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Dibakor Boruah published in Surface and Coatings Technology

Thu, 09 January, 2020

NSIRC and Coventry University PhD student Dibakor Boruah has been successful in publishing his article in the Journal of Surface and Coatings Technology.

The article titled, ‘Experimental evaluation of interfacial adhesion strength of cold sprayed Ti-6Al-4V thick coatings using an adhesive-free test method’ was published in volume 381 on January 15th 2020, and was contributed to by Ben Robinson, Tyler London, Huan Wu, Heidi de Villiers-Lovelock, Phil McNutt, Matthew Doré, and Xiang Zhang.

While discuss the article, Dibakor said “I am sincerely grateful to my colleagues for their valuable contributions to this article. My thanks must also go to Lloyd's Register Foundation, Coventry University, NSIRC and TWI for sponsoring and facilitating this research.”

Cold Spray Additive Manufacturing 

Cold spray (CS) is a rapidly growing solid-state additive material deposition technique, often used for repair of high-value metallic components. Although CS has been proven to be effective for dimensional and aesthetic restoration, to repair load-bearing structural components mechanical property specifications is significantly more challenging. Coating-substrate adhesion strength is an important commonly measured property as a part of structural integrity assessment of load-bearing repair components.

However, due to higher interfacial adhesion strength between CS deposited Ti-64 particles and the Ti-64 substrate, conventional adhesive based test methods (such as ASTM C633) are not suitable to measure the adhesion strength. Therefore, the effect of process parameters, substrate surface preparation and coating thickness on the adhesion strength, is currently unknown.

'Collar-Pin Pull-off Test'

In Dibakor’s study, an adhesive-free test method, referred as 'Collar-Pin Pull-off Test' was developed based on Sharivker's (1967) original design, in order to overcome the limitations of existing test approaches (both adhesive-based and adhesive-free). This method was designed to allow measurement of adhesion strength of high strength coatings such as CS Ti-64, where adhesion strength is higher than 70–90 MPa.

A parametric study was performed to assess the effect of coating thickness, scanning speed, track spacing, toolpath pattern, and substrate surface preparation on the coating adhesion strength. A finite element model was also used to evaluate the stress distribution during the pull-off test, and to check the validity of the proposed test method.The proposed adhesive-free test method was found to be capable of measuring coatings with adhesion strengths beyond the upper limit of conventional adhesive-based methods such as ASTM C633.

To find out more about Dibakor’s on-going research, email