In-situ creep deformation of cold-sprayed aluminum splats at elevated temperatures

SURFACE & COATINGS TECHNOLOGY

卷:372

Article

Nautiyal, Pranjal¹  Zhang, Cheng¹  Champagne, Victor²  Boesl, Benjamin¹  Agarwal, Arvind¹ 

[1] Florida Int Univ, Plasma Forming Lab, 10555 West Flagler St, Miami, FL 33174 USA

[2] US Army, Res Lab, Weap & Mat Res Directorate, Aberdeen, MD 20783 USA

关键词: Cold spray;    High temperature creep;    In situ mechanics;    Splats;    6061 Al alloy;   

DOI  :  10.1016/j.surfcoat.2019.05.045

来源: Elsevier

【 摘 要 】

This study provides new insights into temperature-dependent splat sliding mechanisms in cold-sprayed deposit by mechanical investigations at length scales comparable to the splats. In-situ indentation of 6061 Al splat structure is performed inside a scanning electron microscope from room temperature up to 400 degrees C. Indentation at 176 degrees C, which is the standard heat-treatment temperature, is characterized by enhanced nanohardness (1.65 GPa) as compared to room temperature (1.37 GPa). This is associated with the precipitate formation and improved splat-bonding due to solid-state diffusion. Further enhancement of temperature results in softening, with nanohardness similar to 70 MPa at 400 degrees C. The elastic modulus of the splat structure is similar to 50% of the 'bulk' modulus at room temperature and is attributed to energy-dissipation due to splat-sliding activated during indentation. 'Recovery Resistance' is computed to quantify energy-dissipation, and a five-fold jump in dissipation is noticed from room temperature to 400 degrees C. The elasto-plastic zone under the indenter becomes larger with temperature and comprises of multiple splats. Hence, the splat-sliding is found to be enhanced at higher temperatures. Indentation creep investigations show the transition of deformation mechanism from purely plastic (material pile-up) at lower temperatures to non-plastic (crack propagation) at 400 degrees C. Creep stress-exponents are computed and correspond to solute drag (similar to 3) and dislocation creep (similar to 4-7) mechanisms. At 400 degrees C, stress-concentration along the splat interfaces is observed in the vicinity of the indenter, eventually leading to crack initiation, propagation and splat delamination due to prolonged loading. These observations highlight that splat interfaces play a vital role in determining the deformation behavior of cold-sprayed materials.

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