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Biofilms are an important component in the development of chronic infections, especially when it comes to medical devices. This problem presents a huge challenge to the medical community, as standard antibiotics can only destroy biofilms to a very limited extent. The prevention of biofilm formation has led to the development of various coating methods and new materials. These techniques aim to coat surfaces in a manner that prevents biofilm formation. Vitreous metal alloys, especially those containing copper and titanium metals, have become ideal antimicrobial coatings. At the same time, the use of cold spray technology has increased as it is a suitable method for processing temperature sensitive materials. Part of the goal of this research was to develop a new antibacterial film metallic glass composed of Cu-Zr-Ni ternary using mechanical alloying techniques. The spherical powder that makes up the final product is used as a raw material for cold spraying of stainless steel surfaces at low temperatures. Metal glass coated substrates were able to significantly reduce biofilm formation by at least 1 log compared to stainless steel.
Throughout human history, any society has been able to develop and promote the introduction of new materials to meet its specific requirements, resulting in increased productivity and ranking in a globalized economy1. It has always been attributed to the human ability to design materials and manufacturing equipment, as well as designs to manufacture and characterize materials to achieve health, education, industry, economics, culture and other fields from one country or region to another. Progress is measured regardless of country or region2. For 60 years, materials scientists have devoted a lot of time to one main task: the search for new and advanced materials. Recent research has focused on improving the quality and performance of existing materials, as well as synthesizing and inventing entirely new types of materials.
The addition of alloying elements, the modification of the microstructure of the material and the application of thermal, mechanical or thermomechanical treatment methods have led to a significant improvement in the mechanical, chemical and physical properties of various materials. In addition, hitherto unknown compounds have been successfully synthesized. These persistent efforts have given rise to a new family of innovative materials collectively known as Advanced Materials2. Nanocrystals, nanoparticles, nanotubes, quantum dots, zero-dimensional, amorphous metallic glasses, and high-entropy alloys are just some examples of advanced materials that have appeared in the world since the middle of the last century. In the manufacture and development of new alloys with improved properties, both in the final product and in the intermediate stages of its production, the problem of unbalance is often added. As a result of the introduction of new manufacturing techniques that allow significant deviations from equilibrium, a whole new class of metastable alloys, known as metallic glasses, has been discovered.
His work at Caltech in 1960 revolutionized the concept of metal alloys when he synthesized Au-25 at.% Si glassy alloys by rapidly solidifying liquids at nearly a million degrees per second. 4 Professor Paul Duves’ discovery not only marked the beginning of history metal glasses (MS), but also led to a paradigm shift in how people think about metal alloys. Since the very first pioneering research in the synthesis of MS alloys, almost all metallic glasses have been completely obtained using one of the following methods: (i) rapid solidification of the melt or vapor, (ii) atomic lattice disorder, (iii) solid-state amorphization reactions between pure metallic elements and (iv) solid phase transitions of metastable phases.
MGs are distinguished by the absence of long-range atomic order associated with crystals, which is a defining characteristic of crystals. In the modern world, great progress has been made in the field of metallic glass. These are new materials with interesting properties that are of interest not only for solid state physics, but also for metallurgy, surface chemistry, technology, biology, and many other areas. This new type of material has properties that are different from hard metals, making it an interesting candidate for technological applications in a variety of fields. They have some important properties: (i) high mechanical ductility and yield strength, (ii) high magnetic permeability, (iii) low coercivity, (iv) unusual corrosion resistance, (v) temperature independence. Conductivity 6.7.
Mechanical alloying (MA)1,8 is a relatively new method, first introduced in 19839 by Prof. K.K. Kok and his colleagues. They produced amorphous Ni60Nb40 powders by grinding a mixture of pure elements at ambient temperature very close to room temperature. Typically, the MA reaction is carried out between diffusion bonding of reactant powders in a reactor, usually made of stainless steel, into a ball mill. 10 (Fig. 1a, b). Since then, this mechanically induced solid state reaction method has been used to prepare new amorphous/metallic glass alloy powders using low (Fig. 1c) and high energy ball mills and rod mills11,12,13,14,15,16. In particular, this method has been used to prepare immiscible systems such as Cu-Ta17 as well as high melting point alloys such as Al-transition metal (TM, Zr, Hf, Nb and Ta)18,19 and Fe-W20 systems. , which cannot be obtained using conventional cooking methods. In addition, MA is considered one of the most powerful nanotechnological tools for industrial scale production of nanocrystalline and nanocomposite powder particles of metal oxides, carbides, nitrides, hydrides, carbon nanotubes, nanodiamonds, as well as broad stabilization using a top-down approach. 1 and metastable stages.
