Incorporation Of SiC Particles Research Articles

Nucleation and growth mechanism of Ni/SiC composite coatings electrodeposited with micro- and nano-SiC particles

To study the nucleation and growth mechanism of Ni/SiC composite coatings, electrodeposition was conducted in the Ni bath containing SiC particles with different sizes. Compared to the Ni coating electrodeposited from the bare Ni bath, the Ni/SiC composite coatings exhibited similar grain size but rougher surface morphology due to the incorporation of SiC particles. By means of chronoamperometry (CA) and linear sweep voltammetry (LSV) techniques, it was found that the introduction of SiC particles did not change the nucleation mode of Ni: the Scharifker-Hills three-dimensional instantaneous nucleation mode. However, the nucleation sites on the cathode were reduced due to the inert surface and low conductivity of SiC particles. At a step potential of −0.94 V, Ni presented the maximum nucleation density (N0) of 3.09 × 107 cm−2, which was reduced by one order of magnitude for the Ni/SiC. Furthermore, SiC particles in the bath would extend the diffusion path of Ni2+ ions, resulting in the decrease in diffusion coefficient from 1.04 × 10−7 cm2 s−1 (Ni) to 9.91 × 10−9 cm2 s−1 (Ni/50 nm SiC), 1.83 × 10−8 cm2 s−1 (Ni/500 nm SiC) and 2.29 × 10−8 cm2 s−1 (Ni/5 μm SiC), suggesting the “Blocking effect”. COMSOL simulation further confirmed the “Blocking effect”. The “Blocking effect” would lead to excessive interface gaps around 5 μm SiC particles due to the uneven electrodeposition of Ni. To address the issue, we proposed that adding non-ionic surfactants into the bath to lower the electrochemical reaction rate of Ni2+ ions and accordingly gained composite coatings with fine continuity.

Effect of reinforcement particles and multipass of friction stir processing on microstructure and mechanical properties of aluminium alloy

The present study focuses on the successful fabrication of aluminium metal matrix composites (AMMCs) using friction stir processing (FSP) and micro-sized SiC as reinforcement particles (RPs). The microstructure of Al6061-T6/SiC AMMCs in the stir zone was examined using Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). The incorporation of SiC particles and the refinement of grain structure resulted in upgraded mechanical properties of the AMMCs achieved through three FSP passes. These enhancements were concerning from the reduction in grain size and more orderly dispersal of SiC particles. Moreover, the microhardness of the AMMCs enhanced by 41.79%, by augmenting the FSP passes, which can be characterized by the refinement in grain structure, facilitated by the dynamic recrystallization (DRx) mechanism.

Aluminium-Based Dissimilar Alloys Surface Composites Reinforced with Functional Microparticles Produced by Upward Friction Stir Processing

Surface metal matrix composites offer an excellent solution for applications where surface properties play a crucial role in components’ performance and durability, such as greater corrosion resistance, better wear resistance, and high formability. Solid-state processing techniques, such as friction surfacing and friction stir welding/processing, offer several advantages over conventional liquid-phase processing methods. This research investigated the feasibility of producing surface composites of aluminium-based dissimilar alloys reinforced with functional microparticles through experimental validation, determined the process parameters that resulted in a more homogeneous distribution of the particles in the surface composites, and enhanced the understanding of Upward Friction Stir Processing (UFSP) technology. The production of aluminium-based dissimilar alloys (AA 7075-T651 and AA 6082-T651) surface composites reinforced with SiC particles was studied, and it was concluded that the macrography and micrography analyses, scanning electron microscopy (SEM) analysis, microhardness measurements, and eddy currents technique reveal an extensive and homogeneous incorporation of SiC particles. In the stirred zone, a decrease of approximately 20 HV 0.5 in hardness was observed compared to the base material. This reduction is attributed to the weakening effect caused by low-temperature annealing during UFSP, which reduces the strengthening effect of the T651 heat treatment. Additionally, the presence of particles did not affect the surface composite hardness in the stirred zone. Furthermore, despite the presence of significant internal defects, SEM analyses revealed evidence of the lower alloy merging with the upper zone, indicating that the lower plate had a role beyond being merely sacrificial. Therefore, the production of bimetallic composites through UFSP may offer advantages over composites produced from a monometallic matrix. The results of the eddy currents testing and microhardness measurements support this finding and are consistent with the SEM/EDS analyses.

