Ni-based Filler Research Articles

Investigation on microstructural and mechanical integrity of GTAW dissimilar welded joint of IN 718/ASS 304L using Ni-based filler IN 625 using EBSD and DHD techniques

The current study investigates the relationship between the microstructural and structural characteristics of dissimilar gas tungsten arc welding (GTAW) between Inconel 718 (IN 718) and austenitic stainless steel 304L (ASS 304L) using Inconel 625 (IN 625) as a filler material. The microstructural characterization of the dissimilar weld includes the application of an optical microscope (OM), field emission scanning electron microscopy (FE-SEM) including energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). The optical and FESEM analysis of the base metals (BM) indicates the austenitic nature of the IN 718 BM matrix, which incorporates strengthening precipitates γ′ and γ'' distributed throughout the Nickel matrix. In contrast, the ASS 304L BM exhibits an austenitic microstructure along with twins. Moreover, IN 625 weld metal exhibits austenitic microstructure in the form of cellular, columnar, and equiaxed dendrites. Elemental segregation demonstrates the existence of Nb, and Mo-rich carbides, including the laves phases at the interdendritic regions of the IN 625 weld zone and IN 718 Heat-Affected Zone (HAZ). Ferrite stringers were noticed in the HAZ of ASS 304L. EBSD analysis shows the improved texture of the weld zone exhibiting fine equiaxed recrystallized microstructures. EBSD/Kernel average misorientation (KAM) micrographs reveal the existence of high strain at the weld metal grain boundaries. Vickers microhardness assessment of the dissimilar weld demonstrates the high hardness of 257.5 HV for the IN 625 weld zone because of the occurred NbC, laves phases, and Mo-rich carbides. Room temperature tensile characterization shows the failure of tensile specimens from ASS 304L BM reflecting the high strength of the IN 625 weld metal (662 MPa). Tensile tests at high temperatures were performed at 550 °C, 600 °C, and 650 °C. High-temperature tensile result exhibits a higher tensile strength of IN 625 weld zone than the ASS 304L BM, as the tensile specimens fails from 304L BM. The specimen exposed at 550 °C exhibits the highest tensile strength of 388 MPa. The Charpy impact toughness test was conducted, with notches at the HAZ of ASS 304L, HAZ of IN 718, and the weld center being evaluated. The toughness value of the weld metal decreases (99 J) due to occurrence of the secondary precipitates. To analyze residual stress, the deep hole drilling (DHD) technique was used, which revealed that the peak residual stress (230 MPa) is induced at 6 mm from the weld surface and falls into the tensile stress category.

Study on microstructure evolution and failure behavior of Ni3Al-based single crystal superalloy joints brazed with Ni-based filler

The microstructural characteristics of brazing seams significantly influence the mechanical properties of brazed joints. In this study, a novel Ni3Al-based single crystal superalloy(Alloy 1) with high Mo content was brazed with a Ni–B–Si–Ti filler. The evolution of microstructure and mechanical properties of brazed joints were investigated after thermal exposure at 1000 °C up to 300h. The brazed joint was mainly composed of the athermally solidified zone (ASZ), isothermal solidification zone (ISZ), diffusion affected zone (DAZ), and base metal (BM). As the increase of thermal exposure time, the tensile strength of the joint at 980 °C decreases from 625 MPa at 0h of thermal exposure to 443 MPa after 300h of thermal exposure. It is suggested that as the duration of thermal exposure increases, the skeleton phases gradually aggregate at the ASZ/ISZ interface, reducing the relative barrier effect of the skeleton in ASZ. Simultaneously, the ASZ/ISZ interface becomes smoother over time, which in turn leads to rapid crack propagation.

Experimental-theoretical study of a novel approach for dissimilar welding of ferritic steels in power plants: An investigation of morphology-composition-property

Carbon migration is one of the major challenges in the dissimilar welding of ferritic steels, which severely affects the mechanical and structural integrity of the welds and must be prevented at all costs. A novel procedure for dissimilar welding of T22 and T91 steels was developed considering four different welding configurations. The configurations were investigated using optical and electron microscopy, energy dispersive spectroscopy, and mechanical testing to perform a comprehensive study. In one of the four configurations, a Ni-based filler metal was used, and as expected, no hardness gradient was observed between the filler metal and the base metals. A new theoretical qualification method was also introduced to compare the overall performance of the desired welding consumables.

