Tungsten Grades Research Articles

High pulse number thermal shock testing of tungsten alloys produced by powder injection molding

Abstract The investigation of plasma facing materials (PFM) subjected to a large number (≥10,000) of thermal shocks is of interest to determine long term morphological changes which might influence component lifetime in and plasma performance of a fusion reactor. The electron beam facility JUDITH 2 was used to simulate these conditions experimentally. In this study eight different tungsten grades produced by powder injection molding (PIM) were investigated: Two pure tungsten grades, one with 2 wt% Y2O3, three with 1, 2 and 3 wt% TiC, and two with 0.5 and 1 wt% TaC. Samples of 10 × 10 × 4 mm³ were brazed to a copper cooling structure and subjected to 105 thermal shocks of 0.5 ms duration and an intensity of Labs = 0.55 GW/m² (FHF = 12 MWs½/m2) at a base temperature of Tbase = 700 °C. The PIM grades showed damages in general comparable with a sintered and forged pure tungsten reference grade (>99.97 wt% W) that complies with the ITER specifications. One exception was the 2 wt% TiC doped material which failed early during the experiment by delamination of a large part of the surface. The Y2O3 doped material showed a comparatively good performance with respect to crack width (

Correlation of hardness and surface microcracking in ITER specification tungsten exposed at QSPA Kh-50

In this work, we have investigated the evolution of the hardness of tungsten under successive thermal shock pulses induced under plasma exposure at quasi-stationary plasma accelerator QSPA-Kh50. The applied conditions represent localized modes of plasma instabilities expected under operation in ITER. The base temperature of 300 °C and deposited heat load of 0.45 MJ/m2 is known to be close to the cracking threshold, which is chosen in this study on purpose. Nanoindentation and microstructural characterization (identification of microcracks) is applied to the samples exposed to 10, 50, 70 and 100 pulses to reveal ability of nanoindentation technique to capture the threshold for the microcrack formation. Knowing that under the selected exposure conditions, the subsurface region of the material is a subject to the recrystallization, which is induced by the overheating during the plasma discharge, nanoindentation measurements are performed on the same tungsten grade annealed at 1300 °C, 1500 °C and 1800 °C to achieve different degree of recrystallization. It is shown that multiple microcracks appear after the 50th cycle which correlates with the reduction of the hardness corresponding to the massive grain growth. FEM analysis is applied to identify stress/temperature distribution across the sample depth to clarify the nucleation location, expected to occur in the region with the highest stress concentration close to the ductile to brittle transition temperature.

Petrogenesis and metallogenic significance of multistage granites in Shimensi tungsten polymetallic deposit, Dahutang giant ore field, South China

The Shimensi tungsten polymetallic deposit, situated in the Dahutang ore field, South China, is one of the largest tungsten deposits in the world, with an estimated WO3 reserve of 0.74 million tons. Coarse-grained porphyritic biotite granite (CPBG), fine-grained porphyritic biotite granite (FPBG), fine-grained biotite granite (FBG) and biotite granite porphyry (BGP) are all ore-related, but their diagenetic relationships and contributions to W-Cu-Mo mineralization are still in dispute. LA-ICP-MS monazite U-Pb dating of the CPBG, FPBG, FBG and BGP yield emplacement ages of 147.9 ± 1.1 Ma, 146.4 ± 1.1 Ma, 138.6 ± 0.98 Ma and 142.8 ± 1.7 Ma, respectively. Whole-rock geochemical results indicate that the four granites should be classified as S-type granites, but BGP has distinct features transitional between S- and I-type granites. They were possibly generated by partial melting of upper crustal pelites and basic volcanic rocks with different proportion from the Neoproterozoic Shuangqiaoshan Group in the source. Proportional variation in the magmatic source (clay and basic basalts) induces the change of geochemical compositions of the Shimensi granites. Geochemical characteristics suggest that they were derived from two magma chambers (the CPBG, FPBG and FBG vs. the BGP) and experienced different evolutionary processes and different degree of magmatic differentiation during magmatic evolution. Chondrite-normalized REE patterns for the four granites display low total REE contents, variable and strongly enriched LREE relative to HREE and medium-strong negative Eu anomalies. They are enriched in Rb, Th, U, Ta and depleted in Ba, Nb, Sr, P, Ti. Biotites are iron-rich and aluminum-poor, and can be classified as ferro-biotite (CPBG, FPBG and FBG) and siderophyllite (BGP). The partial melting of tungsten-rich metasediments of the Shuangqiaoshan Group and high degree of fractional crystallization led to enrichment in tungsten in the magma suites. Oxygen fugacities of the CPBG and FPBG declined from early (most above the NNO buffers) to late stages of fractional crystallization (between the NNO and QFM buffers) because of the higher degree of magmatic differentiation in the late stages. In the early stages of fractionation, tungsten accumulated in the residual melts rather than partitioning into accessory minerals. In the late stages, lower oxygen fugacities and high fluorine contents promoted the removal of tungsten from the residual magma into reduced hydrothermal fluids. On the other hand, the FBG and BGP remained constant (above the NNO buffers) over the entire process of crystallization owning to the stable degree of magmatic differentiation, promoting retention of tungsten in the melt and resulting in low grade tungsten mineralization. Tungsten mineralization in the Shimensi deposit is greatly controlled by the redox states of the associated magma. The two porphyritic granites (the CPBG and FPBG) are most likely the main contributors of tungsten, while the FBG and BGP are mainly responsible for copper and molybdenum in the Shimensi deposit. Prolonged multiphase magmatism and prolonged W-Cu-Mo mineralization play important roles in the formation of Shimensi large tungsten polymetallic deposit.

