Machining of nickel based superalloys using coated PCBN tooling

Khan, Sarmad Ali (2014). Machining of nickel based superalloys using coated PCBN tooling. University of Birmingham. Ph.D.

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Abstract

Following a comprehensive literature review on the machinability of nickel based superalloys using conventional carbide, coated carbide and ceramics including uncoated/coated PCBN, the research details statistically designed experimental work to assess the tool life/wear performance and workpiece surface integrity of a range of uncoated and coated PCBN tools, when turning solution treated and aged Inconel 718. Typically, the use of carbide tooling is limited to < 60 m/min cutting speed, even with the use of high pressure cutting fluids (JetStream systems). Hardmetal coatings provide some productivity improvements although cutting speed restrictions still operate. Details of PCBN use at up to 600 m/min have been published but at the expense of tool life. Experimental testing of a number of uncoated PCBN grades involving both high and low CBN concentrations, indicated a preferred operating window of ~ 300 – 400 m/min. Advanced ceramic coatings provided no significant benefits. Primary tool wear mechanisms related to abrasion, workpiece adhesion/diffusion and fracture depending on the specific operating parameters employed. In depth workpiece integrity evaluation involving surface roughness, microstructure, microhardness and residual stress measurement suggested only limited damage when operating with PCBN tooling at preferred/optimised conditions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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