Comparative study on induction brazing of diamond with rare earth Nd-doped crystalline and amorphous Ni-based filler alloy

This essay aims to comparatively study the microscopic morphology and grinding properties of brazed diamonds with amorphous and crystalline filler alloy in the case of rare-earth Nd-doped modified Ni-based filler alloy. The results show that at the same content of Nd, Cr7C3 is mainly generated at the brazing interface of crystalline samples. In contrast, Cr27C6 is mainly generated at the brazing interface of amorphous samples. Amorphous solder material achieves a robust chemical metallurgical union, producing a dense and homogeneous carbide layer. The bonding strength between amorphous solder material and diamond is further enhanced. The addition of rare earth element Nd contributes greatly to the forming ability of amorphous filler alloy. Nd atoms in the amorphous solder material readily bond with Ni atoms, reducing the chemical corrosion of Ni atoms on diamonds and resulting in a lower degree of graphitization. When the amount of Nd added is 1.0 wt%, the morphology of amorphous filler alloy brazing diamond is more complete than the effect of the crystalline state, the degree of thermal damage is lower, and the surface of amorphous filler alloy brazing is smoother. Frictional wear experiments show that the amorphous filler alloy holds diamond better than the crystalline filler alloy, and the diamond specimens prepared with the amorphous filler alloy demonstrate a significantly superior grinding performance in comparison to the diamond specimens prepared with the crystalline filler alloy.

The influence of different alloyed welding materials on the microstructure and mechanical properties of welded interface in TiC cermet MIG welding bonds

The influence of different alloyed welding materials on the microstructure and mechanical properties of the weld interface in TiC cermet was investigated. MIG arc welding was employed to deposit low carbon steel, austenite stainless steel, and Ni-based filler wire onto the surface of the TiC-based cermet to create the weld interface. SEM, EBSD, XRD, microhardness, and shear testing were conducted for characterization. The results indicate that the joints have a (Heat Affect Zone)HAZ-(Partially Melted Zone)PMZ-UZ(Unmixed Zone) -WM(Welding Metal) structure. During the cooling process, the densely distributed TiC particles in the PMZ act as hard phases, leading to stress concentration and microcracks during solidification of the base metal, which affects the shear strength of the joints.

Phase diagram-guided composition design and property investigation of Ni-based filler metals

The fundamental mechanism underlying the formation of brazed joints involves the diffusion of elements between the base metal (BM) and the brazing filler metal (FM). The formation of brittle compounds in FM during the brazing process frequently results in a significant deterioration of the mechanical properties of the brazed joints. Ni and Cu elements exhibit infinite solubility, and the incorporation of Cu element results in a decrease in the liquidus temperature of FM, thereby enhancing its surface wettability on the BM. The present investigation involves the preparation of as-cast and amorphous FMs with varying Cu element concentrations to examine their material properties, such as weldability, wettability, thermophysical behavior, and creep resistance. The thermophysical and mechanical properties of the nickel-based filler metal BNi-2 were evaluated using the JMatPro software for material thermodynamic simulation and compared with data obtained from existing literatures. An analysis is conducted on the creep properties of a novel FM comprising of Ni, Cr, Fe, Si, B, and Cu. The results suggest that the thermophysical properties of BNi-2 filler are minimally impacted by the presence of Cr (6–8 wt%), Fe (2.5–3.5 wt%), Si (4–5 wt%), and B (2.75–3.5 wt%). Furthermore, alterations in the composition of Si and B elements have a significant impact on the distribution of γ and γ′ phases, consequently influencing the creep properties of the material. At 25 °C, the equilibrium phase of BNi-2 with different Cu contents indicates a gradual decrease in the content of γ phase, while the content of γ′ and Cu–Ni phases increases with an increase in Cu content. The BNi-2 filler with 3 % Cu exhibits the most favorable properties in terms of steady creep rate and fracture life compared to other fillers. This is attributed to the competitive equilibrium between the γ phase and Cu–Ni phase. The addition of 6 % Cu element results in the optimal wettability of the filler metal and creep resistance of the brazed joints. It is also observed that as the concentration of Cu reaches 9 %, there is a gradual increase in the FeB phase, a rise in the proportion of brittle compounds, and a decline in the amorphous forming ability.