Inverse identification of tungsten static recrystallization kinetics under high thermal flux

Understanding of recrystallization phenomenon is essential to apprehend damage process of tungsten armored plasma facing components and to optimize their use in tokamak environment. In ITER, plasma facing components will reach extreme surface temperature value up to 2000 °C. Up to now, recrystallization kinetics of ITER tungsten grade were investigated from 1150 °C to 1350 °C. In order to understand tungsten recrystallization process on the wider relevant temperature range, kinetics have to be investigated at higher temperature and on several tungsten grades. Usually, kinetics are investigated by performing successive isothermal annealings on tungsten samples. Due to number of ITER tungsten grades and large temperature range (from 500 °C to 2000 °C), an important amount of tungsten samples have to be prepared to investigate recrystallization kinetics on ITER representative conditions. In this paper, an innovative way is proposed to obtain recrystallization kinetics of ITER tungsten grade based on the use of small-scale plasma facing component tested under high heat flux. Thanks to the use of this inverse method, tungsten recrystallization kinetics are identified at 1348 °C±29, 1480 °C±29, 1586 °C±28 and 1696 °C±27 by using experimental measurements and Johnson–Mehl–Avrami–Kolmogorov model. Then, obtained kinetics are used as input data in numerical post-treatments to obtain tungsten recrystallization gradients after 500 thermal cycles at 20 MW/m2.

Ductile to brittle transition in ITER specification tungsten assessed by combined fracture toughness and bending tests analysis

The evaluation of the fracture toughness of tungsten is required for the design of plasma-facing components in order to ensure safe and durable operation in ITER reactor, being under construction in France. During operation, plasma facing materials will be exposed to cyclic thermo-mechanical loads combined with high energy neutron flux, which, in general, reduce the fracture toughness. Characterization of the degradation of the mechanical properties after exposure to the neutron flux involves time consuming and expensive procedures due to nuclear activation and special handling. Subsequently, development of sample miniaturization and protocols to reduce the volume of material under inspection is critical to speed up the progress in R&D. In this work, we propose a combined approach for the reconstruction of the fracture toughness – temperature curve, which is applied in the ductile to brittle transition temperature range. The approach consists of two steps: (i) application of the three point bending tests using miniaturized samples to reveal the transition temperature range on the basis of flexural strain data; (ii) execution of standardized fracture toughness tests at the upper temperature of the transition regime. The results allow the determination of the fracture toughness as a function of temperature with a reasonable accuracy. The validity of the approach has been demonstrated on two commercial tungsten grades produced according to ITER specification and tested in the as-fabricated state. The conclusions are supported by microstructural analysis performed on both standardized and miniaturized samples.

