| With the development of science and technology, modern aviation industry has put forward higher requirements for material performance and fatigue life of aviation engine parts. Extending the service life of aviation parts has become an important research topic in the field of advanced manufacturing technology. Titanium alloys have been widely applied in manufacturing aeroengine components. Currently 60% of titanium alloy products and 80% of aircraft structure parts are made from α+β titanium alloy TC4 (Ti-6A1-4V).The failure of aeroengine components occurs usually at surface and subsurface of the parts during working in service. The fatigue crack that will decrease engine life starts from the surface, then spreads to the inside of the parts. Therefore, it has become one of the most hotspots of current research that low plasticity burnishing (LPB) process improves surface integrity and low cycle fatigue life of TC4 components.Firstly, surface integrity of TC4 round rods machined by LPB and turning processes, respectively, are compared with each other in this paper. The influence of LPB process parameters which includes burnishing speed, feed speed, hydraulic oil pressure, burnishing passes on surface integrity is studied through single factor experiment method. The technical indicators of surface integrity for burnished TC4 in this paper include surface topography, surface roughness, surface microhardness distribution, surface residual stress.The trace left by turning in the workpiece surface will be eliminated by LPB. The surface roughness is reduced by 30%-50% with contrasted to turned surface. The depth of surface hardening layer is about 100μm microns, and the maximum hardness in the surface is more than 360HV0.05. Higher residual compressive stress which up -636MPa is introduced at the surface by LPB.The plastic flow and plastic strain at surface layer caused by LPB is the direct effect on the improvement of surface integrity. The surface residual compressive stress is generated by the combination of plastic deformation at surface and elastic deformation at the subsurface. The selecting principle of LPB process parameters when manufacturing actual TC4 parts in the case of ensure the machining efficiency and economy is as follows: hydraulic pressure rolling over 24MPa, burnishing pass within 2 times, lower burnishing speed, feed speed the same as pre-elaboration.Secondly,2D finite element model which can predict the residual stress distribution at the surface layer of TC4 workpiece processed by LPB is established based on Abaqus/Explicit software simulation. The influence of hydraulic oil pressure on residual stress distribution is analyzed by the established model. The curve of residual compressive stress distribution at the surface layer is like a spoon. The thickness of the residual compressive stress layer increases with the increase of the hydraulic oil pressure. The thickness is about 0.25-0.4mm according to the result obtained by the established model.Lastly, low cycle fatigue tests are conducted on Instron 8801 fatigue machine. The TC4 specimens are machined by turning and LPB, respectively. Low cycle fatigue life is improved 6 times by LPB, and the fatigue life increases with the increase of hydraulic oil pressure. The reduction of cracking source at the surface of specimens and the delay of fatigue crack initiation and propagation caused by LPB are found in the study. It will improve the low cycle life of TC4 components. |
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