Exploring the trace rare earth Sm on the microstructure and mechanical performance of brazed diamonds by Ni–Cr filler alloy

In this study, the properties of Ni-based filler alloy are improved by adding rare earth Sm to them and brazing them at a temperature of 1080 °C. Relevant tests are carried out on filler alloy and brazed joints by means of electron microscopy (SEM), energy spectroscopy (EDS) and X-ray diffractometry (XRD). The results show that the addition of rare earth Sm can refine the grain of the filler alloy, improve the hardness of the filler alloy and reduce the thermal damage of the diamond after welding. The addition of rare earth Sm affects the diffusion of Cr, which reacts with the diamond at the interface to form Cr3C2 and Cr7C3, and the formation of these two carbides improves the bonding strength between the filler alloy and the diamond. When the addition of rare earth Sm is 1.5 wt%, the melting point of the filler alloy is the lowest, the grain refinement is the best, the hardness is the highest, and the thermal damage of the brazed sample is the lowest. In addition, the filler alloy of 1.5 wt%Sm has the greatest effect on the diffusion of the Cr element, the bonding strength between the filler alloy and diamond is the highest, and the mechanical properties of the brazed specimens are the best.

Strategy of Suppressing the Solidification Cracking Susceptibility of 247LC Superalloy Weld Metals using Commercial Ni-Based Fillers

The solidification cracking susceptibility of 247LC superalloy dissimilar welds with ERNiCrCoMo-1, ERNiCrMo3, and ERNiFeCr-2 commercial fillers was quantitatively evaluated using Varestraint testing for the sound weld geometries of gas turbine blades. We confirmed that the solidification brittle temperature range (BTR) of the 247LC/ ERNiCrMo-3 dissimilar weld was 217 K, which was measured using a thermo-vision camera during the Varestraint testing, and the BTR increased to 260, and 485 K with the ERNiCrCoMo-1 and ERNiFeCr-2 fillers, respectively, Based on theoretical calculations of the weld solidification path (i.e., using Scheil’s model; performed via the software Thermo-Calc) for each dissimilar weld, the variation in the BTR can be considered to be highly dependent on the solid-liquid coexistence temperature range of the dissimilar welds, and it is also correlated with the low-temperature formation of topologically closed packed phases during the terminal stage. Based on the experimental and theoretical results, the commercial Ni-based filler ERNiCrMo-3 is expected to be an effective welding material for 247LC dissimilar welding and the successful manufacturing of high-soundness blades.

Effect of wire composition on microstructure and penetration crack of laser-cold metal transfer hybrid welded Cu and stainless steel joints

In this paper, Cu-based and Ni-based filler metals were used to obtain laser-CMT hybrid welded copper/stainless steel (Cu/SS) joints. The effect of wire compositions on the microstructure and mechanical properties of T2 Cu/304 SS dissimilar metal joint was studied. The results showed that Fe–Cu liquid phase separation occurred in the fusion zone of the Cu-based weld, and Cu penetration cracks appeared in the heat-affected zone (HAZ) on the steel side. The Cu penetration cracks formation is derived from supersaturated Cu atoms penetrating, gathering and merging at the steel side fusion line along the austenite grain boundaries. The penetration cracks can be eliminated effectively by the Ni-based filler metal, because the diffusion of Cu into the fusion zone and the HAZ on the steel side is limited significantly by the increase of Ni content. The Ni-based weld consisted of dendrite grains in the fusion zone, and Fe-rich blocks and Ni-rich islands nearby the HAZ of Cu-side.

The interfacial reaction between diamond (100) surface and CuNi-based filler alloys containing Cr by first-principles calculations

