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SEM micrographs of two defect types in the CrN hard coating deposited on Al-alloy substrate: (a – c) protruding grain, (d – f) hole. Consecutive slices are presented for both defect types.
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Hard coatings CrN, TiAlN and multilayer CrN/TiAlN were prepared on different substrates (HSS, D2 tool steels, Al-alloy) by thermoionic arc ion plating and by sputtering. The defects incorporated into the coating were studied by four techniques: top view conventional and field-emission SEM, cross-section SEM, AFM and stylus profilometry. As a specif...
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... removing of precise sections of material close to the defect by ion milling and after polishing the specimen was tilted and cross-section face was imaged by electrons. The consecutive serial sectioning of thin slices and imaging of cross- section gives us the insight into the defect internal structure (Figs. 2 and 3). EDX analysis was used to determine the composition of inclusions. ...
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... applicability of this new technique was tested on several samples. Fig. 2 presents two types of defects in the CrN coating deposited on Al-based substrate (a thin nickel interlayer was also deposited in order to improve the corrosion resistance of substrate). The first defect (Fig. 2a) has the form of a cone, while the second one (Fig. 2d) resembles a pinhole. The question was weather these defects extend ...
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... applicability of this new technique was tested on several samples. Fig. 2 presents two types of defects in the CrN coating deposited on Al-based substrate (a thin nickel interlayer was also deposited in order to improve the corrosion resistance of substrate). The first defect (Fig. 2a) has the form of a cone, while the second one (Fig. 2d) resembles a pinhole. The question was weather these defects extend through the whole coating or not, and what is the origin for their nucleation. After consecutive serial sectioning we found that the first defect started to grow in the middle of the coating due to the incorporation ...
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... applicability of this new technique was tested on several samples. Fig. 2 presents two types of defects in the CrN coating deposited on Al-based substrate (a thin nickel interlayer was also deposited in order to improve the corrosion resistance of substrate). The first defect (Fig. 2a) has the form of a cone, while the second one (Fig. 2d) resembles a pinhole. The question was weather these defects extend through the whole coating or not, and what is the origin for their nucleation. After consecutive serial sectioning we found that the first defect started to grow in the middle of the coating due to the incorporation of a foreign particle. Fig. 2c shows that the region ...
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... of a cone, while the second one (Fig. 2d) resembles a pinhole. The question was weather these defects extend through the whole coating or not, and what is the origin for their nucleation. After consecutive serial sectioning we found that the first defect started to grow in the middle of the coating due to the incorporation of a foreign particle. Fig. 2c shows that the region under the cone is not completely filled with material. The second defect is extending through the whole coating and originates in a small hole in the substrate (Fig. 2f). It is well known that PVD processes have a poor ability to cover a small hole due to shadowing effect. Fig. 2d-f clearly shows that a small ...
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... consecutive serial sectioning we found that the first defect started to grow in the middle of the coating due to the incorporation of a foreign particle. Fig. 2c shows that the region under the cone is not completely filled with material. The second defect is extending through the whole coating and originates in a small hole in the substrate (Fig. 2f). It is well known that PVD processes have a poor ability to cover a small hole due to shadowing effect. Fig. 2d-f clearly shows that a small crater on the substrate surface cannot be covered completely and that a pinhole extending through the whole coating was formed. We found that corrosion takes place on such defects, while solution ...
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... to the incorporation of a foreign particle. Fig. 2c shows that the region under the cone is not completely filled with material. The second defect is extending through the whole coating and originates in a small hole in the substrate (Fig. 2f). It is well known that PVD processes have a poor ability to cover a small hole due to shadowing effect. Fig. 2d-f clearly shows that a small crater on the substrate surface cannot be covered completely and that a pinhole extending through the whole coating was formed. We found that corrosion takes place on such defects, while solution can reach the base material ...
