Addition Of LaB6 Research Articles

The effects of synthesis route and LaB6-doping on FeCoNiCrTi coating performance: Morphology, microstructure, microhardness and corrosion resistance

In this work, the FeCoNiCrTi HEA coatings were fabricated on the Ti6Al4V surface via laser cladding technology. The effects of synthesis routes (different energy density, Led) and LaB6-doping on the single-track morphology, phase distribution, microstructure, microhardness and corrosion resistance of HEA coatings were comprehensively studied. Interestingly, the regulation of Led and addition of LaB6 significantly reduced the crack sensitivity and dilution rate of the coating. On the one hand, the optimized coating contributed to fine grain size when Led was 73.33 J/mm2. On the other hand, the in-situ generation of TiC, TiB2 and TiC/TiB2 composite structure played an important role in achieving the more excellent propertiy in LaB6/FeCoNiCrTi composite coating. Furthermore, the microhardness and corrosion resistance of the coatings were significantly improved owing to the ceramic phases and fine grain strengthening. Specifically, the average microhardness coating was up to 593 HV0.2. The corrosion current density (Icorr) of the coating with a Led of 73.33 J/mm2 was 4.796 × 10−6 A·cm−2, the carrier density (ND) and thickness (d) of the passivation film were 1.556 × 1022 cm−2 and 3.244 nm, respectively, indicating the best corrosion resistance in HEA coatings. In terms of LaB6/FeCoNiCrTi coating, the Icorr, ND and d were 2.400 × 10−6 A·cm−2, 1.053 × 1022 cm−2 and 4.739 nm, respectively. Consequently, the doping of LaB6 further enhanced the corrosion resistance of HEA coating.

Dynamic Compressive Properties and Failure Mechanism of the Laser Powder Bed Fusion of Submicro-LaB6 Reinforced Ti-Based Composites.

In this study, lanthanum hexaboride (LaB6) particle-reinforced titanium matrix composites (PRTMCs, TC4/LaB6) were successfully manufactured using the laser powder bed fusion (LPBF) process. Thereafter, the effect of the mass fraction of LaB6 on the microstructure and the dynamic compressive properties was investigated. The results show that the addition of LaB6 leads to significant grain refinement. Moreover, the general trend of grain size reveals a concave bend as the fraction increases from 0.2% to 1.0%. Furthermore, the texture intensity of prior β grains and α grains was found to be weakened in the composites. It was also observed that the TC4/LaB6 have higher quasi-static and dynamic compressive strengths but lower fracture strain when compared with the as-built TC4. The sample with 0.5 wt.% LaB6 was found to have the best strength-toughness synergy among the three groups of composites due to having the smallest grain size. Furthermore, the fracture mode of TC4/LaB6 was found to change from the fracture under the combined action of brittle and ductility to the cleavage fracture. This study was able to provide a theoretical basis for an in-depth understanding of the compressive properties of additive manufacturing of PRTMCs under high-speed loading conditions.

Effect of LaB6 addition on the in-situ synthesis of TiBx/TixNiy/TiC reinforced Ni-based composite coatings

The TiBx/TixNiy/TiC reinforced Ni60 composite coatings were successfully prepared on the surface of 35CrMoV substrate using the laser cladding technology by adding different content of LaB6 (0, 0.5, 1.5, 2.5 wt%) powders into the mixture of TC4 (Ti6Al4V) and Ni60 (94 wt% Ni60, 6 wt% TC4). The phase composition, microstructure, element distribution and chemical composition of the cladding layer were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) with energy spectrum analysis (EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. The reinforced phases in the cladding layer were mainly composed of TiB2, TiC, TiB, Ti2Ni, NiTi and Ni3Ti. The addition of LaB6 did not affect the phase composition, but the grains are obviously refined and the distribution of Ni, Cr and Ti elements is uniform at the addition of 1.5 wt% LaB6 addition. The cladding layer obtained excellent tribological and mechanical performance with the addition of 1.5 wt% LaB6, and the hardness, average friction coefficient and wear volume of the cladding layer reach 808 HV1, 0.183, and 8943 μm3, respectively. The reasonable addition of LaB6 significantly improves the friction and mechanical properties of the cladding layer.