Brazed diamond tools have the advantages of high holding strength for diamond abrasives, superior grinding performance, formability, etc. The elements used commonly in filler alloys such as Cr, Cu, and Ni have an important impact on the interfacial bond strength and diamond thermal damage. In this work, the interactions between Cu, Ni, and Cr of the filler alloy and the diamond (100) surface were investigated using first-principles calculations. The results indicated that the adsorption energy of Cu adsorbed on the diamond (100) surface was low, suggesting that C atoms are extremely difficult to dissolve into Cu-based filler alloys, which makes Cu-based filler alloys less wettable with diamond. While the adsorption energy of Ni adsorbed on the diamond (100) surface was greater, which may form Ni 3 C weak carbide. Therefore, Ni-based filler alloys are usually wettable with diamonds. However, Ni 3 C of poor stability may decompose C atoms at the interface, which may lead to greater corrosion of diamonds. The adsorption energy of Cr adsorbed on the diamond (100) surface was the highest among Cu, Ni, and Cr, while the co-adsorption of Cr and C can grow into stable carbides. With the extension of time, the carbides can grow to form continuous layers of carbides. The results are generally consistent with the experimental results. • Analysis of graphitization on diamond surfaces using first-principles calculations. • The co-adsorption and deposition processes of Cr and C were investigated, which provided the conditions for the formation of chromium carbides. • Interfacial reaction processes, such as C precipitation and carbides nucleation growth, were investigated at the atomic level using first-principles calculations.

Effect of CeSi2 addition on microstructures of brazed layers and interfacial characteristics of brazed diamonds with Ni Cr filler alloy

The thermal damage of diamond is the key factor restricting the performance of brazed diamond tools with Ni-based filler. Hence, the Ni Cr filler alloy is modified by adding Ce element to reduce the graphitization and improve the mechanical properties of brazed diamond in this work. The results indicate that the microstructures of brazed layers with Ni Cr filler containing Ce element are obviously refined, and the brazed layer containing 2 wt.% CeSi 2 shows the better wear resistance with stable friction coefficient curve and low wear loss. Meanwhile, the brazed diamond with Ni Cr filler containing 2 wt.% CeSi 2 exhibits a higher exposure, and the Cr 3 C 2 on its surface is finer, which contributes to reduce the stress concentration and cracks formation at interface between diamond and filler. The Raman spectrum results show that the graphitization of brazed diamond is significantly weakened due to addition of CeSi 2 . The Ni Cr filler brazed diamonds containing 2% CeSi 2 remain relatively complete cutting edges and shapes after grinding test, showing the excellent wear resistance. Moreover, the calculation of elastic properties indicates that the in-situ formed CeNi 3 phase exhibits better ductility and plasticity, but lower hardness, and its formation is beneficial to improve the ductility and plasticity of brazed layer. • Diamond grits are brazed with Ni Cr filler containing different contents of CeSi 2 . • Microstructures of brazed layers containing CeSi 2 are refined. • Brazed layer containing 2 wt.% CeSi 2 exhibits the best wear resistance. • Graphitization of diamond brazed with 2 wt.% CeSi 2 -doped filler is weakened. • Brazed diamond with 2 wt.% CeSi 2 -doped filler presents superior mechanical performance.

Retaining Mechanical Properties of GMA-Welded Joints of 9%Ni Steel Using Experimentally Produced Matching Ferritic Filler Metal

Motivated by the loss of tensile strength in 9%Ni steel arc-welded joints performed using commercially available Ni-based austenitic filler metals, the viability of retaining tensile strength using an experimentally produced matching ferritic filler metal was confirmed. Compared to the austenitic Ni-based filler metal (685 MPa), higher tensile strength in gas metal arc (GMA) welded joints was achieved using a ferritic filler metal (749 MPa) due to its microstructure being similar to the base metal (645 MPa). The microstructure of hard martensite resulted in an impact energy of 71 J (-196 °C), which was two times higher than the specified minimum value of ≥34 J. The tensile and impact strength of the welded joint is affected not only by its microstructure, but also by the degree of its mechanical mismatch depending on the type of filler metal. Welds with a harder microstructure and less mechanical mismatch are important for achieving an adequate combination of tensile strength and notched impact strength. This is achievable with the cost-effective ferritic filler metal. A more desirable combination of mechanical properties is guaranteed by applying low preheating temperature (200 °C), which is a more practicable and economical solution compared to the high post-weld heat treatment (PWHT) temperature (580 °C) suggested by other research.