Wear resistance of composite electrolytic coatings

The article analyzes the influence of composite electrolytic coatings (CEC) on the wear resistance of structural steels. The issues of matrix selection and various combinations in composite coatings of different chemical elements and compounds are considered. Coatings based on chromium, nickel, iron, copper, cobalt and others are widely used in industry, but nickel-based composite coatings are the most widely used. Nickel is widely used as a matrix for CEC, because it has an affinity for most particles used as the second phase and easily forms a coating with them. These coatings are used for corrosion protection, increase of physical and mechanical and chemical parameters, increase of hardness and wear resistance, restoration of the sizes, giving to a surface of self-lubricating properties.
 Nickel-based coatings with SiC filler of various fractions from size 100/80 μm to nanoparticles smaller than 50 nm were investigated on the basis of the established installation for CEC application. Thus, SiC powders with the following sizes were used in the works: less than 50 nm - nanoparticles; M5; 28/20; 50/40; 100/80 μm.
 In the studies performed, 0.01… 0.02 g/l sodium lauryl sulfate was additionally introduced into the electrolyte, which promotes the incorporation of SiC particles into the coating and improves the conditions for building the Nickel matrix.
 Amorphous boron powders of about 1 μm size were also added to the silicon carbides as a filler, which is explained by the possibility of boron and nickel interaction during the subsequent heat treatment of the coating and obtaining new structures (solid solutions, eutectic, dispersion-hard alloys).
 It is of practical interest to study the possibility of improving the physical and mechanical properties of nickel-based CEC by introducing metals capable of heat treatment, interact with the metal matrix to form solid substitution solutions and chemical compounds (solid phases of implementation) and determine tribotechnical characteristics of these coatings.

Effect of sodium dodecyl sulfate and different SiC quantities on electrodeposited Ni-Co alloy coatings

Ni-Co nanocomposites Prepared by electrodeposition in a modified Watts bath containing various quantities of silicon carbide SiC and the organic additive sodium dodecyl sulfate SDS as a surfactant. The influence of nanoparticle incorporation on the electrodeposit microstructure, mechanical characteristics, and deformation process was studied. Vickers micro-hardness and weight loss tests were used to study the mechanical properties and morphology. The microstructure has also been analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Co-deposition of uniformly dispersed SiC particles, on the other hand, was found to improve the extreme tensile strength of the deposits significantly; SDS lowered the surface tension, allowing the SiC particles to fill in all remaining gaps to achieve a homogeneous surface. A process involving atoms that can dramatically improve flexibility. The incorporation of SiC particles and raising the strain rate encouraged a ductile fracture mode in a nano-crystalline Ni-Co matrix, which demonstrated a mixed mod behavior of flexible and brittle fracture; it was evident that the addition of SDS increases the concentration of SiC particles in general on Ni-Co samples. Moreover, compare Ni-Co with various amounts of SiC and Ni-Co/SiC with adding SDS. Furthermore, to achieve the highest possible electroplating efficiency.

Thermal Kinetics of SiCp Reinforced AA7075 Alloy Composite

The present study evaluates the process activation energy or thermal diffusion activation energy (TDAE) to understand the aging kinetics or transformation kinetics. AA7075–5 Vol.% of SiCp composite were fabricated through stir casting technique. Differential scanning calorimetry (DSC) was carried out at different heating rates to understand the precipitation sequence and evaluate the process activation energy or thermal diffusion activation energy (TDAE) of composite. Rockwell hardness tests investigated the aging behavior of AA7075–5 Vol.% of SiCp composite. Results show incorporation of SiCp in the matrix does not affect the sequences of formation and dissolution of precipitate but affects the kinetics of precipitation growth. The formation of precipitation in the alloy and composite requires an access amount of vacancies; an increase in dislocation density may result in heterogeneous nucleation of precipitation and create free path for the kinetically faster atomic transportation of precipitates. Hence, incorporation of SiC particles in the composite would offer a lot of nucleation sites for precipitate, resulting in lower activation energy to form precipitates and takes less time to reach the maximum hardness. In contrast, the addition of a lesser volume fraction of SiCp also showing accelerated aging phenomena in the composite during the aging process. The hardness profile shows hardness increases 3.86% compared to the base alloy AA7075. High-resolution transmission electron microscope (HRTEM) micrograph of peak age (T6) condition divulges that enormous fine and plate-like ή (MgZn2) precipitates are uniformly distributed in the composite.