Microstructure and Mechanical Properties of LaB6/Ti-6Al-4V Composites Fabricated by Selective Laser Melting

In this study, TiB + La2O3/Ti-6Al-4V composites were successfully prepared by in situ reaction using selective laser melting technology. The effect of LaB6 content on the fabrication quality, microstructure evolution and mechanical properties of the composite samples was investigated. The results show that the relative density of the sample gradually decreased from 98.56% to 96.57% as LaB6 content increased from 0 wt% to 3 wt%. With increasing LaB6 content, TiB precipitates gradually aggregated and grew from a discrete needle-like structure to a dendritic structure, before eventually developing a cell-like structure. The dislocations piled up around the TiB and La2O3 reinforcements, which impeded the motion of the dislocations and led to the enhancement of the tensile strength of the samples. Different from the addition of a single reinforcement due to the combined strengthening effect of the micrometer-scale and nanoscale reinforcements, the strength of the samples was increased significantly. The Ti-6Al-4V sample with 3 wt% LaB6 addition showed the most significant strengthening effect. Compared to the pure Ti-6Al-4V sample, the 3 wt% LaB6 addition sample gained a 35.71% increase in hardness and a 14.5% increase in tensile strength. Additionally, wear volume was reduced by 47.5%. The results revealed that the addition of LaB6 was a potential way to improve the mechanical performance of the titanium alloys in the additive manufacturing process.

Статистическая оценка механических характеристик горячепрессованной керамики в системе ZrB2–SiC

The effect of the addition of 5 mol.% LaB6 on the Weibull modulus of hot-pressed ceramics in ZrB2-SiC is studied in this paper. The samples with a relative density of 91–92%, a flexural strength of 300–315 MPa, and a Vickers hardness of 14–15 GPa are obtained by hot pressing at an isothermal holding temperature of 1900°C and a pres-sure of 30 MPa within 15 minutes in an argon atmosphere. The addition of LaB6 induces an increase in the Weibull modulus of ceramics from 9.5 up to 15.5 when calculating using the bending strength, and from 22.0 up to 31.4 when calculating using the hardness. The values calculated using the hardness are somewhat overestimated due to the local impact of the Vickers pyramid. An increase in the Weibull modulus with the addition of LaB6 is associated with increasing homogeneity of the ceramic structure due to the formation of a more developed system of interphase boundaries in three-component samples.

In situ phase interface engineering of MoLa alloys for enhanced strength

Incoherent interphases and oxygen segregation at the grain boundaries (GBs) significantly deteriorate the strength of Mo-based alloys. In this study, a new additive, LaB6, was proposed to enhance the mechanical properties. It was found that LaB6 reacted with the matrix to generate coherent La2O3, volatile B2O3 and tiny MoB in situ during sintering. The addition of LaB6 does not increase strength by itself, but can limit grain growth and construct a coherent interface between the as-obtained La2O3 and Mo matrix. More importantly, the oxygen impurity is removed by B in the form of B2O3, which purifies the GBs. As a result, the as-sintered Mo-La-B billets present an extremely high ultimate tensile strength of 965 MPa, which is among the best recorded values for all sintered Mo-based alloys. The enhanced strength can be attributed to the refined grain size, coherent phase interface, and purified GBs.

Thermophysical Properties of Electric Arc Plasma and the Wire Melting Effect with Lanthanum and Sulfur Fluorides Addition in Wire Arc Additive Manufacturing

Achieving a higher quality in wire arc additive manufacturing (WAAM) is a result of the development of welding metallurgy, the development of filler wires, and the control of the thermophysical properties of the electric arc. In this paper, the authors developed composite wires for WAAM with a Ni-LaF3, Ni-LaB6 coating. The addition of LaF3, LaB6, and SF6 increases specific heat, thermal conductivity, enthalpy, and degree of plasma ionization, which leads to the increase in the transfer of heat from the arc plasma to the wire and to the change in the balance of forces during wire melting. The increase in the Lorentz electromagnetic force and the decrease in the surface tension force made it possible to reduce the droplet diameter and the number of short circuits during wire melting. The change in the thermophysical properties of the plasma and droplet transfer with the addition of LaF3, LaB6, and SF6 made it possible to increase the welding current, penetration depth, accuracy of the geometric dimensions of products in WAAM, reduce the wall thickness of products, and refine the microstructure of the weld metal using G3Si1, 316L, AlMg5Mn1Ti, and CuCr0.7 wires.