Schematic showing the fabrication method used to prepare the Cu50(Zr50-xNix)/SUS 304 metallic glass coating in this study. (a) Preparation of MC alloy powders with various concentrations of Ni x (x; 10, 20, 30, and 40 at.%) using the low-energy ball milling method. (a) The starting material is loaded into a tool cylinder along with tool steel balls and (b) sealed in a He atmosphere filled glove box. (c) Transparent model of the grinding vessel illustrating the movement of the ball during grinding. The final powder product obtained after 50 hours was used to cold spray coat the SUS 304 substrate (d).
When it comes to bulk material surfaces (substrates), surface engineering involves the design and modification of surfaces (substrates) to provide certain physical, chemical, and technical properties that are not present in the original bulk material. Some of the properties that can be effectively improved through surface treatment include abrasion, oxidation and corrosion resistance, coefficient of friction, bioinertness, electrical properties and thermal insulation, just to name a few. Surface quality can be improved by metallurgical, mechanical or chemical methods. As a well known process, coating is simply defined as one or more layers of material artificially applied to the surface of a bulk object (substrate) made from another material. Thus, coatings are used in part to achieve desired technical or decorative properties, as well as to protect materials from expected chemical and physical interactions with the environment23.
A variety of methods and techniques can be used to apply suitable protective layers from a few micrometers (below 10-20 micrometers) to more than 30 micrometers or even several millimeters in thickness. In general, coating processes can be divided into two categories: (i) wet coating methods, including electroplating, electroplating, and hot dip galvanizing, and (ii) dry coating methods, including soldering, hardfacing, physical vapor deposition (PVD). ), chemical vapor deposition (CVD), thermal spray techniques, and more recently cold spray techniques 24 (Figure 1d).
Biofilms are defined as microbial communities that are irreversibly attached to surfaces and surrounded by self-produced extracellular polymers (EPS). The formation of a superficially mature biofilm can lead to significant losses in many industries, including food processing, water systems, and healthcare. In humans, with the formation of biofilms, more than 80% of cases of microbial infections (including Enterobacteriaceae and Staphylococci) are difficult to treat. In addition, mature biofilms have been reported to be 1000 times more resistant to antibiotic treatment compared to planktonic bacterial cells, which is considered a major therapeutic challenge. Historically, antimicrobial surface coating materials derived from common organic compounds have been used. Although such materials often contain toxic components potentially harmful to humans,25,26 this can help avoid bacterial transmission and material degradation.
Widespread bacterial resistance to antibiotic treatment due to biofilm formation has led to the need to develop an effective antimicrobial membrane coated surface that can be applied safely27. The development of a physical or chemical anti-adhesive surface to which bacterial cells cannot bind and form biofilms due to adhesion is the first approach in this process27. The second technology is to develop coatings that deliver antimicrobial chemicals exactly where they are needed, in highly concentrated and tailored quantities. This is achieved through the development of unique coating materials such as graphene/germanium28, black diamond29 and ZnO30-doped diamond-like carbon coatings that are resistant to bacteria, a technology that maximizes the development of toxicity and resistance due to biofilm formation. In addition, coatings containing germicidal chemicals that provide long-term protection against bacterial contamination are becoming increasingly popular. While all three procedures are capable of exerting antimicrobial activity on coated surfaces, each has its own set of limitations that should be considered when developing an application strategy.
