Applied Surface Science 320 (2014) 829–837 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Comparative study of surface integrity aspects of Incoloy 825 during machining with uncoated and CVD multilayer coated inserts A. Thakur, A. Mohanty, S. Gangopadhyay ∗ Department of Mechanical Engineering, National Institute of Technology Rourkela, Rourkela- 769008, India a r t i c l e i n f o Article history: Received 18 July 2014 Received in revised form 13 September 2014 Accepted 19 September 2014 Available online 28 September 2014 Keywords: Incoloy 825 CVD multilayer coating White layer Surface–sub surface morphology Microhardness a b s t r a c t One of the major concerns related to machining of Ni-based super alloy is surface integrity since it directly affects the performance of the machined component during its intended application. In the current study, the influence of cutting speed (51, 84 and 124 m/min) and CVD multilayer tool coating (TiN/TiCN/Al 2 O 3 /ZrCN) on various aspects of surface integrity such as surface roughness, crystal structure and microstructure of the surface and sub-surface region, thickness of white layer and work harden- ing tendency have been investigated during dry turning of Incoloy 825. Particular emphasis has been given to understand the mechanism of formation of modified surface layer and the associated process of dynamic recrystallization. The study indicated coated tool resulted in better surface finish compared to that obtained with uncoated tool only at high cutting speed. Various macro features of machined sur- face included feed mark, material smearing, surface ploughing, re-deposited materials and chip debris. Transformation of crystallographic phase of the machined surface could not be detected compared to that of bulk material. Increase in cutting speed caused gradual refinement of grains, and increased white layer thickness. Coated tool, on the other hand, resulted in the generation of large number of nucleation sites and consequently finer grains at high cutting speed, whereas the uncoated tool promoted growth of sharply defined recrystallized grains. The coated tool prevented the formation of white layer at low and medium cutting speed and also decreased work hardening tendency of Incoloy 825 when compared with that of uncoated tool. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Surface integrity refers to the conditions existing at surface and sub-surface region of the machined surface. Surface integrity con- sists of two main constituents i.e. surface topography and surface metallurgy. Surface topography describes the uppermost machined surface condition such as surface texture, roughness, waviness, sur- face morphology, surface defects etc. The major ingredient of the surface integrity is surface metallurgy. It refers to the attributes of the altered layers present below surface i.e. sub-surface region with consideration to the matrix or base material. These include phase transformation, grain refinement and deformation, white layer formation, deformed layer, hardness alteration etc. Such mod- ifications of the surface are induced due to one or combined effect of ∗ Corresponding author. Tel.: +91 9439096336. E-mail addresses: soumya.mech@gmail.com, soumyag@nitrkl.ac.in (S. Gangopadhyay). principal source of energy such as thermal, metallurgical, mechan- ical, electrical and chemical [1] The ability of Ni-based superalloys to sustain and perform under harsh conditions of high temperature and fatigue loading due to its inherent property of hot hardness, high mechanical and chemical property makes it most suitable choice to various strategic sectors. Lower thermal conductivity, work hardening, chemical affinity, presence of abrasive particles are some of the properties which pose a major challenge to machine Ni-based superalloys. High cutting temperature, faster tool wear rate, high cutting force are some of the consequences which in turn result in degradation of machined surface along with some metallurgical alteration in the workpiece. Further Ni-based superalloys are widely employed in fields such as aerospace, nuclear, defence, marine, petrochemical etc. The appli- cation of Ni-based superalloys in various critical components of above mentioned strategic fields makes it highly vulnerable to ther- mal and mechanical shocks, fatigue, creep and various other kinds of loads. The components therefore run into greater risk of early fail- ure [2]. Therefore study of surface integrity of Ni-based superalloys, in particular, is of utmost significance. http://dx.doi.org/10.1016/j.apsusc.2014.09.129 0169-4332/© 2014 Elsevier B.V. All rights reserved.