Strengthening of solid solution (Ti,La)(C,N)-based cermets by LaB6 addition

(Ti,La)(C,N)-based solid solution cermets are fabricated from self-prepared (Ti,La)(C,N) carbonitrides by powder metallurgy with LaB6 addition in the solid solution. Based on the results of XRD and SEM analyses, it is confirmed that there is complete dissolution of (Ti,La)(C,N) powder. The presence of La can effectively suppress grain overgrowth and thus enhance the homogeneity of porcelain microstructure, consequently increasing the particle size of black phase. On the basis of equal mass fraction of La, the performance of (Ti,La)(C,N)-based cermets is better than that of Ti(C,N)-La-based cermets prepared by simple addition of LaB6 to Ti(C,N)-based cermet powder. The discrepancy can be directly related to the effect of adding LaB6 in the solid solution. The physical and mechanical properties of (Ti,La)(C,N)-based cermets comes to optimum when the content of dissolved La is 0.25 wt%, and there is hardness elevation of 20%. With suitable La addition, there is decrease of oxygen content in the solid solution of cermets. It is hence deduced that LaB6 can improve the performance of cermets as a deoxidizer.

Effect of LaB6 addition on mechanical properties and thermal conductivity of silicon nitride ceramics

Si3N4 ceramics was hot-pressed with LaB6–MgO as sintering additives in the temperature range from 1550 °C to 1750 °C for 2 h under the external mechanical pressure of 60 MPa, followed by post-sintering treatment at 1900 °C for 2 h under the N2 pressure of 2 MPa. The effect of sintering temperature on the densification behavior, mechanical properties, thermal conductivity, phase composition and microstructure evolution were investigated in detail. Compared to the Si3N4 ceramics sintered with La2O3–MgO, the addition of LaB6–MgO was beneficial for the improvement of fracture toughness, Vickers' hardness and thermal conductivity of Si3N4 ceramics. The maximum Vickers’ hardness of 18.98 ± 0.63 GPa was achieved at 1550 °C. The bending strength of 1039.1 ± 70.1 MPa and fracture toughness of 8.46 ± 0.23 MPa m1/2 could be obtained at 1750 °C. After post-sintering treatment, the Si3N4 ceramics exhibited improved thermal conductivity of 75.63 W m−1 K−1 and fracture toughness of 8.72 ± 0.11 MPa m1/2 due to the repeated dissolution-precipitation process.

Effect of trace lanthanum hexaboride on the phase, grain structure, and texture of electron beam melted Ti-6Al-4V

This study investigated the effect of trace lanthanum hexaboride (LaB6) addition on the microstructure and mechanical properties of an electron beam melting (EBM) processed Ti-6Al-4V component. LaB6 exhibited a significant effect on the grain structure, phase, and texture of the EBM-processed Ti-6Al-4V alloys. Although prior-β columnar grains were observed in both Ti-6Al-4V and LaB6-modified Ti-6Al-4V (Ti-6Al-4V-LaB6), the width of the columnar grains decreased significantly with LaB6 addition. Alternating acicular α′ martensite and acicular α laths were distributed in the Ti-6Al-4V, whereas refined lamellar α + β structures were observed in the Ti-6Al-4V-LaB6. The texture intensity of α and β phases was also reduced in Ti-6Al-4V-LaB6. We propose that the addition of LaB6 provided a large amount of heterogenous nucleation sites for solidification and α phase formation. Consequently, high tensile strength with considerable elongation was achieved in the EBM-processed Ti-6Al-4V modified by trace LaB6 addition.

