The Research On Surface Strengthening Using Warm-burnishing And Fretting Wear Performance Of TC4 Titanium Alloy

Ti-6Al-4V alloy is short for TC4 titanium alloy. As currently the most widely used titanium alloy, TC4 titanium alloy owns a series of excellent mechanical properties. But its wear resistance is poor and it is sensitive to the crack, which limit its application in various industries. To improve wear resisitance of the alloy, surface strengthening treatment becomes common practice. Owing to its high efficiency and good economy, burnishing treatment has been widely used on surface strengthening of all kinds of materials which include TC4 titanium alloy. But the surface strengthening effects of conventional burnishing processing which is used on TC4 titanium alloy is not abvious because of the alloy’s low plastic and high hardness. Considering this, surface strengthening using warm-burnishing was put forward.The burnishing parameters’ impact on the surface strengthening effects of warmburnishing were study through test, and the results show that within three burnishing parameters, namely burnishing force、burnishing speed and burnishing times, burnishing force affects surface roughness and hardness of the alloy greatly. The burnishing temperature also has a big influence on the surface roughness and hardness of the alloy. As burnishing temperature raising to 100℃, the alloy obtain better surface roughness and higher surface micro-hardness.The structure properties of the alloy after warm-burnishing processing were study, the results show that severe plastic deformation and grain size refinement occurred on the surface organization of the alloy due to warm-burnishing processing. With the increasing of burnishing temperature, the severe plastic deformation area become larger, and the hardening layer is thickened, while the value of residual stress decreased.The mechanism of warm-burnishing was study using related theory. The research result of finishing mechanism show that elastic-plastic deformation is occurred on the peak under the extrusion of burnishing tool, thus leading to the decrease of surface roughness. And the higher burnishing temperature is the more greatly the roughness decreased. While the researches on organization strengthening mechanism show that the influences of burnishing temperature on organization strengthening are duality.The warm-burnishing processing of the alloy was simulated, and the simulated results show that material flow occurred during the burnishing processing and raising burnishing temperature properly is in favor of the uniform distribution of residual stress. The stresses obtained from simulation have good consistency with the test results, which means the simulation results have high accuracy. Moreover, the simulated results also show that residual stress of the top surface layer of the alloy is compressive stress, with the increase of the depth, the residual stress increases to a positive value at first and then decreases to zero, the biggest tensile residual stress is appeared at a depth of 0.5 mm to 0.6 mm.The fretting wear performance of the alloy after warm-burnishing processing was study, and the results show that warm-burnishing processing can improve the fretting wear resistance of the alloy more greatly than that of conventional burnishing processing. Raising burnishing temperature from 25℃ to 100℃ and 170℃ respectively, the wear volume of the HIP TC4 alloy decreases by 18.3% and 22.1% respectively.