TD/TRD Coatings - Thermoreactive DiffusionWe are pleased to provide Thermoreactive Diffusion (TD or TRD) coating processes as part of our line of wear-resistant coatings. TD coatings perfectly compliment the PVD, CVD & DCD treatments that we offer, thereby allowing us to provide the best coating process and composition for a customer's particular application. Our TD coatings will unlock the full potential of your tools.
Thermoreactive Diffusion (TD or TRD) is a high temperature coating process for producing metal carbides (typically vanadium carbide) on the surface of a carbon-containing substrate. This is a multi-stage coating process which utilizes a pre-heat cycle, a coating segment, ultra-sonic cleaning, heat-treating, and post-coating polishing. The coating segment is performed in a molten bath [typically consisting of a solute (Borax), a metal source, and a reducing agent]: carbide-forming compounds in the bath react with carbon in the substrate and produce metal carbides on the substrate surface. TD coatings exhibit a diffusion type bond, thereby providing superb adhesion between the metal carbide layer and the substrate. This bonding characteristic, combined with the coating's high micro-hardness, provides excellent resistance to the types of wear and galling often seen in many metal-forming processes.
A simple truism regarding coatings is as follows: when the substrate and tolerances allow, high temperature coating processes, such as TD & CVD, are almost always the best choice. This is especially true in stamping and forming applications where the superior adhesion characteristics of high temperature coatings are better suited to the high shearing stresses.
TD coatings are commonly used for many of the same applications as CVD coatings. While the choice between these processes can often be a matter of preference rather than performance, there are two specific reasons for choosing TD over CVD:
- Application - Due to oxidation resistance and/or a lack of chemical interaction, there are several applications where TD coatings perform better: aluminum and zinc die-casting components, hot forging tools, and tools for stamping and forming stainless steels.
- Tool Substrate – Some materials are better suited for the TD process than for CVD. Example: S-7 tool steel has an austenizing temperature of 1750° F. CVD is processed at 1925° F (above S-7’s austenizing temperature), thereby causing detrimental grain growth. Conversely, TD can be processed below 1750° F, depositing an excellent wear resistant coating without adversely affecting the tool material. The same is true for A-2 tool steel, medium carbon low alloy steels such as 4340, and others.