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... defect. The BAI 730 M (Balzers) deposition system with thermoionic arc was used for deposition of CrN, while the magnetron sputtering system CC800 (CemeCon) was used for deposition of TiAlN and CrN/TiAlN multilayer hard coatings. Three types of substrates were used: a powder metallurgical high speed steel (ASP30); a cold work tool steel (D2) and an aluminium alloy (7075). The substrates were polished, ultrasonically cleaned and dried in hot air. Prior to coating deposition they were cleaned by ion etching. In BAI 730 deposition system DC bias voltage − 200 V was used, while the etching time was 15 min. In CC800 deposition system the RF bias with maximum power 2 kW was used, while the etching time was 85 min. During deposition the bias voltage and the substrate temperature were − 125 V and 450 °C, valid for both apparatus. Focused ion beam (FIB) workstation [9] was used to prepare cross-section through the defects. We used FIB integrated in FEI QUANTA 200 3D microscope. Ion beam was used to remove precise sections of material (close to the defect) from the specimen surface by sputtering. The initial trough (with dimension of app. 8 × 5 × 4 μ m) was milled at a high beam current (20 nA), while the energy of ions was 30 keV. Then the cross-sectional was polished with a lower beam current (3 nA). After polishing the specimen was tilted and cross-section face was imaged by electrons. Then the specimen was put back in initial position and the next slice of coating material with the thickness of about 0.5 μ m was removed by ion milling. The picture of the new cross-section was taken again by electrons. This procedure was repeated until the selected volume of the defect was removed. A field-emission scanning electron microscope (SIRION 400 NC, FEI) was used for study of the coating microstructure and defect morphology in planar surface view and cross-sectional fracture view. The surface morphology of the substrates was also examined by atomic force microscope (Solver PRO) and 3D stylus profilometer (Taylor Hobson Talysurf). The vertical resolution of our 3D-profilometer was a few nm, while the lateral resolution was limited to 1 μ m. Conventional and field-emission SEM are the most common techniques for the study of defect morphology. Fig. 1a shows SEM image of typical defects embedded in the TiAlN coating deposited on D2 tool steel. We can see that they are of various shapes and sizes. However, the applicability of SEM microsope is limited due to relatively low depth resolution. In order to obtain the 3D-image of defects we performed AFM analysis (Fig. 1c). In spite of very good depth and lateral resolution the use of AFM microscope (Fig. 1c) is limited due to the small scan area (of about 50 × 50 μ m). In contrast to a planar view SEM micrograph, which shows a lot of defects of various sizes, on AFM image only micrometer-sized defects are visible. Therefore it is not appro- priate for the study of larger defects in hard coatings, because its density is rather low. On the other hand the 3D stylus profilometry was performed over a scan area of over 10 × 10 mm and more (Fig. 1d). Thus we obtained a 3D-image of the coating surface on large scanning area with all the micrometer-sized details. From 3D-image we estimated the surface density and height distribution of the defects. At TiAlN coatings deposited on three types of substrates we counted the following average number of peaks per mm 2 : 200 peaks higher than 0.5 μ m, 70 peaks higher than 1 μ m, and 20 peaks higher than 2 μ m. The number of craters is much smaller. Appoximately 25 of them are deeper than 0.5 μ m, 10 craters are deeper than 1 μ m, while only 5 of them are deeper than 2 μ m. The height and depth distributions of defects are independent on substrate type, while the average diameter is larger for D2 tool steel than for ASP30. Further information about structure of defects was obtained from SEM cross-sectional fracture view (Fig. 1b). From the contour of the CrN/TiAlN multilayer structure deposited on D2 tool steel it is evident where individual foreign particles (with typical dimension of few tens of nm) are built in the coating. However, it is a mere coincidence to prepare the fracture which would propagate through the selected defects. We have to be aware that all these techniques (except cross- section SEM) do not allow to examine the internal structure of the defects. The detailed study of defect microstructure and composition was done by SEM in combination with a focused ion beam milling. After removing of precise sections of material close to the defect by ion milling and after polishing the specimen was tilted and cross-section face was imaged by electrons. The consecutive serial sectioning of thin slices and imaging of cross- section gives us the insight into the defect internal structure (Figs. 2 and 3). EDX analysis was used to determine the composition of