Exploring the influence of process parameters on the properties of SiC/A380 Al alloy surface composite fabricated by friction stir processing

Friction stir processing (FSP) has been used successfully to yield surface composites that offer good wear resistance and high hardness. In this work, an attempt was made to produce SiC particles incorporated within the surface of an A380 Al alloy using FSP under various processing parameters. The microstructure of processed surface was characterized using optical and SEM. XRD was employed to investigate the phases of A380 Al alloy matrix and confirm with EDX mapping the presence of SiC particles. Microhardness test was performed to recognize the variation of hardness values along the cross-section of processed alloy. Pin on disk wear apparatus was used successfully to study wear properties under dry sliding conditions using different applied loads. The results showed that the XRD and EDX mapping confirmed the incorporation of SiC particles within the surface of A380 Al alloy. Refining of α-Al and silicon modification were recognized within the stir zone. Microhardness was changed significantly across the processed region depending on the FSP parameters used. The presence of SiC particles improved the wear properties of A380 Al alloy especially at 1460 rpm tool rotation speed and 0.3 mm plunge depth.© 2020 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CCBY-NC-ND license.

Characterization of Aluminum Alloy–Silicon Carbide Functionally Graded Materials Developed by Centrifugal Casting Process

The continuous development of modern industries rises the necessity for functionally graded materials. This research starts from the consideration that the incorporation of SiC particles in the molten aluminum alloy can be difficult due to the very low wettability of SiC particles. In order to increase their wettability, SiC particles were covered with a layer of metallic copper. The incorporation of SiC particles into the aluminum alloy mass was performed by centrifugal casting. The secondary hypoeutectic Al-Si alloy used in this study was elaborated within the crucible of a resistors heated furnace. The metallic coating of SiC particles, in addition to the effect of increasing their wettability by molten metal, also has a role in preventing the formation of aluminum carbide in case of heating above 700 °C. A great amount of attention was paid to the parameters used during the centrifugal casting process. The results showed that adjusting the proportion of SiC particles within the composite allows us to obtain values of the thermal expansion coefficient within previously established limits. The present work demonstrates that the coating of SiC particles covered with a thin layer of metallic Cu creates the conditions to easily incorporate them into the molten Al mass, thus obtaining FGMs with controlled properties.

Study of the effect of pulse plating parameters on the electrodeposition of NiP and NiP/SiC coatings and their microhardness values

ABSTRACT This study is focused on finding optimised conditions for electrodeposition of NiP and NiP/SiC coatings, which enhance the coatings' microhardness. Both the effect of particles and the effect of heat treatment at 400°C for 1 h on the microhardness of the coating were studied. The effects of pulse electrodeposition parameters including duty cycle, frequency, and peak current density on the composition of NiP and NiP/SiC composite coatings were examined, and the results were compared with those from direct current plating. Pulse plating increased the current efficiency of NiP deposition while decreasing the phosphorus content of these coatings in comparison to direct plating, resulting in higher microhardness values. It was also shown that wt.%P in NiP coating depends not only on peak current density but also on bath charge of pulse plating. Pulse plating parameters (duty cycle and frequency) and the low incorporation of SiC particles did not affect microstructure or the microhardness of the coatings, while heat treatment was the main factor that increased microhardness.

A Study on the Effect of Incorporation of SiC Particles during Friction Stir Welding of Al 5059 Alloy

Friction stir welding (FSW) was performed in the current research on Al 5059 alloy. Nano-sized SiC (n-SiC) particles were incorporated during FSW for improving mechanical characteristics of welds. Effect of tool rotating speed and multiple FSW passes was studied on SiC dispersion, micro structural changes and mechanical characteristics of composite joints. Results reflected that rotational speed and multiple FSW passes have significant impact over the distribution of SiC reinforcement. Further, the pattern of SiC distribution in the base metal strongly affects the micro structural evolution and mechanical characteristics of welds. An increase of ~55% in microhardness values was achieved in the stir zone of composite joint. Correspondingly, higher ultimate tensile strength (342 MPa) value was obtained as compared to base metal (321 MPa). The increase in mechanical characteristics is mainly owing to grain refinement caused by recrystallization and pinning effect of SiC particles. Micro structural study was carried out using metallurgical microscope and dispersion of n-SiC was observed using TEM. The results of mechanical testing of the present study are in strong corroboration with the micro structural analysis.

