Using Barkhausen Noise to Measure Coating Depth of Coated High-Speed Steel

Coated high-speed steel tools are widely used in machining processes as they offer an excellent tool life to cost ratio, but they quickly need replacing once the coated layer is worn away. It would be therefore useful to be able to measure the tool life remaining non-destructively and cheaply. To achieve this, the work presented here aims to measure the thickness of the coated layer of high-speed cutting tools by using Barkhausen noise (BHN) techniques. Coated high-speed steel specimens coated with two different materials (chromium nitride (CrN), titanium nitride (TiN)) were tested using a cost-effective measuring system developed for this study. Sensory features were extracted from the signal received from a pick-up coil and the signal features, Root mean square, peak count, and signal energy, were successfully correlated with the thickness of the coating layer on high-speed steel (HSS) specimens. The results suggest that the Barkhausen noise measuring system developed in this study can successfully indicate the different thickness of the coating layer on CrN/TiN coated HSS specimens

Influence of Microstructure in Machining of Nickel and Nickel-Iron Based Alloys

Superalloys are used in applications such as turbines, steam power plants and nuclear power systems in components that require good high temperature properties and/or corrosion resistance. They are classified as difficult-to-cut materials and hence, from a sustainable production point of view, tool wear and tool life are major factors when machining these alloys. The work presented in this thesis provides insight to the influence of microstructure on the machining of the nickel and nickel-iron based superalloys Waspaloy and Alloy 718 (commonly known as Inconel 718), respectively. The influence of microstructure, with respect to grain size and hardness, on machining is investigated in a transverse turning operation through the assessment of tool wear, wear mechanisms, surface deformation in the machined material, burr formation and characteristics of the chips. Concerning flank wear, machining of Waspaloy is associated with less wear than machining of Alloy 718. Fully age hardened Waspaloy showed even less flank wear than solution annealed Alloy 718 irrespective of grain size. This observation cannot be explained by cutting resistance, since Waspaloy shows higher cutting forces. Surface analysis shows a difference in tribological conditions on the flank face of the tool, which influences the magnitude of flank wear. The wear mechanisms when machining these alloys are concluded to be a combination of adhesive, abrasive, diffusion and dissolution mechanisms, but also associated with a beneficial effect of oxidation of tungsten, leading to potential formation of low-friction surface just beneath the flank wear zone. The grain size of the work material was found to affect the deformation behaviour in the metal cutting process. Inhomogeneous deformation occurs when the size of the grains is in the same order of magnitude as the undeformed chip thickness, in both solution annealed and fully precipitation hardened condition irrespective of the alloy composition. The inhomogeneous deformation was connected with large depth of cut notch wear and burr formation, together with formation of segmented chips. Depth of cut notch wear is the tool life limiting factor when machining the work material with the large grain size. Finally, a method for analysing and identifying crucial variables in the material specification that affect the machinability of the work material is presented

Stability Analysis of Radial Turning Process for Superalloys

Stability detection in machining processes is an essential component for the design of efficient machining processes. Automatic methods are able to determine when instability is happening and prevent possible machine failures. In this work a variety of methods are proposed for detecting stability anomalies based on the measured forces in the radial turning process of superalloys. Two different methods are proposed to determine instabilities. Each one is tested on real data obtained in the machining of Waspalloy, Haynes 282 and Inconel 718. Experimental data, in both Conventional and High Pressure Coolant (HPC) environments, are set in four different states depending on materials grain size and Hardness (LGA, LGS, SGA and SGS). Results reveal that PCA method is useful for visualization of the process and detection of anomalies in online processes.Wykrywanie stabilności w procesach obróbki jest podstawowym składnikiem procesu projektowania wydajnych procesów obróbki. Automatyczne metody są w stanie określić kiedy nastąpi niestabilność i zapobiec ewentualnym awariom maszyny. W pracy przedstawiono różne metody wykrywania anomalii stabilności w oparciu o mierzone siły w procesie toczenia promieniowego nadstopów. W celu określenia niestabilności proponuje się dwie różne metody. Każda z nich jest testowana na podstawie rzeczywistych danych uzyskanych podczas obróbki materiałów: Waspalloy, Haynes 282 i Inconel 718. Dane doświadczalne, zarówno w środowisku konwencjonalnym, jak i przy chłodzeniu wysokociśnieniowym (HPC), zostały ustawiane w czterech różnych stanach w zależności od wielkości ziarna i twardości materiału (LGA , LGS, SGA i SGS). Wyniki pokazują, że metoda analizy głównych składowych (PCA) jest przydatna do wizualizacji procesu i wykrywania nieprawidłowości w bieżących procesach

