.2K, the transport JC increased by more than an order of magnitude than the undoped one in magnetic fields above 9T. Nanoscale segregates or defects caused by the ZrB2 additions which act as effective flux pinning centers are proposed to be the main reasons for the improved JC field performance.

Increases in the irreversibility field and the upper critical field of bulk MgB2 by ZrB2 addition

In a study of the influence of ZrB2 additions on the irreversibility field, μ0Hirr and the upper critical field Bc2, bulk samples with 7.5at% ZrB2 additions were made by a powder milling and compaction technique. These samples were then heated to 700–900°C for 0.5h. Resistive transitions were measured at 4.2K and μ0Hirr and Bc2 values were determined. An increase in Bc2 from 20.5Tto28.6T and enhancement of μ0Hirr from 16Tto24T were observed in the ZrB2 doped sample as compared to the binary sample at 4.2K. Critical field increases similar to those found with SiC doping were seen at 4.2K. At higher temperatures, increases in μ0Hirr were also determined by M-H loop extrapolation and closure. Values of μ0Hirr which were enhanced with ZrB2 doping (as compared to the binary) were seen at temperatures up to 34K, with μ0Hirr values larger than those for SiC doped samples at higher temperatures. The transition temperature, Tc, was then measured using dc susceptibility and a 2.5K drop of the midpoint of Tc was observed. The critical current density was determined using magnetic measurements and was found to increase at all temperatures between 4.2K and 35K with ZrB2 doping.