John Long

Influence of chromium content on the dry machining performance of cathodic arc evaporated TiAlN coatings

Physical vapour deposition (PVD) titanium aluminium nitride coated cutting tools are used extensively in global manufacturing for reducing production costs and improving productivity in a number of aggressive metal-cutting operations, namely, dry and high-speed machining. In this investigation, the performance of Ti1−xAlxN and Ti1−x−yAlxCryN coatings was assessed on Co-HSS twist drills used to machine grey cast iron. The failure criterion for drills was defined as a critical sized flank wear land at the outer corners of the drills. Using this criterion, the average tool life of uncoated twist drills was increased by factors of 2.5, 3.0 and 3.0 by Ti0.59Al0.41N, Ti0.27Al0.19Cr0.54N and Ti0.21Al0.14Cr0.65N coatings, respectively. Notwithstanding the similar increase in average tool life, the Ti1−x−yAlxCryN coatings produced more consistent results than the Ti1−xAlxN coated drills with standard deviations of 67, 3 and 19 holes, respectively. This result has significant practical implications in manufacturing, since drills are not replaced on an individual basis, but rather on a preset tool change frequency. The present paper discusses the performance of Ti1−xAlxN and Ti1−x−yAlxCryN coated drills in terms of average and practical drill life and concludes with remarks on the characterisation of PVD coatings and their significance on the performance of Co-HSS twist drills when dry machining grey cast iron.

Cr(N,C) diffusion coating formation on pre-nitrocarburised H13 tool steel

The microstructural processes of Cr(N,C) coating formation by thermoreactive deposition and diffusion (TRD) on pre-nitrocarburised H13 tool steel were studied. Both nitrocarburising and TRD were performed in fluidized bed furnaces at 570 °C. During TRD, chromium was transferred from chromium powder in the fluidized bed, to the nitrocarburised substrates by gas-phase reactions initiated by reaction of HCl gas with the chromium. Addition of 30% H2 to the input inert gas was found to increase the rate of coating formation, although hydrogen reduction resulted in rapid loss of nitrogen to the surface. The reason for the increased rate of coating formation could not be established without further investigation, although several possible explanations have been proposed. It was found that porosity and the formation of an iron nitride ‘cover layer’ during nitrocarburising were the biggest influences on the microstructure of the Cr(N,C) coating. Microstructural characterization of the coatings was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES).

Ferritic nitrocarburising of tool steels

Abstract Four different tool steel materials, P20, H13, M2 and D2, were nitrocarburised at 570°C in a fluidised bed furnace. The reactive diffusion of nitrogen and carbon into the various substrate microstructures is compared and related to the different alloy carbide distributions. The effect of carbon bearing gas (carbon dioxide, natural gas) on carbon absorption is reported, as well as its influence on compound layer growth and porosity. Partial reduction of Fe3O4 at the surface resulted in the formation of a complex, ϵ-nitride containing oxide layer. In H13, carbon was deeply absorbed throughout the entire diffusion zone, affecting the growth of grain boundary cementite, nitrogen diffusivity and the sharpness of the compound layer: diffusion zone interface. When natural gas was used, carbon became highly concentrated in the compound layer, while surface decarburisation occurred with carbon dioxide. These microstructural effects are discussed in relation to hardness profiles, and compound layer hardness and ductility. The surfaces were characterised using glow discharge optical emission spectroscopy, optical and scanning electron microscopy and X-ray diffraction.

Fluidized bed CrN coating formation on prenitrocarburized plain carbon steel

CrN coatings were formed on plain carbon steel by prenitrocarburizing, followed by thermoreactive deposition and diffusion (TRD) in a fluidized bed furnace at 570 °C. During TRD, Cr was transferred from Cr powder in the fluidized bed to the nitrocarburized substrates by gas-phase reactions initiated by reaction of HCl gas with the Cr. The microstructural processes occurring in the white layer, caused by N diffusion toward the surface during this stage were studied. This study compares TRD atmospheres employing inert gas and HCl or inert gas, H2, and HCl. Surface characterization was performed by scanning electron microscopy (SEM), x-ray diffraction (XRD), and glow-discharge optical-emission spectroscopy (GDOES).