The products currently on the market are hampered by the lack of time to analyze and test protective coatings for biologically active ingredients. Companies claim that their products will provide users with the desired functional aspects, however, this has become an obstacle to the success of the products currently on the market. Compounds derived from silver are used in the vast majority of antimicrobials currently available to consumers. These products are designed to protect users from potentially harmful exposure to micro-organisms. The delayed antimicrobial effect and the associated toxicity of silver compounds increase the pressure on researchers to develop a less harmful alternative36,37. Creating a global antimicrobial coating that works inside and out remains a challenge. This comes with associated health and safety risks. Discovering an antimicrobial agent that is less harmful to humans and figuring out how to incorporate it into coating substrates with a longer shelf life is a much sought after goal38. The latest antimicrobial and antibiofilm materials are designed to kill bacteria at close range either by direct contact or after the release of the active agent. They can do this by inhibiting initial bacterial adhesion (including preventing the formation of a protein layer on the surface) or by killing bacteria by interfering with the cell wall.
Essentially, surface coating is the process of applying another layer to the surface of a component to improve the surface characteristics. The purpose of a surface coating is to change the microstructure and/or composition of the near-surface region of a component39. Surface coating methods can be divided into different methods, which are summarized in Fig. 2a. Coatings can be divided into thermal, chemical, physical and electrochemical categories depending on the method used to create the coating.
(a) An inset showing the main surface fabrication techniques, and (b) selected advantages and disadvantages of the cold spray method.
Cold spray technology has much in common with traditional thermal spray techniques. However, there are also some key fundamental properties that make the cold spray process and cold spray materials particularly unique. Cold spray technology is still in its infancy, but it has a great future. In some cases, the unique properties of cold spraying offer great benefits, overcoming the limitations of conventional thermal spraying techniques. It overcomes the significant limitations of traditional thermal spray technology, in which the powder must be melted to be deposited on a substrate. Obviously, this traditional coating process is not suitable for very temperature sensitive materials such as nanocrystals, nanoparticles, amorphous and metallic glasses40, 41, 42. In addition, thermal spray coating materials always have a high level of porosity and oxides. Cold spray technology has many significant advantages over thermal spray technology, such as (i) minimal heat input to the substrate, (ii) flexibility in choosing the substrate coating, (iii) no phase transformation and grain growth, (iv) high adhesive strength1 .39 (Fig. 2b). In addition, cold spray coating materials have high corrosion resistance, high strength and hardness, high electrical conductivity and high density41. Despite the advantages of the cold spray process, this method still has some drawbacks, as shown in Figure 2b. When coating pure ceramic powders such as Al2O3, TiO2, ZrO2, WC, etc., the cold spray method cannot be used. On the other hand, ceramic/metal composite powders can be used as raw materials for coatings. The same goes for other thermal spraying methods. Difficult surfaces and pipe interiors are still difficult to spray.
Considering that the present work is directed to the use of metallic vitreous powders as starting materials for coatings, it is clear that conventional thermal spraying cannot be used for this purpose. This is due to the fact that metallic vitreous powders crystallize at high temperatures1.
Most of the instruments used in the medical and food industries are made from austenitic stainless steel alloys (SUS316 and SUS304) with a chromium content of 12 to 20 wt.% for the production of surgical instruments. It is generally accepted that the use of chromium metal as an alloying element in steel alloys can significantly improve the corrosion resistance of standard steel alloys. Stainless steel alloys, despite their high corrosion resistance, do not have significant antimicrobial properties38,39. This contrasts with their high corrosion resistance. After that, it is possible to predict the development of infection and inflammation, which are mainly due to bacterial adhesion and colonization on the surface of stainless steel biomaterials. Significant difficulties may arise due to the significant difficulties associated with bacterial adhesion and biofilm formation pathways, which can lead to poor health, which can have many consequences that can directly or indirectly affect human health.
This study is the first phase of a project funded by the Kuwait Foundation for the Advancement of Science (KFAS), contract no. 2010-550401, to investigate the feasibility of producing metallic glassy Cu-Zr-Ni ternary powders using MA technology (table). 1) For the production of SUS304 antibacterial surface protection film/coating. The second phase of the project, due to start in January 2023, will study in detail the galvanic corrosion characteristics and the mechanical properties of the system. Detailed microbiological tests for various types of bacteria will be carried out.
