Study On The Mechanical Properties Of Titanium Alloy TC17and Characteristics In Machining

Titanium alloys have been widely used in aircraft industry due to their high specific strength and excellent corrosion resistance. However, titanium alloys are typical difficult-to-machine materials due to their poor thermal conductivity, low elastic modulus and high chemical activation. High cutting temperature generated in titanium alloy machining usually leads to rapid tool wear and poor surface quality. On the other hand, most materials need to be removed from roughcast due to the design characteristics of components used in the aircraft industry. Therefore, the improvement of the efficiency of material removal for titanium alloy machining has been an urgent problem to be solved in aerospace manufacturing. The response of TC17alloy under dynamic loading with different strain rates and temperatures is investigated in this dissertation. The characteristics during machining TC17alloys, systematically analyzes the chip morphology, cutting forces, cutting temperature, tool life and wear mechanism, and surface roughness, using the method of combining theoretical analysis and experimental research, are focused in order to provide theoretical and practical support in high efficiency and high speed machining TC17.This study has investigated the mechanical response of TC17alloy under quasi-static and dynamic loading with different strain rates and temperatures. The results have shown that the stress-strain response of TC17is highly sensitive to both the strain rate and the temperature. TC17has evident heat softening effect, strain rate strengthening effect and strain hardening effect. The flow stress decreases while temperature increases. Flow softening behavior has been observed above700℃under quasi-static loading. The constitutive model of TC17has been established, which has high precision in forecasting material flow stress. It is a foundation for research on deformation mechanism in TC17machining process.The serrated chip formation in orthogonal cutting TC17is studied. A flow localization parameter is expressed in terms of associated cutting conditions and properties of TC17. The effect of cutting conditions on the formation of sawtooth chip in TC17machining is investigated. It is found that the critical value during machining TC17is0.0032m2/min, at which the serrated chip is observed. Intervals of segments, cutting ratio, degree of serrated chip and the inclination angle of shear band are used to characterize the geometric characterization. Microhardness of shear band is used to characterize the mechanical properties characterization. By orthogonal cutting experiments, the relationship among cutting parameters, geometric characterization, and mechanical properties characterization are explored. It is found that, intervals of segments, degree of serrated chip and microhardness of shear band increase with the increase of the cutting speed and feed rate, the inclination angle of shear band decreases with the cutting speed and feed rate increasing.Cutting force and temperature are influenced by the mechanical properties of workpiece. Based on Oxley cutting theory, the mathematic models of stress, strain, strain rate, temperature in shear zone and orthogonal cutting forces are proposed, which is tenable under cutting condition. From the view point of controlling of cutting forces and cutting temperature, appropriate cutting speed, larger depth of cut, medium feed rate are preferred.Systematic researches have been conducted on tool wear patterns and wear mechanisms with TiAlN coated carbides. Adhesive wear is the main failure mechanism, accompanied by abrasive wear, oxidation wear, and diffusion wear. The empirical formula of tool life when turning TC17using coated carbide tool has been founded. The results show that cutting speed and feed rate have a great influence on the tool life. Finally, tool life-cutting efficiency relationship is developed.The effects of cutting conditions on surface roughness when turning and face milling TC17are researched by experiments. The empirical formula has been founded. The sensitivity analysis for the cutting parameters show that the surface roughness is most sensitive to the feed rate, and less sensitive to the cutting speed and cutting depth for turning operations. The surface roughness in face milling process is most sensitive to cutting speed, and less sensitive to the feed per tooth and cutting depth.