Surface Quality Studies with Respect to Grinding Burn of New Typical Nickel-based Superalloy

摘要

Excessive grinding temperature leads to thermal damage that greatly deteriorates the surface quality and has an adverse effect on in-service strength and fatigue properties. Grinding burn is the common type of thermal damage that has been becoming the main conscious issue in grinding difficult-to-cut materials with regard to high efficiency and good integrity as well as high accuracy. Directionally solidified nickel-based superalloy DZ4 is a kind of very important structural material developed nowadays domestically, but the very poor machinability hinders its broad utilization in aircraft. This paper unveiled its grinding burn mechanism by experimentally analyses of grinding process characteristics such as grinding forces and grinding temperature, and also by metallurgical examinations for the surface integrity. With the onset of grinding burn, this paper gives the conclusions as follows. The critical grinding temperature is 950℃. The grinding force ratio F_n/F_t changes remarkably and can be used as the characteristic parameter for the real time grinding burn monitoring. There is no evident change in burn color from slight burn to severe burn, which is much different from that of carbon steel grinding. The residual tensile stress of burned surface layer is very high, and is almost 22 times as much as that of the normal case. The mechanical strength and heat resistance of the DZ4 alloy deteriorates obviously with the decrease of strengthening particles γ' phase. The large and irregularly distributed γ' phases in surface layer severely affect the coincidence of performance of DZ4. The surface hardness of DZ4 alloy weakens by 25% and the depth of affected layer exceeds 0.5mm. This paper will be beneficial to the catastrophic failure inspections and to the development of advanced grinding technologies related to avoidance of grinding burn.