Effect of multi-groove reinforcement strategy on Cu/SiC surface composite fabricated by friction stir processing

In the present study, Cu/SiC surface composite was fabricated by friction stir processing (FSP) via multi-groove technique eyeing to improve SiC dispersion in copper matrix and hence improving mechanical and tribological behaviour. Microstructural features revealed more uniform dispersion of SiC particles in copper matrix when fabricated through multi-groove technique (MGT) as compared to single groove technique (SGT). The interface between copper matrix and SiC particles were clean without any obstruction/interruption in the form of voids or pores or intermediate phases formed which indicated excellent interfacial bonding. Furthermore, the obtained microstructure revealed drastic grain refinement in FSPed copper without reinforcement and the composites fabricated through SGT and MGT and the reduction in grain size was more for the composites fabricated by MGT. Tensile tests revealed incremental behaviour over strength with increase in number of grooves although it was far less as compared to base copper. Fractured surfaces of composites fabricated by both techniques (SGT and MGT) indicated reduction in ductility. However, results obtained for FSPed copper without reinforcement showed higher strength and ductility as compared to base copper. It was also demonstrated that incorporation of SiC particles in copper matrix improved hardness and wear resistance and it further enhanced with increased number of grooves. The wear mechanism changed with introduction of SiC particles in copper matrix and was supposed to be because of reduction in friction coefficient.

Investigations on the corrosion resistance and microhardness of Cu–10Sn/SiC composite manufactured by powder metallurgy process

In this work, Cu–10Sn/SiC composite has been manufactured using powder metallurgy method and its microhardness and corrosion resistance have been evaluated. For this, Cu–10Sn and SiC powders with various ratios were mixed, molded and sintered. Optical microscope, SEM and EDX were applied for study of SiC particles distribution in Cu–10Sn matrix and interfaces between them. Results of microhardness and electrochemical measurements revealed that incorporation of silicon carbide particles in Cu–Sn bronze matrix increase the microhardness and corrosion resistance and the composite containing 10 wt% SiC has the highest microhardness and corrosion resistance in 3.5 wt% NaCl solution. High hardness and chemical stability of SiC particles, perfect matrix/second phase particles interfaces and acceleration in protective layer nucleation and formation by incorporation of SiC particles in bronze matrix were recognized as the main reasons for these properties improvements. Above 10 wt%, incorporation of SiC particles lowers the microhardness and corrosion resistance due to the agglomeration of these particles and incomplete sintering of the specimens.

Microstructure and Tribological Properties of Micro-arc Oxidation TiO2 Coating Before and After SiC Particles Incorporation

In this work, porous TiO2 coating was fabricated on the surface of commercially pure titanium using the micro-arc oxidation (MAO) technique, and the effect of SiC particles incorporation on the microstructure and tribological properties of MAO TiO2 coating was investigated. Results show that submicron SiC particles dispersed in the MAO electrolyte were incorporated into the TiO2 coating during the MAO process and the fabricated TiO2/SiC composite coating mainly consisted of rutile, anatase and SiC phases. The pore size and surface roughness of TiO2/SiC composite coating decreased with the increasing addition amount of SiC particles in the electrolyte. Furthermore, the incorporation of SiC particles in the TiO2 coating suppressed the initiation and propagation of micro-cracks. The tribological test of coatings against GCr15 stainless steel balls show that the incorporation of submicron SiC particles in the MAO TiO2 coating decreased the friction coefficient and wear rate.
 DOI: http://dx.doi.org/10.5755/j01.ms.25.3.20089

Fine grained Al2O3/SiC composite ceramic tool material prepared by two-step microwave sintering