Effect of filler material on the microwave joining of SS-430 steel

ABSTRACT In this research paper, the ferritic stainless steel (SS)-430 was butt-joined using nickel (Ni) and austenitic stainless steel (SS-316 L) as interface powder materials. The trials were conducted using a home microwave device that ran at 2.45 GHz and 1000 W. The fabricated weldments demonstrated metallurgical bonding of the SS-430 faying surfaces with the Ni and SS-316 L-based filler materials. The presence of various carbide phases in the joint region of both Ni and SS-316 L-based filler materials was discovered using XRD investigation. The formation of various carbides particle was significantly high in case of joint formed with Ni-based filler materials as compared to the SS-316 L-based filler materials. Microhardness of the joint zone was reported as 310 ± 25 HV and 290 ± 11 HV for weldment obtained with Ni and SS-316 L-based filler materials. The tensile strength of weldment fabricated with SS-316 L-based filler materials (416.70 MPa) is significantly high as compared to weldment fabricated with Ni-based filler materials (318.70 MPa). This was because of the presence of relatively harder carbide particles present in the joint of Ni-based filler materials, which significantly reduces the ductility and tensile strength of the fabricated weldment.

Significant increase in mechanical performance of the C/C-Mo joint by controlling the interfacial defects

To realize the high-strength bonding of C/C composites and metal Mo, Ti was utilized to modify the BNi-5 filler by controlling the interfacial defects. As 5 wt% Ti was used to modify the filler, the doped Ti could absorb the surrounding Mo atoms and prevent them from reacting with liquid Ni-based filler to form MoNiSi compounds in the carbon-side interfacial region during the joining process, reducing the consumption of liquid filler at the interfacial area. Thus, the sufficient liquid filler offers the necessary formation conditions for a dense interfacial layer without obvious defects like pores, increasing shear strength from 19.56 to 45.80 MPa. Excess Ti would have a negative effect on the joint strength since numerous brittle TiC would be produced to form new defects in the interfacial layer, and the high-performance MoNiSi ternary compounds in the interlayer were restrained due to the formation of brittle Ni-Ti-Si compounds with a big size. This work provides an effective strategy to significantly enhance joint strength by controlling the interfacial defects.

Dynamic formation characteristics and mechanism of hybrid laser arc welding surface layer by Ni-based filler metal based on rotating laser induction

This study used a nickel-based filler metal to fabricate a surfacing layer on a low-carbon steel substrate by a hybrid welding process with a rotating laser and arc. The surfacing layer's weld formation was studied using optical microscopic observation (OM). The microstructure of the layers was studied by using the scanning electron microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The arc, metal transfer, molten pool flow behaviors, and U–I characteristics during hybrid laser arc welding (HLAW) were analyzed using the arc analyzer and high-speed camera. The results show that a rotating laser improves the weld formation of gas metal arc welding (GMAW). The microstructure of the two surfacing layers consists of dendritic γ phase and a small amount of Laves and NbC phases. The high dilution rate of the HLAW surfacing layer results in relatively more Laves and fewer NbC phases. The arc length of HLAW is dynamically deflected with the rotation of the laser, which expands the arc action and heating area of the molten pool. The droplet transfer mode changed from globular transfer dominant in GMAW to the projected transfer dominant in HLAW. The location where the droplet transfer into the molten pool is dynamic changed, forming a multi-point impact on the molten pool. Combined with the deflected arc with the laser rotating laser, the HLAW has a broad and deep molten pool. Understanding the metal transfer behavior of Ni-based alloys in rotating laser-induced arc hybrid surfacing is of great significance for improving surfacing forming.

Preliminary investigation on underwater wet welding of Inconel 625 alloy: microstructure, mechanical properties and corrosion resistance

This paper aimed to investigate the feasibility of underwater wet welding for Inconel 625 alloy using Ni-based filler. The microstructure, elemental distribution, and properties of underwater wet welded Inconel 625 alloy joints were analyzed. The grain boundary type and grain growth orientation across the fusion boundary were particularly investigated. A continuous and smooth weld with no visible defects was obtained. The nickel based welds was fully austenite structure with extensive grain boundary migration. The heat-affected zone experienced obvious grain growth. A compositional transition zone with a width of 50 μm was observed across the fusion boundary. Apparent epitaxial growth across the fusion boundaries was found and the grain boundaries roughly perpendicular to the fusion boundaries are was mainly high angle grain boundaries. The density of low Σ CSL grain boundary in Inconel 625 base metal was higher than that in Ni-based weld metal. The ultimate tensile strength of underwater wet welded joints reached up to 83% that of Inconel 625 alloy. The impact toughness of HAZ was deteriorated because of the segregation of carbide and Laves phase in grain boundary. The corrosion resistance of Ni-based welds maintained at a high level based on the corrosion current density, although it was inferior to that of Inconel 625 alloy. The expected research results could enrich the underwater welding/repair technology of Ni-based alloy structures.