Impact of lanthanum and boron on the growth, thermomechanical properties and oxidation resistance of Ti–Al–N thin films

State-of-the-art machining applications require new developments in the field of protective coatings, to guarantee for excellent dimensional accuracy and effective processes. Recently, we showed an enormous enhancement in deposition rate, mechanical strength, and thermal stability of Ti–Al–N when using Ce-alloyed Ti–Al composite targets. Within this study, we further follow the concept of alloying lanthanides to nitride-based coatings, by sputtering Ti0.5Al0.5 composite targets alloyed with 2 mol% LaB6 in mixed Ar/N2 atmospheres. This allowed us to produce coatings that outperform not only Ti–Al–N (significantly) but also Ce-alloyed Ti–Al–N coatings.Compared with coatings prepared from non-alloyed Ti0.5Al0.5 composite targets (Ti0.43Al0.57N), we achieved an impressive increase in deposition rate from 77 to 139 nm/min. Furthermore, we observed an increase in hardness from 34 to 40 GPa (on polished polycrystalline Al2O3 substrates) in the as-deposited state, accompanied by a delayed spinodal decomposition, and an additional TiB2 precipitation, allowing for still 40 GPa after annealing at 1100 °C. Also the oxidation resistance could be significantly improved through the addition of LaB6. After exposure to ambient air at 850 °C for 10 h or 950 °C for 1 h, the oxide scale thickness is only 500 nm for the LaB6 alloyed coatings, whereas the Ti0.43Al0.57N counterpart was already fully oxidized after 10 h at 850 °C or 1 h at 950 °C.

Effect of LaB6 additions on densification, microstructure, and creep with oxide scale formation in ZrB2-SiC composites sintered by spark plasma sintering

A comparative study has been carried out on densification, microstructure, and creep with oxide-scale formation in ZrB2-20 vol.% SiC-(7, 10 or 14 vol.%) LaB6 composite containing B4C and C as additives, and prepared by spark plasma sintering at 1800 °C under 70 MPa ram pressure. Addition of LaB6 has promoted densification of composites by scavenging oxygen impurity, thereby increasing their hardness. Constant load compressive creep tests at 1300 °C under 47 and 78 MPa stresses have shown the lowest creep rate in the 10 vol.% LaB6 composite. The stress exponents obtained for composites having 10 vol.% LaB6 (∼1.3 ± 0.1) and 14 vol.% LaB6 (∼2.6 ± 0.2) suggest respectively, grain boundary diffusion with intergranular glassy phase formation and dislocation glide as operating mechanisms. Intergranular cracking caused by grain boundary sliding appears as the damage mechanism. Oxide scales formed during creep exhibit greater thickness and defect concentration than those by isothermal exposure at 1300 °C within similar duration.

Effects of LaB6 content on microstructure and mechanical properties of TaC-LaB6 composites

Tantalum carbide (TaC)-based composites containing 0.1–30 mol% lanthanum hexaboride (LaB6) were prepared by hot pressing at 1900 °C for 30 min under 30 MPa pressure. Effects of LaB6 content on densification, microstructure and mechanical properties of the consolidated TaC-LaB6 composites were investigated. Sinter-forge was performed to test creep resistance of the TaC-LaB6 composites at temperatures up to 1950 °C. Addition of LaB6 increased densification of the TaC-LaB6 composites and the compositions with ≥1 mol% LaB6 almost reached full densities. LaB6 reacted with TaC and the Ta2O3 impurity to form minor phases of TaB2, B2O3 and C. Average size of the TaC grains in the consolidated composites showed a decrease trend with increase in the LaB6 content. The TaC-LaB6 composites with 1–2 mol% LaB6 addition had relatively good flexural strength, Vickers hardness and fracture toughness with a value of 530 MPa, 15.6 GPa and 5.29 MPa m1/2, respectively. Addition of LaB6 modified interfacial bonding strength of the TaC grains, hence increase in creep resistance under sinter-forge up to 1950 °C.

