Process	Toyota Diffusion Process - TDP
	The Toyota Diffusion Process is used for forming homogeneous layers of very hard carbides, for increasing wear resistance of tools and machines parts. The size of the parts treated is usually very large. The carbide layer is deposited in a salt bath at high temperatures (800-1250 C / 0,5-10 hours), thanks to the reaction between the diffusion materials and the carbon contained in the substrate. Dimensional changes are possible, due to the high temperatures involved.
Danish Name	TDP
Category	Surface treatments, Thermal diffusion processes
Materials	Diffusion materials: Carbide ceramics (e.g. Titanium carbide Tungsten carbide ) Substrate: Steel (C>0,4%)
References	Industrihærderiet A/S
Price notes	As it is used only for large parts, the most influent variable for the price is the production volume. The minimum price for a single large mill, for example, is 1000 DKK/part, with significant reductions for larger production vulumes (100, 1000 parts).
Price date	March 1997
Additional info	Very high price per part, but the price/kg ratio is comparable to that of CVD. Particularly, if the bath temperature corresponds to that of the following post-hardening, coating and hardening are performed together, and TDP can be cheaper than CVD.
Photo	Thomas Nissen (Computer graphics)
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