This article discusses the effect of Zr alloy content on glass forming ability (GFA) based on morphological and structural characteristics. In addition, the antibacterial properties of the powder coated metal glass/SUS304 composite were also discussed. In addition, ongoing work has been carried out to investigate the possibility of structural transformation of metallic glass powders occurring during cold spraying in the supercooled liquid region of fabricated metallic glass systems. Cu50Zr30Ni20 and Cu50Zr20Ni30 metallic glass alloys were used as representative examples in this study.
This section presents the morphological changes in powders of elemental Cu, Zr and Ni during low-energy ball milling. Two different systems consisting of Cu50Zr20Ni30 and Cu50Zr40Ni10 will be used as illustrative examples. The MA process can be divided into three separate stages, as evidenced by the metallographic characterization of the powder obtained in the grinding stage (Fig. 3).
Metallographic characteristics of powders of mechanical alloys (MA) obtained after various stages of ball grinding. Field emission scanning electron microscopy (FE-SEM) images of MA and Cu50Zr40Ni10 powders obtained after low energy ball milling for 3, 12 and 50 hours are shown in (a), (c) and (e) for the Cu50Zr20Ni30 system, while on the same MA. The corresponding images of the Cu50Zr40Ni10 system taken after time are shown in (b), (d), and (f).
During ball milling, the effective kinetic energy that can be transferred to the metal powder is affected by a combination of parameters, as shown in Fig. 1a. This includes collisions between balls and powders, shear compression of powder stuck between or between grinding media, impacts from falling balls, shear and wear caused by powder drag between the moving bodies of a ball mill, and a shock wave passing through falling balls propagating through loaded culture (Fig. 1a). Элементарные порошки Cu, Zr и Ni были сильно деформированы из-за холодной сварки на ранней стадии МА (3 ч), что привело к образованию крупных частиц порошка (> 1 мм в диаметре). The elemental Cu, Zr, and Ni powders were severely deformed due to cold welding at an early stage of MA (3 h), which led to the formation of large powder particles (> 1 mm in diameter). These large composite particles are characterized by the formation of thick layers of alloying elements (Cu, Zr, Ni), as shown in fig. 3a,b. An increase in the MA time to 12 h (intermediate stage) led to an increase in the kinetic energy of the ball mill, which led to the decomposition of the composite powder into smaller powders (less than 200 μm), as shown in Fig. 3c, city . At this stage, the applied shear force leads to the formation of a new metal surface with thin Cu, Zr, Ni hint layers, as shown in Fig. 3c, d. As a result of the grinding of the layers at the interface of the flakes, solid-phase reactions occur with the formation of new phases.
At the climax of the MA process (after 50 h), flake metallography was barely noticeable (Fig. 3e, f), and mirror metallography was observed on the polished surface of the powder. This means that the MA process was completed and a single reaction phase was created. The elemental composition of the regions indicated in Figs. 3e (I, II, III), f, v, vi) were determined using field emission scanning electron microscopy (FE-SEM) in combination with energy dispersive X-ray spectroscopy (EDS). (IV).
In table. 2 elemental concentrations of alloying elements are shown as a percentage of the total mass of each region selected in fig. 3e, f. Comparing these results with the initial nominal compositions of Cu50Zr20Ni30 and Cu50Zr40Ni10 given in Table 1 shows that the compositions of these two final products are very close to the nominal compositions. In addition, the relative values ​​of the components for the regions listed in Fig. 3e,f do not suggest significant deterioration or variation in the composition of each sample from one region to another. This is evidenced by the fact that there is no change in composition from one region to another. This indicates the production of uniform alloy powders as shown in Table 2.
FE-SEM micrographs of the Cu50(Zr50-xNix) final product powder were obtained after 50 MA times, as shown in Fig. 4a-d, where x is 10, 20, 30 and 40 at.%, respectively. After this grinding step, the powder aggregates due to the van der Waals effect, which leads to the formation of large aggregates consisting of ultrafine particles with a diameter of 73 to 126 nm, as shown in Figure 4.
Morphological characteristics of Cu50(Zr50-xNix) powders obtained after 50-hour MA. For the Cu50Zr40Ni10, Cu50Zr30Ni20, Cu50Zr20Ni30, Cu50Zr10Ni40 systems, the FE-SEM images of powders obtained after 50 MA are shown in (a), (b), (c), and (d), respectively.
