Published on 28 January 2013
When a leading surfacing specialist found difficulty in executing bond strength trials on high velocity oxy-fuel (HVOF) coatings, it turned to TWI for a solution to its difficulties.
The company's coating adhesion tests had failed because it was unable to obtain an adhesive with sufficient bond strength to test the coatings to the exacting standards of ASTM C633-01.
As part of TWI's Yorkshire and Humber Joining Forces programme the firm contacted TWI to accept its offer of a product and process review.
The task the company faced corresponded closely to an area of expertise held by TWI's surfacing team. It involved applying a tungsten carbide cobalt chromium coating to mild steel test coupons using high velocity oxy-fuel spraying. The ultimate objective of the work was to demonstrate that the coating would adhere to a substrate material used in fan manufacture.
So sourcing an adhesive with sufficient bond strength to test the coatings proved crucial. Without this vital element the joint fails between the adhesive and the coating. To test the coating properly the joint should fail between the coating and substrate.
TWI was able to provide the very high strength adhesive and, using its Instron 8500 test machine, successfully carry out the tests to the specification.
Before it consulted TWI, the client company was achieving adhesive strengths of about 8800psi. The minimum requirement for an HVOF coating is 9500psi. The strengths achieved by ten tests following TWI's work averaged well over 10000psi.
For information about TWI's capabilities please contact us.