Surface evaluation of ED machined 316L stainless steel in TiO2 nano-powder mixed dielectric medium

This paper examines the influence of process parameters in the presence of TiO2 nano-powder mixed electric discharge machining (PMEDM) of 316L stainless steel. Commercial grade tungsten electrode with reverse polarity was used for the current experimentation. The responses were assessed in terms of material removal rate and surface roughness using orthogonal array L18 experimental design. It was observed that the most significant factors enhancing material removal (6.75 mg/min.) were current, voltage and powder mixed dielectric medium. There was negligible tool wear due to low wear rate of tungsten electrode. The surface morphology and chemical composition of machined samples were investigated using scanning electron microscopy and x-ray diffraction techniques. It was found that addition of powder in dielectric intensifies the machining stability and material transfer mechanism.

Influence of surface melting on the deuterium retention in pure and lanthanum oxide doped tungsten

The issue of material melting under transient heat fluxes is one of the key concerns associated with the use of tungsten (W) divertor targets in ITER as the next step fusion device. This study aims to closely examine the impact of surface melting on fuel retention with respect to the performance in subsequent operations. Besides pure W, W − 1 wt. % La2O3 (WL10), which is considered as an advanced plasma facing material, is tested as a comparative study. The two tungsten grades are successively exposed to high heat flux loads and low-energy deuterium (D) plasma. The thermal desorption spectroscopy (TDS) measurements indicate that D retention reduces by ~40% after shallow surface melting for both of the two W grades. On the other hand, D retention in the WL10 is almost double that in the pure W regardless of whether surface melting occurs or not. The TDS spectra exhibit two main desorption peaks at around 550 K and 700 K, which largely corresponds to grain boundaries and voids respectively. However, an additional peak appears unexpectedly around 1070 K for the melted WL10. We attribute this additional high-temperature peak to the formation of the hydrogen absorbing metal La in the resolidified layer, which is confirmed by transmission electron microscopy and energy dispersive x-ray spectrometry results.

Unprecedented irradiation resistance of nanocrystalline tungsten with equiaxed nanocrystalline grains to dislocation loop accumulation

Nanocrystalline metals are often postulated as irradiation tolerant materials due to higher grain boundary densities. The efficiency of these materials in mitigating irradiation damage is still under investigation. Here, we present an in-situ transmission electron microscopy with ion irradiation study on equiaxed 35 nm grained tungsten (NCW-35 nm) and compare its radiation tolerance, in terms of dislocation loop damage, to several other grades of tungsten with different grain sizes at two temperatures (RT and 1073 K). The NCW-35 nm was shown to possess significant higher radiation tolerance in terms of loop damage. As demonstrated by Kinetic Monte Carlo simulations, at least part of the higher radiation tolerance of the small grains is due to higher interstitial storage (at the grain boundaries) and defect recombination (in the grain interiors) in the small grain material. In addition, experimental observations reveal rapid and efficient dislocation loop absorption by the grain boundaries and this is considered the dominant factor for mass transport to the boundaries during irradiation, enabling the remarkable radiation tolerance of 35 nm grained tungsten. This study demonstrates the possibility of attaining high radiation tolerant materials, in terms of dislocation loop damage, by minimizing grain sizes in the nanocrystalline regime.

Cutting performance and wear mechanism of TiB2-B4C ceramic cutting tools in high speed turning of Ti6Al4V alloy

TiB2–20vol%B4C (TB20) and TiB2–80vol%B4C (TB80) ceramic cutting tool materials were prepared by hot pressing, and then tested in turning of Ti6Al4V alloy with various cutting parameters. The tool life and wear mechanism of TB20 and TB80 were studied and compared with a commercial grade tungsten carbide tool (WO). The results of turning showed that effective cutting length of TB20 was about one third longer than that of TB80 and WO. Among the three tools, the increment of cutting temperature measured for TB20 was the lowest as flank wear increased from 0 to 600 µm. Analysis showed that dominant wear mechanism was adhesive wear in all of the three tools tested, while chipping was also observed in TB80 and temperature deterioration in WO. In addition, the TB20 exhibited a much better integrity of cutting edge after flank wear reaching 600 µm, due to its higher toughness than TB80 and higher thermal resistance than WO, respectively. The adhesive layers of work-piece material on the rake and flank faces of both TB20 and TB80 were much thinner than that of WO, which suggested a lower adhesive wear rate in TiB2-B4C cutting tools. The high wear resistance of TiB2-B4C cutting tools is attributed to higher thermal resistance, higher hardness, and lower chemical affinity with titanium as compared with tungsten carbides, which makes them very promising materials for high speed machining of titanium alloys.

