Applications of Energy-Assistance to the formation of novel surface coatings

In the area of manufacturing, surface coating of materials is a widely-used process representing a multi-billion pound per annum industry. the choice of a suitable coating allows the design engineer to choose a material for its optimum bulk properties but, at the same time, tailor the surface properties for a specific application. For example, components made of iron have good mechanical strength but, because the iron surface forms an oxide, a suitable coating (usually chromium-based) is used to protect the product. Over the last decade interest has surged in the potential use of more exotic coatings with controlled micro- and nano-structure. Professor John Colligon and Dr Vladimir Vishnyakov have developed techniques for production of such coatings

Amorphous Boron containing silicon carbo-nitrides created by ion sputtering

Silicon carbo-nitride films with Boron were deposited onto Silicon, glass and SS304 Stainless Steel substrates using the ion beam assisted deposition (IBAD) method. The coating composition, rate of ion-assistance and substrate temperature were varied. Films were examined by X-Ray Diffraction, Scanning Electron microscopy, Energy Dispersive X-Ray analysis, Cathodoluminescence, Atomic Force Microscopy and Nano-indentation. The composition and chemical bonding variation was found to be dependent on deposition conditions. All coatings were amorphous, fully dense and showed high hardness up to 33 GPa. It is suggested that the low friction coefficient of about 0.3, measured against Al2O3 using the pin-on-disc method, may be the result of the presence of C nanoclusters which are formed under the low energy deposition conditions. Films deposited on Stainless Steel had an onset of rapid thermal oxidation at 1150 °C in air as determined by thermogravimetric analysis. The films have a Tauc bandgap between 2.2 and 2.8 eV and were also exceptionally high electrical resistive which may indicate the presence of localised state

Ion sputter-deposition and in-air crystallisation of Cr2AlC films

Ternary alloys of composition close to Cr2AlC have been deposited by ion beam sputtering onto unheated and heated to 380 °C Si substrates. As-deposited films are amorphous. Annealing of the film in vacuum at 700 °C leads to crystallisation with 39.2 nm crystallites. Crystallisation also can be achieved by annealing in air but there is also partial oxidation of the film surface to the depth of approximately 120 nm, which represents an oxide layer less than 5% of the total film thickness. There is an increase of lattice size along the c-axis during crystallisation in air, which indicates a small incorporation of oxygen. Film structure and crystallisation have also been analysed by Raman spectroscopy. Changes in Raman spectra in Cr2AlC have been correlated with the film crystallisation and it was observed that MAX-phase related peaks become clearly defined for the crystallised film

Displacement Damage and Self-Healing in High-Entropy Alloys: a TEM with in situ ion irradiation study

Recent developments in the field of materials for future nuclear fusion reactors have led to the design of innovative metallic alloys that can sustain their mechanical and structural properties under a wide variety of extreme conditions, such as fast neutrons (E <= 14 MeV) and alpha particle bombardment (4He with E up to ~ 3.5 MeV). High-Entropy Alloys (HEAs) are promising candidates for new concepts of nuclear reactors as they have mechanical properties and thermodynamic stability that is believed to be superior to conventional metallic alloys, although their radiation resistance is still a subject of intense research. The efforts to understand the behavior of HEAs under particle irradiation indicated a possible “self-healing” effect of radiation induced defects. In this report, a preliminary study using Transmission Electron Microscopy (TEM) with in situ ion irradiation was performed to investigate the formation and evolution of displacement damage in the microstructure of a FeCrMnNi HEA

Structure formation of TiB2-TiC-B4C-C hetero-modulus ceramics via reaction hot pressing

The densification kinetics and structure of TiB2-TiC-C, TiB2-C and TiB2-B4C-C hetero-modulus ceramics produced via reaction hot-pressing of B4C and TiС precursors are investigated. The reaction begins at 1100°C with boron carbide decomposition and progresses in two main stages which can be predominantly determined by the boron atoms to TiC grains diffusion mechanisms. The solid phase grain boundary diffusion starts at 1100°C and effective gas phase transport finalises the reaction at temperatures above 1400°C. Two distinctive waves of the charge consolidation allow densifying investigated refractory materials at 1900°C and 30MPa during 16 minutes. The reaction is shown to define the features of the composite structure: submicron TiB2 particles and faceted voids in B4C matrix, flake-like graphite and TiB2 inclusions in TiC matrix. High concentration of carbon atoms (~ 10 at.%) in synthesized diboride titanium grains have been observed

Nanomechanical testing of thin films to 950 °C

Nanomechanical testing has been a revolutionary technique in improving our fundamental understanding of the basis of mechanical properties of thin film systems and the importance of the nanoscale behaviour on their performance. However, nanomechanical tests are usually performed in ambient laboratory conditions even if the coatings being developed are expected to perform at high temperature in use. It is important to measure nanomechanical and tribological properties of materials under test conditions that are closer to their operating conditions where the results are more relevant. We can then better understand the links between properties and performance and design advanced materials systems for increasingly demanding applications. However, high temperature nanomechanics is highly challenging experimentally and a high level of instrument thermal stability is critical for reliable results. To achieve this stability the NanoTest Vantage has been designed with (i) active heating of the sample and the indenter (ii) horizontal loading to avoid convection at the displacement sensor (iii) patented stage design and thermal control method. By separately and actively heating and controlling the temperatures of both the indenter and test sample there is minimal/no thermal drift during the high temperature indentation and measurements can be performed as reliably as at room temperature. Illustrative results are presented for TiAlN, TiFeN, DLC and MAX-phase coatings. Above 500 °C it is necessary to use Argon purging to limit oxidation of samples and the diamond indenter, although the efficiency of this decreases over 750 °C. To test at higher temperatures without indenter or sample oxidation an ultra-low drift high temperature vacuum nanomechanics system (NanoTest Xtreme) has been recently developed. Results with the vacuum system are presented up to 950 °C