Applied Surface Science 292 (2014) 197– 203

Deformation phase transformation coupling mechanism of white layer formation in high speed machining of FGH95 Ni-based superalloy

Jin Du, Zhanqiang Liu∗, Shaoyu Lv

[Abstract] Ni-based superalloy represents a significant metal portion of theaircraft critical structural and enginecomponents. When these criticalstructural components in aerospace industry are manufactured with theobjectiveto reach high reliability levels and excellent service performance, surfaceintegrity is one of themost relevant parameter used for evaluating the qualityof finish machined surfaces. In the study of sur-face integrity, the formationwhite layer is a very important research topic. The formation of white layeronthe Ni-based superalloy machined surface will reduce the machined parts serviceperformance andfatigue life. This paper was conducted to determine the effectsof cutting speed on white layer formation inhigh speed machining of FGH95Ni-based superalloy. Optical microscope, scanning electron microscopeand X-raydiffraction were employed to analyze the elements and microstructures of whitelayer andbulk materials. The statistical analysis for grain numbers wasexecuted to study the influence of cuttingspeed on the grain refinement in themachined surface. The investigation results showed that white layerexhibitssignificantly different microstructures with the bulk materials. It shows densification,no obvi-ous structural features characteristic. The microstructure and phase ofNi-based solid solution changedduring cutting process. The increase of cuttingspeed causes the increase of white layer thickness whenthe cutting speed isless than 2000 m/min.However, white layer thickness reduces with the cutting speedfurther increase.The higher the cutting speed, the more serious grains refinement in machinedsurface.2-D FEM for machining FGH95 were carried out to simulate the cuttingprocess and obtained the cuttingtemperature field, cutting strain field andstrain rate field. The impact mechanisms of cutting tempera-ture, cuttingstrain and strain rates on white layer formation were analyzed. At last,deformation-phasetransformation coupling mechanism was proposed to illustratethe white layer formation mechanism inhigh speed machining of PM superalloy.

Keywords White layer FGH95 High speed machining FEM

2014-Deformation-phase transformation coupling mechanism of white layer.pdf