Tensile properties of baseline and advanced tungsten grades for fusion applications

This work aims to establish a mechanical reference database of tungsten materials that are currently under assessment of their susceptibility to neutron irradiation. To obtain the mechanical properties, we performed a set of parametric tests using mini-tensile sample geometry and fracture surface analysis. Six different types of tungsten-based materials were assessed: two commercial grades produced according to ITER specifications in Europe and China - i.e., Plansee (IGP) and AT&M (CEFTR), and four perspective lab-scale grades. These are grades reinforced with particles of TiC, Y2O3, and ZrC (W1TiC, W2YO, and W0.5ZC, respectively) as well as fine grain structure W (FG). Tests were performed in the temperature range 150–600 °C, selected specifically to reveal the ductile to brittle transition temperature and mechanisms of full plastic deformation. Most of the materials showed onset of the ductile behavior at 300 °C, except FG and IGP (in transverse orientation) grades. High yield strength and ultimate tensile strength were recorded for CEFTR, W0.5ZC, and W1TiC at the maximum investigated temperature (600 °C), which can be considered as promising for performance in the high-temperature regime. The lowest threshold temperature for ductility was determined to be 200 °C registered for the W0.5ZC grade, CEFTR (in longitudinal orientation) grades, and IGP (in longitudinal orientation) grades, hence demonstrating its high potential for divertor applications.

Loop and void damage during heavy ion irradiation on nanocrystalline and coarse grained tungsten: Microstructure, effect of dpa rate, temperature, and grain size

Displacement damage, through heavy ion irradiation was studied on two tungsten grades (coarse grained tungsten (CGW) and nanocrystalline and ultrafine grained tungsten (NCW)) using different displacement per atom rates and different irradiation temperatures (RT and 1050 K). Percentage of <111> and <100> type loops at the irradiation conditions was determined. Irradiation damage in the microstructure was quantified using average loop areas and densities (method A) and loop areal fraction in the grain matrices under 2-beam diffraction conditions (method B). Average values of <111> and <100> loops were calculated from method A. Loop coalescence was shown to occur for CGW at 0.25 dpa. Using both methods of quantifying microstructural damage, no effect of dpa rate was observed and damage in CGW was shown to be the same at RT and 1050 K. Swelling from voids observed at 1050 K was quantified. The loop damage in NCW was compared to CGW at the same diffraction and imaging conditions. NCW was shown to possess enhanced irradiation resistance at RT regarding loop damage and higher swelling resistance at 1050 K compared to CGW. For irradiation at 1050 K, the NCW was shown to have similar defect densities to the CGW which is attributed to higher surface effects in the CGW, vacancy loop growth to voids and a better sink efficiency in the CGW deduced from the vacancy distribution profiles from Kinetic Monte Carlo simulations. Loop density and swelling was shown to have similar values in grains sizes that range from 80 to 600 nm. No loop or void denuded zones occurred at any of the irradiation conditions. This work has a collection of experiments and conclusions that are of vital importance to materials and nuclear energy communities.

Nano-hardness, EBSD analysis and mechanical behavior of ultra-fine grain tungsten for fusion applications as plasma facing material

Tungsten and its alloys have been extensively studied in order to be used in plasma facing components for future fusion nuclear reactors such as ITER and DEMO. In this work, an evaluation of nano-hardness, microstructure/texture and mechanical behavior using nano-indentation, electron backscatter diffraction (EBSD) and tensile test was performed. The investigated materials were ultra-fine grain lab-scale tungsten and ITER-specification commercial tungsten products, taken as reference in the as-received and annealed (at 1300 °C for 1 h) conditions. Three ultra-fine grain (UFG) tungsten grades were produced under different spark plasma sintering conditions, namely at 2000 °C and 70 MPa, at 1700 °C and 80 MPa and, finally, at 1800 °C and 80 MPa. EBSD analysis provides very relevant data as it is known that the crystallographic orientation affects some features of the surface damage caused by fusion-relevant plasma exposure. The present results will serve as a reference for future studies that will be carried out using plasma-exposed samples in order to correlate the observed damage with the microstructural characteristics and mechanical behavior.