Before loading the powders into the cold spray feeder, they were first sonicated in analytical grade ethanol for 15 minutes and then dried at 150° C. for 2 hours. This step must be taken to successfully combat agglomeration, which often causes many serious problems in the coating process. After the completion of the MA process, further studies were carried out to investigate the homogeneity of the alloy powders. On fig. 5a–d show FE-SEM micrographs and corresponding EDS images of the Cu, Zr and Ni alloying elements of the Cu50Zr30Ni20 alloy taken after 50 h time M, respectively. It should be noted that the alloy powders obtained after this step are homogeneous, as they do not exhibit any composition fluctuations beyond the sub-nanometer level, as shown in Figure 5.
Morphology and local distribution of elements in MG Cu50Zr30Ni20 powder obtained after 50 MA by FE-SEM/Energy Dispersive X-ray Spectroscopy (EDS). (a) SEM and X-ray EDS imaging of (b) Cu-Kα, (c) Zr-Lα, and (d) Ni-Kα.
The X-ray diffraction patterns of mechanically alloyed Cu50Zr40Ni10, Cu50Zr30Ni20, Cu50Zr20Ni30, and Cu50Zr20Ni30 powders obtained after 50-hour MA are shown in Figs. 6a–d, respectively. After this grinding stage, all samples with different Zr concentrations had amorphous structures with characteristic halo diffusion patterns shown in Fig. 6.
X-ray diffraction patterns of Cu50Zr40Ni10 (a), Cu50Zr30Ni20 (b), Cu50Zr20Ni30 (c), and Cu50Zr20Ni30 (d) powders after MA for 50 h. A halo-diffusion pattern was observed in all samples without exception, indicating the formation of an amorphous phase.
High resolution field emission transmission electron microscopy (FE-HRTEM) was used to observe structural changes and understand the local structure of powders resulting from ball milling at different MA times. Images of powders obtained by the FE-HRTEM method after the early (6 h) and intermediate (18 h) stages of grinding Cu50Zr30Ni20 and Cu50Zr40Ni10 powders are shown in Figs. 7a, respectively. According to the bright-field image (BFI) of the powder obtained after 6 h of MA, the powder consists of large grains with clearly defined boundaries of the fcc-Cu, hcp-Zr, and fcc-Ni elements, and there are no signs of the formation of a reaction phase, as shown in Fig. 7a. In addition, a correlated selected area diffraction pattern (SADP) taken from the middle region (a) revealed a sharp diffraction pattern (Fig. 7b) indicating the presence of large crystallites and the absence of a reactive phase.
Local structural characteristics of the MA powder obtained after the early (6 h) and intermediate (18 h) stages. (a) High resolution field emission transmission electron microscopy (FE-HRTEM) and (b) corresponding selected area diffractogram (SADP) of Cu50Zr30Ni20 powder after MA treatment for 6 hours. The FE-HRTEM image of Cu50Zr40Ni10 obtained after 18-hour MA is shown in (c).
As shown in fig. 7c, an increase in the duration of MA to 18 h led to serious lattice defects in combination with plastic deformation. At this intermediate stage of the MA process, various defects appear in the powder, including stacking faults, lattice defects, and point defects (Fig. 7). These defects cause the fragmentation of large grains along the grain boundaries into subgrains smaller than 20 nm in size (Fig. 7c).
The local structure of the Cu50Z30Ni20 powder milled for 36 h MA is characterized by the formation of ultrafine nanograins embedded in an amorphous thin matrix, as shown in Fig. 8a. A local analysis of the EMF showed that the nanoclusters shown in Figs. 8a are associated with untreated Cu, Zr and Ni powder alloys. The content of Cu in the matrix varied from ~32 at.% (poor zone) to ~74 at.% (rich zone), which indicates the formation of heterogeneous products. In addition, the corresponding SADPs of the powders obtained after milling in this step show primary and secondary halo-diffusion amorphous phase rings overlapping with sharp points associated with these untreated alloying elements, as shown in Fig. 8b.
