Abstract

Ternary alloys of cobalt with molybdenum and tungsten deposited from biligand citrate-pyrophosphate electrolyte by pulsed mode exhibit different compositions and surface morphologies depending on current density and on/off time. The structure of binary and ternary alloys was found to be amorphous crystalline, and intermetallic phases Co7W6 and Co7Mo3 were identified in deposits. The coherent-scattering region size of the amorphous part was detected of 2–8 nm. The amorphous structure of ternary alloys and significant content of alloying elements (Mo and W) predetermine improved high corrosion resistance. Corrosion resistance of binary and ternary deposits increases with total content of refractory metals, which associated with molybdenum and tungsten, enhancing corrosion resistance to pitting as well as decreasing in roughness and smoothing out the relief of ternary coatings. Ternary galvanic alloys of cobalt with molybdenum and zirconium with micro-globular morphology with low level of stress and cracks are formed at a current density of 4–6 A dm<sup>2</sup> and polarization on/off time 2/10 ms. High corrosion resistance of ternary coatings based on cobalt is caused by the increased tendency to passivity and high resistance to pitting corrosion in the presence of molybdenum and zirconium, as well as the acid nature of their oxides.

Keywords: coating, electrodeposition, composition, physicomechanical properties

## 1. Introduction

The range of functional coatings with alloys, the creation of which to a large extent predetermined the progress of modern technologies, can be fully attributed to the advances of electrochemical science. Quite obvious consumer advantages of coatings with alloys, in comparison with monometallic analogues, led to prospects for their widespread use, despite a number of technical difficulties encountered. The twenty-first century brought new challenges—amorphous alloys, nanoscale, nanocrystalline, and nanolaminate structures, film materials with gigantic magnetic resistance or high-temperature superconductivity, multiferroics, etc., became the order of the times, the formation of which on the basis of trivial bimetallic compositions proved impossible. This led to the creation of a new paradigm in practical electroplating—the only alternative to the transition to multicomponent and synergistic alloys and composites. The implementation of it put a number of pressing problems in the design of such polymetallic systems.

The essence of the problem lies in the absence of clear design algorithms for multicomponent alloys with a given level of properties and the presence of a significant number of empirical views, the use of which allowed electrochemical gurus to bypass the obstacles of Mother Nature in creating electroplated coatings with alloys. New tasks required new approaches, but before proceeding to their consideration, let us analyze the essence of the problem in the formulation "Galvanic alloys—the philosophy of synergism".

family—molybdenum or tungsten," as well as the formation of amorphous structures, creates the prerequisites for a super-additive increase in the microhardness of

Composition Electrolytic Coatings with Given Functional Properties

DOI: http://dx.doi.org/10.5772/intechopen.84519

Among the methods for solving complex technical problems, we will highlight both a deep understanding of the problem by creating a formalized description based on a systematic approach, followed by analysis and synthesis of complex systems, and a black box principle that does not involve a combination of the above actions, but is no less effective when using artificial intelligence tools, for example, artificial neural networks [9]. It is clear that the most significant results can be achieved with the integrated use of both approaches. In the first case, the electrochemical system (ECS), as a complex object in which the phenomena of substance transfer and electrical and thermal energy are realized, is characterized by a set of input and output variables, a set of parameters of electrode reactions and related

Since all components of the system are in constant development, they should be

considered as processes, extending this procedure to subsystems. Therefore, to describe ECS in the field of external disturbances, it is necessary to identify the elements and links that make up the system and to establish the interaction between them, thus linking the functions and structures [10]. The set of processes in ECS can be represented as the implementation of transformations in the intersection of the subsets: ionic medium (electrolyte), electrode (electrode material), external disturbances (individual factors, as well as their joint or complex effect), as we have previously shown in the framework of corrosion protection analysis [11].

Among the most significant external influences, it is necessary to attribute, mainly, the different nature of the field (vector quantities), among which are:

• an electric field (polarization), including nonstationary modes of electrolysis

• a magnetic field (factor in electrochemical processes is nonexhaustible, but the

Monometallic coatings HV Intermetallic compounds and alloys HV Cr (lustrous) [4] 7.5–11.0 CoW [6] 8.3 Cr (milk) [4] 4.5–6.0 Co3W [6] 5.1 Cr (from tetrachromat bath) [4] 3.5–4.0 Co▬W [5] 3–6.8 Co [5] 1.6 Fe▬W [7] 13 Fe [5] 4.5–7 Ni▬W [5] 2–14 W (from melt) [6] 3.7 Fe▬W▬P [8] ≥11

• a temperature field, which allows control not only the temperature of the reaction volume but also the aggregation state of individual elements (solutions-melts-gas phase), while the rate of change ΔТ/Δt allows you to control the transformation routes (for example, supersaturation of solutions, the formation of 2- and 3-dimensional nuclei, the formation of amorphous

with varying amplitude and temporal characteristics;

• a pressure (creation of excessive pressure or vacuum);

Microhardness (GPa) by Vickers galvanic coatings of metals and metal alloys.

the coatings.

physic-chemical transformations.

structures, etc.);

Table 1.

95

studied is completely insufficient),

## 1.1 Alloys

The physical encyclopedia gives the classical definition of an alloy as "a metallic, macroscopically homogeneous system consisting of two or more metals (less commonly metals and nonmetals) with characteristic metallic properties." The etymology associates the material with the method of its preparation—the combination of individual components during melting followed by crystallization of the melt, although dozens of other methods are currently known. In addition, the definition of "macroscopically homogeneous" raises the question of whether heterogeneous structures (mechanical mixtures) belong to the alloy community. Apparently, it is more correct to speak of metal alloys as homogeneous or heterogeneous systems, as well as intermetallic compounds, although it is quite obvious that real alloys often contain all three types of these structures. Regarding the "metallic properties," we note that a wide class of compounds—"synthetic metals" [1, 2]—has all the above features (hardness, electrical and thermal conductivity, opacity, gloss, etc.), but does not contain metals at all, if you do not take attention cations.