Physical Methods and Flotation Practice in the Beneficiation of a Low Grade Tungsten-Bearing Scheelite Ore

In this paper, beneficiation studies were carried out on a low-grade tungsten-bearing scheelite from Nezam Abad ore with total WO3 grade of 0.11%. Mineralogical studies showed that scheelite is mainly distributed in the ore and gangue minerals include Quartz and Tourmaline. Liberation degree (d80) of tungsten- bearing scheelite is achieved around particles size 150 μm. Gravity concentration, magnetic and flotation methods were conducted by using experimental designs including fractional factorial and response surface methodology. Gravity concentration results indicated that jig separator could not be able to improve tungsten grade in size fraction +600–1750 μm; however, shaking table increased feed grade up to 27.05% with total recovery more than 50% by using four stages concentration in the size range of +125–600 μm. Multi Gravity Separator (MGS) applied on the intermediate products, improved efficiently the total tungsten recovery of the circuit. The results of flotation practice on the pre-concentrated product demonstrated that WO3 grade could be increased up to 9.2% with total recovery of 27.04% by using one stage rougher and four stages of cleaning. Different methods including MGS, wet and dry magnetic separation were considered for upgrading fines from grinding stages; however, only MGS result was satisfactory. The MGS produced a product with WO3 grade 0.64% and total recovery 93%.

Sputtering effects on mirrors made of different tungsten grades

Because tungsten (W) is used in present fusion devices and it is a reference material for ITER divertor and possible plasma-facing material for DEMO, we strive to understand the response of different W grades to ion bombardment. In this study, we investigated the behavior of mirrors made of four polycrystalline W grades under long-term ion sputtering. Argon (Ar) and deuterium (D) ions extracted from a plasma were used to investigate the effect of projectile mass on surface modification. Depending on the ion fluence, the reflectance measured at normal incidence was very different for different W grades. The lowest degradation rate of the reflectance was measured for the mirror made of recrystallized W. The highest degradation rate was found for one of the ITER-grade W samples. Pre-irradiation of a mirror with 20-MeV W6+ ions, as simulation of neutron irradiation in ITER, had no noticeable influence on reflectance degradation under sputtering with either Ar or D ions.

Recrystallization and composition dependent thermal fatigue response of different tungsten grades

Industrial pure tungsten grades, manufactured by using a variety of manufactured techniques, are available worldwide in many different types of semifinished products, i.e. rods, wires, ribbons, and sheets. Thereby, the recrystallization temperature varies depending on the applied degree of deformation but also depending on the materials composition, i.e. the materials purity and in particular the level of certain impurities.In order to compare different available industrial tungsten grades and a newly developed PIM-W grade, on the one hand recrystallization studies at three different temperatures from 1573 to 2073K for 1h were performed using microstructural analyses and Vickers hardness testing. On the other hand, the thermal shock induced low cycle thermal fatigue response of the material in its different recrystallization stages was done using high heat flux tests at 1273K base temperature, applying 1000 shots with 1ms and 0.38GW/m2 and post-mortem characterization, i.e. profilometry and metallography. The obtained results are related to the microstructural and mechanical features of the materials as well as the chemical composition of the individual tungsten grades.

Thermal desorption spectroscopy of high fluence irradiated ultrafine and nanocrystalline tungsten: helium trapping and desorption correlated with morphology

Microstructural changes due to displacement damage and helium desorption are two phenomena that occur in tungsten plasma facing materials in fusion reactors. Nanocrystalline metals are being investigated as radiation tolerant materials that can mitigate these microstructural changes and better trap helium along their grain boundaries. Here, we investigate the performance of three tungsten grades (nanocrystalline, ultrafine and ITER grade tungsten), exposed to a high fluence of 4 keV helium at both RT and 773 K, during a thermal desorption spectroscopy (TDS) experiment. An investigation of the microstructure in pre-and post-TDS sample sets was performed. The amount of desorbed helium was shown to be highest in the ITER grade tungsten and lowest in the nanocrystalline tungsten. Correlating the desorption spectra and the microstructure (grain boundaries decorated with nanopores and crack formation) and comparing with previous literature on coarse grained tungsten samples at similar irradiation and TDS conditions, revealed the importance of grain boundaries in trapping helium and limiting helium desorption up to a high temperature of 1350 K in agreement with transmission electron microscopy studies on helium irradiated tungsten which showed preferential and large facetted bubble formation along the grain boundaries in the nanocrystalline tungsten grade.

