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چکیده
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Despite the high utilization of commercial pure titanium in various applications, its performance in the modern engineering industry has created a new challenge due to its low mechanical properties and poor machinability compared to its alloying conditions. In this paper, equal channel angular pressing (ECAP) as a well-known severe plastic deformation approach was applied to the commercial pure (CP) titanium at the elevated temperature up to six passes. Although the initial sample mainly contains high-angle grain boundaries (HAGBs), some low-angle grain boundaries (LAGBs) are introduced by imposing four ECAP passes and the fraction of LAGBs is considerably increased up to 55 pct. By applying for additional ECAP passes and imposing more plastic strains, more amount of them is transformed into the HAGBs, exceeding 56 pct. It was found that the yield strength and hardness of the six-pass ECAPed sample reached 314 MPa and 249 Hv, indicating 96 and 51 pct increments as compared to the as-received condition, respectively, due to the considerable grain refinement after the process. However, the capability of processed titanium for further deformation was strictly restricted. The obtained moderate ductility of the sample after the processing was related to the decrease in the size and depth of the generated dimples in the fractured surface. The machining results showed that improvement of strength using the grain refinement led to a considerable reduction of originated cutting forces due to the reduction of friction coefficient and decrease in the tool wear rate. The mentioned two factors, as well as the discontinuous short chips, eventually result in a better surface finish of the ECAP-processed CP titanium.
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