The effect of grain size and hardness of wrought Alloy 718 on the wear of cemented carbide tools

The effects of grain size and hardness of wrought Alloy 718 on the wear of cemented carbide tools were examined by measuring the actual progression of wear in a specific transverse turning operation. Four different conditions of the same material from the same batch were studied fine grain material in the soft, solution annealed state and in the precipitation hardened state, and large grain material in the same two conditions. While flank wear, as expected, correlated strongly with hardness the effect of grain size was much more limited. A striking effect was that of the grain size on the notch wear - one of the limiting factors for tool life - which could be clearly related to the amount of burrs formed in the large grain size material both in the solution annealed and fully precipitation hardened condition. The influence of grain size and hardness on the deformed layer of the work piece material and on the morphology of the chips was clearly visible. (c) 2010 Elsevier B.V. All rights reserved

Influence of microstructure on deformation behaviour of alloy 718

Metal cutting of Superalloys can be problematic, partly due to the high temperature strength of the alloys. The deformation mechanisms during metal cutting are complex, and it is practically difficult to measure the local deformations and the stresses involved in the process. This results in a desire to numerically model the cutting process with e.g. the finite element method. For this an accurate material model able to describe the deformation behavior at the strain rates and temperatures occurring in the cutting process has to be developed. In this work the deformation behavior of Alloy 718 with four different microstructures has been studied i.e. aged and solution treated condition with small and large grain size. All studied microstructures are relevant for aero engines as they occur at different stages in production of different components. To study the deformation mechanisms involved in chip forming during metal cutting the alloy has been mechanically tested at various strains, strain rates and temperatures, and the resulting microstructure has been analyzed and compared with samples obtained by metal cutting. Compressive and tensile testing was performed at strain rates ranging from 0.001 to 3000 s-1 and from RT to 800\ub0C. It was found that deformed microstructure from metal cutting experiments and mechanical testing show similar appearance, indicating that mechanical testing can be used to describe and study the deformation mechanisms occurring during metal cutting

Methodology for evaluating effectd of material characteristics on machinability - theory and statistics-based modelling applied on alloy 718

The potential machinability for Alloy 718 (Inconel 718) is examined in terms of five material characteristics considered to play a key role in the machinability: ductility elongation to fracture), strain hardening (ultimate tensile strength over yield strength), thermal conductivity, yield strength and abrasiveness (amount of carbides). The material characteristics are simulated with the software JMatPro from Sente software. The effects of composition, grain size, hardness (size of the precipitated intermetallic particles for given volume fraction), heat treatment, temperature and strain rate have been modelled and statistically evaluated. Combining thermodynamics-based modelling (JMatPro), design of experiments and statistical analysis Minitab), and machinability polar diagram, a concept on methodology to assess variations in material specifications and to optimise these specifications with respect to potential machinability has been developed. The mechanical properties, predicted from the meta-modelling are found to be affected by the same parameters: hardness (intermetallic particles characteristics), grain size, amount of aluminium, strain rate and temperature. The abrasiveness should only be affected by the amount of carbon. Simulated material characteristics for two different types of turbine discs were compared with measured tool wear from production environment machining experiments. Variations in material characteristics between the discs were small as well as the critical tool wear, revealing a robust metal cutting process

High-temperature corrosion of weld overlay coating/bulk FeCrAl exposed in O2 + H2O + KCl(s) at 600 °C – A microstructural investigation

This work investigates the impact of high-temperature corrosion behavior of the newly developed FeCrAl alloy Kanthal® EF101 bulk material and weld overlay coating in the presence of KCl(g)/KCl(s) at 600 °C. The oxide scale formed within the secondary corrosion regime after exposure and the impact of alloy microstructure on corrosion behavior was investigated using scanning transmission electron microscopy. The findings indicated the key microstructural differences is the alloy grain size which influences the formation of a protective scale. In addition, It is indicated that coating exhibited inferior performance than the bulk material, primarily attributed to the microstructural differences