inclusions. The applicability of this new technique was tested on several samples. Fig. 2 presents two types of defects in the CrN coating deposited on Al-based substrate (a thin nickel interlayer was also deposited in order to improve the corrosion resistance of substrate). The first defect (Fig. 2a) has the form of a cone, while the second one (Fig. 2d) resembles a pinhole. The question was weather these defects extend through the whole coating or not, and what is the origin for their nucleation. After consecutive serial sectioning we found that the first defect started to grow in the middle of the coating due to the incorporation of a foreign particle. Fig. 2c shows that the region under the cone is not completely filled with material. The second defect is extending through the whole coating and originates in a small hole in the substrate (Fig. 2f). It is well known that PVD processes have a poor ability to cover a small hole due to shadowing effect. Fig. 2d – f clearly shows that a small crater on the substrate surface cannot be covered completely and that a pinhole extending through the whole coating was formed. We found that corrosion takes place on such defects, while solution can reach the base material [10]. The defect in TiAlN hard coating deposited on sintered high speed steel (ASP30) substrate has also the form of a cone (Fig. 3). The defect extended through the whole coating. Individual foreign particles are visible at the interface with the substrate. Such obstacles cause geometrical shadowing during deposition result- ing a cone. After ion milling an EDX compositional analysis was performed. The particle was proved to be iron based, which probably means that it originates from the vacuum chamber. In order to obtain the complete information about defect size and distribution it is recommended to combine different analytical techniques. In this paper four different techniques were used to study micro- and macrodefects on PVD hard coatings. The emphasis was on SEM in combination with focused ion beam milling. We demonstrated that this technique can give us the useful information about internal structure of the defects. By consecutive serial sectioning of thin slices and imaging of cross- section we found that defects in the form of cones are either the result of the presence of foreign particles at the substrate surface, or a consequence of incroporation of small particles which flake from the vacuum chamber components during deposition. Therefore we can conclude that a careful cleaning of the substrates as well as frequent cleaning of vacuum chamber and fixture components helps to reduce the defect density. This work was supported by the Slovenian Research Agency (project ...
Citations
... Via gas-assisted focused ion beam milling, redeposition effects could be reduced and the relatively low sputter yield of around 0.1 µm³/nC could be further increased [22]. Investigations about the FIB structuring of inorganic nonmetallic materials, such as TiN or CrN, are to the authors' knowledge currently limited to cross-section milling for coating inspection [23,24] or investigations of material properties [25]. ...
Hard coatings can be applied onto microstructured molds to influence wear, form filling and demolding behaviors in microinjection molding. As an alternative to this conventional manufacturing procedure, “direct processing” of physical-vapor-deposited (PVD) hard coatings was investigated in this study, by fabricating submicron features directly into the coatings for a subsequent replication via molding. Different diamondlike carbon (DLC) and chromium nitride (CrN) PVD coatings were investigated regarding their suitability for focused ion beam (FIB) milling and microinjection molding using microscope imaging and areal roughness measurements. Each coating type was deposited onto high-gloss polished mold inserts. A specific test pattern containing different submicron features was then FIB-milled into the coatings using varied FIB parameters. The milling results were found to be influenced by the coating morphology and grain microstructure. Using injection–compression molding, the submicron structures were molded onto polycarbonate (PC) and cyclic olefin polymer (COP). The molding results revealed contrasting molding performances for the studied coatings and polymers. For CrN and PC, a sufficient replication fidelity based on AFM measurements was achieved. In contrast, only an insufficient molding result could be obtained for the DLC. No abrasive wear or coating delamination could be found after molding.
... Studies of the effect of coating deposition conditions on defect surface density were carried out [45]. The effect of embedded microdroplets on the structure of coating nanolayers was considered [45][46][47][48]. It was found that the density of coating defects depends on the position of the sample in the chamber, the deposition time, and the material being deposited [47]. ...
