Research On Titanium Alloy Cutting Surface Integrity And Fatigue Life Prediction Model

The integrity of machined surfaces of titanium alloys has an important influence on fatigue properties.This paper takes titanium alloy TC4 as the research object to explore the influence of feed on surface integrity and fatigue properties of titanium alloy in high-speed cutting and to establish a fatigue life prediction model.The main contents and conclusions of this paper are as follows:Through cutting test,the influence of feed on surface integrity of titanium alloy in four aspects:surface roughness,surface morphology,work hardening and residual stress is studied.It is found that surface roughness of TC4 increases with increasing feed speed.The morphological parameters of the machined surface change in the same direction with the feed amount.The hardness of workpiece increases with the increase of feed rate.With the increase of feed,residual pressure stress occurs on the machined surface.The larger the feed,the greater the residual stress on the surface of the workpiece.The reason is that the larger the feed,the larger the cutting area,the larger the deformation during machining and the greater the thermal load,the greater the residual stress.The high cycle fatigue test was carried out on the cut titanium alloy.The effect of feed and oxide layer on fatigue life was studied through the diagnosis of fatigue fracture.The research shows that the fatigue life decreases with the increase of feed.With the increase of feed speed,notch curvature radius decreases gradually and surface stress concentration increases,which decreases fatigue failure performance and fatigue life of titanium alloy;Residual compressive stress inhibits the fatigue cracking of metal materials and delays the early propagation of fatigue cracks,thus improving the fatigue life of samples.Phase analysis of the fracture shows that with the increasing thickness of the oxide film,the thicker oxide layer is prone to brittle and flaking,which results in dents on the surface of the workpiece and accelerates the formation of fatigue sources.The higher content of Ti O₂in the oxide layer of TC4 decreases the adhesion of the oxide layer,thus causing the TC4 oxide layer to fall off and crack to form a notch,thus reducing the fatigue life.The fatigue growth zone is small in dry cutting.When cutting with coolant,i.e.without oxide layer,the fatigue growth zone is large.The large proportion of fatigue crack growth zone indicates that it has higher toughness and higher fatigue life.2.The fatigue fracture without oxide layer and the crack on the subsurface indicate that the specimen has experienced a long sliding process.The crack is not easy to produce and propagate and has a high fatigue life.For high cycle fatigue test,the relationship between feed and fatigue life is studied,the fatigue life of material is analyzed by critical plane method,and the relationship model between feed and fatigue life is established.The following conclusions are drawn:feed is negatively correlated with fatigue life,and decreases with increase.