Nanoscale local structural features of Beyond 36 h-Cu50Zr30Ni20 powder. (a) Bright field image (BFI) and corresponding (b) SADP of Cu50Zr30Ni20 powder obtained after milling for 36 h MA.
Toward the end of the MA process (50 h), Cu50(Zr50-xNix), X, 10, 20, 30, and 40 at.% powders, without exception, have a labyrinthine morphology of the amorphous phase, as shown in Fig. . Neither point diffraction nor sharp annular patterns could be detected in the corresponding SADS of each composition. This indicates the absence of untreated crystalline metal, but rather the formation of an amorphous alloy powder. These correlated SADPs showing halo diffusion patterns were also used as evidence for the development of amorphous phases in the final product material.
Local structure of the final product of the Cu50 MS system (Zr50-xNix). FE-HRTEM and correlated nanobeam diffraction patterns (NBDP) of (a) Cu50Zr40Ni10, (b) Cu50Zr30Ni20, (c) Cu50Zr20Ni30, and (d) Cu50Zr10Ni40 obtained after 50 h of MA.
Using differential scanning calorimetry, the thermal stability of the glass transition temperature (Tg), supercooled liquid region (ΔTx) and crystallization temperature (Tx) was studied depending on the content of Ni (x) in the Cu50(Zr50-xNix) amorphous system. (DSC) properties in the He gas flow. The DSC curves of powders of Cu50Zr40Ni10, Cu50Zr30Ni20, and Cu50Zr10Ni40 amorphous alloys obtained after MA for 50 h are shown in Figs. 10a, b, e, respectively. While the DSC curve of amorphous Cu50Zr20Ni30 is shown separately in Fig. 10th century Meanwhile, a Cu50Zr30Ni20 sample heated to ~700°C in DSC is shown in Fig. 10g.
The thermal stability of Cu50(Zr50-xNix) MG powders obtained after MA for 50 hours is determined by the glass transition temperature (Tg), crystallization temperature (Tx) and supercooled liquid region (ΔTx). Thermograms of differential scanning calorimeter (DSC) powders of Cu50Zr40Ni10 (a), Cu50Zr30Ni20 (b), Cu50Zr20Ni30 (c), and (e) Cu50Zr10Ni40 MG alloy powders after MA for 50 hours. An X-ray diffraction pattern (XRD) of a Cu50Zr30Ni20 sample heated to ~700°C in DSC is shown in (d).
As shown in Figure 10, the DSC curves for all compositions with different nickel concentrations (x) indicate two different cases, one endothermic and the other exothermic. The first endothermic event corresponds to Tg, and the second is associated with Tx. The horizontal span area that exists between Tg and Tx is called the subcooled liquid area (ΔTx = Tx – Tg). The results show that the Tg and Tx of the Cu50Zr40Ni10 sample (Fig. 10a) placed at 526°C and 612°C shift the content (x) up to 20 at % towards the low temperature side of 482°C and 563°C. °C with increasing Ni content (x), respectively, as shown in Figure 10b. Consequently, ΔTx Cu50Zr40Ni10 decreases from 86°С (Fig. 10a) to 81°С for Cu50Zr30Ni20 (Fig. 10b). For the MC Cu50Zr40Ni10 alloy, a decrease in the values ​​of Tg, Tx, and ΔTx to the levels of 447°С, 526°С, and 79°С was also observed (Fig. 10b). This indicates that an increase in the Ni content leads to a decrease in the thermal stability of the MS alloy. On the contrary, the value of Tg (507 °C) of the MC Cu50Zr20Ni30 alloy is lower than that of the MC Cu50Zr40Ni10 alloy; nevertheless, its Tx shows a value comparable to it (612 °C). Therefore, ΔTx has a higher value (87°C) as shown in fig. 10th century
The Cu50(Zr50-xNix) MC system, using the Cu50Zr20Ni30 MC alloy as an example, crystallizes through a sharp exothermic peak into fcc-ZrCu5, orthorhombic-Zr7Cu10, and orthorhombic-ZrNi crystalline phases (Fig. 10c). This phase transition from amorphous to crystalline was confirmed by X-ray diffraction analysis of the MG sample (Fig. 10d) which was heated to 700 °C in DSC.