A study on microstructural and mechanical properties of gas tungsten arc welded thick cryogenic 9% Ni alloy steel butt joint

Low alloy steel plates containing 9% Ni are generally preferred in the production of LNG storage tanks, due to their outstanding combination of properties such as excellent toughness, high ductility and crack resistance at very low temperatures. Welding is an indispensable manufacturing method in the production of LNG storage tanks. Thus, there is a need for reliable welding procedures which do not diminish low temperature properties of this steel grade. This study introduces the result of microstructural evolution in the weld region and the mechanical properties of the gas tungsten arc welded 10 mm thick 9 Ni steel joint produced by using a Ni-based filler wire, which is widely used in LNG storage tanks. The microstructures evolved in the weld region were examined by extensive optical microscopy and SEM investigations. Mechanical properties and joint performance values of the welded joints were determined by detailed microhardness measurements and transverse tensile tests. Moreover, fracture toughness of the joint fabricated was also determined at − 196 °C by Charpy V-notch test.

Microstructure and mechanical properties of C/C composite joint brazed with Ni-based filler

The novel Ni-based brazing filler was used to join C/C composites. When brazing temperature increased from 1080 to 1100 °C, the wetting angle decreased from 23° to 14°, and the brazing filler had good wettability on the surface of C/C composites. The brazing seam of the brazed joint consisted of Ni(s,s) and Cr3C2 phases. As brazing temperature increased, lots of Cr3C2 phases were generated at the bonding interface, and the thick reaction layer was formed. When brazing temperature was 1120 °C, the shear strength of C/C joint reached the maximum value of 31.5 MPa. The fracture path extended in the C/C matrix close to the bonding interface.

Microstructure and properties of the C/C-superalloy brazed joint by Ni-based filler

Stable and reliable C/C-superalloy joints that can withstand high-temperature service will become extremely important. Ni-based filler was employed for successful brazing of C/C composites and In738LC superalloy in this study. The brazed joints contained isothermal solidification zone (ISZ), diffusion affected zone (DAZ), and penetration zone close to the C/C side. The ISZ contained lots of carbide-borides besides Ni(s,s) and Cr(s,s). The specific composition and atomic arrangement of these phases were characterized by the focused ion beam (FIB) method and transmission electron microscopy (TEM) analysis. Results showed the obvious lattice distortion of the Ti–Mo–B compound indicated the presence of the severe internal residual stress. The microhardness distribution of the brazed joint was analyzed in combination with the microstructure. Brittle Cr–Ti–Mo carbide-borides formed in the reaction layer contributed to the high microhardness, and the shape of borides influenced the DAZ microhardness significantly When the brazing temperature was 1100 °C, the highest joint shear strength was obtained due to a matched proportion of the width and the microhardness of ISZ.

Investigation of arc stability, microstructure evolution and corrosion resistance in underwater wet FCAW of duplex stainless steel

Underwater wet flux-cored arc welding (FCAW) process was used to join 2205 duplex stainless steel using Ni-based filler under three different heat inputs of 16.9 kJ/cm, 23.5 kJ/cm and 32 kJ/cm. The arc stability, microstructure and corrosion resistance with different heat inputs were studied. The results showed that the welding process at the heat input of 23.5 kJ/cm was stable with less spatter and good weld appearance. The weld width, weld penetration and dilution ratio increased with increasing heat input. A single-phase austenitic microstructure was obtained for all welds with varied parameters. The heat-affected zone consisted of coarse ferrite and austenite in grain boundary. The grain size of weld zone and heat-affected zone coarsened as the heat input rose. Compared with the base 2205 base metal, the hardness of HAZ increased about 15% while the weld metal changed little. Electrochemical test in 3.5% NaCl solution indicated that the corrosion resistance of the weld metal under high heat input was better, but its corrosion resistance was inferior to that of base materials. Weld metal obtained at 23.5 kJ/cm possessed comprehensive properties in terms of arc stability and corrosion resistance. These results are helpful to promote the application of duplex stainless steel in the fields of nuclear power fields.