Fundamental Research On Machinability Of Titanium Alloy By Thermohydrogen Treatment

Titanium alloys are widely used in aviation, aerospace, marine, petroleum, chemical and automobile industries due to the high strength-to-weight, good heat resistance and good corrosion resistance. But the machinability of of titanium alloys is very poor, which greatly hinders their more widely application. So people are wild about rsearch the new technology to improve the machinability of titanium alloys. Thermohydrogen treatment, based on the effect of hydrogen as a temporary alloying element on hydrogen contents and phases and kinetics phase transformation in titanium-hydrogen system, has been used as a new method to improve the processability of titanium alloys. Financed by National Natural Science Foundation of China (NO.50775115), the fundamental research on thermohydrogen treatment in improving machinability of Ti-6Al-4V alloys has been carried out. The major research works are included as follows:1. Study of thermohydrogen treatment technology in improving the machinability of titanium alloys. Based on theoretical analysis and experimental study, thermohydrogen treatment process has been obtained to improve the machinability of titanium alloys. And the thermohydrogen treatment technological parameters and hydrogen contemts have been optimized by comparing the cutting force and cutting temperature and tool life, which laid a foundation for researching cutting mechanism of the hydrogenated titanium alloys.2. Microstructures and mechanical properties and physical properties of the hydrogenated titanium alloys. Optical microscope and XRD were utilized to investigate the effect of hydrogen on phases composition, phases size of the microstructure. yield strength, elastic modulus, impact toughness, reduction of area, elongation, tensile strength, hardness and high temperature flow stress of the hydrogenated titanium alloys have been analyzed. Thermal conductivity has also been analyzed. And the reasons of hydrogen on the microstructure, mechanical properties and physical properties were discussed. The study would provide theoretical basis for revealing mechanism of thermohydrogen treatment in improving machinability of the titanium alloys.3. Cutting deformation of the hydrogenated titanium alloys. The chip roots of hydrogenated titanium alloys were acquired by quick stop method, and the cutting deformation zones were analyzed, and the cutting deformation parameters were compared. chip breaking, chip boundary, chip free surface and chip longitudinal section were researched in detail. The fracture mechanism of saw-tooth chips of the hydrogenated titanium alloys were discussed. 4. Cutting tribology of the hydrogenated titanium alloys. The test platform was established to simulate high speed cutting process. The friction tests between carbide tool and the hydrogenated titanium alloys were carried out. The tribological properties and friction morphologies were analyzed, and the wear mechanism was revealed, which would provide evidences for tool wear mechanism.5. Tool wear of the hydrogenated titanium alloys. The three-dimensional video microscope, SEM and EDS were utilized to investigate the effect of hydrogen on tool wear of the hydrogenated titanium alloys. The tool wear losses in cutting process were tracking measured. The tool wear forms were analyzed, and the tool mechanism was revealed. The results would provide evidences for evaluating machinability of the hydrogenated titanium alloys.6. Effect evaluation of thermohydrogen treatment in improving machinability of the titanium alloys. Based on tool life and chip breaking, the optimum hydrogen content was determined. The existence of optimum hydrogen content was related to effect of hydrogen on microstructure, mechanical properties, physical properties, dislocation, cutting temperature, cutting deformation, tribological properties and tool wear.