The paper deals with the features of the structure and phase composition typical for the microdroplets of various elemental composition, including Ti, Zr, Cr, and AlN, and the effect of microdroplets on the structure of nanolayer coatings of TiN-(Ti,Al)N, TiN-(Ti,Mo,Al)N, ZrN-(Zr,Mo,Al)N, and CrN-(Cr,Mo,Al)N. The studies were carried out using the methods of transmission electron microscopy, X-ray spectroscopy and scanning transmission electron microscopy. The experiments revealed the specific features of the deformation of the nanolayer structure of the coating under the impact of microdroplets hitting the coating surface. The study also determined the phases formed in the microdroplets of various compositions. The diffusion processes have been investigated, during which the metals, contained in the coating (in particular, molybdenum (Mo)), dissolve in the surface layers of the core of the main microdroplet element. According to the study, microdroplets can be formed both by pure metals and by their nitrides. The paper considers the possibility of a positive effect of a microdroplet on the cutting process due to the formation of an intermediate layer of a solid lubricant between the coating and the material being machined.
... This type of defect is generally caused by the disintegration of the remaining absorbed particles on the surface of the substrate after the deposition or particles that were generated during the deposition. It is also evident in multi-layered coatings [35,36]. Our previous studies demonstrated that the tribocorrosion performance of a GLC coating at atmospheric pressure is significantly enhanced after using ideal metal buffer layers (Cr doping) for an optimum modulation period [37]. ...
A cleaning intervention is introduced to control the growth defect of Cr/GLC multi-layered coating to avoid premature failure in the deep-sea environment. The results demonstrated that the introduction of the cleaning intervention significantly decreased the penetrating defect density as expected, together without deteriorating the superior mechanical and tribocorrosion properties. The localized corrosion resistance was improved dramatically in the simulated deep-sea environment. It was illustrated that controllable defect engineering can be an effective strategy for improving the anti-tribocorrosion performance of GLC coatings for harsh deep-sea applications.
... One of the microstructural features of vacuum nitride coatings is that microparticles vary in size from 0.5 μm to several micrometers (according to other sources-a microdroplet phase) [42][43][44]. Particularly, microparticles are typical for the applied deposition method that is cathodic arc evaporation. Microparticles (or microdroplet phase) are important for tribological coatings, where they participate in the formation of "a modified tribolayer". ...
... The structural, mechanical and tribological properties of the above coatings have been also studied by our group; for AlCrN, see [58][59][60], and for CrON, see [30,[60][61][62]. It was determined that the microparticles affect the coatings' properties [42][43][44]. The connection between the topography and mechanical properties of the surfaces of AlCrN and CrON coatings and their composition was essentially not studied. ...
Alteration of the phase composition of a coating and/or its surface topography can be achieved by changing the deposition technology and/or introducing additional elements into the coating. Investigation of the effect of the composition of CrN-based coatings (including AlCrN and CrON) on the microparticle height and volume, as well as the construction of correlations between the friction coefficient at the microscale and the geometry of microparticles, are the goals of this study. We use atomic force microscopy (AFM), which is the most effective method of investigation with nanometer resolution. By revealing the morphology, AFM allows one to determine the diameter of the particles, their heights and volumes and to identify different phases in the studied area by contrasted properties. The evaluation of the distribution of mechanical properties (modulus of elasticity E and microhardness H) on the surfaces of multiphase coatings with microparticles is carried out by using the nanoindentation method. It is found that the roughness decreases with an increase in the Al concentration in AlCrN. For the CrON coatings, the opposite effect is observed. Similar conclusions are valid for the size of the microparticles and their height for both types of coating.
... Focused Ion Beam (FIB) is nowadays an established technique for studying depth profile of near-surface material, subsurface analytics, and preparation of TEM lamellae. It turns out to be extremely useful for studying single growth defects [34,35]. Figure 5 shows the general concept of operation. ...
... Fig. 5b) (taken from[35], p. 2304,Fig. 2a), b progressive etching has reached the growth defect, c after consecutive etching a full growth defect cross-section is obtained (cf.Fig. ...
... 2a), b progressive etching has reached the growth defect, c after consecutive etching a full growth defect cross-section is obtained (cf.Fig. 5c) (taken from[35], p. 2304,Fig. 2b), d last remains of the growth defect; CrN coating on Al alloy substrate with a Ni interlayer ...
