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Lots of heat generated in the cutting deformation zone can cause the temperature rising of cutting tool and workpiece during the cutting process. Tool temperature is mainly depended on the heat energy entering into tool in the secondary deformation zone. Higher working temperature can weaken the cutting tool strength and then deteriorate the tool wear. Advanced coating layer deposited on the tool substrate can change the tool-chip friction and affect the heat partition in the tool-chip interface. In order to reveal the mechanism of heat conduction in the secondary deformation zone, the model of heat partition into cutting tool was built. With the aid of finite element method (FEM), the relative parameters which were necessary for the solving of heat partition model were quantified. Actual cutting experiments were carried out to the verification of the FEM models by means of the cutting force and temperature measurement. Influences of coatings (i.e., coating materials, coating thickness) and cutting speeds on the heat partition were analyzed. And then, rake face temperatures obtained at four kinds of coated tools were compared. The investigation results showed that TiC coating appears as the maximum value and Al2O3 coating appears as the minimum value of heat partition coefficient into cutting tool among these four kinds of coatings (i.e., TiC, TiN, TiAlN, Al2O3). With the increasing of coating thickness and cutting speeds, heat partition into cutting tool all showed a decrease trend. Al2O3-coated tool had the maximum rake face temperature among these four kinds of coated tools; however, the location of peak temperature on the rake face of Al2O3-coated tool was the shortest distance from the tool tip.

FGH95 is one kind of powder metallurgy (PM) superalloy which has excellent mechanical proper- ties at high temperature. It has been developed for turbine disc applications to improve aeroengine efficien- cy under higher operating temperatures. However, this kind of superalloy is very difficult to machine because of its poor thermal diffusivity and work-hardening prop- erties during the machining process. The machining process can lead to damage of the machined surface and subsurface. Thus, the purpose of this paper was to investigate damage of the machined surface and subsur- face in hard machining of FGH95 PM superalloy. Or- thogonal milling experiments using coated carbide inserts were carried out on a CNC machining center. The machined surface was observed and recorded using an optical microscope, white light interferometer, and scanning electron microscope. Machined surface defects were recorded and analyzed. The effects of cutting speed on machined surface roughness, white layer thick- ness, plastic deformation, and microhardness were in- vestigated. The research results show that better surface roughness can be generated at higher cutting speeds, while several defects appeared on the FGH95 machined surface. White layer thickness and machined surface microhardness increase with the cutting speed. Also, plastic shear strain in the machined surface layer in- creases with cutting speed. The depth of plastic defor- mation decreases with the increase of cutting speed. These investigation results are essential for the evalua- tion of PM superalloy surface integrity and are signifi- cant for the prediction of PM superalloy service life.

High-speed machining is being recognized as one of the key manufacturing technologies for getting higher productivity and better surface integrity. FGH95 powder metallurgy superalloy is a kind of nickel-based superalloy which is produced by near-net-shape technology. With increasing demands for high precision and high performance of FGH95 components in aerospace industry, it is essential to recognize that the machined surface integrity may determine machined part service performance and reliability. Then, little is known about the machined surface integrity of this superalloy. Thus, the surface integrity in high-speed machining of FGH95 is investigated in this paper. Experiments are conducted on a CNC milling center with coated carbide tools under dry cutting conditions. The surface integrity is evaluated in terms of surface roughness, microhardness, and white layer. The influence of cutting speed on chip morphology is also investigated. Experiment results show that surface integrity and chip morphology of FGH95 are very sensitive to the cutting speed. When cutting speeds are below 2,400 m/min, the values of surface roughness have little variation, while when cutting speeds are in the range of 2,800–3,600 m/min, the values of surface roughness are higher than that of other cutting speeds. Severe work hardening is observed resulting from high-speed machining of FGH95 superalloy. The higher the cutting speed, the higher the surface hardness. When cutting speeds are in the range of 2,800–3,600 m/min, the white layer thickness is slightly higher than that of other cutting speeds. In high-speed machining of FGH95, the chip is segmented and has a typical sawtooth shape. The degree of serrated chip increases with the cutting speed. When the cutting speeds exceed 2,400 m/min, serrated chips change into fragment chips.

Powder metallurgy (PM) nickel-based superalloy FGH95 has been widely used for components, which requires the greatest service performance. The surface integrity is becoming more and more important in order to satisfy the increasing service demands. However, the machined surface of FGH95 is easily damaged due to its poor machinability. The purpose of this paper is to investigate the effects of dry milling process parameters on the surface integrity of FGH95. Experiments were conducted on a CNC machining center under different cutting speeds. The machined surface is evaluated in terms of surface roughness, microhardness and white layer. Experiments results show milled surface integrity of FGH95 is sensitivity to the cutting speeds. The machined surface roughness decreases with increase of the cutting speed, but with further increase of cutting speed between 80 m/min to 100 m/min an increase in surface roughness appears. For microhardness, it can be seen that the machined workpiece surface hardens seriously. It can also draw the conclusion that cutting speed has the marginal effect on the white layer thickness generated in the machined subsurface.