In situ synthesis and strengthening of ultra high-carbon martensitic stainless steels in addition of LaB6

A powder metallurgy route which is characterized by the vacuum solid state sintering is utilized to fabricate Fe-20Cr-3C and Fe-20Cr-3C-2Mo-3V-2Co ultra high-carbon martensitic stainless steels. A sintering window from 1190 °C to 1210 °C is chosen to obtain high density samples and avoid liquid phase simultaneously. The densification process is promoted by solubility effect during formation of M7C3 and grain boundary diffusion. TEM analysis demonstrates three types of reaction products: the La(BO2)3 phase, the La2O3 phase and the La(Fe0.5V0.5)O3 phase, after adding 0.1 wt% LaB6. The impurity elements such as S and O are absorbed following the LaB6 addition to form non-gaseous products, which promotes densification by decreasing the sintering resistance and thus contributes to the improvement of bending strength and hardness. Both of the electrochemical and immersion results lead to the fact that the corrosion resistance of the steels are improved by 0.1 wt% LaB6 addition, in 3.5 wt% NaCl solution. However, the corrosion resistance of Fe-20Cr-3C-0.1LaB6 still can not compete with that of 316L stainless steel. Nevertheless, Fe-20Cr-3C-2Mo-3V-2Co and Fe-20Cr-3C-2Mo-3V-2Co-0.1LaB6 after quenching at high temperature present comparable corrosion resistance with that of 316L in 3.5 wt% NaCl solution.

In situ synthesis and strengthening of powder metallurgy high speed steel in addition of LaB6

A novel technology which was characterized by the vacuum solid state sintering was developed for powder metallurgy high speed steels production. During sintering, both the WC and Mo2C reacted with Fe and transformed to W and Mo rich M6C carbides which were the common hard phases in high speed steels. Also, a high number of W, Mo and Fe were dissolved in VC, forming the MC carbides. The densification of the material mainly relied on the solubility effect during the M6C and MC carbides formation. By alloying with a 0.1 wt% of LaB6 to the steel, the bending strength and the fracture toughness were improved from 3290 MPa and 25.6 MPam1/2 to 4018 MPa and 29.4 MPam1/2, respectively. The TEM analysis demonstrated three types of reaction products by the LaB6 addition: the amorphous phase, the core-shell structure and the La2O3 phase. The impurity elements such as the Mg, Al, Si, S, Ca, and O were absorbed following the LaB6 addition. Moreover, the deoxidization effect caused by the LaB6 addition promoted the sintering at a high-temperature period which contributed to the bending strength and fracture toughness improvement.

Room Temperature Corrosion Behavior of ZrB2-HfB2 Solid Solutions in Acidic and Basic Aqueous Environments

Several solid solutions mixtures of ZrB2 and HfB2 with and without additives were investigated for corrosion behavior in aqueous solutions in a wide range of pH. The samples were prepared through ball milling followed by spark plasma sintering (SPS). In addition to the single component diborides and mixtures thereof, additives of Hf, Zr, and Ta pure metals as well as LaB6 and Gd2O3 were mixed in to test for corrosion improvements. Several electrochemical methods were employed including potentiostatic polarization, potentiodynamic polarization and electrical impedance spectroscopy (EIS). The results showed that mixed diboride solid solutions had better corrosion resistance than their unmixed counterparts. ZrB2-rich compositions performed better in the high pH solutions; whereas HfB2-rich compositions showed better corrosion resistance under acidic conditions. Metal-rich compositions and Ta additions did not show improvements in the corrosion resistance, the addition of LaB6 to the Hf0.5Zr0.5B2 solid solution, however, exhibited enhanced corrosion resistance in non-acidic solutions.

Effect of LaB6 content on the gas evolution and structure of ZrC coating for carbon/carbon composites during ablation

ZrC coatings with different contents of LaB6 for SiC-coated carbon/carbon composites were fabricated by supersonic atmosphere plasma spraying. The mechanism of gas evolution during oxidation at ultra-high temperatures and the oxide scale structure evolution of the coating after addition of LaB6 with different contents were studied. Results showed that rare earth borate rather than rare earth oxide mainly reduced the melting resistance of the oxide scale. The oxide scale for ZrC coating with 10% LaB6 was unfavorable to the gas escape. After addition of 20% LaB6, the oxide scale was favorable to the gas escape but disadvantageous to the coating applied in the environment containing scouring because of the reduced melting resistance. High content of LaB6 also could cause evident boiling of B2O3, leading to producing big pores in the oxide scale during ablation. Appropriate content of LaB6 for ZrC coating was found to be 15%.

