Project B3: Engineered Surfaces
Project Leaders: Dr Nick Birbilis, Professor Peter Hodgson & Associate Professor Ming-Xing Zhang
Project B3.1 – Gradient structures
Development of light alloys with structurally or chemically modified surfaces – or a combination of both structural and chemical modification. These alloys will have graded properties designed such that the surface behaves superior to the bulk for specific properties.
Theme A: Enhanced Wear resistance
•	Provide base level wear information for alloys developed under other programs within the Centre.
•	Development of an understanding fundamental nature of the wear behaviour of surface modified light alloys; particularly those with nanostructured surfaces.
•	Evaluation of specific coatings developed for enhanced wear performance through techniques such as SMAT (UQ), Cold Spray, KM or fluidized bed.
•	Develop an understanding of the strengths and limitations of different wear tests in relation to light alloys (eg pin-on-disc, crossed cylinder and full scale tests).
Theme B: Enhanced Corrosion resistance
1)	Successful production of Mg and Al light alloys with structural modification arising from all of: - Surface Mechanical Attrition - SMAT (UQ) - Equal channel angular pressing - ECAP (Monash) - Cryo-rolling - CR (Monash / Deakin) - High Pressure Torsion - HPT (Monash) - Friction Stir Processing - FSP (Monash / CSIRO)
2)	Locally alloy Al and Mg alloy surface via the fluidised bed method (at Deakin).
3)	Combine (1) and (2) to create Al and Mg alloys with modified surface structure and chemistry. The above will be carried out on substrates that include pure Mg, AZ31, pure Al, AA7075 and AA2024.
4)	Utilise activity in (3) to create materials with optimum surface properties (graded towards conventional bulk properties). This is focused on enhancing the corrosion resistance of the alloy/material in question. Initial targets are to improve the corrosion resistance by 50% (i.e. half the rate of corrosion). Ultimate strategic targets would be to produce Al alloys with corrosion rates as low as 1μA/cm2 and Mg alloys with corrosion rates <5μA/cm2.
Project B3.2 – Surface Coatings / Cladding
“Cold sprays” or more properly, cold-gas dynamic-spray process, including the more recent kinetic metallization (KM) technology, is a high-rate coating and free-form fabrication process in which fine, solid powder particles, typically 1–50 µm in diameter, are accelerated via drag to velocities ranging between 500 and 1000 m/s using either supersonic or sonic gas jet. The solid particles are directed toward a substrate, where upon impact, they undergo plastic deformation and bond to the surface, rapidly building up a layer of the depositing material. This project consists of two parts.
Theme 1: Kinetic Metallization
KM is a special type of cold spray process using sonic gas jet with advantage in composie coating. However, due to the lack of understanding of the bonding mechanism between the substrates and the coatings, and the microstructure of the coatings generated by kinetic metallization (KM), the strategic design targets for the project are: to investigate the effects of KM treatment parameters, including powder particle flow velocity, particle size, , distance between the s nozzle and the substrate surface and the composition of the coating powder mixture, on the quality of coatings; to comprehensively understand the bonding mechanism between the coatings and substrates; to analyze the microstructure, including the bonding between the particles, of the coating materials; and to investigate the effect of post-spray heat treatment on the bonding force and properties of the coatings; finally, based on these results to deposit various high quality surface coatings on light metals in order to improve their wear resistance and corrosion resistance.
Theme 2: Computational simulation of Cold Spray
One of the critical parameters in cold spray, including KM, coating is the impinging particle velocity of the coating particle on the substrate. As the spray process control depends entirely on the  particle-laden gas flow, the geometry  of the nozzle and and temperatures, it is imperative to understand the flow physics of the compressible two-phase flow within the converging-diverging nozzle for conventional cold spray and in the converging nozzle for KM and the two-phase gas flow outside the nozzle and its impingement on the substrate including interaction with shock waves. Understanding the complex compressible flow and the trajectories of the powder particles is essential in the development of realistic physical models that describe the evolution history of the powder particles and their interaction with the substrate. The understanding of the complex physics and the models are crucial in the design and efficient application of cold spray technology to complex geometric components and in free-form fabrication processes. This requires prior knowledge of the gas flow field. It is clear from the literature review that current understanding of the fluid dynamics behind the process is still in a state of infancy. The aim of the current project is to employ computational fluid dynamics as a research tool for providing insight into the fluid dynamics behinds the compressible two-phase flow impinging onto the substrate.