Promising methods of surface hardening for titanium alloys and steels with rapid heating
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Surface electron-beam heat treatment of steels leads to formation of hardened layers 1–5 mm thick having a finely acicular martensitic structure with increased hardness. There is redistribution of alloying elements, acceleration of decomposition processes during heating of hardened specimens, and compressive stresses arise. Heating in a flashing schedule for steels reduces the overall area of inclusions up to a factor of 6.6, and combined with subsequent heat treatment it excludes nonuniform distribution of alloying elements.
Use of electrodeposited coatings during electrochemical heat treatment sharply intensifies reaction diffusion processes. During siliciding of titanium alloys with a copper underlayer the thickness of diffusion layers reaches 975 μm, and during carburizing of titanium with an iron coating it reaches 1050 μm. In this way there is a sharp increase in titanium alloy wear resistance.
With rapid heat treatment of alloys with electrodeposited and gas heat-treatment coatings there is rebuilding of the surface structure with formation of fine blocks 0.5–10 μm in size, twins, and slip bands. The size and structure of the transitional diffusion zone depends on the presence of a metal underlayer, and treatment schedule. As a result of electron-beam surface treatment the adhesive strength is improved (up to σad= 200−210 N/mm2) and the wear resistance of gas heat treatment coatings (by a factor of two to three). The friction coefficient for electrodeposited chromium coatings increases by a factor of 1.5–2 with an increase in loads by a factor of two to three.
KeywordsWear Resistance Titanium Alloy Chromium Coating Iron Coating Heat Treatment Coating
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