On fig. 11 shows photographs taken during the cold spray process carried out in the current work. In this study, metal glassy powder particles synthesized after MA for 50 hours (using Cu50Zr20Ni30 as an example) were used as an antibacterial raw material, and a stainless steel plate (SUS304) was cold spray coated. The cold spray method was chosen for coating in the thermal spray technology series because it is the most efficient method in the thermal spray technology series where it can be used for metallic metastable heat sensitive materials such as amorphous and nanocrystalline powders. Not subject to phase. transitions. This is the main factor in choosing this method. The cold deposition process is carried out using high-velocity particles that convert the kinetic energy of the particles into plastic deformation, deformation and heat upon impact with the substrate or previously deposited particles.
Field photographs show the cold spray procedure used for five successive preparations of MG/SUS 304 at 550°C.
The kinetic energy of the particles, as well as the momentum of each particle during the formation of the coating, must be converted into other forms of energy through such mechanisms as plastic deformation (primary particles and interparticle interactions in the matrix and interactions of particles), interstitial knots of solids, rotation between particles, deformation and limiting heating 39. In addition, if not all of the incoming kinetic energy is converted into thermal energy and deformation energy, the result will be an elastic collision, which means that the particles simply bounce off after impact. It has been noted that 90% of the impact energy applied to the particle/substrate material is converted into local heat 40 . In addition, when impact stress is applied, high plastic strain rates are achieved in the particle/substrate contact region in a very short time41,42.
Plastic deformation is usually considered as a process of energy dissipation, or rather, as a heat source in the interfacial region. However, the increase in temperature in the interfacial region is usually not sufficient for the occurrence of interfacial melting or significant stimulation of the mutual diffusion of atoms. No publication known to the authors has investigated the effect of the properties of these metallic vitreous powders on powder adhesion and settling occurring when using cold spray techniques.
The BFI of the MG Cu50Zr20Ni30 alloy powder can be seen in Fig. 12a, which was deposited on the SUS 304 substrate (Fig. 11, 12b). As can be seen from the figure, the coated powders retain their original amorphous structure as they have a delicate labyrinth structure without any crystalline features or lattice defects. On the other hand, the image indicates the presence of a foreign phase, as evidenced by the nanoparticles included in the MG-coated powder matrix (Fig. 12a). Figure 12c shows the indexed nanobeam diffraction pattern (NBDP) associated with region I (Figure 12a). As shown in fig. 12c, NBDP exhibits a weak halo-diffusion pattern of amorphous structure and coexists with sharp spots corresponding to a crystalline large cubic metastable Zr2Ni phase plus a tetragonal CuO phase. The formation of CuO can be explained by the oxidation of the powder when moving from the nozzle of the spray gun to SUS 304 in the open air in a supersonic flow. On the other hand, devitrification of metal glassy powders resulted in the formation of large cubic phases after cold spray treatment at 550°C for 30 min.
(a) FE-HRTEM image of MG powder deposited on (b) SUS 304 substrate (Figure inset). The NBDP index of the round symbol shown in (a) is shown in (c).
To test this potential mechanism for the formation of large cubic Zr2Ni nanoparticles, an independent experiment was carried out. In this experiment, powders were sprayed from an atomizer at 550°C in the direction of the SUS 304 substrate; however, to determine the annealing effect, the powders were removed from the SUS304 strip as quickly as possible (about 60 s). ). Another series of experiments was carried out in which the powder was removed from the substrate approximately 180 seconds after application.
Figures 13a,b show Scanning Transmission Electron Microscopy (STEM) dark field (DFI) images of two sputtered materials deposited on SUS 304 substrates for 60 s and 180 s, respectively. The powder image deposited for 60 seconds lacks morphological details, showing featurelessness (Fig. 13a). This was also confirmed by XRD, which showed that the overall structure of these powders was amorphous, as indicated by the broad primary and secondary diffraction peaks shown in Figure 14a. This indicates the absence of metastable/mesophase precipitates, in which the powder retains its original amorphous structure. In contrast, the powder deposited at the same temperature (550°C) but left on the substrate for 180 s showed the deposition of nanosized grains, as shown by the arrows in Fig. 13b.