Paranjayee Mandal

Effect of deposition parameters on TiAlN coating using pulsed DC CFUBMS

Abstract This paper aims to investigate the parametric effect of deposition and target frequency on the mechanical properties and machining performance of the TiAlN coatings deposited in a dual cathode pulsed dc CFUBMS system. Coating composition is not directly dependent on deposition temperature or target frequency individually but increase in both the parameters has led to Al rich coating. The coating thickness is influenced by target frequency only. The fatigue fracture resistance of the TiAlN coating has been evaluated by the nanoimpact test and it has been found to be at least as good as commercial Ti0·5Al0·5N coating deposited on cemented carbide. In dry machining SAE 1037 steel, it has been observed that the resistance to crater wear is influenced by target frequency. Simultaneous increase in the deposition temperature and target frequency has provided improved resistance to crater wear due to their favourable influence on the coating thickness and Al percentage.

Studies on Titanium Alloys for Aerospace Application

Since the development of the Ti54M titanium alloy in 2003, its application within the aerospace sector has gradually increased due to the combination of properties such as improved forgeability and machinability, low flow stress at elevated temperatures, and superplastic characteristics. However, for the successful exploitation of Ti54M a comprehensive understanding of its mechanical characteristics, microstructure stability, and superplastic behaviour is required. The superplastic forming of titanium alloys is characterised by high deformation at slow strain rates and high temperatures which influence the material microstructure, and in turn, determine the forming parameters. These mechanisms make the prediction of the material behaviour very challenging, limiting its application within the aerospace industry. Even though Ti54M has been commercially available for over 10 years, further studies of its mechanical and superplastic properties are still required with the aim of assessing its applicability within the aerospace industry as a replacement for other commercial titanium alloys. Therefore, in this work a study of the mechanical and superplastic properties of Ti54M, in comparison with other commercial titanium alloys used in the aerospace industry - i.e. Ti-6AL-4V, and Ti-6-2-4-2 - is presented. The final objective of this study, carried out at the Advanced Forming Research Centre (AFRC, University of Strathclyde, UK), is to obtain material data to calibrate and validate a model capable of estimating the behaviour and grain size evolution of titanium alloys at superplastic conditions.

Cross sectional TEM analysis of duplex HIPIMS and DC magnetron sputtered Mo and W doped carbon coatings

A FIB lift-out sample was made from a wear-resistant carbon coating deposited by high power impulse magnetron sputtering (HIPIMS) with Mo and W. TEM analysis found columnar grains extending the whole ∼1800 nm thick film. Within the grains, the carbon was found to be organised into clusters showing some onion-like structure, with amorphous material between them; energy dispersive X-ray spectroscopy (EDS) found these clusters to be Mo- and W-rich in a later, thinner sample of the same material. Electron energy-loss spectroscopy (EELS) showed no difference in C-K edge, implying the bonding type to be the same in cluster and matrix. These clusters were arranged into stripes parallel to the film plane, of spacing 7-8 nm; there was a modulation in spacing between clusters within these stripes that produced a second, coarser set of striations of spacing ∼37 nm.