Amorphous alloys, and the partially or fully crystallised materials derived from them, can have properties attractive for a diverse range of applications. In some cases, their wear resistance can be of primary concern, in others, it is an important secondary property. The distinctive mechanical properties of amorphous alloys make their wear resistance of fundamental interest also. This review focuses on the influence of a variety of factors in wear testing, on the mechanisms of wear, on the characteristics of different categories of amorphous alloy, and on the effects of partial or complete crystallisation. It is shown that amorphous alloys can have very good resistance to sliding and abrasive wear. The wear resistance of related quasicrystalline phases is also considered.

Wear resistance of amorphous alloys and related materials

The present work aims to study the hardness and wear resistance of electroless Ni–B coatings. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni–B coatings. The structure, microhardness and wear resistance of electroless Ni–B coatings, both in as-plated and heat-treated conditions, were evaluated using X-ray diffraction (XRD), Leitz microhardness tester and a pin-on-disc wear test apparatus. XRD patterns reveal that electroless Ni–B coatings are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. The microhardness of the electroless Ni–B coatings increases with increase in heat-treatment temperature and exhibit two maxima in the hardness vs. heat-treatment temperature curve. The specific wear rate increases with increase in applied load from 20 to 40 N and at all applied loads, the specific wear rate and coefficient of friction are less for heat-treated electroless Ni–B deposits compared to that obtained for as-plated ones. The wear process of electroless Ni–B coatings is governed by an adhesive wear mechanism.

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Electroless Ni-B coatings: preparation and evaluation of hardness and wear resistance

Flexible and wearable electronics is one major technology after smartphones. It shows remarkable application potential in displays and informatics, robotics, sports, energy harvesting and storage, and medicine. As an indispensable part and the cornerstone of these devices, soft metal electrodes (SMEs) are of great significance. Compared with conventional physical processes such as vacuum thermal deposition and sputtering, chemical approaches for preparing SMEs show significant advantages in terms of scalability, low-cost, and compatibility with the soft materials and substrates used for the devices. This review article provides a detailed overview on how to chemically fabricate SMEs, including the material preparation, fabrication technologies, methods to characterize their key properties, and representative studies on different wearable applications.

Chemical formation of soft metal electrodes for flexible and wearable electronics

A mechanism is proposed for the reactions in electroless plating solutions with different reducing agents. The mechanism is based on the formation of atomic hydrogen during the oxidation of the reducing agents. The hydrogen atoms can either be oxidized or be desorbed as a gas. The mechanism accounts for both the electrochemical and the catalytic nature of the process.

On the mechanism of electroless plating. II. One mechanism for different reductants

The present review describes the electrochemical aspects of electroless plating in four sections: (1) electrochemical polarization behaviours; (2) catalytic aspects of electroless plating; (3) mechanism of anodic oxidation of reductants; (4) methods for determination of the rate of electroless plating. It is stressed that electrochemical polarization studies in an electroless plating bath is a powerful method for assessing the adaptability of the bath and for obtaining mechanistic information, although the anodic and cathodic reactions are more or less interdependent when they occur simultaneously. Catalytic aspects of electroless plating are discussed on the basis of the polarization curves for the anodic oxidation of reductants. The mechanism of anodic oxidation of reductants is discussed on the basis of a computer simulation of the current density-potential curve assuming several reaction schemes. Attention is focused especially on the occurrence of the volcano-shaped polarization curve. It is established that the polarization resistance (the slope of the current-potential curve at the electroless plating potential) is inversely proportional to the rate of electroless plating.

Electrochemistry of electroless plating

The conditions for electroless nickel‐boron plating, the process mechanism, and the structure of the alloys as‐plated and after annealing at 150°–700°C were investigated. A correlation of the mechanical and magnetic properties with the changes of phase structure was established.

https://iopscience.iop.org/article/10.1149/1.2403514/pdf

Electroless Deposition of Nickel‐Boron Alloys Mechanism of Process, Structure, and Some Properties of Deposits

1.

A thermographic study was made of the process of dehydration and decomposition of 12-phosphotungstic and 12-silicotungstic acids.




2.

A consideration of the x-ray diffraction data on the structure of 12-heteropolyanions made it possible to elucidate the observed thermal effects, related to structural changes in the processes of dehydration and decomposition of these acids.




3.

As a result of the thermal decomposition of 12- phosphotungstic and 12-silicotungstic acids, crystalline compounds of the type of solid solutions of phosphorus and silicon in tungsten trioxide are formed, and not mixtures of the oxides.




4.

The rate of heating during thermographic study displaces the temperature intervals of the thermal effects, which leads to a change in the rate of the diffusion processes.

Thermographic investigation of the process of dehydration and decomposition of certain 12-heteropolyacids

1.

The hydrogen content in chemically reduced Ni-B coatings is ≈0.02%, regardless of the amount of boron in the alloy.




2.

The rate of evolution of hydrogen during the heating of the coatings is related to the structural-phase transformations that occur in them.




3.

A comparison of the data on the evolution of hydrogen with thermographic data gives a basis for believing that the hydrogen contained in the coatings is partially present in the atomic state, partially in a protonated state.




4.

The laminarity detected for certain coatings is considered as a consequence of a periodic variation in the ratio of the rates of reduction of nickel and boron, which are inversely dependent on the acidity of the medium.

V. P. Moiseev

Papers

Electroless Deposition of Nickel‐Boron Alloys Mechanism of Process, Structure, and Some Properties of Deposits

Thermographic investigation of the process of dehydration and decomposition of certain 12-heteropolyacids

Some data on the mechanism of the liberation of hydrogen and the microstructure of chemically reduced Ni-B-H alloys