INFLUENCE OF DIFFUSION CARBONIZING OF THE SURFACE METAL LAYER ON INCREASING THE FATIGUE LIFE OF TITANIUM AND ITS ALLOYS
Keywords:titanium alloy, diffusion carbon saturation, fatigue life, fatigue strength, pure bending, bending with rotation
Background. The presence of a carbon-enriched near-surface layer affects the fatigue properties of titanium. Depending on the saturation conditions, the carburized layer can consist of a carbide phase and/or a diffusion layer (interstitial solid solution based on carbon). The formation of only a diffusion layer without a carbide phase, can serve as a means for increasing the durability of titanium under alternating loading. Therefore, it becomes necessary to establish the parameters of the carburized layer (the level of surface hardening K and the hardened layer thickness l), which will provide an increase in fatigue properties.
Objective. The purpose of the paper is to establish the effect of thermal diffusion saturation with carbon from a gas medium on the durability of titanium alloys.
Methods. Carburizing of titanium alloys in a carbon-containing gas mixture has been carried out. On titanium alloys, only an interstitial solid solution based on carbon is formed with different levels of surface hardening – K and the hardened layer thickness – l. Fatigue tests of specimens were carried out under conditions of pure bending and bending with rotation.
Results. The influence of the surface hardening level K of the VT1-0 titanium on the fatigue life in low-cycle pure bending is shown and its optimal value is revealed. The fatigue strength of the carburized VT5 and OT4-1 titanium alloys in bending with rotation with different levels of surface hardening K is presented. The dislocation structure of the VT1-0 alloy in the initial state and at the optimal level of surface hardening is investigated.
Conclusions. It was found that the fatigue life of the carburized VT1-0 titanium specimens in pure bending increases at the level of surface hardening K = 90% and the hardened layer thickness l = 20 μm. It was found that the fatigue strength of specimens from the VT5 and OT4-1 alloys in bending with rotation increases at the level of surface hardening K = 90%. It was revealed that an ordered dislocation structure is formed on the VT1-0 titanium at the optimal level of surface hardening K = 90%.
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