#### 1.2 Galvanic alloys

In this formulation, the nature of the material and the method of its production are inextricably linked, but with all the apparent uniqueness, and there is a number of significant differences not only in the structure and properties of metallurgical and galvanic alloys but also in the concentration ratios of the components in the material. During electrolytic deposition, alloys can be formed that differ essentially in their phase composition and properties from those obtained by thermal means. This expands the range of technical capabilities of electrolytic alloys and their field of application.

#### 1.3 Synergism

The term "synergetic" means joint or corporate action, and the synergistic effect is an increase in the efficiency of activity as a result of integration, the merging of separate parts into a single system. The question is to what extent the terminology of synergetic, or rather, actually synergism, is applicable to such objects as electrolytic alloys? From the definition of the object of research of synergetic "processes in complex open non-equilibrium systems …" [3], it follows that the combination of these system-forming features is fully applicable to process in electrochemical systems, which include alloy formation. Indeed, such an electrochemical system is complex, open, and nonequilibrium under the conditions of application external polarization.

For example, the advantage of coatings with alloys in comparison with individual metals, as well as the realization of synergism during the electrolytic alloy formation, manifests themselves in a change in the microhardness of materials depending on their composition and structure (Table 1). It is obvious that the formation of intermetallic compounds in the systems "metal of the iron

The essence of the problem lies in the absence of clear design algorithms for multicomponent alloys with a given level of properties and the presence of a significant number of empirical views, the use of which allowed electrochemical gurus to bypass the obstacles of Mother Nature in creating electroplated coatings with alloys. New tasks required new approaches, but before proceeding to their consideration, let us analyze the essence of the problem in the formulation "Galvanic

The physical encyclopedia gives the classical definition of an alloy as "a metallic, macroscopically homogeneous system consisting of two or more metals (less commonly metals and nonmetals) with characteristic metallic properties." The etymology associates the material with the method of its preparation—the combination of individual components during melting followed by crystallization of the melt, although dozens of other methods are currently known. In addition, the definition of "macroscopically homogeneous" raises the question of whether heterogeneous structures (mechanical mixtures) belong to the alloy community. Apparently, it is more correct to speak of metal alloys as homogeneous or heterogeneous systems, as well as intermetallic compounds, although it is quite obvious that real alloys often contain all three types of these structures. Regarding the "metallic properties," we note that a wide class of compounds—"synthetic metals" [1, 2]—has all the above features (hardness, electrical and thermal conductivity, opacity, gloss, etc.), but

In this formulation, the nature of the material and the method of its production are inextricably linked, but with all the apparent uniqueness, and there is a number of significant differences not only in the structure and properties of metallurgical and galvanic alloys but also in the concentration ratios of the components in the material. During electrolytic deposition, alloys can be formed that differ essentially in their phase composition and properties from those obtained by thermal means. This expands the range of technical capabilities of electrolytic alloys and their field

The term "synergetic" means joint or corporate action, and the synergistic effect is an increase in the efficiency of activity as a result of integration, the merging of separate parts into a single system. The question is to what extent the terminology of synergetic, or rather, actually synergism, is applicable to such objects as electrolytic alloys? From the definition of the object of research of synergetic "processes in complex open non-equilibrium systems …" [3], it follows that the combination of these system-forming features is fully applicable to process in electrochemical systems, which include alloy formation. Indeed, such an electrochemical system is complex, open, and nonequilibrium under the conditions of application external

For example, the advantage of coatings with alloys in comparison with individual metals, as well as the realization of synergism during the electrolytic alloy formation, manifests themselves in a change in the microhardness of materials

depending on their composition and structure (Table 1). It is obvious that the formation of intermetallic compounds in the systems "metal of the iron

does not contain metals at all, if you do not take attention cations.

alloys—the philosophy of synergism".

1.1 Alloys

Applied Surface Science

1.2 Galvanic alloys

of application.

1.3 Synergism

polarization.

94

family—molybdenum or tungsten," as well as the formation of amorphous structures, creates the prerequisites for a super-additive increase in the microhardness of the coatings.

Among the methods for solving complex technical problems, we will highlight both a deep understanding of the problem by creating a formalized description based on a systematic approach, followed by analysis and synthesis of complex systems, and a black box principle that does not involve a combination of the above actions, but is no less effective when using artificial intelligence tools, for example, artificial neural networks [9]. It is clear that the most significant results can be achieved with the integrated use of both approaches. In the first case, the electrochemical system (ECS), as a complex object in which the phenomena of substance transfer and electrical and thermal energy are realized, is characterized by a set of input and output variables, a set of parameters of electrode reactions and related physic-chemical transformations.

Since all components of the system are in constant development, they should be considered as processes, extending this procedure to subsystems. Therefore, to describe ECS in the field of external disturbances, it is necessary to identify the elements and links that make up the system and to establish the interaction between them, thus linking the functions and structures [10]. The set of processes in ECS can be represented as the implementation of transformations in the intersection of the subsets: ionic medium (electrolyte), electrode (electrode material), external disturbances (individual factors, as well as their joint or complex effect), as we have previously shown in the framework of corrosion protection analysis [11].

Among the most significant external influences, it is necessary to attribute, mainly, the different nature of the field (vector quantities), among which are:



• a pressure (creation of excessive pressure or vacuum);