Growth defects are imperfections in coating microstructure at the size level in the order of 0.1–1 µm. Though they are encountered in most techniques of thin film deposition, this paper is generally limited to hard protective coatings deposited by physical vapor deposition. Most results have been obtained by magnetron sputtering. The starting point of a growth defect is a seed, which may have a geometrical origin; it may be an inclusion or a foreign particle. Methods to analyze individual growth defects are presented, with an emphasis on focused ion beam. Using this technique, types of defects are discussed based on seed type, their evolution, and consequences, particularly in terms of corrosion resistance. Experiments involving a single growth defect are presented too. A different approach is a statistical analysis on growth defect density, predominately limited to nodular defects. Stylus profilometry is proposed as the principle technique; however, poor reproducibility should be taken into account and thus interpretation taken accordingly.
... This technique allowed precise cross-section of an individual growth defect to examine its internal structure and to identify the seed for its formation. In recent years, this technique has been widely employed for studying the growth defects [18][19][20][21][22]. ...
... However, we will mainly focus on the growth defects in PVD hard coatings for protection of tools and other manufacturing components, although we will also touch upon other areas of growth defect studies, particularly in optics and microelectronics. Thermionic arc ion plating deposition system BAI 730M (Oerlikon Balzers, Balzers, Liechtenstein) [22] was used for deposition of TiN and CrN single layer and TiN/CrN double layer hard coatings. Part of the samples was coated in the cathodic arc ion plating deposition system AIPocket (Kobelco, Kobe, Japan), which is equipped with superfine cathode sources. ...
The paper summarizes current knowledge of growth defects in physical vapor deposition (PVD) coatings. A detailed historical overview is followed by a description of the types and evolution of growth defects. Growth defects are microscopic imperfections in the coating microstructure. They are most commonly formed by overgrowing of the topographical imperfections (pits, asperities) on the substrate surface or the foreign particles of different origins (dust, debris, flakes). Such foreign particles are not only those that remain on the substrate surface after wet cleaning procedure, but also the ones that are generated during ion etching and deposition processes. Although the origin of seed particles from external pretreatment of substrate is similar to all PVD coatings, the influence of ion etching and deposition techniques is rather different. Therefore, special emphasis is given on the description of the processes that take place during ion etching of substrates and the deposition of coating. The effect of growth defects on the functional properties of PVD coatings is described in the last section. How defects affect the quality of optical coatings, thin layers for semiconductor devices, as well as wear, corrosion, and oxidation resistant coatings is explained. The effect of growth defects on the permeation and wettability of the coatings is also shortly described.
... While the mechanism of pitting corrosion of coatings is quite well described [4,7,9], we know only a little about the formation of microstructure imperfections and their influence on the corrosion resistance of hard coatings. Previously, we tried to explain the origin of the growth defects in PVD hard coatings [28,29]. In this paper, we focused on the identification of those growth defects in sputter-deposited TiAlN hard coatings, where the pitting corrosion occurs after it has been exposed to the corrosive medium. ...
... During polishing of tool steel substrates, shallow protrusions are formed at the inclusions which are harder than the ferrous matrix (e.g., carbides and oxides), while shallow craters are formed at the inclusions which are softer (e.g., MnS) [29]. The reason is the difference in the removal rates of different inclusions in comparison to the ferrous matrix. ...
In this work, the causes of porosity of TiAlN hard coatings sputter deposited on D2 tool steel were studied since its corrosion resistance is mainly affected by imperfections within the coating (e.g., pinholes, pores, crevices). The corrosion test was performed in a chlorine solution using electrochemical impedance spectroscopy. The coating morphology of growth defects before and after the exposure was studied by scanning electron microscopy (SEM), while focused ion beam (FIB) was used to make series of cross-sections through individual selected defects. We confirm that pitting corrosion is closely related to the through-thickness growth defects. It was also found that in the case of nodular defects, the intensity of corrosion depends on the shape of the seed.
... This kind of defects are widely known and it is mainly due to a droplets removal or others particles deposited on the substrate surface. [20]. Figure 3 show Additionally, It is important to consider that the values found have been higher to reported by Tan [12], who obtained a hardness between 7 GPa to 15 Gpa with CrN coatings deposited with a graded bias voltage (from -20 V to -200 V with intervals of 5V, 10V, and 60V). ...
