Advanced numerical modeling and experimental validation of hard particles in cold spray additive manufacturing

Abstract

This research aims to numerically model and experimentally verify hard non-melting or refractory particulate materials in cold spray additive manufacturing (CSAM). It primarily focuses on ceramics and metallic glasses, which have been overlooked in the modeling process during CSAM. Although many metallic materials can be accurately modeled and calculated using the Johnson and Cook constitutive equation, this modeling method encounters challenges in adequately explaining the observed deposition behavior in CSAM for hard ceramic or metallic materials. Advanced modeling of the micron-scale alumina particle was conducted using the cohesive zone model (CZM) approach. The CZM method enables the prediction of the critical crushing speed of 30 microns alumina particles, facilitating numerical simulations of advanced multi-particle deposition systems. These simulations are combined with experimental verification to elucidate the performance of ceramic materials in conjunction with soft materials like aluminum alloys and harder particles such as Inconel. This comprehensive analysis unravels the deformation behavior and underlying depositional mechanisms experienced during co-deposition. This section of the study undertakes a meticulous investigation into the co-deposition of ceramic and metal materials using CSAM, effectively addressing the previously unexplored modeling aspects of these materials in the CSAM process. Moreover, a preliminary examination of the mechanisms of CSAM-tailored alumina particulate-reinforced metal matrix composites (APMMC) was carried out using advanced numerical modeling techniques and X-ray CT reconstruction. CSAM was employed to fabricate APMMC samples at temperatures of 200, 300, and 400 celsius degrees. The morphology and distribution of ceramic particles within the cross-sectional of the sample were examined using SEM. Moreover, X-ray CT reconstruction was utilized to evaluate the volume distribution and content of the internal ceramic particles, providing quantitative analysis. Numerical calculations unveil the characteristics of particles with higher susceptibility to breakage under low parameters. Conversely, the increase in spraying parameters amplifies the thermal softening effect of metal particles, resulting in a direct augmentation of the deposition content of ceramic particles. Consequently, a greater number of large-sized particles can be effectively deposited. Notably, higher deposition parameters promote a more uniform distribution of ceramic particles, with complete forms even observable at the coating/substrate interface. In addition, the deposition behavior of metallic glass (MG) particles in CSAM was modeled using the framework of continuum theory. Contrary to conventional metallic materials, MGs exhibit unique characteristics of both melting and fracture during the deposition process in CSAM. The developed viscoplasticity model demonstrates a predictive capability in accuracy and precision of the deformation behavior of MGs under ultra-high strain rates. At the lower deposition parameters of 350m/s and 400K, the finite element (FE) results discovered that the MG particle experienced fracture along two prominent shear bands, with these bands extending into the interior of the particles. As the deposition parameters were increased to 600m/s and 550K, it was revealed that the shear fracture zones of MG particles expanded, causing a broader range of melting at the bottom. Additionally, the study highlighted the presence of a concentrated high-stress region at the top of the metallic glass shear band, which facilitated the failure of MG particles. Furthermore, the FE simulation revealed that the damage inflicted by the MG particle on the substrate during high-speed impact facilitated the deposition of particles. Furthermore, a 3mm coating of bulk metallic glass was successfully prepared through the utilization of CSAM method. Utilizing advanced experimental characterization techniques and the FE analysis, the deposition process and defect characteristics, elasticity mechanical properties, and retention capabilities of the amorphous structure were examined for the BMG deposits at the micro to nanoscale. Research indicates that higher deposition parameters cause greater plastic deformation of MG particles, leading to a deposition efficiency of up to 22.64% at 800 celsius degrees spraying settings. The significant increase in plastic dissipation energy also helps generate thick BMG deposits. The deposited particles show flaws of around 6 microns at the particle-substrate interface due to non-fusion, resulting in a nearly 4% decrease in coating hardness. HRTEM analysis of the nanostructure shows that atom diffusion at the particle/particle bonding contact helps build short-range ordered structures. EDS studies also show that the BMG structure with high Zr content can inhibit nanocrystal growth. Calculation results show that BMG material reduces contact stress by 20% in elastic service. Compared to standard Cu coating, BMG reduces Mises stress and shear deformation in the inner structure.