Transition Metal Diborides as Electrode Material for MHD Direct Power Extraction: High-temperature Oxidation of ZrB2-HfB2 Solid Solution with LaB6 Addition

Transition metal borides are being considered for use as potential electrode coating materials in magnetohydrodynamic direct power extraction plants from coal-fired plasma. These electrode materials will be exposed to aggressive service conditions at high temperatures. Therefore, high-temperature oxidation resistance is an important property. Consolidated samples containing an equimolar solid solution of ZrB2-HfB2 with and without the addition of 1.8 mol pct LaB6 were prepared by ball milling of commercial boride material followed by spark plasma sintering. These samples were oxidized at 1773 K (1500 °C) in two different conditions: (1) as-sintered and (2) anodized (10 V in 0.1 M KOH electrolyte). Oxidation studies were carried out in 0.3 × 105 and 0.1 Pa oxygen partial pressures. The anodic oxide layers showed hafnium enrichment on the surface of the samples, whereas the high-temperature oxides showed zirconium enrichment. The anodized samples without LaB6 addition showed about 2.5 times higher oxidation resistance in high-oxygen partial pressures than the as-sintered samples. Addition of LaB6 improved the oxidation resistance in the as-sintered condition by about 30 pct in the high-oxygen partial pressure tests.

Effects of LaB6 additions on the microstructure and mechanical properties of a sintered and hot worked P/M Ti alloy

A trace amount of LaB6 powder was added to P/M Ti and Ti–6Al–4V alloy to improve mechanical properties and refine the microstructure. After sintering, TiB whiskers and La2O3 dispersoids had formed in the microstructure. In a CP Ti alloy, the generation of secondary phases leads to a much refined microstructure, but the alignment of TiB whiskers led to a variation in mechanical properties. Open die forging (ODF) or powder compact extrusion (PCE) was carried out on sintered Ti–6Al–4V alloy to further improve the mechanical properties. This caused severe deformation and re-alignment of the TiB whiskers. Comparing the properties of hot worked Ti–6Al–4V alloy and Ti–6Al–4V alloy with boron additions, an addition of LaB6 leads to slightly lower strength but gives significant better ductility.

Metal-Rich Transition Metal Diborides as Electrocatalysts for Hydrogen Evolution Reactions in a Wide Range of pH

Solid solutions of HfB2-ZrB2 mixtures were prepared by high-energy ball milling of diboride and additive powders followed by spark plasma sintering (SPS). A mixture of stoichiometric 1:1 HfB2-ZrB2 borides was the base composition to which Hf, Zr, Ta, LaB6 or Gd2O3 was added. Hf, Zr and Ta were added in order to bring the boron-to-metal ratio down to 1.86, rendering the boride as MeB1.86. In the case of LaB6 and Gd2O3, 1.8 mol% was added. Electroanalytical behavior of hydrogen evolution reactions was evaluated in 1 M H2SO4 and 1 M NaOH solutions. The LaB6 additive material showed Tafel slopes of 125 and 90 mV/decade in acidic and alkaline solutions respectively. The Hf and Zr rich samples showed Tafel slopes of about 120 mV/decade in both electrolytes. The overpotentials of hydrogen evolution reactions (at 10 mA/cm2) in the alkaline solution were about 100 mV lower than those in acidic solution. The metal-rich diborides and addition of LaB6 showed better hydrogen evolution reaction (HER) activities than the base 1:1 HfB2-ZrB2 stoichiometric diboride solid solution. The higher activity of metal-rich borides could be attributed to the increased electron population at the d-orbitals of the metal shown by band structure modeling calculations using the Density Functional Theory approach.