Effect of grinding temperatures on the surface integrity of a nickel-based superalloy

An experimental study was carried out to investigate the influence of temperatures on workpiece surface integrity in the surface grinding of a cast nickel-based superalloy with alumina abrasive wheels. The temperature response at the wheel–workpiece interface was measured using a grindable foil/workpiece thermocouple. Specimens with different grinding temperatures were obtained through changing the grinding conditions, including the depth of cut, the workpiece feed, and the coolant supply. Changes in the surface roughness, residual stress, metallography, ground surface morphology, and micro-hardness of the specimens were then analyzed. Bending fatigue tests were separately conducted at room temperature and at 950°C in order to evaluate the influence of temperatures on the service life of the ground specimens. A different burning color was found on the ground workpiece surfaces when grinding temperatures are over a critical value. Along with the emergence of a burning color, the roughness of the ground workpiece surface increased greatly compared with the surfaces without burning color, which was attributed to plastically deformed coatings on the workpiece surface occurring with elevated temperatures. Excepting the surface roughness, surface integrity of the ground workpiece was not affected by temperature, provided that grinding temperature is not high enough to cause grinding cracks. Based on the findings in this study, the grinding of nickel-based superalloy can be divided into two stages in order to increase production efficiency, in which case the first stage is to reach high material removal rate without concern for the presence of a burning color, whereas the second stage is to remove the plastically deformed coatings in order to decrease the surface roughness.