Advances in Surface Engineering: Alloyed and Composite Coatings

Abstract

The use of composite and alloyed coatings is a widely used strategy for obtaining desired properties in a surface coating. Several advantages are envisaged by use of these coatings. Some of these include a desirable change in fracture toughness, wear resistance, corrosion resistance, as well as electrical and thermal properties. It is known that no single material can provide all the properties. The selection of the constituents and their relative amounts determines the properties of the coatings, and hence, this provides a way for tailoring the properties of the composites. The interaction of the composite mixture during the spray process is interesting to study because the constituents may have different deposition efficiencies and process optimization needs to be carried out to get the desired composition in the coating. Instead of pure metals, alloyed coatings offer higher wear and corrosion resistance. Amorphous and nanocrystalline coatings are potential candidates for applications in severe conditions. Amorphous materials are typically multicomponent and are known to have high corrosion resistances. Similarly, pitting corrosion is expected to be discouraged by use of nanocrystalline coatings. To capture the recent advances in this area, a symposium with the same title as this article was held at the TMS 2012 Annual Meeting and Exhibition in Orlando, Florida. The symposium included 54 presentations with several invited talks from U.S. and international researchers. Talks concerning wear resistance, indentation behavior, development of residual stresses, and electrochemical behavior of composite and alloy coatings were presented over five sessions. This included several processing methods such as laser deposition, electrochemical techniques, thermal spraying, spark plasma sintering, and physical and chemical vapor deposition techniques. There was a huge interest in many of the talks, and attendance was good compared with previous years. The discussion in this JOM issue on surface engineering highlights some of the current views and presents six papers touching on these topics. The first paper by Boris D. Bryskin and co-workers titled ‘‘Chemical Vapor Deposition of Iridium and Rhodium Coatings from Hydridotetrakis (triflourophosphine) Complexes’’ presents a study on iridium and rhodium coatings on molybdenum substrates by chemical vapor deposition. These coatings are important in applications because of their inertness. They show the use of new organometallic complexes that result in pure coatings without contamination of carbon and oxygen, which is otherwise difficult to obtain from conventional precursors. The second paper by J. Chen and L. Xue on ‘‘Laser Cladding of CPM Tool Steels on Hardened H13 HotWork Steel for Low-Cost High-Performance Automotive Tooling’’ presents studies on laser cladding H13 tool steels with high-alloy, high-vanadium tool steels. It improves the surface of molding and extrusion dies leading to improved performance. The paper discusses the microstructure and hardness of the coatings and the effect of hardening and tempering treatments on the evolution of hardness. The third paper by M. Aghaie-Khafri and M. Mohamadpour Nazar Abady presents a study on the chromo-boronizing treatment of DIN1.2714 steel. The authors show the multilayers of Fe and Cr borides, namely, CrB, Cr2B, FeB, and Fe2B, which have high hardness. Kinetic analysis of the layer formation is also provided along with the effect of the treatment on the corrosion resistance. The fourth paper by Mingdong Bao and co-workers titled ‘‘The Tribological Behavior of Plasma Sprayed Al-Si Composite Coatings Reinforced with Nanodiamond’’ discusses the microstructure and tribological behavior of Al-Si coatings reinforced JOM, Vol. 64, No. 6, 2012