Abstract Fine-grained Al2O3/SiC composite ceramic tool materials were synthesized by two-step microwave sintering. The effects of first-step sintering temperature (T1), content and particle size of SiC on the microstructure and mechanical properties were studied. It was found that the sample with higher content of SiC was achieved with finer grains, and the incorporation of SiC particles could bridge, branch and deflect the cracks, thus improving the fracture toughness. Higher T1 was required for the densification of the samples with higher content of SiC (>5 wt%). The sample containing 3 wt% SiC particles with the mean particle size of 100 nm, which was sintered at 1600 °C (T1) and 1100 °C (T2) for 5 min had the fine microstructure and optimal properties. Its relative density, grain size, Vickers hardness and fracture toughness obtained were 98.37%, 0.78 ± 0.31 μm, 18.40 ± 0.24 GPa and 4.97 ± 0.30 MPa m1/2, respectively. Compared to the sample prepared by single-step microwave sintering, although near full densification can be achieved in both two methods, the grain size was reduced by 36% and the fracture toughness was improved by 28% in two-step microwave sintering.

Electrodeposition and properties of Ni–B/SiC nanocomposite coatings

ABSTRACTNi–B/SiC composite coatings were electrodeposited using trimethylamine borane as a boron source. The effects of bath composition and operating parameters on the microstructure and properties of the composite coatings were investigated. The results show that Ni–B/SiC composite coating exhibits uniform structure with a desirable interface. Incorporation of SiC particles led to a significant increase in hardness. Both boron and SiC content in the coating increases initially and then decreases as the current density increased. Incorporation of inert SiC particles also enhanced their corrosion resistance, which attributed to the dense structure, barrier effect and the reduction in the active surface area of Ni–B matrix. XPS analysis indicated that the as-deposited coating contains metallic nickel, oxide or hydroxide nickel, and the SiC particles. Owing to dispersion hardening of the added SiC particles and the reduction in the active surface area of Ni–B matrix, Ni–B/SiC composite coating shows superior anti-corrosion and wear resistance.

Effect of current density on corrosion and mechanical properties of Zn-SiC composite coating

Abstract The Zn-SiC composite coating is an effective protection measure for steel structures. Incorporation of SiC particles within zinc matrix and well dispersion of these particles through coating thickness are found a practical problems. In order to get uniform and dense Zn-SiC composite coating using electrodeposition process, operating parameters should be well controlled. Current density is one of important electrodeposition parameter that effects formation of Zn-SiC composite coating and hence could influence the mechanical and corrosion properties of composite coating. The main objective of this study was to investigate the effect of current density on the deposition of Zn-SiC composite coating. The deposition of zinc with SiC particles was conducted by electrodeposition process and using zinc sulfate bath containing 20 g/L of 2 micron of SiC particles. The stirring speed of 600 rpm and current density over range of 20, 30, 40 and 50 mA/cm2 were used to obtain Zn-SiC composite coatings. Morphology and microstructure of composite coating were observed using scanning electron microscopy. Corrosion behavior of Zn-SiC composite coating was investigated by potentiodynamic polarization analysis while microhardness was studied using Vickers hardness method. The incorporation of SiC particles along zinc coating layer was confirmed using SEM and EDS study. Significant reduction in corrosion rate of Zn-SiC composite coating was observed with 3.0 x 10-1 mm/yr for Zn-SiC composite coating deposited at current density of 40 mA/cm2. An improvement in microhardnesss due to incorporation of SiC particles into zinc matrix was noted. Microhardness of 166 Hv was obtained at current density of 40 mA/cm2. An average coating thickness of Zn-SiC composite coatings were measured and found 20 microns. Microhardness and corrosion properties of Zn-SiC composite coatings were improved further due to incorporation of SiC particles into zinc matrix under the optimum value of current density of 40 mA/cm2.

Vibration Analysis of Carbon and Kevlar Fiber Reinforced Composites Containing Sic Particles

Present study explores the vibration and damping characteristics of Kevlar and carbon fiber reinforced composites with incorporation of SiC particles within the common matrix of epoxy resin. Experimental modal analysis was performed to extract natural frequency and damping property with aim of the enhancing dynamic performance of the composite system containing SiC particles. A numerical model using ABAQUS software was developed for comparison of experimental results in attempt to predict higher mode frequencies with mode shapes. Results showed that interaction of SiC particles with the carbon or Kevlar/epoxy resulted in a significant effect in terms of vibration and damping characteristics due to interface strength between SiC particles and polymer matrix those influencing elastic properties.

