Study Of Structure Changes In Adiabatic Shear Band And Forming Mechanism Of Saw-toothed Chip In Cutting Titanium Alloy

Continuous development of science research brings on great advancement which includes every walk of life and society, just like nowaday commodities. Whatever is reasonable, Hegel's explanation for the physical world. Each thing contains the natural law of its existence, and we can find the truth as long as we have a pair of bright eyes. Chips from machining which ware abandoned in the past have become a research object of some researchers. There're many differences that the manner of force loading, large strain, high strain ratio and heat generation in chip formation from the force loading and deformation mode of structural materials.Saw-toothed chip is common type of chips in cutting. It shows obvious regularity that saw-toothed chips form as alternating effect of thermal softening and strain hardening, or periodic alternating cracks formation. The phenomenon that deformation localization and adiabatic temperature rise occur between segments of saw-toothed chip in cutting many materials is called adiabatic shear, which often appears in other high speed deformation processes of high strain ratio like explosions, high-speed collisions and impacts. The study of adiabatic shear is of important theoretical and engineering application value.The experiment material is titanium alloy TC4. The saw-toothed chips were obtained under different cutting speeds, rake angles and feed speeds. Shape and structure of saw-toothed chips were observed or tested by optical microscope, scanning electron microscope (SEM) and microhardness tester. The cutting temperatures were measured by infrared thermo detector. The shape data of chips and structure evolution law of material in shear bands were showed in the paper. It also shows formation mechanism of saw-toothed chip by comparing with chips from cutting hardened 42CrMo and high carbon steel Cr12MoV and relationship of the two formation mechanisms of saw-toothed chip.The investigation shows that shape and dimension changes of chips indicate stress and strain conditions and developing current. Adiabatic shear occurred in some given condition. As cutting condition changed, shear bands were structured by deformed band, both of deformed band and transformed band, or transformed band (or a few deformed band added). The transformed band's formation indicates that adiabatic shear has occurred. The theories of saw-toothed chip include thermal viscoplastic instability theory and periodic brittle fracture theory. The analysis shows that chip formation mechanism of titanium alloy belongs to thermal viscoplastic instability theory. There's a good grain refinement effect of adiabatic shear, by which we can give a good idea for producing ultrafine grain material here.