Thu, 28 September, 2023
We are pleased to announce the publication of our latest research article, titled, ‘Understanding the effect of substrate preheating temperature and track spacing on laser assisted cold spraying of Ti6Al4V,’ led by Dr Dibakor Boruah, Senior Project Leader, TWI. This comprehensive investigation focuses on the parameters affecting the quality and efficacy of laser assisted cold spray (LACS) of Ti6Al4V, a titanium alloy widely used in aerospace applications. The paper is co-authored by Dr Philip McNutt and Dr Henry Begg from TWI, alongside Prof Xiang Zhang from Coventry University and Dr Deepak Sharma from the University of Leicester
In LACS, in-situ laser substrate preheating is employed to create transient heating regions on the substrate ahead of impinging spray particles. This approach, combining standard or conventional cold spray (CS) with laser processing techniques, has shown promising results. Laser substrate preheating induces substrate softening, enabling better shear localisation when both the impacting powder and substrate co-deform, ultimately yielding superior bonding and enhanced deposit properties with minimal microstructural alterations. LACS presents a substantial potential for depositing traditionally difficult-to-spray alloys and improving their characteristics (porosity, adhesion, cohesion, etc).
Figure 1 presents the schematic of the LACS process at TWI Ltd, Cambridge:
Figure 1. (a) Schematic of the Laser Assisted Cold Spray (LACS) process showing the positions of the laser processing head, pyrometer, and Cold Spray (CS) nozzle. (b) LACS hardware configuration attached to the Impact 5/11 gun
The preheating temperature of the substrate and the spacing between deposition tracks are identified as key factors significantly impacting coating characteristics, including adhesion, microstructure, and mechanical properties. Figure 2 illustrates a comparison of Ti6Al4V deposits in conventional CS versus LACS, highlighting a significant reduction in porosity (2.3% in conventional CS deposits vs. 0.4% in LACS deposits). Figure 3 presents the enhanced interfacial adhesion achieved through LACS when compared to CS.
Figure 2. Optical micrographs of Ti6Al4V deposits comparing mesostructure, illustrating the presence of pores/defects in standard Cold Spray (CS) and Laser Assisted Cold Spray (LACS) deposits
Figure 3. Cross-sectional SEM microstructure of interfaces showing Cold Spray (CS) and Laser Assisted Cold Spray (LACS) deposits of Ti6Al4V onto Ti6Al4V substrates
Key contributions of this study include enhanced coating-substrate adhesion through extensive interfacial mixing, a substantial improvement in deposit density, and valuable insights into the effects of residual stresses.
Collectively, these findings deepen our understanding of LACS technology and its potential advantages over conventional CS, presenting new possibilities for enhancing the quality and performance of Ti6Al4V deposits.
The knowledge derived from this study has the potential to revolutionise the application of Ti6Al4V deposits, offering improved performance and durability in critical industrial applications, including protective coating, repair, and additive manufacturing.
For a detailed exploration of these findings and access to the complete research article, please see here.
Please contact us if you need more information.