Fundamental Research On Machining Of Ti₂AlNb Intermetallic Alloys

Ti₂AlNb intermetallic alloys become one of the most potential lightweight high-temperature-resistance materials due to their excellent mechanical properties.However,these excellent properties bring great challenges for their machining,such as high cutting forces,high cutting temperature,severe tool wear and poor surface integrity.In this thesis,the machinability of Ti₂AlNb intermetallic alloys are systemic investigated from chip formation,tool wear and surface integrity,respectively.A methodology of identifying the constitutive models for FE-machining simulations has been developed.The high-jet pressure coolant technology has been proposed to prolong the tool life and improve the surface quality.Based on the tool life and surface integrity as assessment,the cutting process parametres have been optimized.The main contents are as follows:（1）In view of the serious problem that the constitutive model cannot accurately describe the deformation behavior during cutting process,the feathers of flow stress curves has been investigated under the thermo-stress conditions,and the mechanisms of how the constitutive models affect the simulation results has been revealed.The metholody of inversely identifying the constitutive parameters based on particle swarm optimization has been proposed.The accurate constitutive models of Ti₂AlNb intermetallic alloys under high strain and high strain rate have been obtained,which improved the accuracy of simulations for machining.（2）The orthogonal cutting FEM has been developed,and the evolutions of physical field（stress,strain,temperature）during chip formation has been investigated.The effect of cutting speed on formation and developments of the adiabatic shear band has been revealed.The chip roots under different cutting conditions have been obtained,and the effect of cutting parameters on the chip formation process has been revealed.The effect of cutting parameters and coolant conditions on the chip morphologies has been analysized,and the mechanisms of saw-tooth-edge of chips formation has been revealed.（3）The tool wear characteristics and the tool life of coated carbide tools when machining Ti₂AlNb intermetallic alloys are investigated during tool wear experiments.The mechanisms of tool wear including adhesion wear,abrasive wear and oxidation wear has been clarified.The effect of cutting parameters and coolant conditions on the tool rake face and notch wear has been revealed.The three dimension tool wear simulation models have been developed,which shows the distribution disciplinarian of physical field on the tool surface.The effect of temperature and contact pressure on the tool wear rate has been revealed.（4）The machined surface integrity of Ti₂AlNb intermetallic alloys have been investigated based on the finite element analysis and machining experiments.The critical undeformed chip thickness has been revealed.Based on the distribution field of temperature,stress,strain,the mechanism of formation of residual stress on the machined surface of Ti₂AlNb intermetallic alloys has been revealed.The evolution law of residual stress,microstructure and macro-morphologies with varied cutting parameters and pressure of coolant has been achieved.