Constitutive law for thermally-activated plasticity of recrystallized tungsten

A physically-based constitutive law relevant for ITER-specification tungsten grade in as-recrystallized state is proposed. The material demonstrates stages III and IV of the plastic deformation, in which hardening rate does not drop to zero with the increase of applied stress. Despite the classical Kocks-Mecking model, valid at stage III, the strain hardening asymptotically decreases resembling a hyperbolic function. The material parameters are fitted by relying on tensile test data and by requiring that the strain and stress at the onset of diffuse necking (uniform elongation and ultimate tensile strength correspondingly) as well as the yield stress be reproduced. The model is then validated in the temperature range 300–600 °C with the help of finite element analysis of tensile tests which confirms the reproducibility of the experimental engineering curves up to the onset of diffuse necking, beyond which the development of ductile damage accelerates the material failure. This temperature range represents the low temperature application window for tungsten as divertor material in fusion reactor ITER.

Cracking and surface roughening of beryllium–tungsten alloy due to transient heating

A controlled beryllium–tungsten (Be–W) alloy was created in a beryllium-seeded deuterium plasma in the PISCES-B facility and irradiated by a pulsed laser in order to investigate how transient surface heating from plasma instabilities will affect the performance of mixed materials in ITER. Standardized wavelength dispersive x-ray spectroscopy was used to measure the depth profiles of beryllium and tungsten atomic concentrations, revealing beryllium penetration of ∼100 μm in ITER comparable grade tungsten with 5000 s of plasma exposure at 1123 K and ion flux 8 × 1022 m−2 s−1. The deep Be penetration into W is a concern for the lifetime of the ITER divertor, which may form mixed Be–W material. Pulsed laser heating was used to investigate the thermo-mechanical response of Be–W alloy and pure W using temporal shape mimicking that expected for edge-localized modes in ITER, with up to 1.9 MJ m−2 of absorbed energy density. Transient heating creates a lower surface roughness than pure W, but cracks appear in the alloy layer surface at lower absorbed energy density and lower pulse number.

Fabrication of sintered tungsten by spark plasma sintering and investigation of thermal stability

Tungsten has been considered as the most promising candidate for plasma-facing materials (PFMs) in a next generation fusion reactor. It is well known that commercialized ITER (International Thermonuclear Experimental Reactor) grade tungsten is manufactured by the mechanical processing at high temperature after sintering to ensure a high density with an improved structural stability. In this study, in order to obtain the high-density sintered tungsten with more enhanced structural stability, spark plasma sintering (SPS) method was employed, where a pulsed direct electric current was applied during heat treatment of powders with a pressure in the specimen. It is well known that by utilizing SPS, high-density sintered materials at a relatively lower temperature for a shorter time could be achieved compared to the other conventional sintering methods. In particular, in this study, reduction in H2 atmosphere and two-step sintering were introduced to remove the residual oxygen and achieve the full densification with suppressed grain growth at relatively low operating temperature. In an optimized condition, a fully densified sintered tungsten with a relative density of 99.9% and an average grain size of 4.4μm was fabricated. The thermal stability of tungsten specimens was evaluated by high heat flux (HHF) test, where the surface temperature was set up to 2300°C by nitrogen plasma. Then, the microstructural changes of the specimen surface have been examined after the HHF test. As a result, it was confirmed that the high-density sintered tungsten samples fabricated by SPS show an excellent microstructural stability for PFMs.

Experimental investigation on different patterned bolted/welded structural connection in steel and GFRP plates

The experimental investigation is explained different structural connection like various patterned single shear lap bolted connections and slot complete penetration welded connection. Totally 12 numbers of 300 x 50 x 4 mm steel connections made by lap joint as per IS800: 2007 provisions. The patterns are linear, diamond and staggered for the bolted and slot complete penetration welded connections, 4.6 grade bolt and tungsten electrode rods are used for structural slot complete penetration welded connection conforming to IS 800: 2007. And 6 numbers of 300 x 50 x 6mm Glass fibre reinforced polymer (GFRP) plate with bolted connection was casted, shear resistance capacity is considerably higher in the staggered pattern structural connections then the linear and diamond pattern connections. The connection which is made by GFRP, failure occurred in the plate itself and the shear resistance capacity is lowered 60% then the steel plate even though GFRP plate high resistivity against aggressive environment