The effect of graded or constant bias voltages (-40 V, -80 V and -40/60/80 V) on size grain and surface defects of arc PVD deposited CrN films was investigated. Corrosion resistance evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic curves (Tafel) and the mechanical behavior evaluated by means of instrumented nanoindentation and scratch testing was correlated with the microstructural changes. It was found that the bias voltage variation affects corrosion behavior due to the presence of defects (i.e. open voids, droplets) which also affects the failure mechanisms and increasing spallation. High bias voltage (-80 V) increases nano-hardness and the elastic modulus due to the dense microstructure of the CrN coating.
... However, modern development in the PVD machine has significantly enabled the reduction in the droplets population and size. As also shown in the authors earlier study [14], the droplets of the coating are mostly less than 1 m, which is very small as compared to up to 40 m droplet size, which is considered typical [27,28]. The roughness parameters of the coating as obtained from optical profilometer are presented in Table 3. ...
In this study, the mechanical and tribological properties of cathodic arc physical vapor deposited AlCrN coating on spark plasma sintered W–25%Re–HfC composite tool material were investigated. AlCrN coated and uncoated W–25%Re–HfC samples were tested using pin-on-disk wear test configuration to evaluate the coating performance. Scratch test result shows that the adhesion strength of the coating is about 25 N, which indicates that the coating exhibited good adhesion to the composite material. Specific wear rate of the coated sample is 10 times lower than that of the uncoated sample under identical conditions. The high wear rate of the uncoated W–25%Re–HfC sample is due to extensive abrasive wear. However, the coated sample is dominated by oxidation wear mechanism leading to the formation of dense Al2O3 and Cr2O3 oxides with good wear resistance properties. The improved wear resistance of the coating is attributable to the combined excellent mechanical properties, high adhesion to the substrate, low coefficient of friction and the formation of protective oxides. This study demonstrates by way of tribological analysis the feasibility of improving the life and performance of expensive FSW tools by the application of cathodic arc AlCrN PVD coating.
... Typical cathodic arc PVD coating morphology is obvious from the micrograph with characteristic micrometer sized droplets (microparticles), shallow micrometer sized craters (pits) and macroparticles as classified by Harlin et al. [38]. Generally, these defects are between 1-40 μm in diameter [39]. However, the majority of the surface defects in these coatings are less than 1 μm in diameter which indicate considerable reduction in the size of these particles. ...
... These defects are often caused by molten metal droplets from low melting point elements in the target which solidifies en route to the substrate via stationary and quasi-stationary processes or explosive emission [40,41]. They are generally unwanted as they affect the surface roughness and morphology of the coating and can result in high friction, sticking to workpiece, localized coating failure and pitting corrosion [25,39,42]. The cross-sectional SEM images of the coatings are presented in Fig. 3(a-b). ...
Tool wear during friction stir welding (FSW) of hard particulate reinforced aluminum metal matrix composites (Al MMCs) are more prominent due to the tool interaction with the particulates at high strain rate. Considering the excellent mechanical and wear resistance properties of cathodic arc PVD coatings, they are expected to abate the wear of tools during FSW of Al MMCs. Hence, it is the aim of this study to investigate the contribution of cathodic arc PVD deposited AlCrN and TiAlN coatings in alleviating tool wear during FSW of Al MMCs. AlCrN and TiAlN coated H13 FSW tools were used to butt weld 8 mm thick aluminum alloy 2124 reinforced with 17 vol% SiC of 3 μm particle size. Interestingly, the coated tools exhibited significant improvement in wear resistance of about 92 and 80%, respectively, over the bare H13 tool. Over 97% reduction in the wear of the FSW tool was recorded during the plunging stage with the use of the coated tools. Additionally, AlCrN and TiAlN coated tools considerably improved the surface finish of the welded Al MMC. The coated tools demonstrated superior wear resistance due to the improved scratch crack resistance, high mechanical and oxidation resistance properties of the coatings. Dominant wear mechanisms on AlCrN and TiAlN coated tools were abrasive erosion and chipping off by sharp and hard SiC particles while severe striation and oxidation characterized the wear mechanism of the bare tool. The use of these coatings did not deteriorate the weld properties, rather some improvement in the hardness of the nugget zone was observed due to the characteristic dynamic stirring and refinement of the Al matrix and SiC particles
