On the machinability of the Ni-30 high-temperature iron-based superalloy

Superalloys are high-performance materials which combine high tensile, creep and fatigue strength, besides good ductility, toughness and resistance to corrosion, properties that are also responsible for their low machinability. The VAT 30 ® alloy contains an austenitic stainless steel base with additions of chromium, nickel, titanium and aluminum, and it is mainly applied on the manufacture of valves of combustion engines, due to its advantageous characteristics. This alloy exhibits both high ductility and abrasiveness, features that may promote both attrition and abrasion wear mechanisms on the tool used to cut it. This work contains some investigations about the effect of cooling condition, tool rake angle and cutting speed on the machinability of Ni-30 alloy in terms of cutting power consumption, surface roughness and tool life, besides the tool wear mechanisms. Conventional and high-pressure coolant injected toward the tool rake face was compared, as well as negative rake angle and neutral tooling, besides two different cutting speeds. Results show that high-pressure coolant may reduce cutting power consumption and even increase the volume of material removed during tool life up to 45% in some cases, but this same influence has not been verified regarding the workpiece arithmetical mean roughness value. Negative and neutral rake angle tools did not present very different results in terms of power and roughness, but negative tools provided considerably higher volume of material removed per tool life (up to 75% in one condition). Cutting speed showed strong effect on the cutting power, as expected, but no reasonable effect on workpiece surface roughness; regarding tool life, the cutting speed increase typically reduced the volume of material removed per tool life with conventional cooling, but when high-pressure coolant was used, this effect was attenuated. Abrasion and attrition were the main tool wear mechanisms in any tested condition.