High Entropy Alloys Coatings Deposited by Laser Cladding: A Review of Grain Boundary Wetting Phenomena

Abstract

High-entropy alloys (HEAs) are called also alloys without a main component or multiprincipal alloys. They consist of five, six or more components in more or less equal proportions and possess unique properties. Several dozens of thousands of publications have already been devoted to bulk HEAs, while HEA coatings are just beginning to develop. More than half of the works on the deposition of HEA coatings are devoted to laser cladding. In the laser cladding process, a mixture of powders on a substrate is melted in a focused laser beam, which sequentially scans the substrate. In the heated zone, the powder mixture melts. At the end of the crystallization process, a solidified polycrystal and a small amount of residual melt are found in the heated zone. It is possible that the grain boundaries (GBs) in the solidified polycrystal are incompletely or fully wetted by this liquid phase. In this way, the GB wetting with a melt determines the morphology and microstructure of HEAs coatings. This review analyzes GB wetting in single-phase HEAs, as well as in HEAs containing two or more phases. We analyze how the HEAs’ composition, laser scanning speed, laser beam power, external magnetic field or ultrasonic impact affect the microstructure and GB wetting. It is also shown how the microstructure and GB wetting change over the thickness of the rather thick as well as multilayer coatings deposited using a laser cladding.

Phase Transformations Caused by Heat Treatment and High-Pressure Torsion in TiZrHfMoCrCo Alloy

“…The presence of two or more phases in the alloy makes it possible to observe a phenomenon known as grain boundary wetting. In case of complete grain boundary wetting one phase substitutes the grain boundaries in another phase [ 17 , 42 ]. As a result, instead of one grain boundary, two interphase boundaries are formed.…”

“…The TiZrHfMoCrCo alloy studied in this paper belongs to promising biomaterials, its biocompatibility is comparable to commercially pure titanium, which is used for orthopedic implants. Detailed reviews on HEAs can be found in References [ 17 , 18 , 19 ].…”

Preparation and investigation of high-temperature oxidation resistance of TiCrAlNbSi alloy coating on Ti-6Al-4V substrate

“…Si, Nb, and Cr elements have the potential to enhance the coating's high-temperature properties on a Ti6Al4V base. High-purity raw materials are required for HEAs, and material cost and availability must be considered [7][8][9][10] . Coating thickness and structure significantly impact performance, and parameters such as grain size and lattice orientation must be controlled during preparation [11][12][13] .…”

Influence of Heat Treatment and High-Pressure Torsion on Phase Transformations in TiZrHfMoCr High-Entropy Alloy

“…Since the high-entropy alloys (HEAs) were originally proposed by Cantor et al [1] and Yeh et al [2], there has been a growing interest in these multicomponent metallic materials. With a wide range of chemical compositions available, HEAs exhibit a variety of phase transformations, mechanical properties, and microstructural types, leading to a wealth of research publications, including numerous reviews [3][4][5][6]. Typically, HEAs consist of five or more components, with proportions ranging from 5 to 35 at.%.…”