Measuring oxygen stoichiometry in YBa2Cu3O7-x by micro-raman spectroscopy

Micro-Raman spectroscopy is well suited for microstructural analysis of (YBCO) superconductors. Of particular interest is the oxygen stoichiometry, 7-x, on which many superconducting properties depend. It is common to use the frequency of the Raman spectral peak near to obtain a quantitative measure of 7-x. Another peak exists near . The variation of the position of this peak appears to be minimal as 7-x changes. However, this peak is asymmetric for orthorhombic YBCO and symmetric for tetragonal YBCO. We have observed a variation in the asymmetry of this peak with 7-x, in Raman spectra obtained from single grains in a sample of polycrystalline YBCO. We propose the use of this peaks asymmetry as a quantitative means to measure oxygen stoichiometry.

Pin on disc wear investigation of nitrocarburised H13 tool steel

Abstract Nitrocarburised H13 disks were tested in dry, sliding wear against a stationary ruby ball (pin). Three different 4 h nitrocarburising treatments were compared, using N2/NH3/CO2, N2/NH3/natural gas and N2/NH3 gas mixtures, resulting in compound layers of varying thickness, hardness, porosity and oxide morphology. During mild, oxidative wear, with the formation of abrasive wear debris, the most brittle and oxidised surfaces performed poorly. Polishing to a bright, reflective finish greatly reduced wear. However, the N2/NH3/CO2 sample also frequently maintained a ‘very mild’ wear regime, owing to the formation of a protective film between the wear surfaces, and resulting in a lowering of the friction coefficient. This treated surface was porous and covered in a complex layer of coarse oxide+ϵ-carbonitride. Nitrocarburised samples and wear tracks were characterised by optical microscopy, SEM, atomic force microscopy and stylus profilometry.

Cloud-based teaching in an engineering-physics course

This paper presents a transition from passive, traditional delivery of teaching to an active, “cloud-based” method, in a freshman engineering-physics course. The course is delivered to a traditional on-campus cohort, and also to an off-campus cohort by means of distance education and online learning. Cloud teaching refers to delivering education by means of websites and mobile-technology applications, where constant student attendance at the host campus is not always necessary. This is contrasted with traditional on-campus teaching, which occurs in a classroom. The use of lectures has been reduced while the use of tutorial and lab classes has increased. The new course structure was delivered for the first time in 2014, has run for two semesters, and will continue in 2015. It was found that student performance in the new structure was no worse than that in the older structure. Off-campus students in general welcomed the changes, while on-campus satisfaction did not change from before to after the transition.

Evaluation of student learning outcomes in fourth year engineering mechatronics through design based learning curriculum

This paper focuses on evaluation of student learning outcomes in fourth year engineering mechatronics through design based learning curriculum. The purpose of all engineering degrees is to provide strong grounding with principles of engineering science and technology. By learning engineering methods and approaches in an academic environment, graduates can enter the world of work and tackle real world problems with innovation and creativity. In many cases, academic staff are responsible for driving and setting high expectations in their classrooms. Sometimes staff are expected to teach subjects outside their expertise. This research paper is concerned with evaluating student learning outcomes through feedback sought from students on design-based learning approach.

Materials analysis of yttrium-barium-copper-oxide by micro-Raman spectroscopy and optical microscopy

Optical microscopy has proven to be a useful technique for obtaining general, qualitative information from the entire surface of YBa/sub 2/Cu/sub 3/O/sub 7-x/ samples. Micro-Raman spectroscopy is well suited for routine microstructural analysis of YBCO superconductors. We demonstrate the complementary use of both techniques for the analysis of polycrystalline YBCO. Observed colors of polarisation on YBCO were correlated with information provided by Raman spectroscopy on individual grains to deduce microstructural characteristics across the whole surface of a sample.