Effect of SiC concentration on electrochemical and mechanical behavior of Zn-SiC composite coating

Electrodeposition of zinc with SiC particles is a promising process that could effectively replace chromate process. Increasing of SiC concentration in the bath solution could increase the incorporation of SiC particles into zinc matrix and help in improvement of corrosion resistance and hardness of composite coating. However, it is difficult to obtain composite coating with uniform, dense and high SiC content. The aim of this study to investigate the effect of SiC concentration on electrochemical and mechanical behavior of Zn-SiC composite coating. Zn-SiC composite coatings were successfully deposited on mild steel plate using electrodeposition technique. Zinc sulfate bath containing 2 micron-sized of SiC particles were prepared to deposit the composite coating. The deposition was carried out under operating conditions of current density 40 mA/cm2 and 600 rpm of agitation rate. Various concentrations of SiC (0, 5, 10, 15 and 20g/l) were investigated. Electrochemical behavior of Zn-SiC coating was performed using linear polarization method. The hardness of the coating was carried out using Vickers hardness tester and the measurements were taken through cross section of the coating. Coating thickness and morphology of the coating were examined using SEM. The experimental results observed an improvement in corrosion resistance and hardness of the coating with increasing SiC content. The microhardness value of 166 (Hv) was obtained at optimum concentration of 20 g/l. The corrosion results showed that the corrosion rate of 6.05 x 10−1 mm/yr and 3.0 x 10−1 mm/yr were obtained for Zn (0 g/l of SiC) and Zn-SiC (20g/l of SiC) coatings respectively. SEM images of the surface and cross section of the coating showed an embedding of SiC into zinc coating and its particles were distributed along cross section of the coating. Finally average thickness of the coating was recorded at 19 microns.

Abrasive Wear Characteristics of Silicon Carbide Particle Reinforced Zinc Based Composite

Herein, abrasive wear characteristics of SiCp dispersed zinc-aluminum based composites have been analyzed under high-stress condition. The wear tests were conducted on a Pin-on-Disc machine at a constant linear velocity of 1.57 m/s in the applied load range of 1-7 N while the abrasive platform used is 600 grit emery paper. A matrix alloy was also characterized under identical conditions to assess the influence of the dispersoid (SiC) particle on the wear behaviour. Wear rate, frictional heating and friction coefficient are the focused parameters of the study. The base alloy used has a dendrite structure comprising of α-dendrites surrounded by an α + η eutectoid and metastable e phase in interdendritic regions. The composite shows similar features to those of the base alloy except the additional presence of the reinforcing SiC particles. The wear rate and friction coefficient decrease with increase in abrading distance while a reverse trend was observed in the case of frictional heating which gradually increases with the increase in abrading distance. Incorporation of SiC particles improves the wear resistance of the matrix alloy and increasing the percentage of SiC increases the frictional heating and reduces the friction coefficient of the test material. The wear mechanism has been understood through SEM examination of wear surface, subsurface, debris particles and degraded abrasive grit papers.

Effect of SiC particles and the particulate size on the hot deformation and processing map of AZ91 magnesium matrix composites

Isothermal hot compression at the temperature range of 573–698K and strain rates of 0.005–1.0s−1 was used to investigate the flow behavior and processing characteristics of the nano-SiCp/AZ91 composites. Effects of the incorporated particles and their particulate size on the workability of the base alloy were then compared and discussed. Results show that compared with the monolithic AZ91 alloy, the incorporated nano-SiC particles effectively increase the flow stress of the composites by blocking the strain-induced dislocations, while effect of the micro-SiC particles varies due to the competition between pinning effect and particle stimulating nucleation (PSN) mechanism. Three domains of peak energy dissipation efficiency are identified in the processing map and the corresponding microstructures examined by EBSD indicate that continuous dynamic recrystallization (DRX) occurs during the compression. The instability characteristics at low temperature are severe mechanical twinning and micro-cracks, while that at high temperature is intergranular cracking. The incorporation of SiC particles enhances the high temperature (>655K) workability of AZ91 by increasing the upper limit of the processing strain rate and enables low temperature processing by decreasing the lower limit of the temperature. However, the added particles impose a side effect by enlarging the instability domain of the base alloy to a lower strain rate and even higher temperature.