Elsevier

Materials & Design

Volume 109, 5 November 2016, Pages 503-510
Materials & Design

Cold-spray bonding mechanisms and deposition efficiency prediction for particle/substrate with distinct deformability

https://doi.org/10.1016/j.matdes.2016.07.103Get rights and content

Highlights

  • Cold-spray of particle/substrate with distinct deformability has been investigated.

  • Deposition is controlled by particle plasticity for soft particle/hard substrate.

  • Trapping and interlocking in hard particles/soft substrate is elucidated via numerical simulations.

  • The operation and playoff of different bonding mechanisms is demonstrated.

  • Predictive assessment of deposition efficiency is in good agreement with experiments.

Abstract

Cold-spray involving particle and substrate that are of distinct deformability, i.e., soft (particle)/hard (substrate) and hard (particle)/soft (substrate) systems, has been investigated using systematic numerical simulations. For the soft/hard system, the bonding and deposition is dominantly controlled by particle plasticity. In contrast, physical trapping and mechanical interlocking play an important role for the hard/soft system. Employing a layered-particle/substrate model and a crater-particles model, we demonstrated the operation and playoff of different bonding mechanisms, and provided predictive assessments of the deposition efficiency that correspond well to experimental measurements. The present study offers key mechanistic insights towards rational process design of cold-spray.

Introduction

Cold-spray is a rapid kinetic coating process where feedstock particles are accelerated by an expanding gas stream towards a substrate while maintaining temperatures well below their melting temperatures [1], [2], [3]. At or above a critical velocity, particles will experience significant plastic deformation rate that induces adherence of deformed particles on the substrate, and with each other, to form a coating [4], [5], [6]. Owing to its low-temperature operation, cold-spray possesses many technological advantages such as minimum modification of material microstructure, and low-degree of oxidation and chemical degradation or reaction [7], [8], [9], [10]. These advantages enable the preferable applications of cold-spray in coating temperature-sensitive materials, e.g., polymers [11], [12] and nanocrystalline materials [13], [14], and oxidation-sensitive materials e.g., aluminum, copper and etc. [15], [16], [17]. In addition, cold-spray is capable of handling a wide spectrum of feedstock materials. This promises great versatility and possibilities of achieving new functionalities in coating. For instance, cold-spray provides a quick route to manufacture complex and/or heterogeneous coatings that integrate different material systems, e.g., ceramic [18], [19] and metal [20], [21], [22] matrix composite and polymer/metal [11], [23] coating.

In the application of cold-spray technology, one metric people strive to improve is the deposition efficiency (DE), defined as the ratio of the weight of adhered particles to the total weight of sprayed particles. To date, the optimized spraying conditions that yield high DE for cold-spray are mostly determined on a trial-and-error basis [1], [2], [4], [24], which not only incurs substantial cost but also time-consuming. In this regard, substantial research has been conducted to investigate detailed deformation behaviors and deposition mechanisms occurring in particle/substrate and particle/particle contacts [6], [24], [25], [26], [27], [28], [29] in order to identify a rational strategy for the optimization of the spraying parameters to attain high DE. Assadi et al. [6] suggested shear instability as an indication of the occurrence of bonding. Li et al. [27] postulated a model to examine the effects of particle size and spray angle on base of the critical velocity [4], [5], [6]. Those studies provide important mechanistic information towards understanding the onset of particle deposition. However, they did not provide predictive assessment of the evolution of DE as spraying conditions (e.g., particle velocity) vary.

In a recent study, we demonstrated that for particle/substrate systems with similar deformability, the evolution of DE can be quantitatively analyzed in terms of the plastic deformation of the particle [30]. In particular, we showed that the experimental DE is linearly correlated with an effective plastic deformation rate through a material-independent correlation parameter [30]. However, the deposition scenario is necessarily different in systems comprising particle/substrate of largely dissimilar deformability where plastic deformation is predominately occurring in either the particle or the substrate [28], [31], [32]. In this regard, here we probe the detailed deposition process in those systems with distinct deformability during cold-spray using finite-element modeling, aiming to clarify the complexities induced by the deformability mismatch between the particle and substrate. Two different models, namely a layered-particle/substrate model and a crater-particles model, were employed to simulate distinct material deformation behaviors and particle-substrate interactions, and to clarify the playoff of different bonding mechanisms. Based on numerical simulations, predictive assessments of DE curves were obtained, showing good agreements with experimental measurements. The present study provides crucial insights towards predictive modeling of the cold-spray process.

Section snippets

Computational methodology

The particle/substrate deformation and subsequent deposition process is simulated using the non-linear finite element analysis (FEA) package from Abaqus/Explicit [33]. Aluminum and copper are the two materials chosen for modeling the particle/substrate systems, i.e., Alp/Cu and Cup/Al, where the subscript p indicates particle. The above choice is based on the availability of reliable and systematic experimental DE vs. particle velocity data [1], [4]. Given that coating is produced by the

Soft/hard system (Alp/Cu)

In our previous work [30], we have demonstrated that for systems where the particle and substrate exhibit similar deformability, DE is well correlated with an effective deformation rate, REQ, which was calculated as the average slope of the PEEQ2 evolution curve in its stable region [30] with PEEQ defined as the average PEEQ over all particle elements [42]. As discussed in Section 2, the deposition process of the soft/hard system can be represented by the layered-particle/substrate model (see

Conclusion

In summary, systematic numerical simulations have been performed to study the cold-spray in material systems where the particle and substrate exhibit significantly different deformability. Two particle/substrate systems, namely Alp/Cu and Cup/Al, were selected to represent the soft/hard and hard/soft scenarios, respectively. Our study showed that in the soft/hard system, the dominant bonding mechanism is attributed to the particle plasticity and deposition efficiency (DE) can be accurately

Acknowledgements

This work was supported by McGill Engineering Doctoral Award and Discovery Grant of Canada National Sciences and Engineering Research Council [grant number RGPIN 418469-2012]. We also acknowledge Supercomputer Consortium Laval UQAM McGill and Eastern Quebec for providing computing power.

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