Simulation models are being developed in order to determine the optimum conditions for cold spray repairs and nozzle designs. An effective and novel simulation of material jet formation and growth during cold spray of Al2024 and Ti6Al4V was explored. For particle impact velocity, fluid dynamic calculations have been adopted to optimize particle velocity at the outlet of nozzle. For critical velocity, finite element simulation was used to study material jet formation at the periphery of particles during high velocity impact. Primary investigations were performed on Al-2024 and Ti6Al4V which are the main materials for the project. The models were then extended from a single impact to multiple impact simulation and eventually to a full consolidated coating. Damage models were also incorporated in the coating simulation to account for inter-particle imperfect bonding, which may be further used to assess mechanical behavior of cold spray coating under different loading conditions.
The knowledge developed is used for the design and development of the CORSAIR Portable Cold Spray Unit. The different parts have been studied thoroughly, including the hand-hold gun. Discussions with the industrial representative favour the design of light-weight gun. At the same time, partners are working on the new powder feeder while four pieces of “IMP TECH NITRO” type were calculated and fabricated. Two designs for the overall system were developed and discussed among the partners. By the end of the second year, the hardware is assembled to 90%. Additional modifications and optimizations are under consideration and development.
Continuous repairs are being realized in order to provide feedback on the efficiency of the technology, including the feedstock developed. A series of Ti-6Al-4V (Ti64) powders were supplied to TWI by LPW. These were characterised by laser particle size analysis, and a long term trial into oxygen uptake into powder (while stored) is under way, with regular measurements of oxygen content of a stored powder. Cold spray trials were carried out on flat coupons, depositing cold sprayed Ti64 layers approximately 700µm thick. The coating quality was evaluated by cross-sectioning and examination of coating microstructure, apparent porosity, and microhardness. Several of these coupons were supplied to other project partners for further testing ahead of development of a full characterisation protocol for these specimens.
By the end of the second year, repairs on TI-alloy components are considered complete, and the majority of WP6 Ti-6Al-4V cold spraying has been successfully completed at TWI using LPW Technology’s feedstocks. A variety of geometries were sprayed including notched tensile specimens, notched fatigue specimens, adhesion specimens, tubular coating tensile specimens, tribological testing specimens, stress-corrosion cracking specimens (two different geometries) and many other samples. This represents completion of a large project milestone.